TE37

Control and Instrumentation

Study Station

User Guide

© TecQuipment Ltd 2009

Do not reproduce or transmit this document in any form or by
any means, electronic or mechanical, including photocopy,
recording or any information storage and retrieval system
without the express permission of TecQuipment Limited.
TecQuipment has taken care to make the contents of this
manual accurate and up to date. However, if you find any
errors, please let us know so we can rectify the problem.

TecQuipment supply a Packing Contents List (PCL) with the

equipment. Carefully check the contents of the package(s)
against the list. If any items are missing or damaged, contact
TecQuipment or the local agent.

DB/0409
 TE37 Control and Instrumentation Study Station

Contents
Introduction .................................................................. 1

TE37DCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Description ................................................................... 3

Controllers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Patch Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Reference Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Computing Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Paperless Chart Recorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Flow, Level and Pressure Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Temperature Transmitter (TT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Pressure Relief Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Fault Switches (Pushbuttons) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Sight Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Drain Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Overflow Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Technical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Installation and Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Handling Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Assembly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Basic Control Theory and Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Manual and Automatic Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Proportional Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Proportional and Integral Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Proportional, Integral and Derivative Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Industry Standard Abbreviations, Terms and Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Calculation of Actual Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Preparation Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Experiment P1 - To Set up the Flow Transmitters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Experiment P2 - To Set Up the Level Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Experiment P2a - Comparison of Wet and Dry Leg Operation . . . . . . . . . . . . . . . . . . . . . . . 34
Experiment P3 - To Set Up the Pressure Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Experiment P4 - To Check the Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Experiment P5 - Use of the Paperless Chart Recorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

TecQuipment Ltd User/Safety Guide

 Experiment P6 - Basic Use of a Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Experiment P7 - To Check a Computing Relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Process Control Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Experiment PC1 - Basic Flow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Experiment PC2 - Basic Level Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Experiment PC3 - Basic Pressure Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Experiment PC4 - Basic Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Experiment PC5 - Cascade Control of Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Experiment PC6 - Feedforward Control of Level by Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Experiment PC7 - Three Element (Feedforward-Feedback) Control . . . . . . . . . . . . . . . . . . 61
Experiment PC8 - Ratio Control of Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Experiment PC9 - Coupled Interactive Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Experiment PC10 - Decoupled Interactive Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Experiment PC11 - Split Range Control of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Experiment PC12 - The Elements of PID Feedback Control and Their Effects . . . . . . . . . 79

Fault Finding Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Test FF1- Pressure Transmitter Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Test FF2 - Temperature Transmitter Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Test FF3 - Level Transmitter Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Test FF4 - Hot/Drain Flow Transmitter (FT2) Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Test FF5 - Cold Flow Transmitter (FT1) Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Test FF6 - Controller 1 Output Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Test FF7 - Controller 2 Output Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Test FF8 - Control Valve 2 Input Fault. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Test FF9 - Control Valve 1 Input Fault. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Test FF10 - Computing Relay 1 Output Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Important Note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Preparation Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Process Control Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Maintenance and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Spare Parts and Customer Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Spare Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Customer Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
 TE37
Control and Instrumentation
Study Station

User Guide
Introduction

Aims

• To show the
principles of
automatic
control and
how they are
used in
industrial
processes.
• To make
students
familiar with
standard
industrial
equipment.

Figure 1 The TE37 Control and Instrumentation Study Station

Most industrial plants and service suppliers use some form of process to control the movement,
containment and mixing of materials or liquids. This could be cooling, heating, fresh water supply, water
treatment, cement mixing or a petrochemical process. To save labour and remove boring and repetitive
jobs, the process is automatically controlled, so that the system will run with minimal supervision and
with more precise control than could be done by humans.

The Control and Instrumentation Study Station uses industry-standard parts to show the basic principles
of automatic control used in industry. For safety and ease of use, it uses water as the process material
and has water measurement and control instruments.

The Station includes:

• Electronic Controllers and Computing Relays

• a Process Vessel
• Flow, Pressure, Level and Temperature Transmitters
• Control Valves
• a Paperless Chart Recorder
• a ‘Patch Panel’ to easily connect the instruments together
• Fault Switches to create artificial faults in the process

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TE37DCS
The Controllers of the Study Station may also be connected to the optional TE37DCS Distributed
Control System for computer control and data acquisition. This system increases the students awareness
and understanding of how industrial plants are controlled by a remote workstation. The TE37DCS
includes a computer and software to remotely control and log data from the TE37 controllers.
TecQuipment supply an application for use with the TE37DCS that includes most of the process control
experiments shown in this User Guide.

Figure 2 Screenshot of One Experiment with the TE37DCS

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Description

Figure 3 shows the main parts of the Study Station.

Reference Signals
Computing Relays

Controllers
Process Vessel

Sight Glass
Patch Panel

Chart Recorder

Air Regulator
Control Valves

Flow Transmitter

Figure 3 The TE37 Control and Instrumentation Study Station

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C = Controller
C C
PT PT = Pressure Transmitter

TT = Temperature Transmitter
PROCESS
VESSEL
LT = Level Transmitter
TT
FT = Flow Transmitter
LT

OVERFLOW

DRAIN

FT
HOT

FT

COLD

Figure 4 Basic Layout of the Control and Instrumentation Study Station

Controllers
The Study Station has two identical electronic controllers, each has two fully configurable outputs (a and
b). Output a is used as the main output for most experiments. Output b of each controller may be
configured as a second output for Split Range control, or as a set point output for the Chart Recorder
trace (if the controller set point is local).

Each controller includes feedback inputs for automatic operation and has fully adjustable PID
(proportional, integral and derivative) feedback parameters. In manual control mode, each controller
can be operated by means of the buttons on its front panel. When set to automatic control, the
controllers will automatically control their output, determined by their PID parameters and the feedback
(measurement variable) from the transmitters.

The measurement variable (MV) is the signal from any of the transmitters connected to the input of the
controller and is shown on the display of the controller. The display also shows the local or remote Set
Point and output levels. The Set Point can be set at the Controller (Local Set Point) by means of the front
panel buttons and remotely by means of a Remote Set Point input (RSP).

The output of each controller can be connected by means of the Patch Panel to the Computing Relays,
the Control Valves and to the other controller as a remote Set Point signal for cascade operation.

Each input accepts industry-standard 4 mA to 20 mA loop signal current (indicated as 0 to 100%). Each
output gives industry-standard 4 mA to 20 mA (indicated as 0 to 100%).

Both controllers can be remotely controlled by means of the optional TE37DCS control system. The
communications connections of each controller are connected in parallel and to a d-type socket on the
side panel of the Study Station.

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Table 1 shows the most important settings for the controllers, set by TecQuipment. If you change any
of these settings, make sure that you return them to the values shown in Table 1. If you do not return
them to the correct settings, the controllers will not work as described in the experiments and will not
communicate with the optional TE37DCS.

These controllers use the terms PF, IF and DF for the PID control elements of
NOTE feedback.
Refer to the Controller User Guides for more information (supplied with the TE37).

Details Setting

Controller 1 and 2 ACK, ACK, ACK, ACK

Security Passcode

Remote Setpoint (RSP) Analogue Input 4

Strategy One Function

Controller 1 address 1

Controller 2 address 2

Baud 19200 (19.2K)

Table 1 Important Settings for the Controllers

Patch Panel
The Patch Panel includes multiple sockets to allow easy connection between each instrument and
controller. There are two sets of output sockets from the controllers, transmitters and computing relays.
They are connected in series so that they can be used to connect up to two different instruments at the
same time. The series sockets include 220 Ω resistors that are in circuit when the sockets are not used,
these allow a loop current to flow through the instruments even when they are not in use.

The Patch Panel includes:

• Six sockets for the six channels of the Chart Recorder

• Ten (five sets of two in series) sockets for the outputs of the transducers
• Two sockets for the two control valves
• Four (two sets of two in series) sockets for the outputs of the two reference signals
• Eight (four sets of two in series) sockets for the outputs of the controllers
• Two sockets for the feedback inputs to the controllers
• Two sockets for remote setpoint inputs to the controllers
• Six sockets (two sets of three) for the three inputs of each computing relay
• Four sockets (two sets of two in series) for the outputs of each computing relay

Jumper cables are supplied to allow easy connection between the sockets on the Patch Panel. Note the
polarity of the Jumper cable connections.

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TE37 Control and Instrumentation Study Station

+ -
(Positive) (Negative)

- +
(Negative) (Positive)

Figure 5 The Polarity of the Jumper Cables

Reference Signals

Figure 6 The Reference Signals

There are two fully adjustable reference signals available at the Patch Panel. These two signals are
measured and adjusted by the two meters and controls above the Patch Panel. The signals are industry
standard 4 to 20 mA, but their scale shows 0 to 100 (%). Table 2 shows how the signal current converts
into a percentage.

The reference signals can actually supply a current of slightly less than 4 mA and
NOTE slightly more than 20 mA. This is to allow for the different resistances of
instruments that can be connected to.

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Signal % of maximum
Current Signal

4 mA 0

6 mA 12.5

8 mA 25

10 mA 37.5

12 mA 50

14 mA 62.5

16 mA 75

18 mA 87.5

20 mA 100

Table 2 Signal Current to % Conversion

Computing Relays

Figure 7 The Computing Relays

Two computing relays are fitted that provide a useful mathematical function.

The inputs and outputs of the relays accept and emit the industry standard 4 to 20 mA current signals.

Each relay has three inputs - A, B and C, and an output. On the front panel of each relay is a control
that adjusts the gain or multiplier - K of the relay. The mathematical function of the relay is:

Output = Input B + K (Input A - Input C)

The gain value K can be adjusted from 0 to 5 and is indicated in percentage. Table 3 shows how they
are related.

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All three inputs of the relays must be connected to a signal between 0 and 100%,
NOTE or the output will be wrong. They will ‘see’ unused inputs as an unpredictable
negative value.

K (%) Actual Gain

0 0

10 0.5

20 1

30 1.5

40 2

50 2.5

60 3

70 3.5

80 4

90 4.5

100 5

Table 3 Percentage Indicated Against Actual Gain for the Computing Relays

Paperless Chart Recorder

The chart recorder has six channels that may be connected to any of the input and output signals of the
controllers and instruments. The chart speed may be adjusted to suit the experiments. The input signal
range of the chart recorder is 4 to 20 mA, corresponding to 0% to 100% on its scale. The chart recorder
allows you to see the signals in real-time on its display and store them on a memory stick, so you may
analyze them and print them off using suitable computer.

You must use the stylus (supplied) to operate the touch-screen display of the chart recorder.

Refer to the chart recorder manufacturer’s manual for more details.

NOTE Normally, the compact disk supplied with the chart recorder includes the
instruction manuals and any software you need to use with the chart recorder.

Flow, Level and Pressure Transmitters

These transducers are all basically the same type of transmitter. They are Differential Pressure
Transmitters. Each has two inputs, a high pressure input and a low pressure input. They can be set to
display their measured pressure in two basic ways:

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Engineering Units (EGU), which can be: bar, mmH2O, Pa, inH2O and other units of pressure.

Percentage (PCT), which shows a percentage of the maximum pressure difference.

For ease of use, the transmitters are set to display percentage for the experiments, but the user can
change them to engineering units if they are happy to perform the mental arithmetic to convert the
value back into percentage.

In some experiments you will need to re-calibrate the zero and span of the transmitters. To do this you
must unscrew the front cover and use the ‘NEXT’ and ‘ENTER’ buttons to cycle through a range of
menus (see Figure 8). Refer to the manufacturers’ instructions for more details (supplied with the TE37).

Figure 8 Unscrew the Front Cover and Use the ‘Next’ and Enter’ Buttons to Adjust the Transmitters

Flow Transmitters (FT1 and FT2)

Flow Transmitters FT1 and FT2 are each connected across calibrated orifices (see Figure 9) in the water
supply pipework. The flow transmitters measure the pressure drop across the orifices, so that their
output is proportional to the flow (as flow increases, pressure drop across the orifice increases).

Flow Transmitter 2 (FT2) is connected to two-way valves so that it can be connected to calibrated orifices
in the hot water supply or the drain pipework. The handles of the two-way valves indicate the orifice to
which they become connected (see Figure 10).

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Orifice diameter = 6.5 mm

Water Flow

Figure 9 A Sharp-edged Orifice used in the TE37

For experiments with this equipment, the actual measured flow rate in litres per second is not important,
as the transmitters must be set to transmit 100% at whatever the maximum flow rate to the equipment
is.

Handles point up to measure

the flow in the drain

Handles point down to

measure the flow in the hot
water feed

Figure 10 Use of the Two-way Valves

Level Transmitter (LT)

The level transmitter high pressure connection is connected to the bottom of the process vessel, the low
pressure connection is connected to a point near to the top of the process vessel. As the water level in
the Process Vessel increases, the pressure at the high pressure connection increases, so the output of the
transmitter is proportional to the level. The low pressure connection can be left empty for dry leg use or
filled with water for wet leg use (see later in this manual for details).

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Pressure Transmitter (PT)

The pressure transmitter high pressure connection is at the top of the Process Vessel, its low pressure
connection is left open to atmosphere. It simply measures the pressure in the vessel with respect to
atmosphere.

Temperature Transmitter (TT)

A RTD (resistance temperature detector) is built into an enclosed short pipe (Immersion Well) that
penetrates near the bottom of the Process Vessel. The Immersion Well protects the RTD from direct
connection to the water in the Process Vessel. The RTD is connected to a Temperature Transmitter that
converts the resistance change of the RTD into the industry standard 4 to 20 mA signal output, so that
0 to 100°C equates to 4 to 20 mA and (0 to 100%).

Control Valves
The two control valves are identical. They are spring loaded to be normally closed, and are opened by
compressed air. The compressed air supply to each control valve is electrically controlled by an air valve
(positioner). A 4 to 20 mA signal to the air valve makes it regulate the air pressure to the control valve
(see Figure 11).

At the top of each valve is a control to allow manual opening of the valve.

The air valve/positioner allows a small amount of air to pass, even when it is not
NOTE in use. You will hear it ‘leaking’ from underneath its casting - this is normal.
The manual control is not for repeated use.

Manual Control

4 to 20 mA Air Valve/Positioner Control Valve

(Electrical)
Control Signal

Compressed Air
Control Valve

Water Circuit

Figure 11 The Control Valve Signal Path

The actual valve in the water line is a ‘plug and seat ring’ type valve, similar to a globe valve. The
mechanical settings for this type of valve are preset for the best performance. However, this type of valve
does not have a linear or proportional characteristic. Refer to the experiments and results for valve
linearity.

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Pressure Relief Valve

Near the top of the Process Vessel is a Pressure Relief Valve, that opens if the pressure is greater than 2
bar. This valve can be manually opened, which can be useful to clear any unwanted pressure differences
in some experiments, or if the overflow becomes temporarily blocked with a water pocket.

Fault Switches (Pushbuttons)

Figure 12 Fault Switches

To the left side of the Study Station is a set of labelled latching fault switches (pushbuttons). A cover is
fitted to the pushbuttons to hide them from students while they do the experiments. Each switch
includes an internal fault lamp that goes on when its fault switch is pressed. When pressed, each fault
switch breaks a signal loop at the instruments shown by the label. These buttons are used to create faults
on the equipment to help to train students in fault finding. Table 4 shows the signal loops that each
pushbutton breaks.

Fault Switch (Pushbuttons) Signal Loop

PB1 Pressure Transmitter Output

PB2 Temperature Transmitter Output

PB3 Level Transmitter Output

PB4 Flow Transmitter 2 Output

PB5 Flow Transmitter 1 Output

PB6 Controller 1 Output a

PB7 Controller 2 Output a

PB8 Control Valve 2

PB9 Control Valve 1

PB10 Computing Relay 1 Output

Table 4 Fault Switch (Pushbuttons) Circuits

Sight Gauge
The sight gauge is the vertical glass tube to the front of the Process Vessel. It indicates the water level in
the Process Vessel. The sight gauge includes two valves that allow the user to ‘lock’ the indicated water
level in position for measurement purposes (see Figure 13). They are normally open for all experiments

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in this guide, but can be useful to help in precise calibration of the level transmitter, or other precision
level control experiments.

NOTE Leave the sight gauge valves open for all experiments in this guide.

Figure 13 Valves on the Sight Gauge

Drain Valve

Figure 14 The Drain Valve

The Drain Valve is underneath the main enclosure and controls the water flow out of the base of the
Process Vessel. It is also useful to create outlet flow disturbances.

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Overflow Valve

Figure 15 Overflow Valve

The Overflow Valve is at the side of the Process Vessel and is left open for most experiments (except
pressure control), to allow air to enter and leave the Process Vessel and act as an overflow if the water
level becomes too great.

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Technical Specifications

Item Details
Nett Weight 272 kg

Dimensions 1850 mm High x 1100 mm Wide x 750 mm Front to Back.

Water Supply (Nominal Cold Water 10 L.min-1 2 bar

values)
Hot Water (Nominal 50°C) and 3 L.min-1 2 bar

Air Supply Clean, oil-free compressed air at 2 bar, 0.07 m3.min-1

Regulated on the equipment to between 1.3 and 1.5 bar

Electrical Supply Single Phase

220 V
1A
50 Hz
This apparatus must be earthed.

Flow, level and pressure Industry-standard differential pressure transmitters with 4

Transmitters to 20 mA current loop signal.

Temperature Industry standard RTD to current transducer with 4 to 20

Transmitter mA current loop signal. Range 0 to 100°C.

Control Valves and Compressed air actuated valves, fitted with air valve
Positioners (positioner) and manual control.
Nominal supply pressure to positioner 1250 mbar
Nominal valve working range 207 to 1035 mbar

Chart Recorder Fully adjustable with six channels to accept 4 to 20 mA

signals.

Controllers Fully configurable with automatic and manual control,

dual output and external communication facility.

Reference signals 24 V DC with variable series resistance and series current

meters (4 to 20 mA).

Circuit Protection Fuse 1 - Isolators - 20 mm 1 A Type T

(Fuses 1 to 5 are inside Fuse 2 - Computing Relays - 20 mm 1 A Type T
the main enclosure) Fuse 3 - Controllers - 20 mm 1 A Type T
Fuse 4 - Chart Recorder - 20 mm 1 A Type T
Fuse 5 - Reference Signals, Transmitter, and Fault Lamp
power supplies - 20 mm 1 A Type T
If a UK style three pin plug is fitted to the supply lead, it will
include a 3 A fuse.

Table 5 Technical Specifications for the TE37

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Installation and Assembly

The terms left, right, front and rear of the apparatus refer to the operators’ position, facing the
Controllers.

NOTE Obey any regulations that affect the installation, operation and maintenance of
this apparatus in the country where it is to be used.

Handling Instructions
Net Weight: 272 kg

Obey your local handling procedures when you move this apparatus.
WARNING This unit has a high centre of gravity - support it on all sides as you move
it.

The TE37 has no wheels. Use suitable lifting equipment to move the apparatus. Use a powered ‘fork lift’
or similar machine to lift the apparatus from underneath. Use assistance to support each side of the unit
as you move it.

Location
Install the TE37 in a clean, well lit laboratory or classroom type area, on a solid level floor.

The unit occupies a floor space of 1700 mm x 750 mm. Allow at least 2 m of space to the front of the
unit for access by users. Allow at least 1 m of space to the left and right of the unit for access to its
controls and water connections.

This apparatus uses water and electricity, put it in a position that is

WARNING more than 1.5 m away from any electrical sockets or other mains
powered electrical equipment.

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Assembly
The TE37 is supplied already assembled. Use suitable lifting apparatus to put it into position, then
connect it to suitable water and electrical services.

TE37

Electrical Supply

To Optional TE37 DCS

Compressed Air 2 bar

at 0.07 m3.min-1

To suitable drain Overflow

û Do not join! Drain

Hot Water
(approx 50°C)
Cold Water
(approx 10°C or lower)

Multi-turn ON/OFF Valves

Valves
Both water supplies must include
valves nearby.

Figure 16 Connections to the TE37

Air and Water Connections

Connect the TE37 to a clean, dry, oil-free compressed air supply as shown in Figure 16. Adjust the air
pressure regulator on the unit to between 1.3 and 1.5 bar.

WARNING Do not exceed 2 bar air pressure.

Connect the TE37 to a source of clean cold water and clean hot water as shown in Figure 16. To make
experiments easier and repeatable, each water supply must include two valves near to the equipment
as shown. One valve may be a simple on/off valve to isolate the supply and provide a means to create a

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simple disturbance to the flow. The other valve must be a multi-turn control valve to allow good control
of the flow rate.

NOTE The water supplies must be stable (constant flow and pressure) for stable and
consistent experiment results.

Connect the drain and overflow outlets to a suitable drain. Do not connect them together before they
enter the drain, as any pressure differences in the pipes will affect the experiments.

Alternatively, the optional SM37 (Service Module) includes a compressor, regulators and water heater
to provide (from a suitable cold water supply) compressed air and hot water for the TE37.

Electrical Connection
Connect the apparatus to an electrical supply using the cable(s) supplied.

Connect the apparatus to the supply through a switch, circuit breaker

WARNING
or plug and socket. The apparatus must be connected to earth.

Refer to the following colour code to identify the individual conductors:

GREEN AND YELLOW: EARTH E OR

BROWN: LIVE

BLUE: NEUTRAL

NOTE A suitable UK style three-pin plug may already be fitted to the supply lead. This
plug includes a 3 A fuse.

Paperless Chart Recorder

The chart recorder should be ready to work as soon as you apply power to the Study Station. You should
only need to change between chart speeds for different experiments. Refer to its manufacturer’s
instructions (supplied) for full details.

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Basic Control Theory and Definitions

This theory is very basic. Refer to suitable textbooks for advanced Process Control Theory.

Manual and Automatic Control

Control Feedback

Set Point

Figure 17 Manual Control

Figures 17 and 18 show the basic elements of a system to control the level in a tank. In the manual
control system, the operator’s brain is the controller and compares the level feedback from the eyes with
the known Set Point and sends a control signal to the hand to adjust the valve. In the automatic control
system, the level controller compares the level feedback from the level transmitter with a known Set
Point and sends a control signal to a Control Valve. Note that both control systems use a Feedback
Signal.

Control Valve Level Controller

Control Feedback
LC

Set Point

LT Level
Transmitter

Figure 18 Automatic Control

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Proportional Control

Proportional Controller

Set Point Error Signal

(Difference) Output
Process
Measured Variable
(Feedback)
Comparator Gain
(Sum)

Figure 19 Basic Proportional Control

In proportional control, the Controller compares the feedback with the Set Point and amplifies the
difference to give an output. A large difference between the Set Point and the Measured Variable gives
a large error signal. This is amplified by a gain block.

Output = Error Signal x Proportional Gain

The Proportional term can be described in three ways:

1. Proportional Gain - A gain figure. A Proportional Gain of 2 doubles the controller output.

2. Proportional Feedback - A feedback ratio (100%/gain). A feedback ratio of 50% gives a

Proportional gain of 2. A feedback ratio of 100% gives a gain of 1.

3. Proportional Band - Another name for Proportional Feedback.

Proportional Control by itself is useful, but as the error signal becomes small, the output becomes small,
unless the proportional gain is very large. Unfortunately, a high gain gives instability and so is normally
kept quite low. A small output may not be enough to activate a valve or other control device to
compensate for the slight error, so the Measured Variable may be always slightly lower than the Set
Point.

Proportional and Integral Control

Proportional and Integral Controller

Adder
Set Point Error Signal
(Difference) Output
Measured Variable
+ Process
(Feedback)
+
Gain
Comparator
(Sum)

Integrator

Figure 20 Basic Proportional and Integral Control

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Integral Control is normally used in addition to Proportional Control. As Figure 20 shows, an integral
function is added to the output of the gain element.

Output = (Error x Proportional Gain) + Integral

The integral term is most often described in two ways:

1. Integral Time - A time figure (Ti), this determines the amount of time that the integral operates
over

2. Integral Gain - A gain figure. The inverse of the integral time (1/Ti)

Proportional Control with the additional Integral block gives better control than Proportional only. Small
outputs from the gain element are added to the integral, to give sufficient output to open a control valve
or other control device. The Measured Variable has a much better chance of meeting the Set Point.

Proportional, Integral and Derivative Control

Proportional, Integral and Derivative Controller

Derivative

Set Point Error Signal Adder

(Difference) + Output
Measured Variable
+ Process
(Feedback)
+
Gain
Comparator
(Sum)

Integrator

Figure 21 Basic Proportional, Integral and Derivative Control

Derivative Control is usually in addition to Proportional and Integral Control. As Figure 21 shows, the
output of a derivative function is added (derivative output is normally negative) to the output. The
amount added is determined by the speed of change in the error signal.

Output = (Error x Proportional Gain) + Integral + Derivative

The derivative value is most often described in two ways:

1. Derivative Time - The ‘rate time’ (Ti) over which the derivative action takes action

2. Derivative Gain - Another term for Derivative Time

Proportional Control with the additional Integral and Derivative blocks can give better control than
Proportional and Integral control only. The derivative block modifies the output of the controller only
when a rapid change in Measurement Variable occurs. The derivative block is not needed for slow
reacting processes. It is most used where rapid Measurement Value changes could cause adverse effects
on the process plant.

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As the derivative block responds to counter any rapid changes in Measured Value, it must be used with
a noise filter. Without a filter, it can amplify the effects of any high frequency (short period) noise present
on the Measured Variable signal loop.

Industry Standard Abbreviations, Terms and Definitions

Parallel and Series PID Form

There are two basic forms of PID control (P and PI control can only be in one standard form):

1. Parallel Form

+ Output
Error Signal I +
+

Figure 22 Parallel Form of PID Control

This is the most common form of PID control, also termed ‘Standard Form’, ‘ISA Form’ and ‘Non-
Interacting Form’. Each block operates independently.

2. Series Form

Error Signal Output

+ P +
+ +

D I

Figure 23 Series Form of PID Control

This is a less common and older form of PID controller, also known as ‘Interacting Form’. The outputs of
the P and I blocks depend on the output of the D block.

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Output Reset (or Bias)

Proportional Controller with Reset or Output Bias

Set Point Error Signal

(Difference) Output
Measured Variable
+ Process
(Feedback)
+
Comparator Gain
(Sum) Bias

Figure 24 Proportional Control with Output Reset (or Bias)

As mentioned, proportional control by itself has limitations. When the error signal is small, the output is
small, and may not be enough to open a valve or other control device. An integral term is normally
added to compensate for this, but it is often more convenient to add a fixed bias to the output of a
proportional controller. In modern controllers this facility is only usually available when you use
proportional control only or proportional and derivative control.

Direct and Reverse Action

For most applications, the Controller uses an error signal that is the direct comparison of the Set Point
and the Measured Variable, so that

Error Signal = MV - SP

In some applications, it is better to have an error signal of the reverse polarity, so that

Error Signal = SP - MV

Most modern controllers have the choice of Direct or Reverse Action.

Step Change
To accurately measure the response time of any system, you must introduce an instant ‘step’ change to
its conditions. This can be done by disturbing the measurement variable or changing the set point. You
then measure how long the system takes to force its output to a level so that the measurement value
meets the set point again. Any delays between a change in output and a change in measurement value
are caused by the type of system and will affect the overall response of the system. Temperature control
usually has large delays, due to the need for heaters or pipes and containers to warm up before the
measurement value starts to change. Flow control usually has small delays, flow increases as soon as the
control valve opens.

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Overal System Response

(restore) Time

Output

Measurement Variable
Set Point

Step change Delay or ‘lag’

in Set Point due to the system

Time

Figure 25 To use a Step Change to test the System Response

Abbreviations
These abbreviations are based on standard terms used in process control.

Abbreviation Definition Symbol

FT Flow Transmitter

LT Level Transmitter

TT Temperature Transmitter

FC Flow Controller

LC Level Controller

TC Temperature Controller

PV Process Variable

SP Set Point

MV Measurement Variable

G Gain (General Term) G or k or K

P Proportional

I Integral

Ti Integral Time

D Derivative

Td Derivative Time

SP - MV Error Signal ε or e
or MV - SP

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Calculation of Actual Flow Rate

If needed, you could calculate the actual hot and cold flow rate by setting the Flow Transmitters (FT) to
display pressure (in Pascals) and using this equation:

π 2
q m = CE --- d 2∆p × ρw (1)
4

Where:

Orifice details

C = 0.60
D = 15.9 mm (0.0159 m)
d = 6.5 mm (0.0065 m)
β = 0.41

E = (1-β4)-0.5

Note that this equation is based on mass flow. To convert from volume flow (L/min) to mass flow (kg/s)
accurately and back again:

Volume Flow (L/min) Water Density (kg/m^3)

Mass Flow (kg/s) = ------------------------------------------------------- × ----------------------------------------------------------------
60 1000

Mass Flow (kg/s)

Volume Flow (L/min) = ---------------------------------------------------------------- × 60000
Water Density (kg/m^3)

Where qm = Mass Flow in kg.s-1

d = diameter of orifice in metres

D = diameter of pipework in metres

β = d/D

C = Discharge coefficient of the orifice = 0.60 for this orifice (as per BS 1042)

ρw = Water density in kg.m-3

∆p = Pressure drop in Pascals

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Typical Tap Water Density

1005

1000
Density (kg/m3)

995

990

985

980
0 10 20 30 40 50 60
Temperature (°C)

Figure 26 Typical Water Density

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Preparation Experiments

These experiments are to help the students become familiar with the equipment and prepare it for use
in other experiments.

The Temperature Transmitter (TT) and RTD are very accurate devices, already
NOTE calibrated by their manufacturer. They do not need any setting up and should not
need recalibrating.

Experiment P1 - To Set up the Flow Transmitters

Aims
To set up the Flow Transmitters for a percentage output.

To demonstrate how to bleed and set the Flow transmitters.

You will bleed a small amount of water from the transmitters, so you will need a
cloth or small container to help catch the water.
NOTE
You do not need hot water for this procedure.
Do not forget to switch over the two-way taps to connect to the Hot Water or
Drain orifice units.

Procedure
1. Use a fundamental volumetric (measured volume of water) or gravimetric (measured weight of
water) measurement method to check that the cold water supply is approximately as shown in
Technical Specifications on page 15. Use your inline control valve of your water supply to
reduce the flow if needed. When the flow rate is correct, use your in-line on/off valve to stop the
flow.

2. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

3. Connect the compressed air supply.

4. Fully open the Process Vessel Drain Valve and Overflow Valve, and your cold water on/off valve.

5. Refer to the instructions supplied for the Cold Flow Transmitter (FT1) and check that it is set for
percentage output (PCT), not engineering units (EGU).

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6. Use the spanner (supplied) to open the bleed screws of the Flow Transmitter and bleed out any
trapped air (see Figure 27).

NOTE Trapped air in the Transmitter pressure pipes will cause faulty readings.

High pressure Low pressure

leg bleed screw leg bleed screw

Suitable
container to
catch any
water drips

Figure 27 To Open the Bleed Screws

7. With no flow, zero the Flow Transmitter display and save its new settings.

8. On the Patch Panel, connect Reference Signal 1 to Control Valve 1 (CV1) and set it to 100% (fully
open).

9. Allow water to enter the Process Vessel and drain out of the Drain pipe at the maximum flow.

10. With full flow, set the span of the Flow Transmitter display and save its new settings.

11. The transmitter is now set to give 0 to 100% output (4 to 20 mA) for flows between zero and
maximum available. It should not need re-setting unless the maximum cold water input flow rate
changes.

12. Reduce the output of Reference Signal 1 down to 0% (valve closed). Connect Reference Signal 1 to
the Control Valve 2 (CV2) and repeat the procedure for the Hot Flow/Drain Transmitter. The hot
water flow rate must as described in Technical Specifications on page 15.

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Experiment P2 - To Set Up the Level Transmitter

Aims
To set up the Level Transmitter for a percentage output.

To show the difference between dry leg and wet leg operation.

To demonstrate how to bleed and set the Level Transmitter.

You will bleed a small amount of water from the transmitter, so you will need a
NOTE cloth or small container to help catch the water.
You do not need hot water for this procedure.

Procedure 1 - Dry Leg Operation

Note: This is for dry leg operation, where the low pressure leg remains dry, only the high pressure leg
measures the pressure increase as the water level increases.

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Connect the compressed air supply.

3. Fully open the Process Vessel Overflow Valve and close its Drain Valve.

4. Refer to the instructions supplied for the Level Transmitter (LT) and check that it is set for percentage
output (PCT), not engineering units (EGU).

5. On the Patch Panel, connect Reference Signal 1 to Control Valve 1 (CV1) and set it to 100% (fully
open).

6. Open the cold water on/off valve and allow water to enter the Process Vessel until it is just seen at
the bottom of the water level indicator (see Figure 28). Shut the cold water on/off valve (or unplug
the Patch Panel lead to CV1).

7. Use the spanner (supplied) to open the bleed screws of the Level Transmitter and bleed out any
trapped air in the high pressure leg, and any trapped water in the low pressure leg (see Figure 29).
Check that the water level in the Process Vessel is still just at the bottom of the water level indicator.

Trapped air in the high pressure leg will cause faulty readings.
NOTE
For dry leg operation - trapped water in the low pressure leg will cause faulty
readings.

8. With minimum level, zero the Level Transmitter display and save its new settings.

9. Open the cold water inlet valve and allow water to fill the Process Vessel until it reaches the top of
the level indicator (see Figure 28). Shut the cold water on/off valve (or unplug the Patch Panel lead
to CV1).

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Figure 28 Set the Water Level Minimum (Bottom of Level Indicator) and Maximum (Top of Indicator)

Figure 29 To Open the Bleed Screws of the Level Transmitter

10. With maximum level, set the span of the Level Transmitter display and save its new settings.

11. The level transmitter is now set to work in dry leg condition. It will give 0 to 100% output (4 to 20
mA) for levels between minimum and maximum as indicated on the level indicator. It should not
need re-setting unless it is needed for wet leg operation.

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Procedure 2 - Wet Leg Operation

Note: This is for wet leg operation, where the low pressure leg remains full of water. The high pressure
leg measures the pressure increase as the water level increases.

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Connect the compressed air supply.

3. Fully open the Process Vessel Overflow Valve and close its Drain Valve.

4. Refer to the instructions supplied for the Level Transmitter (LT) and check that it is set for percentage
output (PCT), not engineering units (EGU).

5. On the Patch Panel, connect Reference Signal 1 to Control Valve 1 (CV1) and set it to 100% (fully
open).

6. Open the cold water on/off valve and allow the Process Vessel to fill up until water leaves the
Overflow pipe. Shut the Overflow Valve and allow more water into the Process Vessel, so that it fills
the upper (low pressure) leg of the Level Transmitter. Shut the cold water inlet valve (or CV1).

7. Use the spanner (supplied) to open both bleed screws of the transmitter and bleed out any trapped
air.

NOTE For wet leg operation, trapped air in both pressure legs will cause faulty readings.

8. Open the Overflow Valve and use the Drain Valve to carefully reduce the level in the Process Vessel
until it just reaches the bottom of the water level indicator.

9. With minimum level, zero the Level Transmitter display and save its new settings.

10. Open your Cold Water on/off Valve (and CV1) to allow more water back into the Process Vessel until
it reaches the top of the level indicator.

11. With maximum level, set the span of the Level Transmitter display and save its new settings.

12. The Level Transmitter is now set for wet leg operation. It will give 0 to 100% output (4 to 20 mA)
for levels between minimum and maximum as indicated on the level indicator. It should not need
re-setting unless it is needed for dry leg operation.

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Experiment P2a - Comparison of Wet and Dry Leg Operation

Aim
To demonstrate the difference between Wet and Dry Leg operation of the Level Transmitter.

Procedure
1. Set up the Study Station as described in Procedure 1 - Dry Leg Operation on page 31.

2. Close the Drain Valve and open the Overflow Valve. Slowly fill the Process Vessel and monitor the
reading increase on the Level Transmitter.

3. As the level in the Process Vessel reaches maximum, shut the Overflow Valve. Note the reading on
the level transmitter as water starts to pour into its ‘dry leg’.

4. Now stop the water supply, open the Overflow Valve, and slowly open the Drain Valve until the
water level reaches the bottom of the Process Vessel. Note the reading on the Level Transmitter.

5. Set up the Study Station as described in Procedure 2 - Wet Leg Operation on page 33.

6. Repeat the test.

Questions
Why is the low pressure leg connected to the Process Vessel and not just open to atmosphere?

For the dry leg operation:

• What happened to the Level Transmitter reading as the water started to fill its ‘dry leg’?
• As the water level dropped, what effect did the water in the dry leg have on the 0% water
level reading?

For the wet leg operation, did the excessive water level cause any problems for the Level Transmitter?

Can you describe the disadvantages and advantages of wet leg and dry leg operation?

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Experiment P3 - To Set Up the Pressure Transmitter

Aim
To set up the Pressure Transmitter for a percentage output.

To demonstrate how to set the Pressure Transmitter.

This transmitter is actually measuring air pressure in the vessel, so it does need to
NOTE be bled.
You do not need hot water for this procedure.

For safety reasons and ease of use you must use 1 bar as the maximum pressure
CAUTION for any pressure experiments. The Pressure Relief Valve will start to open at
approximately 2 bar.

Procedure
1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Shut the Cold Water on/off Valve. Fully open the Overflow and Drain Valves.

3. Connect the compressed air supply and set it to 1.5 bar.

4. Refer to the instructions supplied for the Pressure Transmitter (PT) and check that it is set for
engineering units (EGU) and displayed in bar.

5. With no pressure (other than atmospheric), zero the Pressure Transmitter display and save its new
settings.

6. Shut the Overflow and Drain Valves.

7. On the Patch Panel, connect Reference Signal 1 to Control Valve 1 (CV1) and set it to 100% (fully
open).

8. Fully open the Cold Water Inlet Valve and allow water to flow into the Process Vessel. When the
Pressure Transmitter indicates 1 bar, close CV1.

9. With 1 bar pressure, set the span of the Pressure Transmitter display and save its new settings.

10. Now set the pressure Transmitter Display to read in percentage (PCT) and not engineering units
(EGU).

11. The Pressure Transmitter is now set. It will give 0 to 100% output (4 to 20 mA) for gauge pressures
between minimum (atmospheric) and 1 bar. It should not need re-setting.

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Experiment P4 - To Check the Control Valves

Aim
To check the working range of the valves and determine their flow linearity.

The Control Valves and Positioners are calibrated and set at the factory and
NOTE should not need re-calibrating.

Procedure
1. Create a blank Results Table, similar to Table 6.

Increasing Signal Decreasing Signal

Reference Signal Reference Signal

(%) Flow (%) (%) Flow (%)

0 100
10 90
20 80
30 70
40 60
50 50
60 40
70 30
80 20
90 10
100 0

Table 6 Blank Results Table

2. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

3. Connect the compressed air supply and set it to 1.5 bar.

4. On the Patch Panel, connect Reference Signal 1 to the cold water Control Valve (CV1) and set it to
0%.

5. Fully open the Overflow and Drain Valves and the Cold Water on/off Valve. Water will enter the cold
water inlet pipe, but will be stopped by Control Valve 1 (CV1).

6. Bleed the pressure connections to the Cold Water Flow Transmitter (FT1) as described in
Experiment P1 - To Set up the Flow Transmitters on page 29. Check that with no flow, the
Flow Transmitter indicates 0% flow (+/-1%).

7. Re-check that the Reference Signal is set to 0% and note the cold water flow into your results table.

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8. Increase the reference signal in steps of 10% as shown in the results table and at each step, allow
the flow to stabilize and record the cold water flow.

9. Repeat for a decrease in signal.

10. Repeat the procedure for the Hot Water Control Valve (CV2) and its flowmeter (FT2).

11. Plot graphs of flow (in %) against reference signal (in %) to see the flow linearity of the valves.

Questions
How linear is the flow through each valve?

Was there a difference between the curves for increasing and decreasing signals?

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Experiment P5 - Use of the Paperless Chart Recorder

Aim
To demonstrate the use of the Chart Recorder to show varying signals.

Procedure

NOTE You do not need any water flow for this experiment.

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. On the Patch Panel, connect Reference Signal 1 to Channel 1 of the Chart Recorder.

3. Set the Reference Signal to 0%.

4. On the Chart Recorder, set to a chart speed of approximately 300 mm/hour.

5. Increase the Reference Signal slowly to 100% and check that the Chart Recorder shows the trace,
showing the increase from 0 to 100%.

6. Repeat for the other five channels.

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Experiment P6 - Basic Use of a Controller

Aim
To demonstrate the basic use of a Controller, including manual and automatic control and the use of a
Remote Set Point (RSP).

Procedure

You do not need any water flow for this experiment.

NOTE You may use either controller, but this experiment shows the use of Controller 1.
You must press the W/P button on the controller to set it to ‘P’ (panel operation).

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Use the R/L button to set the controller to ‘L’ (local set point).

3. On the Patch Panel, connect:

Output Input Signal Loop

Reference Signal 1 Controller MV (C1)

(socket 1) Measurement
Reference Signal 1 Chart Recorder Variable (MV)
(socket 2) (Channel 3)

Controller Output a (C1) Chart Recorder Output

TO (Channel 2)

Reference Signal 2 Chart Recorder

(socket 1) (Channel 1)
Remote Set Point
Reference Signal 2 Controller
(socket 2) RSP (C1)

Manual Operation with Local Set Point

4. Use the A/M button to set the Controller to Manual operation. Set Reference Signal 1 (Measurement
Variable) to 0% and the controllers local set point to 0%.

5. Adjust the Controller output slowly from 0 to 100% and back down to 0%. Check that its output
display rises up and down.

6. Adjust the Controller local set point slowly from 0 to 100% and back down to 0%. Check that its
set point display rises up and down.

7. Adjust Reference Signal 1 from 0% to 100% and back down to 0%. Check the measurement value
display of the Controller rises up and down.

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Remote Set Point

8. Reduce all levels back to 0%. Use the R/L button to set the controller for a Remote Set Point (R).

9. Adjust Reference Signal 2 from 0% to 100% and back down to 0%. Check that the Controller Set
Point display rises up and down.

Automatic Operation

10. Set the Controller Parameters to:

PF IF DF
Proportional Integral Feedback Derivative Feedback
Feedback (%) (minutes) (minutes)

100 0.01 0.01

11. Set the Chart Recorder speed to approximately 300 mm/h.

12. Reduce the Reference Signals and Controller Output down to 0% and set the Controller into
Automatic Control with Remote Set Point. Note that the Controller output will immediately increase
to maximum.

13. Slowly increase the Remote Set Point (Reference Signal 2) to 50%. Slowly increase the Measurement
Variable (Reference Signal 1) to 50% and check that the Controller Output automatically reduces
as the Measurement Value becomes similar to the Set Point.

14. Now increase the Measurement Value (Reference Signal 1) to 100% and note that the Controller
output automatically falls to 0%.

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Experiment P7 - To Check a Computing Relay

Aim
To demonstrate the mathematical function of a Computing Relay.

Procedure

You do not need any water flow for this experiment.

NOTE
You may use either relay, but this experiment shows the use of Relay 1.

1. Create a Blank Results Table, similar to Table 7.

Theoretical
Input A Input B Input C Actual Output Output (%)
(%) (%) (%) Gain k (%) = B+k(A-C)

0 0 0 0 (0%) 0

50 50 50 1 (20%) 50

50 50 50 2 (40%) 50

100 50 50 1 (20%) 100

Table 7 Blank Results Table

2. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

3. On the Patch Panel, connect:

Output Input

Reference Signal 1 Computing Relay

(socket 1) Input A (R1)

Reference Signal 2 Computing Relay

(socket 1) Input B (R1)
TO
Controller Output a (C1) Computing Relay
Input C (R1)

Computing Relay Chart Recorder

Output (R1) Channel 1

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4. Set Controller 1 to manual operation and its output to 0%. Set both Reference Signals to 0%.

5. Set the gain (k) of the Computing Relay to 0.

6. Adjust the Reference Signals, the Controller output and the Computing Relay gain to different
levels. Calculate the theoretical output and compare it with the actual output. Table 7 gives some
suggested examples.

All three inputs of the relays must be connected to a signal between 0 and 100%,
NOTE or the output will be wrong. They will ‘see’ unused inputs as an unpredictable
negative value.

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Process Control Experiments

These experiments demonstrate the most common examples of process control. The user may create
their own experiments to meet the needs of their training course.

Students must do the Preparation Experiments (see Preparation Experiments on page 29) before
they do the Process Control Experiments.

Important Note - PID Values

The PID values used for these experiments may not be the optimum values for the best response. The
values used are approximate and based on repeated tests or found by use of the controllers self-tuning
ability. You may find that you can improve the system response by careful adjustment of the PID values.

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Experiment PC1 - Basic Flow Control

Aim
To demonstrate the basic principles of flow control by means of flow feedback.

Notes
The cold flow is measured by the Flow Transmitter and fed back to the Flow Controller, that adjusts the
Control Valve.

Controller 1 is used as the Flow Controller (FC).

Process Diagram

FC
PT

PROCESS
VESSEL

TT

LT

OVERFLOW

DRAIN

Fully open
FT2 CV2
HOT

FT1 CV1
Disturbance

COLD

Figure 30 Diagram for Basic Flow Control

Procedure

NOTE You do not need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Shut the hot and cold water supply valves. Fully open the Overflow and Drain Valves.

3. Set the Controller for Remote Set Point.

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4. On the Patch Panel, connect:

Output Input Signal Loop

Flow Transmitter FT1 Controller MV (C1)

(socket 1) Measurement
Flow Transmitter FT1 Chart Recorder Variable (MV)
(socket 2) (Channel 2)

Controller Output a (C1) Control Valve CV1

(socket 1)
TO Output
Controller Output a (C1) Chart Recorder
(socket 2) (Channel 3)

Reference Signal 1 Chart Recorder

(socket 1) (Channel 1)
Set Point
Reference Signal 1 Controller RSP (C1)
(socket 2)

5. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

480 0.04 0

6. Open the Cold Water supply ON/OFF Valve and set the Controller Remote Set Point (Reference 1)
to 50%.

7. Check that the Flow Transmitter has been bled as described in Experiment P1 - To Set up the
Flow Transmitters on page 29.

8. Set the Controller to automatic control. The controller output should slowly adjust itself to open the
Control Valve until the Measurement Variable is similar to the Set Point.

9. Allow a few seconds for the system to stabilize and set the Chart Recorder speed to approximately
300 mm/h.

10. To test the flow control system, use the Cold Water ON/OFF Valve to reduce the flow slightly (a flow
disturbance). The Controller output should increase and open the Control Valve to restore the flow
to 50%.

11. Fully open the Cold Water ON/OFF valve to return the incoming flow to full and observe the
Controller output.

12. Repeat the experiment with Controller Remote Set Points of 40% and 60%.

Questions
How well does the Flow Control operate?

After a disturbance, how long does it take for the Measurement Variable to be equal to the Set Point?

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Experiment PC2 - Basic Level Control

Aim
To demonstrate the basic principles of level control by means of level feedback.

Notes
The level is measured by the Level Transmitter and fed back to the Level Controller, that adjusts the
Control Valve.

Controller 1 is used as the Level Controller (LC).

Process Diagram

LC
PT

PROCESS
VESSEL

TT

LT

OVERFLOW

DRAIN

Part open
+ disturbance FT CV2
HOT

FT CV1
COLD

Figure 31 Process Diagram for Basic Level Control

Procedure

NOTE You do not need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Make sure that the Level Transmitter has been set up as described in Experiment P2 - To Set Up
the Level Transmitter on page 31.

3. Shut the hot and cold water supply valves. Fully open the Overflow Valve.

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4. Set the Controller for Remote Set Point.

5. On the Patch Panel, connect:

Output Input Signal Loop

Level Transmitter LT Controller MV (C1)

(socket 1) Measurement
Level Transmitter LT Chart Recorder Variable (MV)
(socket 2) (Channel 3)

Controller Output a (C1) Control Valve CV1

(socket 1)
TO Output
Controller Output a (C1) Chart Recorder
(socket 2) (Channel 3)

Reference Signal 1 Chart Recorder

(socket 1) (Channel 1)
Set Point (SP)
Reference Signal 1 Controller RSP (C1)
(socket 2)

6. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

100 0.19 0

7. Open the Cold Water ON/OFF Valve and set the Controller Remote Set Point to 50%. Set the
Controller to automatic control.

8. Set the Drain Valve partly open, to allow a small amount of water to flow out of the Process Vessel.
The controller output should adjust itself to open the Control Valve until the Measurement Variable
is similar to the Set Point. You should see the water level approximately 50% up the level gauge on
the Process Vessel.

9. Allow a few minutes for the system to stabilize and set the Chart Recorder to approximately 300
mm/h.

10. To test the level control system, fully open the Drain Valve for a few seconds to reduce the level
slightly (a level disturbance) and return it to its original setting. The Controller output should
increase and open the Control Valve to restore the level to 50%.

11. Return the Drain Valve back to give a small outlet flow and observe the Controller output.

12. Repeat the experiment with Controller Local Set Points of 40% and 60%.

Questions
How well does the Level Control operate?

After a disturbance, how long does it take for the Measurement Variable to be equal to the Set Point?

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Experiment PC3 - Basic Pressure Control

Aim
To demonstrate the basic principles of pressure control by means of pressure feedback.

Notes
The pressure is measured by the Pressure Transmitter and fed back to the Pressure Controller, that adjusts
the Control Valve.

Controller 1 is used as the Pressure Controller.

Process Diagram

PC
PT

PROCESS
VESSEL

TT

LT
Closed

OVERFLOW

DRAIN

Slightly open
FT CV2
HOT

FT CV1
COLD

Figure 32 Process Diagram for Basic Pressure Control

Procedure

NOTE You do not need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Make sure that the Pressure Transmitter has been set up as described in Experiment P3 - To Set
Up the Pressure Transmitter on page 35.

3. Shut the hot and cold water supply valves, and the Overflow Valve.

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4. Set the controller to Remote Set Point.

5. On the Patch Panel, connect:

Output Input Signal Loop

Pressure Transmitter PT Controller MV (C1)

(socket 1) Measurement
Pressure Transmitter PT Chart Recorder Variable (MV)
(socket 2) (Channel 2)

Controller Output a (C1) Control Valve 1

(socket 1)
TO Output
Controller Output a (C1) Chart Recorder
(socket 2) (Channel 3)

Reference Signal 1 Chart Recorder

(socket 1) (Channel 1)
Set Point (SP)
Reference Signal 1 Controller RSP (C1)
(socket 2)

6. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

25 0.19 0

7. Open the Cold Water ON/OFF Valve and set the Controller Remote Set Point to 50%. Set the
Controller to automatic control.

8. Set the Drain Valve partly open, to allow a tiny amount of water to flow out of the Process Vessel.
The controller output should adjust itself to open the Control Valve until the Measurement Variable
is similar to the Set Point. You should see the water level rise up the level gauge on the Process
Vessel.

9. Allow a few minutes for the system to stabilize and set the Chart Recorder to approximately 300
mm/h.

10. To test the pressure control system, fully open the Drain Valve for a few seconds to reduce the
pressure slightly (a pressure disturbance) and return it to its original setting. The Controller output
should increase and open the Control Valve to restore the pressure to 50%.

11. Repeat the experiment with Controller Local Set Points of 40% and 60%.

Questions
How well does the Pressure Control operate?

After a disturbance, how long does it take for the Measurement Variable to be equal to the Set Point?

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Experiment PC4 - Basic Temperature Control

Aim
To demonstrate the basic principles of temperature control by means of temperature feedback.

Notes
The temperature is measured by the Temperature Transmitter and fed back to the Temperature
Controller, that adjusts the Cold Water Control Valve.

A fixed low amount of hot water continually enters the Process Vessel.

The Temperature Controller need to shut the cold water supply to increase the temperature, so its
output must be reversed.

Process Diagram

TC
PT
Output reversed

Reference Signal
+ disturbance
PROCESS
VESSEL

TT

LT
Open

OVERFLOW

DRAIN

FT
HOT

FT

COLD

Figure 33 Process Diagram for Basic Temperature Control

Procedure

NOTE You need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Open the Overflow and Drain Valves.

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3. Set the Controller for Remote Set Point and REVERSE output.

4. On the Patch Panel, connect:

Output Input Signal Loop

Temperature Transmitter TT Controller MV (C1)

(socket 1) Measurement
Temperature Transmitter TT Chart Recorder Variable (MV)
(socket 2) (Channel 3)

Controller Output a (C1) Control Valve CV1

(socket 1)
Output
Controller Output a (C1) TO Chart Recorder
(socket 2) (Channel 2)

Reference Signal 1 Chart Recorder

(socket 1) (Channel 1)
Set Point (SP)
Reference Signal 1 Controller RSP (C1)
(socket 2)

Reference Signal 2 Control Valve CV2 Preset Hot Flow

5. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

100 0.1 0

6. Open both water ON/OFF valves. Set Reference Signal 2 (hot water flow) to give a flow rate of
approximately 12%. The measurement variable should increase to a maximum of approximately
50% (50°C), set by the maximum temperature of the hot water supply.

NOTE It is of no use to adjust the Set Point to any higher than 50% (50°C), as the
maximum temperature is actually set by the hot water supply.

7. Set the Controller Remote Set Point to 25%. Set the Controller to automatic control. The controller
output should adjust itself to open the cold water Control Valve until the Measurement Variable is
similar to the Set Point.

8. Allow a few minutes for the system to stabilize.

9. To test the temperature control system, increase the value of Reference Signal 1 to give an increase
in hot water flow by 5% to increase the temperature slightly (a temperature disturbance). The
Controller output should increase and open the Cold Water Control Valve to restore the
temperature to 25%.

10. Reduce Reference Signal 1 to return the hot water flow to 12% and observe the Controller output.

11. Repeat the experiment with Controller Remote Set Points of 20% and 30%.

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Questions
How well does the Temperature Control operate?

After a disturbance, how long does it take for the Measurement Variable to be equal to the Set Point?

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Experiment PC5 - Cascade Control of Level

Aim
To demonstrate the principles of cascade control of level by means of level feedback and slave flow
control.

Notes
Controller 2 is the Master (Level) Controller. Controller 1 is the Slave (Flow) Controller. The Process Vessel
level is fed back to the Master Controller. The Master Controller output is the Remote Set Point for the
Slave Controller. The Slave Controller maintains a constant flow, with a value determined by the output
of the Master Controller.

Process Diagram

Remote
Setpoint

FC LC
PT

PROCESS
VESSEL

TT

LT
Open

OVERFLOW
Part open
+ disturbance

DRAIN

FT
HOT

FT

COLD

Figure 34 Process Diagram for Cascade Control of Level

Procedure

NOTE You do not need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Make sure that the Level Transmitter has been set up as described in Experiment P2 - To Set Up
the Level Transmitter on page 31.

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3. Shut the hot and cold water supply valves, and the Drain Valve. Open the Overflow Valve.

4. Set both controllers for Remote Set Points.

5. On the Patch Panel, connect:

Output Input Signal Loop

Level Transmitter LT Controller MV (C2)

(socket 1) Level
Measurement
Level Transmitter LT Chart Recorder Variable (MV)
(socket 2) (Channel 3)

Flow Transmitter FT1 Controller MV (C1) Flow Measurement

(socket 1) Variable (MV)

Controller Output a (C1) Control Valve CV1

(socket 1)
Output
Controller Output a (C1) Chart Recorder
(socket 2) TO (Channel 2)

Controller Output a (C2) Controller RSP (C1)

(socket 1) Remote Set Point
Controller Output a (C2) Chart Recorder (SP)
(socket 2) (Channel 1)

Reference Signal 1 Chart Recorder

(socket 1) (Channel 4)
Level Set Point
Reference Signal 1 Controller RSP (C2)
(socket 2)

6. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Controller Feedback (%) (minutes) (minutes)

Level 25 0.19 0

Flow 200 0.04 0.00

7. Open the Cold Water ON/OFF Valve and set the Level Controller Remote Set Point to 50%.

8. Bleed the Flow Transmitter as described in Experiment P1 - To Set up the Flow

Transmitters on page 29.

9. Set both Controllers to automatic control. Partly open Drain Valve to allow a small flow of water to
pass out of the Process Vessel.

10. The Level Controller output should increase to raise the Set Point for the Flow Controller until the
Measurement Variable is similar to the Level Set Point. You should see the water level rise up the
level gauge on the Process Vessel.

11. Allow a few minutes for the system to stabilize.

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12. To test the level control system, open the Drain Valve for a few seconds to reduce the level slightly
(a level disturbance), then return it to its original setting. The Level Controller output should
increase and force the Flow Controller to increase the flow to restore the level back to 50%.

13. Allow the conditions to stabilize.

14. Reduce the cold water supply flow slightly for a few seconds (a flow disturbance). The Flow
Controller should automatically open the valve a little more to maintain the flow.

15. Repeat the experiment with Level Controller Local Set Points of 40% and 60%.

Questions
How well does the control operate?

After a level disturbance, how long does it take for the Measurement Variable to be equal to the Level
Set Point?

What effect does a flow disturbance have on the level?

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Experiment PC6 - Feedforward Control of Level by Flow

Aim
To demonstrate the basic principles of control by means of signal feedforward.

Notes
It is often better to compensate for disturbances before they happen. In this experiment, the disturbance
is monitored by the flow transmitter downstream of the Process Vessel and fed back upstream to the
controller that should take corrective action before the disturbance affects the level. In this case the
process is a constant level in the Process Vessel, maintained by a constant flow.

Note that the Controller must work in reverse - a drop in drain flow (measurement value) needs a
reduction in inlet flow (output).

This experiment is for demonstration only. This type of control is never used by itself in a real application,
as there is no level feedback and the reversed output strategy gives very poor flow control.

Process Diagram

Reversed Output

FC
PT

PROCESS
VESSEL

TT

LT

OVERFLOW

DRAIN

Disturbance
FT
HOT

FT

COLD

Figure 35 Process Diagram for Feedforward Control of Level

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Procedure

NOTE You do not need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Make sure that the Hot Water/Drain Flow Transmitter is set to measure the pressure drop across the
orifice in the Drain and has been set up as described in Experiment P1 - To Set up the Flow
Transmitters on page 29.

3. Shut the hot and cold water supply valves. Fully open the Overflow Valve.

4. Set the Controller for Remote Set Point. Set its output for REVERSE.

5. On the Patch Panel, connect:

Output Input Signal Loop

Flow Transmitter FT2 Controller MV (C1)

(socket 1)
Outlet Flow (MV)
Flow Transmitter FT2 Chart Recorder
(socket 2) (Channel 3)

Controller Output a (C1) Control Valve CV1

(socket 1)
Output
Controller Output a (C1) Chart Recorder
(socket 2) TO (Channel 2)

Reference Signal 1 Controller RSP (C1)

(socket 1)
Set Point (SP)
Reference Signal 1 Chart Recorder
(socket 2) (Channel 1)

Level Transmitter LT Chart Recorder Level

(socket 1) (Channel 4)

6. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

25 0.19 0

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7. Open the Cold Water ON/OFF Valve and set the Controller to manual control, with an output of
50%.

NOTE The Controller output is reversed, so an increase in indicated output is actually

a decrease in inlet flow.

8. Carefully adjust the Drain Valve until water level in the Process Vessel remains constant at a level of
approximately 25%. Adjust the Controller Remote Set Point to make it equal to the flowrate (SP =
MV).

9. Set the Chart Recorder to approximately 300 mm/h.

NOTE For the next step in the procedure, the level and flow will slowly drop - this is
normal, but it means that you must do the test in a short time.

10. Set the Controller to automatic control. The controller output will try to maintain the Measurement
Variable to equal the Set Point, but the measurement value will slowly drop. The water level will also
slowly drop - this is normal.

11. To test the level control system, open the Drain Valve slightly for a few seconds to increase the outlet
flow (a downstream disturbance). The Controller output should increase and open the Control
Valve to compensate before it affects the slow drop in level.

Questions
How well does the feedforward control operate?

After a disturbance, what happens to the level in the Process Vessel.

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Experiment PC7 - Three Element (Feedforward-Feedback) Control

Aim
To demonstrate the basic principles of three element control.

Notes
Previous experiments have used two elements, a feedback or feedforward signal element and a control
element. Three Element Control uses feedback, feedforward and a control element. This reacts to
changes downstream and in the process. The Flow Controller is the Feedforward Controller, the Level
Controller is the Feedback Controller.

Note that the Flow Controller must work in reverse (a drop in drain flow needs a reduction in inlet flow).

Process Diagram

FC LC
PT
Output
Reversed

PROCESS
VESSEL
A

B TT
B+K(A-C) K = 1

Output

LT
Open

OVERFLOW

Part open
+ disturbance
DRAIN

FT
HOT

FT

COLD

Figure 36 Process Diagram for Three Element Control of Level

Procedure

NOTE You do not need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

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2. Make sure that the Hot Water/Drain Flow Transmitter is set to measure the pressure drop across the
orifice in the Drain and has been set up as described in Experiment P1 - To Set up the Flow
Transmitters on page 29.

3. Make sure that the Level Transmitter has been set up as described in Experiment P2 - To Set Up
the Level Transmitter on page 31.

4. Shut the hot and cold water supply valves. Fully open the Overflow Valve.

5. Set both controllers for Remote Set Point. Set the Flow Controller to reversed output.

6. On the Patch Panel, connect:

Output Input Signal Loop

Flow Transmitter FT2 Controller MV (C1)

(socket 1)
Drain Flow (MV)
Flow Transmitter FT2 Chart Recorder
(socket 2) (Channel 3)

Controller Output a (C1) Computing Relay

(socket 1) Input B (R1)
Flow Output
Controller Output a (C1) Chart Recorder
(socket 2) (Channel 2)

Controller Output a (C2) Computing Relay

(socket 1) Input A (R1)
Level Output
Controller Output a (C2) Chart Recorder
(socket 2) (Channel 1)
TO
Level Transmitter LT Controller MV (C2)
(socket 1)
Level (MV)
Level Transmitter LT Chart Recorder
(socket 2) (Channel 4)

Computing Relay 1 Output (R1) Control Valve

(Socket 1) (CV1)
Control Output
Computing Relay 1 Output (R1) Chart Recorder
(Socket 2) (Channel 5)

Reference Signal 1 Controller RSP (C1) Flow Set Point

(socket 1)

Reference Signal 2 Controller RSP (C2) Level Set Point

(socket 1)

7. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Controller Feedback (%) (minutes) (minutes)

Flow 25 0.19 0

Level 25 0.19 0

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8. Open the Cold Water ON/OFF Valve and set the Controllers to manual control, with an output of
25% for the Level Controller and 75% (reverse of 25%) for the Flow Controller.

9. Set the Computing Relay for a gain of 1 (20%).

10. Adjust the Drain Valve until water level in the Process Vessel remains constant at a level of
approximately 50%. Adjust the Level Controller Set Point (Reference 2) to make it equal to the level
(SP=MV). Adjust the Flow Controller Set Point (Reference 1) to make it equal to the flow (SP = MV).

11. Set the Controllers to automatic control.

12. Allow a few minutes for the system to stabilize.

13. To test the level control system, note the outlet flow and open the Drain Valve slightly for a few
seconds to increase the outlet flow (a downstream disturbance) then carefully shut it to return the
outlet flow back to its original setting. The Relay output should increase and open the Control Valve
to increase the inlet flow before the level drops (you may see a very small drop). The level controller
should maintain the level.

Questions
How well does the feedforward-feedback control operate?

After a disturbance, what happens to the level in the Process Vessel.

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Experiment PC8 - Ratio Control of Flow

Aim
To demonstrate the basic principles of ratio control of flow.

Notes
Flow Controller 1 controls the cold water flow, with feedback from the cold water flow transmitter. The
cold water flow is also fed to Flow Controller 2, which controls the hot water flow to be at a ratio of
exactly half that of the cold water.

Process Diagram

Remote Setpoint x Ratio 0.5

FC1 FC2
PT

PROCESS
VESSEL

TT

LT

OVERFLOW

DRAIN

Fully open
FT
HOT

FT

COLD

Figure 37 Process Diagram for Basic Ratio Control

Procedure

NOTE You do not need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Shut the hot and cold water supply valves. Open the Drain and Overflow Valves.

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3. Use the Controller manufacturers User Guide to check that output b (C1) is configured to output
its measured value from the Cold Flow Transmitter. Check that output b (C2) is set to output its Set
Point. Controller 1 must be set for Remote Set Point, Controller 2 must be set for Remote Set Point.

4. The Remote Set Point (analogue input 4) of Flow Controller 2 must be set to signal source D. Signal
D must be set with a gain of 0.5.

5. On the Patch Panel, connect:

Output Input Signal Loop

Flow Transmitter FT1 Controller MV (C1)

(socket 1)
Cold Flow
Flow Transmitter FT1 Controller RSP (C2)
Measurement
(socket 2)
Variable (MV)
Controller Output b (C1) Chart Recorder
(Channel 1)

Controller Output a (C1) Control Valve CV1

(socket 1)
Cold Output
Controller Output a (C1) Chart Recorder
(socket 2) (Channel 2)

Flow Transmitter FT2 Controller MV(C2)

(socket 1) TO Hot Flow
Measurement
Flow Transmitter FT2 Chart Recorder Variable (MV)
(socket 2) (Channel 3)

Controller Output a (C2) Control Valve CV2

(socket 1)
Hot Output
Controller Output b (C2) Chart Recorder
(socket 2) (Channel 4)

Reference Signal 1 Chart Recorder

(socket 1) (Channel 5) Cold Flow Set
Reference Signal 1 Controller RSP (C1) Point
(socket 2)

6. Set both Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

100 0.19 0

7. Open the Cold Water ON/OFF Valve and set Controller 1 Remote Set Point to 20%. Set both
Controllers to automatic control.

8. Controller 1 output should adjust itself to open the Cold Water Control Valve until the Measurement
Variable is similar to the Set Point. Controller 2 output should adjust itself to achieve a flow of exactly
half that of Controller 1 (approximately 10%).

9. Allow a few seconds for the system to stabilize.

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10. Alter the Remote Set Point of Controller 1 and note the changes in the hot and cold water flow.
They should alter in proportion to the ratio of 0.5.

Questions
How well does the Ratio Control operate?

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Experiment PC9 - Coupled Interactive Control

Aim
To demonstrate the basic principles of coupled interactive control of level and temperature.

Notes
This system has two independent control loops, but each has an effect (interaction) on the other. The
Level Controller controls the water level (cold feed control), with feedback from the Level Transmitter.
The Temperature Transmitter controls the water temperature (hot feed control) with feedback from the
Temperature Transmitter.

Process Diagram

LC TC
PT

PROCESS
VESSEL

TT

LT

OVERFLOW

DRAIN

Part open
FT
HOT

FT

COLD

Figure 38 Process Diagram for Basic Interactive Control - Coupled

Figure 38 shows the Process Diagram for this experiment. Figure 39 shows the Control Diagram for this
type of control. The blocks indicate relative gains of each area of the control system, so that GP = a gain
in the process, and GC = a gain in the Controller. The diagram helps to show how the output of one
controller can affect the process of the other control loop. The affect is represented by the gain blocks
GP12 and GP21, which form a hidden part of the feedback loop.

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Control Block Diagram

Level Temperature
Setpoint Setpoint

+ +
- -
Controllers

GC1 GC2
Feedback Signal

Feedback Signal
GP11 GP12 GP21 GP22
Process

+ +
+ +

Figure 39 Control Block Diagram for Basic Interactive Control

Procedure

NOTE You need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Shut the hot and cold water supply valves, and the Drain Valve. Open the Overflow Valve.

3. Use the Controller manufacturers User Guide to check that output b (C1) of the Level Controller
and output b (C2) of the Temperature Controller are configured to output their Local Set Points.
Both controllers must be set for Local Set Points.

4. On the Patch Panel, connect:

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Output Input Signal Loop

Level Transmitter LT Controller MV (C1)

(socket 1) Level
Measurement
Level Transmitter LT Chart Recorder Variable (MV)
(socket 2) (Channel 1)

Controller Output a (C1) Control Valve CV1

(socket 1)
Level Output
Controller Output a (C1) Chart Recorder
(socket 2) (Channel 2)

Controller Output b (C1) Chart Recorder Level Set Point

(socket 1) (Channel 3)
TO
Temperature Transmitter TT Controller MV (C2)
(socket 1) Temperature
Measurement
Temperature Transmitter TT Chart Recorder Variable (MV)
(socket 2) (Channel 4)

Controller Output a (C2) Control Valve CV2

(socket 1) Temperature
Controller Output a (C2) Chart Recorder Output
(socket 2) (Channel 5)

Controller Output b (C2) Chart Recorder Temperature Set

(socket 1) (Channel 6) Point

5. Set both Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

100 0.19 0

6. Open the Cold Water ON/OFF Valve and set the Level Controller 1 Local Set Point to 20%. Adjust
the Drain Valve so that a low flow leaves the Process Vessel. Set the Temperature Controller Local
Set Point to 25% (or just above your ambient local temperature). Set both Controllers to automatic
control.

7. The Level Controller output should adjust itself to open the Cold Water Control Valve until the Level
Measurement Variable is similar to the Set Point. The Temperature Controller output should adjust
itself to achieve a Temperature Measurement Variable similar to the Set Point.

8. Note the interactive effect each control system has on each other. The measurement values may
never actually stabilize due to this coupled system.

Questions
How well does the Coupled Interactive Control operate?

What kind of problems would you expect from the interaction?

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Experiment PC10 - Decoupled Interactive Control

Aim
To demonstrate the principles of decoupled interactive control of level and temperature.

Notes
This system is similar to the Coupled Interactive Control. It has two independant control loops and each
has an effect (interaction) on the other, but the Computing Relays decouple the hidden feedback loops.
The Level Controller controls the water level (cold feed control), with feedback from the Level
Transmitter. The Temperature Transmitter controls the water temperature (hot feed control) with
feedback from the Temperature Transmitter.

Process Diagrams

LC TC
PT

PROCESS
VESSEL

B B TT
A
S X C A
S X C
B+K(A-C) B+K(A-C)
LT

OVERFLOW

DRAIN

Half open
FT
HOT

FT

COLD

Figure 40 Process Diagram for Decoupled Interactive Control

Figure 40 shows the Process Diagram for this experiment. Figure 40 shows the Control Diagram for this
type of control. As in the coupled interactive control, the blocks indicate relative gains of each area of
the control system, so that GP = a gain in the process, and GC = a gain in the Controller. It can be seen
how the addition of the gain blocks of the Computing Relays (GR12 and GR22) decouple the influence
of each control loop on each other. The external references must be carefully set when the system is in
a steady state.

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Control Block Diagram

Level Temperature
Setpoint Setpoint

+ +
- -
Controllers

GC1 GC2

C A
A GR12 GR22 C
Computing
A-C A-C Relays
B B
Feedback Signal

Feedback Signal
+ +
+ +

GP11 GP12 GP21 GP22

Process

+ +
+ +

Figure 41 Control Block Diagram for Decoupled Interactive Control

Procedure

NOTE You need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Shut the hot and cold water supply valves, and the Drain Valve. Open the Overflow Valve.

3. Use the Controller manufacturers User Guide to check that output b (C1) of the Level Controller
and output b (C2) of the Temperature Controller are configured to output their Set Points. Both
controllers must be set for Local Set Points.

4. On the Patch Panel, connect:

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Output Input Signal Loop

Level Transmitter LT Controller MV (C1)

(socket 1) Level
Measurement
Level Transmitter LT Chart Recorder Variable (MV)
(socket 2) (Channel 1)

Controller Output a (C1) Computing Relay

(socket 1) Input B (R1) Level Output to
Controller Output a (C1) Computing Relay Relays
(socket 2) Input A (R2)

Controller Output b (C1) Chart Recorder Level Set Point

(socket 1) (Channel 3)

Temperature Transmitter TT Controller MV (C2)

(socket 1) Temperature
TO Measurement
Temperature Transmitter TT Chart Recorder Variable (MV)
(socket 2) (Channel 4)

Controller Output a (C2) Computing Relay

(socket 1) Input C (R1) Temperature
Controller Output a (C2) Computing Relay Output to Relays
(socket 2) Input B (R2)

Controller Output b (C2) Chart Recorder Temperature Set

(socket 1) (Channel 5) Point

Reference Signal 1 Computing Relay Preset Decoupling

Input A (R1) Value

Reference Signal 2 Computing Relay Preset Decoupling

Input C (R2) Value

Computing Relay Output (R1) Control Valve (CV1) Level Output

Computing Relay Output (R2) Control Valve (CV2) Temperature

Output

5. Set both Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

100 0.19 0

6. Open the Cold Water ON/OFF Valve and set the Level Controller 1 Local Set Point to 20%. Adjust
the Drain Valve so that a low flow leaves the Process Vessel. Set the Temperature Controller Local
Set Point to 25% (25°C) or approximately 5% above your local ambient temperature.

7. Set both computing relay gains to 1 (20%) and both reference signals to 40%. With both controllers
in manual control, carefully adjust their outputs so that their measured values become
approximately equal to the set points and maintain a steady state (this may take several minutes).

8. Carefully adjust each reference signal to match the output of its opposite controller (for example -
reference signal 1 must match the output of the Temperature Controller). This decouples the
influence of the controller.

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9. Set both Controllers to automatic control. The Level Controller output should maintain the Level in
the Process Vessel. The Temperature Controller output maintain the Temperature in the Process
Vessel.

10. Allow a few seconds for the system to stabilize.

11. Alter the Local Set Point of the Level Controller and note the reduced effect it has on the
Temperature.

12. Alter the Local Set Point of the Temperature Controller and note the reduced effect it has on the
Level.

Questions
How well does the Decoupled Interactive Control operate?

Does the decoupling solve any problems?

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Experiment PC11 - Split Range Control of Temperature

Aim
To demonstrate the basic principles of split range control.

Notes
The Temperature Controller output is split to control the hot and cold water flow as shown in Figure 43,
with feedback from the Temperature Transmitter.

Process Diagram

Remote
Set Point
TC C
PT

PROCESS
VESSEL

Reference TT
Signal 1

LT

OVERFLOW

DRAIN

FT
HOT

FT

COLD

Figure 42 Process Diagram for Split Range Control

Overall Split Range

Controller Output
Output to Valves
100% 100%

Hot Valve
Opens - Output 1 (a) INC/INC

50% 0%

Cold Valve
Closes - Output 2 (b) INC/DEC

0% 100%

Figure 43 Split Range Operation

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Procedure

NOTE You need hot water for this experiment

1. Switch on the power to the Study Station and make sure that all fault switches are off (lamps off).

2. Shut the hot and cold water supply valves. Open the Drain and Overflow Valves.

3. Use the Controller manufacturers User Guide to check that the outputs of Controller 1 are
configured for split range output, with analogue output 1 set to INC/INC and analogue output 2
set to INC/DEC. Do not set a deadband. Use Reference Signal 1 as an external Set Point and check
that Controller 1 is set for Remote Set Point.

4. On the Patch Panel, connect:

Output Input Signal Loop

Temperature Transmitter TT Controller MV (C1)

(socket 1) Temperature
Measurement
Temperature Transmitter TT Chart Recorder Variable (MV)
(socket 2) (Channel 1)

Controller Output a (C1) Control Valve CV2

(socket 1)
Hot Output
Controller Output a (C1) Chart Recorder
(socket 2) (Channel 2)
TO
Controller Output b (C1) Control Valve CV1
(socket 1)
Cold Output
Controller Output b (C1) Chart Recorder
(socket 2) (Channel 3)

Reference Signal 1 Controller Remote Set

(socket 1) Point RSP (C1) Temperature
Reference Signal 1 Chart Recorder Set Point
(socket 2) (Channel 4)

5. Set the Controller Parameters to:

Proportional Integral Time Derivative Time

Feedback (%) (minutes) (minutes)

25 0.19 0.1

6. Open the Hot and Cold Water ON/OFF Valves and set the Temperature Controller Remote Set Point
to 30% (or approximately 10°C above your ambient temperature). Set the Controller to automatic
control.

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7. The Controller outputs should adjust one or both valves until the Measurement Variable is similar
to the Set Point.

8. Allow a few seconds for the system to stabilize.

9. Alter the Remote Set Point of the Controller and note the effect.

10. Try the different split range control output methods available from the Controller and decide which
method works best.

Overall Split Range

Controller Output
Output to Valves
100% 0%

Hot Valve
Closes - Output 1 (a) INC/DEC

50% 100%

Cold Valve
Opens - Output 2 (b) INC/INC

0% 0%

Method 2

Overall Split Range Overall Split Range

Controller Output Controller Output
Output to Valves Output to Valves
100% 100% 100% 0%

Hot Valve Hot Valve

Opens - Output 1 (a) INC/INC Closes - Output 1 (a) INC/DEC

0% 100%
50% 50% 0%
100%

Cold Valve Cold Valve

Opens - Output 2 (b) INC/INC Closes - Output 2 (b) INC/DEC

0% 0% 0% 100%

Method 3 Method 4

Figure 44 Different Methods of Split Range Control

Questions
How well does the Split Range Control operate?

Which method works best?

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Experiment PC12 - The Elements of PID Feedback Control and

Their Effects

Aim
To demonstrate the three elements of PID feedback control and their effects in a flow control system
with feedback of flow.

Procedure
1. Set up the equipment as in Experiment PC1 - Basic Flow Control on page 44.
This experiment gives a short response time, which helps to demonstrate the effects of PID control
more clearly and quickly.

2. Set the Chart Recorder for approximately 600 mm/h chart speed.

3. Leave the Set Point at 50% and repeat the experiment four times (as shown in Table 8). Each time,
adjust the Controller function (‘P, PD’ or ‘PI, PID’) and its parameters to those given in Table 8.

Proportional
Controller Feedback Integral Time Derivative Time Type of
Function Test (%) (minutes) (minutes) Feedback

1 200 N/A 0
P, PD Proportional Only
2 100 N/A 0

Proportional plus
3 200 0.1 0
Integral (P+I)
PI, PID 4 200 0.1 5.0 Proportional plus
Integral plus
Derivative (P+I+D)

Table 8 Different PID Parameters

Question
Note the Measurement Valve before and after a flow disturbance, does it reach the Set Point in all the
tests?

From the Chart Recorder Traces, what do you notice about the effects of each parameter?

For the proportional only control, can you suggest an improvement without the need to add an integral
term?

In your opinion, what settings give the best overall control?

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Fault Finding Tests

The fault switches (pushbuttons) at the side of the Study Station allow the teacher to create faults in the
control system. These faults can be applied during repeat runs of the experiments in this manual, or one
at a time as part of a series of fault finding tests.

TecQuipment recommend that the student is familiar with the Study Station and has done all the
Preparation and Process Control Experiment before they do the Fault Finding Tests.

These Fault Finding Tests are basic suggestions. The user may extend the tests to meet the needs of their
course.

Test FF1- Pressure Transmitter Fault

1. Ask the student to set up the Study Station for Experiment PC3 - Basic Pressure Control on
page 49.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB1.

3. The student should immediately note the absence of a Measurement Value and the automatic
increase in output.

Test FF2 - Temperature Transmitter Fault

1. Ask the student to set up the Study Station for Experiment PC4 - Basic Temperature
Control on page 51.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB2.

3. The student should immediately note the absence of a Measurement Value and the automatic
increase in output.

Test FF3 - Level Transmitter Fault

1. Ask the student to set up the Study Station for Experiment PC2 - Basic Level Control on
page 47.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB3.

3. The student should immediately note the absence of a Measurement Value and the automatic
increase in output.

Test FF4 - Hot/Drain Flow Transmitter (FT2) Fault

1. Ask the student to set up the Study Station for Experiment PC6 - Feedforward Control of
Level by Flow on page 57.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB4.

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3. The student should immediately note the absence of a Measurement Value and the automatic
decrease in output.

Test FF5 - Cold Flow Transmitter (FT1) Fault

1. Ask the student to set up the Study Station for Experiment PC1 - Basic Flow Control on
page 44.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB5.

3. The student should immediately note the absence of a Measurement Value and the automatic
increase in output.

Test FF6 - Controller 1 Output Fault

1. Ask the student to set up the Study Station for Experiment PC1 - Basic Flow Control on
page 44.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB6.

3. The student should immediately note the sudden stop in flow and no recorded output on the chart
recorder, yet the controller still shows an indicated output.

Test FF7 - Controller 2 Output Fault

1. Ask the student to set up the Study Station for Experiment PC5 - Cascade Control of Level on
page 54.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB7.

3. The student should immediately note the sudden stop in flow, the absence of a recorded output
signal from the Level Controller and the Remote Set Point signal to the Flow Controller. Yet, the
controller still displays an output.

Test FF8 - Control Valve 2 Input Fault

1. Ask the student to set up the Study Station for Experiment PC4 - Basic Temperature
Control on page 51.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB8.

3. The student should immediately note the absence of the reference signal and the uncontrolled
reduction in temperature.

Test FF9 - Control Valve 1 Input Fault

1. Ask the student to set up the Study Station for Experiment PC1 - Basic Flow Control on
page 44.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB9.

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3. The student should immediately note the sudden stop in flow, yet the controller still indicates an
output.

Test FF10 - Computing Relay 1 Output Fault

1. Ask the student to set up the Study Station for Experiment PC7 - Three Element
(Feedforward-Feedback) Control on page 61.

2. Allow the student to do the experiment with one Set Point, then switch on Fault Switch PB10.

3. The student should immediately note the uncontrolled reduction in level, yet one or both
controllers may still indicate an output.

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Results

Important Note
For process control experiments, repeatable results are determined by the stability of your water supply
(temperature, flow and pressure) and ambient temperatures. Therefore, these results are sample results
only, based on conditions available at TecQuipment. Your results may be slightly different.

Preparation Experiments

Experiment P2a - Comparison of Wet and Dry Leg Operation

Wet Leg Operation Dry Leg Operation

Pressure

LT LT

Liquid or process material Liquid or process material

Figure 45 Comparison of Wet Leg and Dry Leg Operation

The Process Vessel is pressurised in some experiments, so the Level Transmitter must take this into
account. If the low pressure leg were left open to atmosphere and the Process Vessel is under pressure,
the high pressure leg would read a pressure that is the sum of the water level and the air pressure in the
vessel. This would of course give very high readings. For this reason, the Level Transmitter has the low
pressure leg connected near to the top of the vessel, so that any overall pressures in the vessel are equally
measured and ignored by the differential transmitter.

Students should note that in dry leg operation, the readings become incorrect when water enters the
dry (low pressure) leg. This problem does not occur in wet leg operation, as this leg is already full of
water when the transmitter is calibrated.

Dry leg operation is used for unpressurised and open tanks, the low pressure (dry) leg is left open to
atmosphere. Wet leg operation is best used in pressurised tanks, especially where the Process Vessel
could accidentally become overfilled.

Note that dry leg and wet operation is only applicable to level measurement transmitters that are based
on pressure measurement. There are other types of level transmitters that do not use pressure and are
not affected by the wet leg and dry leg problems.

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Experiment P4 - To Check the Control Valves

Although the valves will mechanically open and close in a very linear manner, their characteristics are
not linear. For each valve your results will show that flow increases more rapidly as the valve approaches
its fully open position, and that flow changes very little (if at all) until the valve is opened to at least 30%.
Graph 1 shows typical results of the test. The results for increasing and decreasing signals should be
similar (but reversed). This helps to check for any mechanical ‘stickiness’ or hysteresis in the valve control
mechanism. The results for each valve should be very similar.

The valve characteristic is determined by the physical construction of that part of the valve that allows
the water to pass. Different types of valves would give very different flow characteristics, for example -
a ‘ball valve’ gives a very different flow characteristic to a ‘needle valve’. The valves fitted to the TE37 are
similar to ‘Globe’ type valves.

CV1 Flow Linearity - Increasing Signal

120

100

80
Flow (%)

60

40

20

0
0 20 40 60 80 100
Signal (%)

Graph 1 Flow Characteristics of the Control Valves

Experiment P7 - To Check a Computing Relay

Theoretical
Input A Input B Input C Actual Output Output (%)
(%) (%) (%) Gain k (%) = B+k(A-C)

0 0 0 0 (0%) 0 0

50 50 50 1 (20%) 49 50

50 50 50 2 (40%) 49 50

100 50 50 1 (20%) 94 100

Table 9 Typical Results for Experiment P7

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The results should show that actual and theoretical results for a Computing Relays should be similar,
which proves the accuracy of the mathematical function. The accuracy is determined by the analogue
meters of the Reference Signals and the adjustment of the gain control on the relay.

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Process Control Experiments

Important Note - PID Values

The PID values used for these experiments may not be the optimum values for the best response. The
values used are approximate and based on repeated tests or found by use of the controllers self-tuning
ability. You may find that you can improve the system response by careful adjustment of the PID values.

Experiment PC1 - Basic Flow Control

Measurement Set Point (Ch1) Output (Ch3)

Variable (Ch2)

14 minutes
at 300 mm/h

0% 50% 100%

Figure 46 Typical Flow Control Results for a 50% Set Point

The flow control should be good, with a short restore time (a few seconds) to a disturbance. The
Controller Output should be almost a mirror image of the Measurement Variable.

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Experiment PC2 - Basic Level Control

Measurement Set Point LC Output

Variable

18 minutes
at 300 mm/h

Disturbance

0% 50% 100%

Figure 47 Typical Level Control Results for a 50% Set Point

The level control should be good with a longer restore time (several minutes) to a disturbance than the
flow control. The Controller Output should be almost a mirror image of the Measurement Variable, with
a few seconds delay and greater magnitude.

Experiment PC3 - Basic Pressure Control

Set Point
Measurement
PC Output Variable

14 minutes
at 300 mm/h

Disturbance

0% 50% 100%

Figure 48 Typical Pressure Control Results for a 50% Set Point

The pressure control should be good with a longer restore time (several minutes) to a disturbance than
the flow control. The Controller Output should be almost a mirror image of the Measurement Variable,
with a few seconds delay and greater magnitude.

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Experiment PC4 - Basic Temperature Control

Temperature
TC
Set Point (25%/25°C)
Measurement Output
Value

Disturbance
18 minutes
at 300 mm/h

0% 50% 100%

Figure 49 Typical Results for Temperature Control at a 25% Set Point

The temperature control should be good with a longer response time (several minutes) to a disturbance
than flow control. The controller output should be very similar (almost in phase) with the Measurement
Variable, but with a greater magnitude. The output is in phase because the controller increases the cold
water feed to counteract an increase in temperature.

Experiment PC5 - Cascade Control of Level

Level Set Point

Measurement Flow
Level Output/RSP Value Output

18 minutes
at 300 mm/h

Level
Disturbance

0% 50% 100%

Figure 50 Typical Results for Cascade Control of Level at a 50% Set Point

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The level control should be good with a longer restore time (several minutes) to a disturbance than the
flow control.

For level disturbances, (see Figure 50) the two controller outputs should be similar to each other and
almost a mirror image of the Measurement Variable, with a few seconds delay and greater magnitude.

For flow disturbances, the flow controller output should be the most active and the level should not be
greatly affected.

Experiment PC6 - Feedforward Control of Level by Flow

Outlet Flow
Level (Measurement Flow Set Point
Value) = MV at start
Controller
Output

Automatic control
18 minutes
at 300 mm/h

Disturbance

0% 50% 100%

Figure 51 Typical Results for Feedforward Control of Level

The feedforward reaction should be good, with a very quick response time to the flow disturbance. The
disturbance is counteracted before it affects the level. However, the level slowly drops due to the lack of
actual level feedback. The outlet flow (measurement value) slowly drops, because the controller works
in reverse. In normal (forward) operation, it would always apply a constant positive output to maintain
the flow (measurement value). In reverse it gives a constant negative output, which eventually becomes
a signal to fully shut the inlet valve, when the difference between the measured variable and set point
exceeds a certain value (determined by its PID feedback values). This effect can be reduced by different
PID values, but the response to the change in flow will not be as good.

Experiment PC7 - Three Element (Feedforward-Feedback) Control

Response to outlet flow changes should be similar to Experiment PC6 - Feedforward Control of
Level by Flow, but level control should be good, with no long term drift.

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FC Output LC Output Output to Valve

Level
Drain Flow

18 minutes
at 300 mm/h

0% 50% 100%

Figure 52 Typical Results for Three Element Control of Level

Experiment PC8 - Ratio Control of Flow

Ratio control should be excellent with hot water flow at exactly half that of cold water flow.

Hot controller
(FC2) output
Cold Flow Setpoint
Hot water flow
Cold water flow Cold controller
(FC1) output

12 minutes
at 300 mm/h

0% 50% 100%

Figure 53 Typical Results for Ratio Control of Flow

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Experiment PC9 - Coupled Interactive Control

Level Set Point Temperature

Temperature Level
Set Point
Temperature MV Output
Output Level MV

14 minutes
at 300 mm/h

0% 50% 100%

Figure 54 Typical Results for Coupled Control of Level and Temperature

Control should be poor to acceptable. Measurement Values will vary quite widely, overall control can be
a little unstable, due to the addition of each Controllers influence on the opposite loop.

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Experiment PC10 - Decoupled Interactive Control

Increase in
Temperature
Set Point

Increase in
30 minutes Level Set Point
at 300 mm/h

Level MV

Temperature MV

0% 50% 100%

Level Set Point

Temperature Set Point

Figure 55 Typical Results for Decoupled Control of Level and Temperature

Control should be good and Measurement Values should be more stable than with coupled control. You
should be able to make changes to the set point or create disturbances and see the response.

The change in output of either controller has very little effect on the measurement variable of the other
control loop. This helps to solve the problem caused by coupled control loops.

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Experiment PC11 - Split Range Control of Temperature

Temperature Measurement
Set Point Variable
Cold Output 2

Hot Output 1

14 minutes
at 300 mm/h

0% 50% 100%

Figure 56 Typical Results for Split Range Control of Temperature

Control should be good (within the limits of the achieveable temperatures). Method 1 should be best.

Output 2 (cold water) should be in phase (with a slight delay) with the measurement variable. Output
1 (hot water) should be 180 degrees out of phase (with a slight delay) with the measurement variable.

Experiment PC12 - The Elements of PID Feedback Control and Their

Effects

Proportional Feedback Only

Flow Set Point

Proportional = 200%
Flow MV Flow Output

600 mm/h

0% 50% 100%

Figure 57 Typical Results for 200% Proportional Feedback only Control of Flow

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Flow Set Point

Proportional = 100%
Flow MV Flow Output

600 mm/h

0% 50% 100%

Figure 58 Typical Results for 100% Proportional Feedback Only Control of Flow

An increase in proportional gain (smaller feedback %) should demonstrate a bigger output response to
a disturbance or change in Set Point, but the Measurement Value will always be much lower than the
Set Point. Proportional gain above unity (lower than 100%) may give unstable operation. Unity gain
may give oscillatory response. With gains higher than 100% (lower than unity), the response to
disturbances may be too small to notice.

The student could add a simple bias to the output to bring its level up enough to meet the set point,
however, this only works well for small variations in set point or disturbances.

Proportional and Integral

Flow Set Point

Proportional = 200%
Integral = 0.1

Flow MV Flow Output

Flow Disturbance

600 mm/h

0% 50% 100%

Figure 59 Typical Results for 200% Proportional and Integral Feedback Control of Flow

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The addition of an integral term should demonstrate an overall increase in output, possibly with
overshoot and the Measurement Value should meet or slightly exceed the Set Point. For a reduction in
inlet flow (disturbance) the measurement value should drop and the controller output should respond
very quickly. Too much derivative will cause large overshoot, so the output will force the measurement
variable to exceed the set point by a large amount.

Proportional, Integral and Derivative

Flow Set Point

Proportional = 200%
Integral = 0.1
Derivative = 5.0

Flow MV Flow Output

Flow Disturbance

600 mm/h

0% 50% 100%

Figure 60 Typical Results for PID Feedback Control of Flow

The addition of derivative should demonstrate a damping of the overall control. Slow, (low frequency)
changes are ignored by the derivative but fast (high frequency) changes cause an increased response.
The Measurement Value should meet or slightly exceed the Set Point. Too much derivative (smaller time)
will cause unstable operation.

This should show that all three elements are needed for good overall control in many control
applications.

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Maintenance and Inspection

General
When it is not in use, disconnect the apparatus from the water supply and open all valves to drain out
any water. Disconnect the apparatus from the compressed air and electrical supplies.

At least once a month, reconnect the compressed air and electrical supplies and open and close all the
valves (do not connect the water supply). This will help to prevent their mechanisms sticking.

To clean the apparatus, wipe clean with a damp cloth - do not use abrasive cleaners or solvents.

Electrical

Only qualified people may do any electrical maintenance that is needed.

WARNING
Ensure the following procedures are followed.

• Assume the apparatus is energised until it is known to be isolated from the electrical supply.
• Use insulated tools where there are possible electrical hazards.
• Confirm that the apparatus earth circuit is complete.
• Identify the cause of a blown fuse or tripped circuit breaker before renewing or resetting.

TE37 Circuit Protection

The fuses for each circuit in the equipment are fitted and labelled inside the main enclosure of the Study
Station. To access the fuses you must remove the back panel. Refer to the Technical Specifications on
page 15 for fuse details.

If a UK-style three pin plug is supplied already fitted to the supply lead, it will contain a 3 A fuse.

NOTE Renew faulty or damaged parts with an equivalent item of the same type or rating.

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Glossary

This guide uses some terms which are in common use in control engineering but need clarifying because
they could be misunderstood.

Deadband or Dead Time An area of operation where there is no control response for a change
in input variable - similar to hysteresis

Derivative Control Control that gives an output determined by a derivative of the

error signal. A fast change in error signal will be countered by a large
derivative action. A slow change in error signal may not be countered by
the derivative action

Error Signal The difference between the setpoint value and the actual measured value
or process variable

Feedback Signal A signal fed back from a process to a controller. This could be the process
variable or the measurement value

Feedforward Signal A signal fed forward to a controller from a stage after the process

Integral Control Control that gives an output determined by the integer of the error signal

Loop Current The signal current from a transmitter to a controller or recorder.

Usually 4 to 20 mA

Measurement Variable (MV) The value of the signal from any measurement device, usually in its actual
units (for example; mmH2O or bar)

PID/PID Control Proportional, Integral and Derivative Control

Process The valves, tanks, pipes and pumps of the plant that convey or hold the
process material

Process Variable (PV) A general term for a variable value in a process, this could be an output
variable or an input variable or a measurement variable

Proportional Control Control that gives an output that is proportional to the error signal. The
amount of proportional control is determined by a gain or proportional
band value.

Rate Action or Pre-act Old terms for derivative control

Reset or Floating Control Old terms for integral control

Set Point (SP) The preset value at which you need the process variable or measurement
variable to be maintained

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Spare Parts and Customer Care

Spare Parts
Check the Packing Contents List to see what spare parts we send with the apparatus.

If you need technical help or spares, please contact your local TecQuipment Agent, or contact
TecQuipment direct.

When you ask for spares, please tell us:

• Your Name
• The full name and address of your college, company or institution
• Your email address
• The TecQuipment product name and product reference
• The TecQuipment part number (if you know it)
• The serial number
• The year it was bought (if you know it)

Please give us as much detail as possible about the parts you need and check the details carefully before
you contact us.

If the product is out of warranty, TecQuipment will let you know the price of the spare parts.

Customer Care
We hope you like our products and manuals. If you have any questions, please contact our Customer
Care department:

Telephone: +44 115 9722611

Fax: +44 115 973 1520

email: customer.care@tecquipment.com

For information about all TecQuipment Products and Services, visit:

www.tecquipment.com

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