YOKOGAWA CENTUM CS
3000 DCS Training Course
UPLOADED BY
Hamid Eghbalpour
WELCOME TO TRAINING CENTER
WELCOME TO TRAINING CENTER
General Rules and regulation
We request the trainee to adhere to the following rules.
♦ Be punctual for all the sessions.
♦ Avoid entering into restricted premises in the office – Factory acceptance
test area and Staff offices.
♦ Smoking is strictly confined to smoking area only.
Training Center i
A. INTRODUCTION TO PROCESS CONTROL SYSTEM
A. INTRODUCTION TO PROCESS CONTROL SYSTEM
This chapter deals with the introduction to process control system, system
concepts of distributed control system and the development history of process
control system.
A.1. PROCESS CONTROL BY CONTROLL ERS
A temperature control loop using a controller is shown in the figure below. The
operator sets the temperature “setpoint (SV)”, and the controller automatically
adjusts the “manipulated variable (MV)” i.e. output (opening of valve which
controls steam flow) so as to minimize the deviation between measured
(temperature) “process variable (PV)” and target value “setpoint”. The process of
adjusting the manipulated variable to minimize the deviation between process
variable and setpoint is called “Feedback control”.
The indicating (PID) controller displays the measured process variable
(temperature of the liquid of the tank), and using a PID (P-Proportional, I-Integral
and D-Derivative) control algorithm, computes the manipulated variable output
(steam flow) that will minimize the deviation between process variable and
setpoint temperatures; i.e. it controls the tank temperature.
Setpoint (SV)
Process Variable (PV)
Water
E/P
Tank Manipulated Variable (MV)
Steam
Valve
Figure: Process Control by A nalog Controller
Training Center A-1
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Sephora Collection Colorful Eyeshado…
A. INTRODUCTION TO PROCESS CONTROL SYSTEM
Setpoint
Input
(Measured or Process Variable) Output (Manipuated Variable)
Control Unit
I/P
Time Lag
Figure: Basic Control Loop
A.2. PROCESS CONTROL FUNCTIONS
The method to directly control process is roughly divided into two categories: the
loop control that inputs analog measured values (including feedback control and
feed forward control) and the sequential control that inputs operating sequences
and process status signals.
♦ Feedback Control
Control that acts to correct the process variable (e.g. Temperature in a
tank) to agree with the target value (setpoint) by comparing both.
♦ Feed forward Control
Control which takes a corrective action by measuring the disturbances
(e.g. Ambient temperature) and directly driving the valve before it affects
the process.
♦ Sequential Control
Control that successively advances each control step in accordance with
the pre-determined sequence.
Training Center A-2
A. INTRODUCTION TO PROCESS CONTROL SYSTEM
A.3. PROCESS CONTROL SYSTEMS
To perform temperature control as discussed before, a control system ( a device
to perform the control computation) is required. There are many control systems
available, which are generally classified into analog, and digital control system.
Analog Contro l Syst em
Control device that makes a control computation with analog signals (e.g.
Voltage) using operational amplifiers etc. I this case sequence control is not
available.
Digital Control System
Control device that makes control computation with digital values using a
processor (processing unit). Not only the feedback and feed forward controls
(called DDC-Direct digital controls collectively) but also sequential control is
available.
Operational Amplifier
Signal 1 to 5 V DC
Conversion +
4 to 20 mA DC -
I/P
Figure: Overview of Analog Control System
Training Center A-3
A. INTRODUCTION TO PROCESS CONTROL SYSTEM
Memory
Unit
Control
1 to 5 V Unit
DC Engg.
Data Input
A/D Unit
Data Arithmetic
4 to 20 Conversion Unit
0-100% Output
mA DC D/A Unit
I/P
Figure: Overview o f Digital Control System
DDC – Direct Digital Control
Generally referred to control in which the controller functions are implemented
with digital equipment. Inputs and outputs of the controller may be analog
signals. Also refers to a supervisory control scheme when a higher-level
computer drives the output of a digital controller directly.
A.4. DEVELOPMENT HISTROY OF CONTROL SYSTEM
Electronic computers were first introduced into the process control filed in 1960’s.
Digital control technology developed widely in the following years.
The purpose of introducing computers was mainly (1) data logging and (2) set
point control (SPC) at first.
Training Center A-4
A. INTRODUCTION TO PROCESS CONTROL SYSTEM
Display Display
Computer Printing Computer Printing
System System
Setpoint Setpoint
(SV) (SV)
Process Variable (PV) Process Variable (PV)
E/P E/P
Tank Manipulated Tank Manipulated
Variable (MV) Variable (MV)
Figure: Data Loggin g Figure: Set Point Control
As the introduction of computers into process control advanced, controller
functions were superseded by computers, and DDC in which computers directly
controlled processes began to be employed.
In the early stages, the control system was centralized where a central computer
executed not only monitoring and operation but also all process controls. The
most important reason was cost effectiveness.
The advent of microprocessors greatly changed the above situation. The study
theme moved to how diversification could be implemented (risk distribution,
function distribution, etc) and how exclusiveness and versatility could be united.
The distributed control system (DCS) now has inputs points distributed for 1 loop,
8 loops, 16 loops and upto 80 loops to be able to apply approximately when seen
from processes.
Training Center A-5
