Industrial Instrumentation and New Generation of Digital Process

Control Systems: Smart Protection Devices and Network

Equipment Control & Monitoring (ICS & SCADA)

Section 7

Timers

Section 7 Haward Technology Middle East 1

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Timers
There are very few industrial control systems that do not
need at least one or two timed functions. They are used
to activate or de-activate a device after a preset interval
of time.
Time delay relays and solid-state timers are used to
provide a time delay. They may have displays, pots or
other means of operator interface for time settings and
electromechanical.

Section 7 Haward Technology Middle East 2

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Timers

Section 7 Haward Technology Middle East 3

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Timing Relay

Non timed contacts are
controlled directly by
the timer coil, as in a
general-purpose control
relay.

When the coil is

energized, the timed
contacts are prevented
from opening or closing
until the time delay
period has elapsed.
However, when the coil
is de energized, the
timed contacts return
instantaneously to their
normal state.

Section 7 Haward Technology Middle East 4

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Timed Contact Symbols

Normally open, timed closed Normally closed, timed open

contact (NOTC) contact (NCTO)
Contact is open when relay Contact is closed when relay
coil is de energized coil is de energized
When relay is energized,
there is a time delay in When relay is energized,
closing there is a time delay in
opening
Section 7 Haward Technology Middle East 5
 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Timed Contact Symbols

Normally open, timed open contacts Normally closed, timed closed

(NOTO). contacts (NCTC).
Contact is normally open when relay
coil is de-energized. Contact is normally closed when
When relay coil is energized, contact relay coil is de-energized.
closes instantly. When relay coil is energized,
When relay coil is de-energized, there contact opens instantly.
is a time delay before the contact
opens. When relay coil is de-energized,
there is a time delay before the
contact closes.
Section 7 Haward Technology Middle East 6
 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Relay Timer Circuit (NOTC

Contact)
Sequence of operation

SI open, TO de-energized,
TD1 open, LI is off.

SI closes, TO energizes,
timing period starts,

TD1 still open, L1 is still off.

After 10 s, TD1 closes, LI is
switched on.
S1 is opened, TO de-energizes,
TD1 opens instantly, L1 is
switched off.

Section 7 Haward Technology Middle East 7

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Relay Timer Circuit (NCTO

Contact)
Sequence of operation

S1 open, TD de-energized,
TDI closed, LI is on.
S1 closes, TD energizes,
timing period starts, TD1 is
still closed LI is still on.
After 10 s, TD1 opens, L1 is
switched off.
S1 is opened, TD de-
energizes, TD1 closes
instantly, L1 is switched on.

Section 7 Haward Technology Middle East 8

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Relay Timer Circuit (NCTO

Contact)
Sequence of operation
51 open, TD de-energized,
TDI open, LI is off.

S1 closes, TD energizes,
TD1 closes instantly,
L1 is switched on.
S1 is opened, TO de-
energizes, timing period
starts, TD1 is still closed, LI
is still on.
O After 10 s, TD1 opens, LI is
switched off.

Section 7 Haward Technology Middle East 9

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Relay Timer Circuit (NCTO

Contact)
Sequence of operation
SI open, TO de-energized,
TDI closed, LI is on.
SI closes, TO energizes, TOl
opens instantly, LI is
switched off.
SI is opened, TO de-
energizes, timing period
starts, TOl is still open, LI is
still off.

After 10 s, TOl closes, LI is

switched on.

Section 7 Haward Technology Middle East 10

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Programmed Timer Instructions

PLC timers are output instructions that provide the same
functions as timing relays and solid state timers.

Some advantages of PLC timers:

 their settings can be altered easily
 the number of PLC timers used can be increased or
decreased by
 programming changes without wiring changes
 timer accuracy and repeatability are extremely high

Section 7 Haward Technology Middle East 11

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

RSLogix Timer Commands

Command Name Description

TON Timer On-Delay Counts time base
intervals when
the instruction is"
true”

Section 7 Haward Technology Middle East 12

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

RSLogix Timer Commands

Command Name Description

TOF Timer Off-Delay Counts time base
intervals when the
instruction is"
false”

Section 7 Haward Technology Middle East 13

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

RSLogix Timer Commands

Section 7 Haward Technology Middle East 14

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Quantities Associated with the Timer

Instruction
Preset Time — Represents the time duration of the timing
circuit. For example, if a time delay of 10 s is required,
the timer will have a preset of 10 s.
Accumulated Time — Represents the amount of time that
has elapsed from the moment the timing coil became
energized.
Time Base — Timers can typically be programmed with
several different time bases: I s, 0.1 s, and 0.01 s are
typical time bases. For example, if you enter 0.1 for the
time base and 50 for the preset time the timer would
have a 5 s delay (50x0.1 s=5s).

Section 7 Haward Technology Middle East 15

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Coil-Formatted Timer Instruction

Section 7 Haward Technology Middle East 16

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Coil-Formatted Timer Instruction

When the timer rung has logic continuity, the timer’s

accumulated value increases. When accumulated value
equals the preset value, the output is energized and the
timed output contact associated with the output is
closed. The timed contact can be used as many times as
you wish throughout the program as a NO or NC contact.

Section 7 Haward Technology Middle East 17

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Generic Block-Formatted Timer

Instruction
Timers are most often represented by boxes in a ladder
logic. Control line controls the actual timing operation of
the timer. Whenever this line is true the timer will time.

Section 7 Haward Technology Middle East 18

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Generic Block-Formatted Timer

Instruction

The timer continuously compares its accumulated time

with its preset time. Its output is logic 0 as long as the
accumulated time is less than the preset time. When the
two become equal the output changes to logic 1.

Section 7 Haward Technology Middle East 19

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Timer Instruction

The on-delay timer operates so that, when the rung
containing the timer is true, the timer time-out period
commences.

Section 7 Haward Technology Middle East 20

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Timer Instruction

Section 7 Haward Technology Middle East 21

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction

Allen-Bradley PLC-5 and SLC-500 controller timer

elements each take three data table words: the control
word, preset word, and accumulated word.

The control word uses three control bits: Enable (EN) bit,
Timer-Timing (TT) bit, and Done-Bit (DN).

Section 7 Haward Technology Middle East 22

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction

Section 7 Haward Technology Middle East 23

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction
The Enable (EN) bit is true (has a status of 1) whenever the
timer instruction is true. When the timer instruction is false,
the enable bit is false (has a status of 0)

Section 7 Haward Technology Middle East 24

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction
The Timer-Timing (TT) bit is true whenever the
accumulated value of the timer is changing, which means
the timer is timing.

Section 7 Haward Technology Middle East 25

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction
The Done-Bit (DN) changes state whenever the
accumulated value reaches the preset value. Its state
depends on the type of timer being used.

Section 7 Haward Technology Middle East 26

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction
The preset value (PRE) word is the set point of the timer, that is,
the value up to which the timer will time.
The accumulated value (ACC) word is the value that increments as
the timer is timing. The accumulated value will stop incrementing
when its value reaches the preset value.

Section 7 Haward Technology Middle East 27

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction
The information to be entered includes:

Section 7 Haward Technology Middle East 28

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Allen-Bradley On-Delay Timer

Instruction

Timer number which must come from the timer file.

Time base which is expressed in seconds.
Preset value which is the length of the time delay.
Accumulated value which is normally entered as 0.

Section 7 Haward Technology Middle East 29

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Timer Program

Section 7 Haward Technology Middle East 30

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Timer Program

Section 7 Haward Technology Middle East 31

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Timer Program

Timers are 3-word elements

Word 0 is the control word

Word I stores the preset value
Word 2 stores the accumulated value
Section 7 Haward Technology Middle East 32
 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay timer With Instantaneous

Output

Section 7 Haward Technology Middle East 33

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

On-Delay Timer With Instantaneous

Output

Section 7 Haward Technology Middle East 34

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Start-Up Warning Signal Circuit

Section 7 Haward Technology Middle East 35

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Start-Up Warning Signal Circuit

Section 7 Haward Technology Middle East 36

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Timed Closed Solenoid Value Program

Section 7 Haward Technology Middle East 37

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Automatic Sequential Control System

Section 7 Haward Technology Middle East 38

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Automatic Sequential Control System

Section 7 Haward Technology Middle East 39

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Off-Delay Programmed Timer

The off-delay timer (TOF) operation will keep the output
energized for a period after the rung containing the timer
has gone false.

Section 7 Haward Technology Middle East 40

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Off-Delay Programmed Timer

Timing Diagram

Section 7 Haward Technology Middle East 41

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Off-Delay Programmed Timer

Section 7 Haward Technology Middle East 42

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Off-Delay Timer Used to Switch Motors Off

Section 7 Haward Technology Middle East 43

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Programmed Pneumatic Off-Delay Timer

Section 7 Haward Technology Middle East 44

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Retentive Timer

 A retentive timer accumulates time whenever the

device receives power, and maintains the current time
should power be removed from the device.
 Once the device accumulates time equal to its preset
value, the contacts of the device change state.
 The retentive timer must be intentionally reset with a
separate signal for the accumulated time to be reset.

Section 7 Haward Technology Middle East 45

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Retentive On-Delay Timer Program

The PLC-programmed RETENTIVE ON-DELAY timer (RTO)
operates in the same way as the non retentive on-delay
timer (TON), with one major exception.

Section 7 Haward Technology Middle East 46

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Retentive On-Delay Timer Program

Section 7 Haward Technology Middle East 47

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Retentive On-Delay Timing Chart

Section 7 Haward Technology Middle East 48

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Annunciator Flasher Circuit

Two timers can be interconnected to form an oscillator
circuit. The oscillator logic is basically a timing circuit
programmed to generate periodic output pulses of any
duration. They can be used as part of an annunciator
system to indicate an alarm condition.

Section 7 Haward Technology Middle East 49

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Annunciator Flasher Circuit

Section 7 Haward Technology Middle East 50

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Cascading of Timers for Longer Time Delays

Output
Ladder logic program

Section 7 Haward Technology Middle East 51

 Industrial Instrumentation and New Generation of Digital Process
Control Systems: Smart Protection Devices and Network
Equipment Control & Monitoring (ICS & SCADA)

Control of Traffic Lights in One Direction

A typical application for PLC timers is the control of
traffic lights.

Section 7 Haward Technology Middle East 52