Additional PLC Functions

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Assoc. Prof. Dr. Zahurin Samad

School of Mechanical Engineering

http://elearning.usm.my/

Universiti Sains Malaysia

Lecture 6

EMC 311/3 Mechatronics Additional PLC Functions

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EMC 311/3 Mechatronics Lecture 7/2

Introduction

Explain additional functions including timer,internal relay & counter and shift register

Students will learn

Programmable logic controller (PLC) Additional functions

– Timer (Chapter 21.8.1 pg 455-456)

– Internal Relay (Chapter 21.6.1 pg 453)

– Counter (Chapter 21.8.2 pg 456-458)

Shift register (Chapter 21.9 pg 458-459)

Knowledge and experience on computerhelp understanding.

http://161.142.72.206/Zahurin/Kursus/EMK261/

http://161.142.72.206/Zahurin/Kursus/EMK261/Kuliah17.htm







Additional functions

Logic functions only sometimes are notenough for performing task, especially thetask that involved time delay & evencounting

Thus, all PLCs provide timer, internal relay &counter that can be controlled by using logicfunctions & can be drawn in ladder diagram

Numbering System for the functions differsaccording to PLC manufacturer











Timer (TIM) Operand Data Areas:

N: T/C Number 000 - 511 SV: Set value (word, BCD)

– IO, AR, DM, HR, #

Purpose: A timer is activated when its

execution condition goes ON

and is reset (to SV) when theexecution condition goes OFF. Once activated, TIM measures

in units of 0.1 second from theSV.

If the execution conditionremains ON long enough for

TIM to time down to zero, theCompletion Flag for the TCnumber used will turn ON andwill remain ON until TIM is reset(that is, until its executioncondition goes OFF).

ON: timer will start

decreasing 0.1s from 5s.

OFF: timer reset to 5s.

Timer reaches zero,

the status of the timer

will change to ON

Timer

address

Delay

time

(× 0.1second)

Output

controlled

by timer











Internal Relay (Marker)

Memory address 200.00-231.15It is not connected to external device.

Marker











Counter (CNT) Operand Data Areas:

N: T/C Number 000 - 511 SV: Set value (word, BCD)

– IO, AR, DM, HR, #

Purpose: CNT is used to count down from SV when

the execution condition on the countpulse, CP, goes from OFF to ON, that is,the present value (PV) will bedecremented by one whenever CNT isexecuted with an ON execution conditionfor CP and the execution condition wasOFF for the last execution.

If the execution condition has notchanged or has changed from ON to OFF,the PV of CNT will not be changed.

The Completion Flag for a counter isturned ON when the PV reaches zero andwill remain ON until the counter is reset.

CNT is reset with a reset input, R. WhenR goes from OFF to ON, the PV is reset toSV. The PV will not be decremented whileR is ON.

Counting down from SV will begin again

when R goes OFF. The PV for CNT willnot be reset in interlocked programsections or b ower interru tions.

OFF→ON:

Counter value is

decreased by 1

Counter

starting

value

ON: Counter value

is set to 200

When counter value

reaches 0, the

counter will ON

Counter

address

Output

controlled by

counter











Shift Register Register is formed by a group of

marker Shift can be performed on register

content

Register can provide storage space

for a series of sequences

I = 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

St 200 0 0 1 1 1 0 0 0 0 1 1 1 1 1 1 1

201 0 1 1 0 0 0 1 1 1 1 1 1 1 0 0 0

E 202 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1

P = 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

St 200 1 0 0 1 1 1 0 0 0 0 1 1 1 1 1 1

201 1 0 1 1 0 0 0 1 1 1 1 1 1 1 0 0

E 202 0 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1











Summary

Students have learned Timer is used for delaying even

Internal relay is used for simplifying rung

Counter is used for counting even

Shift register can be used for controllingsequences

Foundation for using PLC











References Omron, “A beginner’s guide to PLC”

Webb, John W., “Programmable logic controllers”

Swainston, Fred, “A systems approach to programmable controllers”

Parr, E. A. & E. Andrew, “Programmable controllers: an engineer'sguide”

Warnock, Ian G., “Programmable controllers: operation and

application”

Den, Otter J., “Programmable logic controllers”

Bolton, Martin, “Digital systems design with programmable logic”

Kissell, Thomas E., “Understanding and using programmablecontrollers”

Treseler, Michael, “Designing state machine controllers using programmable logic”

Stenerson, Jon, “Fundamentals of programmable logic controllers,sensors, and communications”

Knapp, William, “Introduction to programmable logic controllers(videorecording)”











Exercise Questions1. Draw a ladder diagram for activating a

motor after 10 seconds pressing a switchusing timer.

2. Simplify the ladder diagram shown usingmarker.

3. Draw a ladder diagram for activating asolenoid valve after an optical sensordetecting 15 products on a conveyor line.

4. Based on the ladder diagram shown,

explain what will happen if switch 000.00is pressed once and then switch 000.01 ispressed and released 3 times.






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Additional PLC Functions