PID Controllersand introduction to

PLC systems

By

Dr. Palitha Dassanayake

Control Systems

Speed

Time

Motionprofile

Micro-processor control system

Fly ball governor

Steam valve

James watt

(speed increases,Steam value closes)

Control Systems in early days

Input- Voltage

Output-Rotated angle

Control System

Voltage

Voltage

Amplifier

Telephone line

AmplificationsAmplificationsAmplifications

Telephone line amplification problem

noise noise noise noisenoise

With the amplification, noise gets increased and increased…

Input voltage(a) Amplifier

gain

Outputvoltage

Amplifiergain

Attenuatorcircuit

Input voltage

Outputvoltage(b)

_

+

-

Feedbackgain

+

Referenceinput (b) Controller

Controlledvariable

Process

Actuatingsignal

Referenceinput

(a)Controller

Controlledvariable

Process

Actuatingsignal

Open Loop control system

Closed Loop control system

PID controller

P= proportional

I=Integral

D=Derivative

90%-95% closed loop automatic

controllers are PID

Automatic Controller

-

Sensor

+

Referenceinput r(t)

Controller PlantActuator

Output y(t)

Step input and on and off controller

r(t)

Time

A

If y(t)<r(t) ON

If y(t)>r(t) OFF

Time

y(t)

P controllers

_

Sensorfeedback

+

Set value r(t) Output y(t)

P process

Steady State Error ?

Transient Response

Time

u(t)

SSE

)()(()( trtykptu

P controller outputsInput r(t)= step input value 2

s

11

function Transfer

Kp=1Kp=5

Steady state error decreases with kp for this particular application

Plant

Reducing S.S.E

_+

Set value OutputP

+

+plant

U(t)

We may place an external input,

but different set points have different SSE ?

PI Controller

))()(()( tytrte

P

_+

Set value OutputI

+

+process

U(t)e(t)

dttekitekptu )(*)(*)(Integral part

PI controller outputStep input value =2 Kp=5

KI=1

KI=5

S.S.E exists

S.S.E is zero

KI=20 There is an overshoot

PID controllers

P

_+

Set value OutputI

D

+

++

plant

dttde

kddttekitekptu)(

*)(*)(*)(

))()(()( tytrte

PID controller outputStep input value =2 Kp=5 and KI=20

KD=1

KD=10

S.S.E still exists

Transient response is also less

PID controller output contd. Kp=5, KI=20 and KD=10

input r(t)- pulse input

output y(t)

Tuning of PID controllersPID values are different from one system to another

It is required to tune a P, PD, PI or PID controller

Basic industrial approaches Design a stable tuned PID controller after modeling Develop a simulator after modeling and tune

observing the simulator result On site tuning Combination of all three approaches

PLC is similar to using a computer but has certain features that are specific to their use as controllers. These are:1. They are rugged and designed to withstand vibrations,

temperature, humidity and noise.2. The interfacing for inputs and outputs is inside the controller.3. They are easily programmed and have an easily understood

programming language. Programming is primary concerned with logic and switching operations.

Programmable Logic Controllers

Data busAddress bus

Control bus

CPUclock

MemoryInput/Outputunit

Programpanel

Inputchannels

Outputchannels

Architecture of a Programmable Logic Controller

Normally opened contact

Normally closed contact

AND operation

LADDER DIAGRAMS

OR operation

Output

Special Instruction

I0.0 Q0.0

I0.1 Q0.1

I0.0 I0.1 Q0.0

Ladder diagram using S7 200

Q0.0I0.0

I0.1

Setting and Resetting an output

I0.0 Q0.0

I0.1 Q0.0

S

R

Setting and Resetting a Memory

I0.0 M0.0

S

I0.1 M0.0

R

Memory Input Register IType Symbol ExampleBit I0.1Byte IB4 Output Register OType Symbol ExampleBit Q1.1Byte QB5 

Variable Memory VStore intermediate results performed by the control logic in a programType Symbol ExampleBit V10.1Byte VW100 Bit Memory MStore intermediate status of an operation or other control informationType Symbol ExampleBit M26.7Byte MD20

Two types of timers available

1. On Delay Timer2. Off Delay Timer

On Delay Timer (T33- steps of 10ms)

I0.0 T33

2000+

IN

PT

TON

QET

T33 Q0.0

TimeonSwitch

ON

Bulb

OFF

20s

offSwitch

Off Delay Timer (T33- steps of 10ms)

I0.0 T33

1500+

IN

PT

TOF

QET

T33 Q0.0

TimeonSwitch

ON

Bulb

OFF15s

offSwitch

Counters

I0.0 C48

5

UP

R

C48 Q0.0

PV

I0.1

Logo Programming

&

I1

I2

Q1

AND Operation

I1

I2

Q1

OR Operation

1

S7 200 Programming Techniques

1. Ladder Programming2. Statement Lists (SLT)3. Function Block Diagrams

Statement List (SLT)This programming method introduces a list of statements. Let’s look at the basic programming using SLT. 

Statement List (SLT)This programming method introduces a list of statements. Let’s look at the basic programming using SLT. AND OperationLD I I0.0 // Read I0.0A I I0.1 //and with I0.1= Q0.0 //write the value to Q0.0 

Statement List (SLT)This programming method introduces a list of statements. Let’s look at the basic programming using SLT. AND OperationLD I I0.0 // Read I0.0A I I0.1 //and with I0.1= Q0.0 //write the value to Q0.0 OR OperationLD I I0.0 // Read I0.0O I I0.1 //or with I0.1= Q0.0 //write the value to Q0.0

On delay Timer Network 1LD I0.0TON T33,+2000 Network 2LD T33= Q0.0

 Network 1LD I0.0LD I0.1CTU C48,+5 Network 2LD C48= Q0.0

Timers Counters

I0.0

I0.1

ANDQ0.0

Functional Block Diagrams

I0.0

I0.1

ORQ0.0

END