TOPIC 1 :

INTRODUCTION TO

INDUSTRIAL CONTROL

SYSTEM

INTRODUCTION

The industrial revolution began in England during the mid-1700s when it was discovered steam-powered engines.

Further inventions and new ideas in plan-layout in

1850s by United States. Electric motor replaced

steam and water wheels as a power source.

TERM OF INDUSTRIAL CONTROL SYSTEM

The term industrial controls is used to define this type of system, which automatically monitors manufacturing processes being executed and takes appropriate corrective action if the operation is not performing properly.

CLASSIFICATIONS OF INDUSTRIAL CONTROL

Industrial control systems are often classified

by what they control :

either motion or process.

MOTION CONTROL

is an automatic control system that controls the

physical motion or position of an object.

- One example is the industrial robot arm which

performs welding operations and assembly

procedures

MOTION CONTROL Motion control is a sub-field of automation, in

which the position or velocity of machines are controlled using some type of device such as a hydraulic pump, linear actuator, or electric motor, generally a servo

Hydraulic pump Linear actuator

CHARATERISTICS OF MOTION CONTROL

(i) motion control devices control the position, speed, acceleration or deceleration of a mechanical

object. (ii) the motion or position of the object being controlled is measured. (iii) motion devices typically respond to input

commands within fractions of a second rather

than seconds or minutes as in process control.

CHARATERISTICS OF MOTION CONTROL

motion control systems are also referred to

as servos

or servomechanisms

MOTION CONTROL APPLICATIONS

- CNC machine tool equipment

- printing presses

- office copiers

- packaging equipment

- electronics parts insertion machines that

place components onto a printed circuit

board

MOTION CONTROL APPLICATIONS

CNC Machine Automation Robotics

Printing machine

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PROCESS CONTROL

- one or more variables are regulated during

the manufacturing of a product.

- these variables may include temperature,

pressure, flow rate, liquid and solid level, pH

or humidity.

PROCESS CONTROL

PROCESS CONTROL

Can be divided into 2 categories :

i.batch

ii.continuous

BATCH PROCESS

Definition:

is a sequence of timed operations

executed on the product being

manufactured.

BATCH PROCESS

also known as

sequence

or

sequential process

BATCH PROCESS

CONTINUOS PROCESS

Definition:

one or more operations are being

performed as the product is being passed

through a process

raw materials are continuously entering

and leaving each process step.

CONTINUOS PROCESS

Example: producing paper

CONTINUOUS PROCESS APPLICATIONS

Oil refining Gas Pipe Lines

Waste water treatment

CONTINUOUS PROCESS

another terms commonly used of process

control is

instrumentation

PRIMARY DIFFERENCE BETWEEN PROCESS & MOTION CONTROL

In process control

The emphasis is place on sustaining a constant condition of a parameter such as level, pressure or flow rate of a liquid

In servo control

The input command is constantly changing. The emphasis of the system is to follow the changes in the desired input signal as closely as possible. Variations of the input signal typically very rapid

ANOTHER TERMINOLOGY

Servomechanism

sometimes shortened to servo, is an automatic device that uses error-sensing negative feedback to correct the performance of a mechanism

DEC 2012/JUNE 2013 QUESTION 1 (A)

Briefly explain TWO (2) categories of process control

(4 marks)

ANSWER

Batch proces

Sequence of time operation on the product being manufactured

Continuous process

One or more operations are being performed as the product is being passed through a process

DEC 2012 QUESTION 2 (A)

Briefly explain about the following terminologies

-controlled variable

-disturbance

(4 marks)

JUNE 2013 QUESTION 2 (A)

Describe the functions of the following terminology used in closed loop network

-error detector

-disturbance

(4 marks)

OPEN - LOOP SYSTEM

Definition

A type of control system that uses only an input signal to actuate an output

There is no automatic feedback to adjust the process, so adjustments must be made manually by operator

OPEN - LOOP SYSTEMS

OPEN - LOOP SYSTEM

OPEN - LOOP SYSTEM

OPEN - LOOP SYSTEM Advantages

Simplicity and stability: they are simpler in their layout and hence are economical and stable too due to their simplicity.

Construction: Since these are having a simple layout so are easier to construct.

OPEN - LOOP SYSTEM

Disadvantages Accuracy and Reliability: since these systems

do not have a feedback mechanism, so they are very inaccurate in terms of result output and hence they are unreliable too.

Due to the absence of a feedback mechanism, they are unable to remove the disturbances occurring from external sources.

CLOSED-LOOP SYSTEM

Definition

A type of control system that automatically changes the output based on the difference between the feedback signal to the input signal

CLOSED-LOOP SYSTEM

In closed loop control, the system is self

adjusting. Ex: Solar water heating

CLOSED-LOOP SYSTEM

Data does not flow one way, it may pass back

from a specific amplifier (such as velocity or

position) to the start of the control system,

telling it to adjust itself accordingly.

CLOSED-LOOP SYSTEM

CLOSED-LOOP SYSTEM

A closed-loop system that uses a linkage mechanism as a feedback device to provide self-correcting capabilities

CLOSED-LOOP SYSTEM

Advantages

Accuracy: They are more accurate than open loop system due to their complex construction. They are equally accurate and are not disturbed in the presence of non-linearities.

Noise reduction ability: Since they are composed of a feedback mechanism, so they clear out the errors between input and output signals, and hence remain unaffected to the external noise sources.

CLOSED-LOOP SYSTEM

Disadvantages:

Construction: They are relatively more complex in construction and hence it adds up to the cost making it costlier than open loop system.

Since it consists of feedback loop, it may create oscillatory response of the system and it also reduces the overall gain of the system.

ELEMENTS OF CLOSED LOOP SYSTEMS

Closed-loop block diagram that shows elements, input/output

signals, and signal direction

TERMINOLOGIES USED IN CLOSED-LOOP SYSTEMS

Controlled Variable :

The controlled variable is the actual variable being monitored

and maintained at a desired value in the manufacturing

process.

Examples in a process control system may include

temperature, pressure, and flow rate.

Another term used is process variable

Measured Variable :

To monitor the status of the controlled variable, it

must be measured.

One method of determining a controlled variable such

as the level of water,

Measurement Device :

The measurement device is the eye of the system.

It senses the measured variable and produces an

output signal that represents the status of the

controlled variable. Examples in a process control

system may include a thermocouple to measure

temperature or a humidity detector to measure

moisture.

Other terms used are detector, transducer, and sensor.

Feedback Signal:

The feedback signal is the output of the measurement

device.

Other terms used are measured value, measurement

signal, or position feedback if in a position loop, or

velocity feedback if in a velocity loop.

Set Point :

The set point is the prescribed input value applied to

the loop that indicates the desired condition of the

controlled variable.

The set point may be manually set by a human

operator, automatically set by an electronic device, or

programmed into a computer.

Other terms used are command, or reference.

Error Detector :

The error detector compares the set point to the

feedback signal.

It then produces an output signal that is proportional

to the difference between them.

Other terms used are comparator or comparer and

summing junction

Error Signal :

The error signal is the output of the error detector. If

the set point and the feedback signal are not equal, an

error signal proportional to their difference develops.

When the feedback and set point signals are equal,

the error signal goes to zero.

Other terms used are difference signal and deviation

Controller :

The controller is the brain of the system.

It receives the error signal (for closed-loop control) as

its input, and develops an output signal that causes

the controlled variable to become the value specified

by the set point.

Most controllers are operated electronically, although

some of the older process control systems use air

pressure in pneumatic devices.

Actuator :

The actuator is the muscle of the system.

It is a device that physically alters some type of energy or fuel supply, causing the controlled variable to match the desired set point.

Examples of energy or fuel are the flow of steam, water, air, gas, or electrical current.

Other terms used are the final control element, or final correcting device. Common types of actuators are hydraulic cylinders, pumps, and motors.

Manipulated Variable :

The amount of fuel or energy that is physically

altered by the actuator is referred to as the

manipulated variable.

The amount at which the manipulated variable is

changed by the actuator affects the condition of the

controlled variable.

Manufacturing Process :

The manufacturing process is the operation performed by the actuator to control a physical variable, such as the motion of a machine or the processing of a liquid.

Disturbance :

A disturbance is a factor that upsets the manufacturing process being performed, causing a change in the controlled variable.

DEC 2012 QUESTION 2 (A)

Briefly explain about the following terminologies:

i. Controlled variable

Ii. Disturbance