Chapter 01_Introduction to Industrial Control Systems

8/2/2019 Chapter 01_Introduction to Industrial Control Systems

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Chapter 1

Introduction to Industrial

Control Systems

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Introduction

The Industrial Revolution represented the

change from manufacturing processesbased upon one-at-a-time production tomass production because of the advent ofthe steam engine. Eventually, the electricmotor and hydraulic systems replacedsteam and Industrial Controls weredeveloped to automate the manufacturingprocess.

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Industrial Control Classifications

Motion and Process Control Motion control: position or velocity

Process control: temperature, pressure,

flow, level, pH, humidity, or chemicalcomposition

Batch processing

Continuous processing

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Industrial Control Systems automatically monitor manufacturing

processes being executed and take appropriate corrective action if

the operation is not performing properly.


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Motion Control Automatic control system that controls the

physical motion or position of an object.Motion control is also referred as servos or

servo mechanisms. Example: robot arm

performing welding, CNC machine toolequipment

Three characteristics:

1- control position, speed, acceleration2- measurement of motion or position

3- instant response to commands (faster than

process control 4


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Process Control

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One or more variables are regulated during the manufacturing of a

product. This can include temperature, pressure, flow rate, liquid

or solid levels.

Response time of PC is typically slowvaries from seconds to

minutes and is the type of industrial control used in manufacturing

Two Categories: batch and continuous

1- Batch Processing aka sequential process

is a sequence oftimed operations. Ex. Machine producing cookies. See P5 in book

2Continuous Process aka instrumentation: one or more

operations are being performed as the product is being passed

through a process. The raw materials enters and leaves severalstations in each process step. It can hours, days or weeks. Ex.

Nuclear pwr distribution, waste water treatment, oil refining,

natural gas distribution


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Typical Industries

Process industries Petroleum

Chemical

Power

Pulp and paper

Food and beverage

Textile

Pharmaceutical

Waste Treatment

Water Treatment

Discrete parts Automotive

Electrical/electronic manufacturing

Instrument/parts manufacturing

Toys

Sporting Goods

Appliances

Tools


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Open- and Closed-Loop Systems

How systems are controlled can also definethe control process

Open-loop systems depend upon a (manual)

command signal to inform the output devicewhat to do. Has no comparator.

Closed-loop systems are self-correcting andallow for continuous operation without

interruption.

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Open- and Closed-Loop Level Control

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Open-loop level control

requires manual operation to

maintain proper level with noautomatic feedback. It is the

simplest way to control a

system. Has to reach a steady

state or balance condition.Closed-loop level control allows

for unattended continuous levelcontrol with feedback


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Closed-loop level control allows for unattended level control.

Feeback control systems were developed between WWI and

WWII.


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Elements of Open- and Closed-Loop Systems

PP 8 9 in book

Controlled Variable Measurement Device Feedback Signal Set Point Error Detector Error Signal Controller Actuator Manufacturing Process Disturbance

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More feedback control references

An error can develop in 3 ways in feedback control

1. The set point is changed

2. A disturbance appears

3. The load demand varies

See p. 12 for good example

There is Positive and Negative feedback.

Ex. A home thermostat uses negative feedback tokeep its temperature correct, a uses positive

feedback to get/find the stronger signal

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Process Lag Time

Describes the time it takes for a correctiveaction to be reflected in the process. It takestime to re-establish a balanced condition.

This is referred to a pure lag and is proportional

to the amount of its mass.

Factors influencing lag time are:

Inertia - mass

Capacity

physical quantity

Resistance type of material

Dead-time ex. liquid temperature in a pipe12


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Feed-Forward Controltakes corrective action after an error develops

Two factors can make feedback controlineffective:

Large magnitude disturbances

Large process lag times

Feed-forward control prevents errors fromoccurring; however, feed-forward control isseldom used alone, typically in conjunction

with feedback systems. Not perfect due to other disturbances and used only

for critical apps.

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Examples of Feed-Forward Controls

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Feed-forward control of level Feed-forward control loop

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Chapter 01_Introduction to Industrial Control Systems