Computer Control

What is “computer control” ?

Computer control means that a computer is part of the control system. The computer is normally used to run the control program.

We use the term ‘computer’ very loosely.  It does not necessarily mean the kind that you are working on right now, it often means a processor or microchip embedded with the equipment.

Example of “Computer Control”

At home :Washing machines

Microwave cookers

Dishwashers

Remote control television

Central heating systems

Burglar Alarm system

At work :Air conditioning systems

Lifts

Automatic doors

Factory robots

Outside the home : Traffic light systems Car park barriers Cars – engine management systems Lifts Rides at theme parks Computer controlled lighting systems at discos and concerts

sensors

A sensor is a device designed to measure some physical quantity in its environment.  An example might be a heat sensor that measures the temperature in a room or a pressure sensitive mat that detects someone walking over it.

processOnce the input data from the sensors has been received by the computer, it can then begin to process it.

The data will be compared against a set of rules which have been programmed into the control system and a decision will be made. The result is an output of some kind.

For example, think about a central heating system:

The system is set to keep the room at a comfortable 22 degrees C. 

The sensor takes regular temperature readings in the room and sends the readings to the computer. 

The computer will then process the data to see if it matches the set temperature of 22 degrees.

If it is lower, for example 20 C, then the computer turns the boiler on.  

If the room has reached the set temperature of 22 C then the computer turns off the boiler.

This stage is called processing.  The computer can only follow the rules that it has programmed into the control system, it cannot make its own decisions.

output

If it is lower, for example 20 C, then the computer turns the boiler on. 

For a central heating system, this might be to turn the heating on or off.  For a greenhouse watering system this might be to turn the sprinklers on or off.

Sending the message and the resulting action is known as the ‘output’ stage.

Actuator

An actuator is often part of a computer control system.

The actuator is a mechanical device or motor which carries out the action or decision made by the control system.

Advantages of “computer control”

Advantages:

Can operate 24 hours a day without taking a break. 

Can work without holidays or sick days

Will work without any wages.

Will accurately repeat actions over and over again.

Can process data from sensors very quickly.

Can take account of hundreds of inputs at the same time.

Can make reliable and accurate decisions.

Can be used in dangerous or awkward environments.

Disadvantages of “computer control”Disadvantages :

The software for the control system is specialist and may cost a lot of money to develop.

If the computer malfunctions the system will not work.

If there is a power cut the system will not work.

The computer cannot react to unexpected events as perhaps a person could. It can only respond in the way it has been programmed.

People sometimes want to know that an expert is in control even if a computer could do it as well. e.g. a pilotless commercial aircraft is not likely to be popular although in theory it is possible. Or a robotic surgical procedure.