| | Control : Sensors | 
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Control systems use sensors to gather information about the world. A sensor is a device which measures a physical quantity such as the temperature and then sends a voltage to the computer representing the quantity. Sensors can be either analogue or digital :
Digital : Sensors are either on or off. For example a switch of pressure pad.
Analogue : Sensors can measure a range of values. The size of the voltage the sensor produces is determined by the size of the quantity that the sensor has measured. For example if a cold temperature is measured a small voltage will be sent, whilst if a hot temperature is measured a larger voltage will be sent.
There are lots of different sensors available, each of which is designed to measure a specific quantity. Examples of sensors include :
| Sensor | Type | Quantity Measured | Application |
| Temperature sensor | Analogue | How hot/cold it is. | Monitoring the temperature of a science experiment. |
| Light sensor | Analogue | How light/dark it is. | Turning street lights on when it is dark. |
| Pressure sensor | Digital | If a pad is being pressed. | Detecting cars arriving at a car park barrier. |
| pH sensor | Analogue | The acidity of a liquid. | Monitoring river pollution. |
| Button | Digitial | If the button is being pressed. | Obtaining a ticket at a car park entry barrier. |
| Light Gate | Digital | Detects an object passing through the gate. | Measuring the speed or acceleration of objects. |
| Passive Infra Red (PIR) | Digital | Detects when an object moves into an area. | Activating a burglar alarm if someone enters a room. |
If you are designing a control system you will need to decide which sensors to use and where to put them. Control systems will use lots of sensors at the same time.
The data gathered by the sensors is used to decide when to turn the devices connected to the control system on and off.
GCSE ICT Companion 04 - (C) P Meakin 2004