3.5.6 Define analog & digital data

On this page: [ analog & digital | sampling | sensors | applications ]

Analog (or analogue) data is real world stuff like sounds, electrical currents, paintings, temperatures, time. It has no precisely measurable or discrete value - we measure to the accuracy of our recording instruments.

Digital data, on the other hand is discrete , consider the bitmap as compared to an original image for example, a bitmap is made up of discrete pixels in one colour or another, the water-colour is not. When sounds are digitised they must be stored as discrete values representing the pitch, volume, duration and other qualities of the sound

Computers can only work with digital data .

analog data	digital data

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Sampling
To convert analog data to digital data, the analog data has to be sampled and then converted to an approximate value. Some information is lost in the process, for example the curve of the analog temperature can not be reproduced exactly from the digital data - the data between each sample has been lost.

Digitised data, although approximate, can be processed and transmitted by computer systems efficiently and reliably than analog data. More efficiently because the digital data is more compressed and more reliably since it is transmitted as digital states which are less subject to distortion by noise.

In addition digital data can be manipulated by computer - for example, pictures can be scaled and rotated quickly, digital effects can be added to sounds (eg echo) and temperature data can be used in a computer control system.

Analog to Digital Conversion
To convert signals from analogue to digital require as an analogue-to-digital converter (ADC). The signals are gathered by sensors which are often also transducers (a device which converts one form of energy to another). Transducers used as sensors for input to ADC devices usually convert energy from (eg) heat, light, pressure to electrical impulses. These analog impulses are then sampled and digitised.

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Sensors
These are used in very many control processes , for example, microwaves, washing machines, video recorders, building heating systems, security systems etc etc. Often the actual computer program will be small enough to be located in ROM (or EPROM) and combined with a small memory chip (for storing sensor data) and a microprocessor. A washing machine will typically have water level sensors, drum rotation sensors and heat sensors.

Actuators
To produce actions in the real world, computer instructions typically have to be converted to analogue form ( Digital-to-Analogue-Conversion ) and sent to an actuator a device that produces some effect in the real world (turning on a heater, activating a door lock, opening or closing a valve).

A typical control process thus consists of a computer (or microprocessor), an interface and senors/actuators:

Applications that require analog to digital conversion
Temperature sensing applications include room controls (for central heating or air-conditioning), control of commercial processes like growing vegetables in greenhouses, washing machines and conventional ovens.

The temperature is sensed and the measurement converted to digital. The temperature is then compared by the computer or microprocessor to the desired temperature. If the temperature is too high or too low, appropriate action is taken (heater, air pump, cooler, switched on or off). Other inputs are usually controls that change the desired set temperature level.

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related: [ Core home | previous: number systems | next: errors ]

PDF worksheet on Analog & Digital.

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