Analog computer

An analog/analogue computer is a form of computer that uses electronic or mechanical phenomena to model the problem being solved by using one kind of physical quantity to represent another. The central concept among all analog computers can be better understood by examining the definition of an analogy. The similarities of an analogy define the salient characteristics of the comparison. But the differences in an analogy are important too.

Related Topics:
Computer - Analogy

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For example, the similarity between linear mechanical components (springs, dashpots) and electrical components (capacitors, inductors, resistors) is striking in terms of mathematics.

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They can be modeled using equations that are of the same form. However, the difference between

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these systems is what makes analog computing useful. Consider a simple mass-spring system.

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To construct the physical system would require buying the spring and mass, attaching them

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to each other and an appropriate anchor, collecting test equipment with the appropriate input range, and finally, taking measurements. The electrical equivalent can be constructed with a

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few operational amplifiers (Op amps) and some passive linear components; all measurements can be taken with an oscilloscope. In the circuit, the mass of the spring can be changed by adjusting potentiometers. The electrical system is an analogy to the physical system hence the name, but it is less expensive to construct, safer, and easier to modify.

Related Topics:
Op amp - Oscilloscope - Potentiometers

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The drawbacks of the mechanical-electrical analogy is that electronics are limited in the range over which the variables may, well, vary. This is called dynamic range. They are also limited by noise levels.

Related Topics:
Dynamic range - Noise level

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There is a lack of understanding about electrical systems that gives the terms analog and digital confusing and somewhat dubious meanings. Analog systems are understood only as continuous, time variant electrical systems. From the above discussion, it should be obvious that this is not correct. It is most likely an outgrowth of language from a time when the electrical-mechanical analogy was the most common type of analog computer. The popular understanding of digital is not very specific but definitely linked to consumer electronics and personal computers. In fact, digital has a technical definition. In the context of circuits, it refers to the advantage of binary circuits in terms of signal-to-noise ratio.

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There is an intermediate group, hybrid computers, in which a digital computer is used to control and organize inputs and outputs to and from attached analog devices; for instance analog devices might be used to help generate initial values for iterations, or the analog computer might be used to solve a non-analytic differential equation problem.

Related Topics:
Hybrid computer - Digital computer

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Some examples:

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• the abacus is a hand-operated digital computer
• the slide rule is a hand-operated analog computer
• early gun directors used mechanical analog computers to direct gunnery fire
 
Analog computer: How analog computers work ►