Adaptive sampling frequency for sampled-data control systems
Farren, Merritt C.
Phillips, Charles A.
Dorf, Richard C.
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Sampled-data control systems generally have fixed sampling frequencies which must be set high enough to give satisfactory performance for all anticipated conditions, A study is made here of an adaptive system which varies the sampling frequency by measuring a system parameter. It is shown, that a sampler followed by a zero-order hold whose sampling period is controlled by the absolute value of the first derivative of the error signal will be a more "efficient" sampler than a fixed frequency sampler. That is, over a given time interval, fewer samples are needed with the variable frequency system than with a fixed frequency system while maintaining essentially the same response characteristics. Analog computer studies of simple type 1 and type 2 sampled-data servo systems with error sampling and unity feedback verified the method . Standard analog computer components were used to set up a simulated servo system, a rate detector, absolute value detector, a voltage controlled oscillator, and a sampler and zero-order hold. The system described reduced the number of samples required for response to a step input to about three-quarters that required in a fixed sampling frequency system. Over a long period of time, savings in the number of samples required can be expected to be between twenty-five and fifty per cent. In many applications, the saving produced by reducing the overall number of samples required may outweigh the added complexity of the adaptive sampling frequency system.
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