Sample Time is a Fundamental Design and Tuning Specification

There are two sample times, T, used in process control design and tuning.
One is the control loop sample time that specifies how often the controller
samples the measured process variable (PV) and computes and transmits a new controller output (CO) signal. The other is the rate at which CO and PV data are sampled and recorded during a bump test.
In both cases, sampling too slow will have a negative impact on performance. Sampling fast will not necessarily provide better performance, though it may lead us to spend more than necessary on high-end instrumentation and computing resources. Fast and slow are relative terms defined by the process time constant, Tp.
Best practice for both control loop sample time and bump test data collection are the same: sample time should be 10 times per process time constant or faster (T = 0.1Tp)...
Read the rest of this article at: http://www.controlguru.com/
Doug Cooper
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