| Summary: | Three speed estimation methodologies: pulse count, elapsed time, and constant sample-time digital
tachometer (CSDT) methods, used with optical incremental encoders, are
implemented and compared in a closed-loop system setup using a specialised
Analog Devices CM403f DSP. Dedicated hardware for quadrature encoders on the DSP
facilitates the implementation of advanced speed estimation methods, such as the
CSDT, by minimising the delay resulting from software intervention. The error of
each methodology is evaluated theoretically and experimentally. The CSDT has
limited error over all its speed range. The error of the elapsed time method
increases as the speed increases. On the contrary, the relative error of the
pulse count method (which is often substantial) decreases with increased speed.
Several filtering techniques can be used to reduce the error of the elapsed time
method; here an oversampling technique is implemented with that aim.
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