of rotating shafts have been reported in the literature [3-81. Older
methods are based on analog principles; they generally suffer from
low resolution and severe noise contamination. Early versions of
digital methods were reported in the late sixties and early seventies
[3-51. In these versions the sampling period varied with the speed.
This had the disadvantage of having very slow readings at low
speeds and the necessity of processing the time information. Corrective
methods to increase the number of pulses per revolution
and obtain fast readout were suggested [6,7]. However, these
methods required theuse of either a fairly complex sensing method
[6] or an accurate servomotor [7]. A recent digital method to obtain
angular velocity was given by Christiansen [8]. None of these digital
methods can be used to obtain speed by differentiation because of
the coarseness of the quantization. Even if a fast clock is used, one
runs into either clock overrun or too many counts per intervals. An
intelligent device which switches between modes might conceivably
be constructed, but the complexity outweighs the use as a conventional
tool on an industrial test platform, and its proper functioning
has yet to be proven.