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Chapter 4 Velocity and position transducers 115

conversion time, resolution, and gain. A variant of the successive approximation con-
verter is the tracking converter that forms an integral part of a resolver’s decoder; this is
discussed later in this chapter.
Digital-to-analogue (D/A) converters are used to provide analogue signals from a
digital system. One of the problems with a D/A converter is that glitches can occur as the
digital signal change state, requiring a finite settling time. As the code changes, the
output will not change state at the same instant; this is particularly acute when the input
code changes from, for example when the encoder changes from 01111 to 10000, an
output of 11111 may transiently appear. It is possible to add a deglitching function to a
D/A converter by increasing the transfer time of the converter.

4.1.5 Dynamic performance
Only the static characteristics of transducers have been considered up to this point.
However, if the measured signal is rapidly changing, the dynamic performance of the
measurement system has to be considered. A transducer with a linear characteristic will
achieve a constant performance for all inputs; but this is not true in a practical system, since
the input will have a non-linear distortion caused by the transducer’s frequency-dependent
gain and the phase shift, Fig. 4.9. The formal analysis of these effects can be conducted, and
represented, by a first-order, linear, differential equation. The dynamic performance needs
to be considered in the selection of any transducer; even if the speed or position changes
slowly, to ensure that any transient effects are considered. A limited bandwidth transducer
will seriously limit the overall system bandwidth, and hence its ability to respond to
transients (such as the application or removal of torques from the load).

4.1.6 Errors introduced by the process
The above sections have detailed the impact of errors confined to the measurement
system, in practice the users of high-performance measurement systems need to be

FIG. 4.9 The effects of a transducer’s frequency-dependent gain and phase shift between the input and output
signal.