Motor Speed Measurement Considerations When Using TMS320C24x DSPs

The TMS320C24x? generation of DSPs provide appropriate internal hardware for
interfacing with low-cost, external-speed sensors for motor speed measurement
applications. The periodic output signal from the speed sensor is applied to the capture input
pin of the DSP and the signal’s period is measured. This information is then used to calculate
the motor speed. However, this calculation of motor speed depends on several system
parameters. These parameters affect the scaling and normalization factors that must be used
in the speed calculation routine for accurate measurements. This application report,
therefore, gives an analysis of the speed measurement system to show the effect of system
parameters on the calculated speed. The choice of appropriate scaling and normalization
factors for a given system is also discussed. Finally, code examples are given to show the
software implementation of the speed calculation routine.