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.