Slew Rate (Electric Motors)

10.4.6
Position sensors generate data based on the resolution of the sensor, multiplied by the interpolation factor of the interface electronics. The maximum slew, or tracking rate, of an RDC is limited to & of the resolver reference frequency. For example, the Analog Devices AD2S80A RDC, using a 400-Hz reference, has a tracking limit of

FIGURE 10.26 Comparative resolution of various technologies.
1500 rpm. This value can be increased to 18,750 rpm by using a 5-kHz reference. When the tracking rate of the converter is exceeded, the position value cannot be computed fast enough to keep up with the input, and the digital output becomes totally unpredictable (Boyes, 1980). A similar condition exists if the maximum acceleration rate is exceeded.
For encoders, the tracking rate is limited primarily by the frequency response of the sensor. Low- to intermediate-cost encoders generally have a maximum frequency response capability of 200 kHz, and there is no reference frequency dependency. Newer product offerings are beginning to push the envelope up to approximately 400 kHz, which allows a 4096-cpr encoder to turn at 6000 rpm without missing counts. Higher performance is available at a higher cost, with a maximum frequency response capability of approximately 1 MHz.