PMAC/PMAC2 V1.17C Addendum Ideally, the magnitude of the sum-of-squares result should be constant throughout the sine/cosine cycle, at least at constant frequency. If there is significant variation, this is an indication of signal imperfection. In most cases, the most important imperfection is a DC bias on the sine and/or cosine signals. This entry can be used in its alternate format to determine the optimal bias correction.
Once that bias correction has been determined (the result word in that format), it can be copied into the active correction setup word for the diagnostic entry, and the entry put back into sum-of-squares mode, as an important verification that a good bias correction has been determined. A/D Bias Result Word : When bit 16 of the first setup line is 1, the final (fifth) result word contains the suggested bias correction word containing the bias correction terms for the sine and cosine terms.
This 24-bit value, containing two signed 12-bit correction terms, can be copied into the third setup word for the interpolator diagnostic entry for confirmation of its effect, and to the third line of the interpolator feedback entry, or the resolver feedback entry, for actual use. The sine bias-correction term is in the high 12 bits (bits 12 – 23); the cosine bias-correction term is in the low 12 bits (bits 0 – 11). In this mode, the encoder should be moved for several seconds (motion by hand is OK) to ensure good sampling of maximums and minimums of both waveforms and accurate bias-correction terms.
It is probably best to do this test with the amplifier disabled to prevent the possibility of noise distorting the maximum and minimum readings. 26 V1.17C Firmware Version