Re: Adjust CP4 Clock Frequency

Craig Young

ATrack is used to determine the actual tracking rate.  I know this is correct because the drift (RA,DEC) is +/- 0.57 arcsec or less over 60 seconds, typically about +/- 0.2 arcsec.  If I then turn off ATrack correction and turn on APCC tracking correction (w/refraction) I then get a significant drift.  When comparing the two rates I get: ATrack Rate / APCC rate = approximately 0.001, or 0.1%.  This is consistent no matter which hemisphere or DEC,HA I have the telescope pointed at.  In other words, both ATrack and APCC change the RA and DEC tracking rates to accomodate the error in the mount pointing and refraction.  They both change in the same direction and about the same amount.  The problem I think is the Sidereal Rate is running too fast.  APCC assumes sidereal rate is accurate and adds the pointing model correction to it.  Which means the resultant corrected tracking rate is still running too fast.  So the base Sidereal Rate has to be slowed down by about 0.1%.  On the other hand, if the sidereal rate is corrected using the encoders and the encoder calibration is off then the sidereal rate will be off and APCC tracking correction will also be off.


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