Re: Adjust CP4 Clock Frequency

Craig Young

ATrack monitors a science images folder for new images recorded by the camera.  New images are added by Voyager/MaximDL.  When a new image is detected ATrack does a plate solve and measure both drift (difference between last image and this image) and shift (difference between a reference position or image and this image).  The drift is then used to adjust the tracking rate, the shift is used to temporarily change the motor speed for a period of time to recenter the next image.  Through an observing run of several hours ATrack will change the tracking rate (RA, DEC) to minimize the drift rate and keep the image centered.  It does this very accurately.  ATrack does not care what the cause of the drift, it simply measures it and readjusts the motor speeds to cancel it.  Through the night the changes are very small and consistent .. there is no wild jumps.  It is also very repeatable, from night to night.  No matter what the temperature is .. a warm summer night or a cold winter night .. the tracking corrections are always the same.

Now, if I turn off tracking correction on ATrack and turn on tracking correction in APCC then the stars drift away very quickly .. pixels per minute .. about 1 arc sec a minute.  This happens whether I use a 25 point model or a 200 point model.  When I compare the correction rates in APCC with ATrack I see the same difference no matter where I am pointed.  East side or West side.  The mount is always tracking in RA too fast and has to be slowed down.  This is consistent with ATrack which always shows the mount tracking too fast and it uses correction values that are negative .. in other words, it tries to slow down the sidereal tracking rate.

The fact that DEC is similar would seem to indicate there is a base constant in the motor speeds that is incorrect.  DEC is always a positive number in the range 0.02000 to 0.01200 arcsec/sec and is the same in both East and West sides.


Join to automatically receive all group messages.