Random Clocked Motion in Dec.

Friday, January 11, 2013 3:05 PM

Problem(s) Encountered:

I would like to report unauthorized or spurious motion of the 1.3 m telescope. As I summarized in the night report for this night, the LN2 fill line snapped while filling the dewar.  I found that the telescope had moved about 3 deg north in declination while filling which caused the snap.  THis afternoon I filled the dewar with the interlock enabled and there was no problem.  However, when I disabled the interlock the telescope started moving north in declination right away.  The rate was about 2-3 arcmin per 10 seconds.  Observers should exercise caution and be aware of this problem.  Also, all LN2 fills  should be done with the interlock enabled.


This random motion appears to be something low level in the TCS code.  Occasionally, when disengaging the E-stop, the telescope will start to clock slowly in declination.  Placing a probe on the dec drive circuit shows sporadic dirty pulses being issued (HA shows a 0V trace when the system is brought up).  Attempts have been made to fine tune the servo loop but the adjustment is too subtle to zero.  Barring any future fix, it is worthwhile to know that the clocking ceases if any command at all is issued within the TCS GUI.