Date: Sun, 14 Mar 1999 06:42:27 -0700
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 990313
                          SATURDAY MARCH 13, 1999
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
   Tonight the weather cooperated so we got to the point of taking data
with the imager.  Good images were obtained, or at least as good as we
could get with 1.1 to 1.7 arcsecond seeing.  Unfortunately it was not any
easy time getting to that point.
   The enclosure was off when I arrived this afternoon.  Bill Boroski,
Steve Bastian, Jim Gunn, and Mike Carr were adjusting the front/back
balance of the telescope by moving the clamshell weights at the front of
the truss.  During this process an accident occured.  Someone had put the
altitude locking pin in with the telescope at zenith and the telescope was
operated in manual mode to bring it away from zenith.  The result was the
windscreen motor overloaded and stopped.  The turnbuckle bent and the
bumper between the windscreen and PSS took the load.  It did not prevent
the windscreen from contacting the top of the truss.  The pin mouning was
loosened some, and the manual brake release for the windscreen altitude was
engaged, relieving the tension on the pin.  After an inspection of the
telescope it was decided that the only real damage was to the turnbuckle,
and we proceeded with balancing.
   In the end we put one counterweight cover on the front in addition to
the two on the back and put the clamshell weights near the center of the
tube to achieve a good balance.
   The top/bottom balance also needed adjusting.  The number 3 and 4
counterweights were set to 700.  Numbers 1 and 2 were left at 550 since the
controller switch could not access those ( 1 mapped to 3 and 2 mapped to 4
even after power cycling the controller ).
   Once balanced, we went to computer control.  Altitude would not move due
to a plus and minus 15 V Glentek power supply failure on alititude drive
amp #1.  After a call to Claudio we swapped the chassis for the spare and
put the analog and digital modules from the broken one into the spare and
it worked fine.
   The next thing we found was that the azimuth lvdt for the windscreen was
significantly off center.  This explains why last week after I would center
the telescope in the windscreen using the alignment clamp, that when the
windscreen was re-servoed, there was significant motion of the windscreen
as it "centered" up.  The truss was only half an inch from the telescope
left side of the windscreen, and over three inches from the right side.
The fork was also about half and inch from the telescope right front corner
of the floor, and nearly two inches from the telescope left front corner of
the floor.  The lvdt was moved about 5/8" back ( away from the plunger ) in
its bracket.  This allowed the windscreen to much better center on the
telescope.
   We had to close for about an hour between 22:00 and 23:00 due to
windspeeds exceeding the limit.
   When we opened back up there was an odd problem with getting the
altitude going.  After pulling the last stop button, I reset the
amplifiers.  I would then issue a hold and then release the brake.  The
windscreen would center up, but the altitude amplifiers would still
indicated bidirectional inhibit.  No interlocks were actually inhibiting
altitude motion.  I could reset the amplifiers and for a split second all
would go green, but then immediately re-inhibit.  After not being able to
find an interlock/mcp cause for this, I power cycled the Glenteks.  They
behaved properly after that.
   We set up on the equator at the meridian ( or as close as we could get
without absolute fiducials ).  Several itterations of finding out where we
were and adjusting got us to the proper place.  It was made more difficult
by the fact that the rotator scale was off by something like 21%.  Another
problem with the rotator is that when a move to position is issued, it
always stops about 30 arcseconds short.  It also doesn't move predictably
at slow rates ( like 100 cts/sec ).  It moves in small jumps of a few
arcseconds, or doesn't move at all.
   Now for the good news.  We got very nice images tonight.  The
astigmatism corrector seems to be doing a good job.  The primary numbers
Pat and I got last week appear to work well for the imager.  The linear
guages read nearly what they did last week for the same primary position
numbers ( measured after a trip to zenith for primary relaxing ).  Note:
in order to be able to read the linear guages I had to disconnect it from
the TPM and reconnect it to port 16 of the terminal server in the lower
enclosure.
   Primary numbers:
   setmir:  0 -25.8  17.2  939  1409
   galil:   6298 -3829 131 9683 24769 24104
   linear guages:  1:+01.9265
                   2:+00.5610
                   3:+00.5565
                   4:+00.3575
                   5:+01.9295
                   6:+00.4300
   Secondary numbers:
   setmir:  0*  -255   0   0 133
       *The piston was taken over by the focus loop and did not remain zero.
   At the end of the night the enclosure was left open and Bill Boroski and
Steve Bastian took over at 06:20.
                                  Dan