Azimuth encoder1,2 failures
encoder failures(that i've recorded)
10apr17: az enc1 fault. value
jumps by > 1000 deg. need to reset with az pointer.
11oct16: testing when system
returns to enc1 after enc1 fault.
10oct16 az encoder 1 fault
15:00 to 07:00 next day.
02oct16 az encoder 1 replaced
10jan16 az encoder 1 replaced
az encoder 1 replaced
az encoder 1 becomes loose
az encoder 2 replaced
az encoder 1 multiple encoder errors
az 1 encoder. 2 faults.
az 1 enocder fault.
az 1,2 encoders reset. broken cable in cable drape.
az 1 encoder fails. replaced
az 1 encoder interface board zapped by lightning
az 1 encoder replaced. it had jumped on 07,08mar06.
az 1,2 encoder faults. replaced enc 1, 13,14nov enc1
faults again. enc2->enc1. 16nov05 replaced enc2
az 1 encoder jumps by 3 teeth,
az 1 encoder jumps.
azimuth Encoder failures:
There are two azimuth encoders. Encoder 1 is on
the gregorian side and is used for pointing. Encoder 2 is on the
carriage house side and is used to measure azimuth pending (as well
as a check on the gregorian side encoder).
When encoder 1 fails, the vertex system
automatically switches to encoder to for the pointing. This causes a
degradation in the pointing since the encoder 1 and encoder 2
values vary as a function of azimuth. This is caused by the "out of
roundness" of the azimuth encoder rack gear as well as the bending
of the azimuth arm.
After vertex system will continue to use encoder
2 for pointing until the encoder 1 error is cleared. The error can
be cleared by:
- On the vme system:
- pnt reset 1.. this will clear the error without
stopping the tracking (unless a motion failure occurs).
- pntpwrdip : this will stop the tracking, clear the fault and
then start tracking again.
- From the ocu:
- Going to the faults window, then azimuth, the pushing the
The telescope may get a motion failure and stop
tracking during the reset if the difference between encoder 2 and
encoder 1 are large enough (the software sees a large jump in the
position and then stops). In this case pntpwrdip will try to restart
- verified that system continues to use encoder 2 until the
encoder 1 fault is reset.. even if encoder 1 returns to work
The plots show a
jump in the azimuth position while clearing an encoder1 fault
- The telescope had been sitting at az=285, za=12 when the
failure occurred. It was still sitting there when the failure
- Page 1:
- Top: shows the azimuth status vs time. The encoder 1 failure
is the lower red trace. It was cleared at 11:35 and again at
- Bottom: shows the azimuth position returned from the vertex
system during this time. The azimuth is jumping by about .01
degrees. After the failure occurs, the new position stays at
encoder 2 until the failure is reset.
- Page 2: how large a pointing error can a failure introduce?
- 6 azimuth swings (-90 to 270) were done on 02aug09 (looking
- The top plots shows the encoder difference (encoder 1 -
encoder) in little circle azimuth degrees. The jump that
occurred at 11am was at an azimuth of 285 (-80). The
difference plot shows this to be about .01 azimuth degrees
which matches the jump we saw.
- bottom plot: This is the pointing error on the sky for an
- the sky error is sin(za)*azencoder jump\
- black is at za=12
- red is at za=19
- the error gets up to about -65 asecs (great circle). The
encoder difference is not currently centered at 0.
- Encoder 1 failures cause the system to use encoder 2 for
- The system remains with encoder 2 until the fault is reset.
- The pointing error can get up to about 65 Asecs (great circle)
depending on the za and the azimuth position.
- See also: enc1failures