tiedown 8 stops moving
On 07apr08 at 21:30 tiedown 8 stopped moving. A
430 dual beam transmitter experiment was running. The telescope
It remained motionless until we stop, restarted it at around 11 am on
- az=348, gr=17, ch=0 degrees.
The plots show the tiedown motions
during td8 failure (.ps) (.pdf).
The plots on each page show:
- Tiedown position in inches vs hour of day. 0 inches is fully
extended (up), 24 inches is pulled all the way down.
- Velocity feedback. This is a read back of the DtoA voltage that
is sent to the motor amplifier. The Purple line is the requested value
- Amplifier speed vs hour is read from the motor amplifier.
- Drive status: 0 off, 2 powered on , 1 enabled (ready to move or
moving), 3 failure
- The motor drive current read back from the motor amplifier.
- Page 1: 07apr08 20 to 22 hours
shows when td 8 stopped moving.
- The steps are when the tiedowns were requested to move.
- At 20.3 the drive current for td8 (green) started to spike.
- At 20.45 the current jumped up and stayed high even though
there was no motion command or velocity feedback. The td 8 did not move.
- Page2: 07apr08 21.57 blowup
of when td8 stopped.
- td12,td4 show encoder motion while td8 is stationary.
- The td8 commanded velocity is 0 implying that the td8 was not
asked to move.
- The velocity feedbacks show td12,4 with voltages to the amps
with td8 showing 0 (since the request was 0).
- The torque for td8 remained constant at .7
- Page 3: 08apr08. 8am to 11am
- td8 remained stationary, td4,12 where moving.
- td8 commaned velocity was 0 so it was never being requested to
- The torque for td8 began to rise at 9am until we shut the
system off at 10.
Motor torque offsets:
The plots above show a jump in the motor torque
readback values. I looked at 02apr08 (when the transmitter was off) to
see if there were any dc offsets/level jumps.
Tiedown motor torque
data for 02apr08 (.ps) (.pdf):
- The 3 black plots show the motor torques for td12, 4, 8 in A/D
counts (55 a/d counts=1 amp).
- The 3 purple plots are the velocity feedback for the command
going to the amp. When it is 0, there should be no motion
- You can see offsets in all 3 of the torque readings while the
velocity feedback is 0. I blew up td8 to 4 hours since there is so much
junk in the velocity feedback values.
- I checked the amp speed monitor that is also read from the
amplifier. It did not show any of these jumps. This says that it is
probably not the A/D converter
- td8 velocity feedback has a lot more noise that the other 3. We
should probably put a scope on this line.
- At 21.57 on 07apr08 the little star digital commanded velocity
for td8 went to 0 and stayed there. This is the value that goes to the
d/a to create the amplifier voltage. So the reason td 8 stopped moving
was because it was not longer being commanded to move. I don't know
whether this occurred in the little star or in the vme program.
- Things that i checked that did not cause the problem:
- If the clock on td8 jumped the the program track time stamps
could have been in the past and the little start program would have
ignored the requests. I checked the td8 clock values each second
and they were ok.
- The vme system can command a tiedown to go offline. I checked
the td8 status flag and this did not happen.
- I/O errors could make you lose communications. The i/o error
counts were not increasing and we were getting the status info back so
there was not communictions proble
- The readback of the motor torque has level jumps of up to 50 a/d
counts. It happens in all 3 tiedowns even when the transmitter is off.
- td 8 velocity feedbac is very noisy compared to td 12 and td 4.