tiedown 8 stops moving

    On 07apr08 at 21:30 tiedown 8 stopped moving. A 430 dual beam transmitter experiment was running. The telescope position was:

• az=348, gr=17, ch=0 degrees.

1. Tiedown position in inches vs hour of day. 0 inches is fully extended (up), 24 inches is pulled all the way down.
2. 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 for td8.
   
3. Amplifier speed vs hour is read from the motor amplifier.
4. Drive status: 0 off, 2 powered on , 1 enabled (ready to move or moving), 3 failure
5. 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 move.
  
• The torque for td8 began to rise at 9am until we shut the system off at 10.

Motor torque offsets:

• 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.
  

Summary:

• 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.
  

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