Tiedowns

• Load cell amplifiers: scm5b. data sheet schematic  pinouts.
  

Limit switch positions/encoder reference:

    There is a pre and final hardware limit switch for the upper limit and the lower limit on each jack. The actions of the limts are:

• The final limit is a relay in the safety chain. When it opens, the safety relay opens causing the power to the motors to be cut off. To drive the jack out of this limit you must use the manual control built into each tiedown.
• When the prelimit relay is tripped (or the encoder value is within the pre limit) the program will automatically issue a stop commad. After it is stopped, the program will allow motion requests that move the jack out of the limit. It will limit the dac voltage to the sign that drives the jack in the correct direction. This assumes that the zero offset value for the dac is correct. When new dacs are installed, this value (parameter 19) needs to be updated. To check this, just watch the value of the Ki constant while the jack tracks the current position (eg montie 8). The integrated value needed to keep the jack fixed is the offset that needs to be added to the current value. The prelimit will stop the motion of the jacks if the dacs are controlling the motor amplifier. If the dac is blownout, the tiedown is in autorelease, or the manual control (hagens box) is enabled, then the prelimit will not stop the motion of the jacks (but the final limit will).
• There is also a software limit that is .2 inches inside the final limit. The VME software will never request a position outside of this software limit. When moving in rate mode (constant velocity) this limit has no affect.

1. move to a limit position (when the limit switch triggers) and then adjust the encoder to match the last encoder measurement at this position.
2. Measure the jack position with a tape measure and then interpolate what the encoder position should by using the encoder reading/tape measuremets and the two limits
3. Move the jack until the tape measure agrees with a miscLocation measurement and then set the encoder position accordingly.

    Whenever we survey from AO9, we use the current encoder values to determine how to move the tiedowns. So by definition, after an ao9 survey, the tiedown positions are now correct. This is not quiet true since we have been using the focus curves to determine the focus rather than the ao9 survey value.

The table below has the measured values of the position using encoder and tape measure. Encoder values 24 inches is when the jack is fully retracted (high tension). 0 encoder inches is when the jack if fully extended (low tension).The cols in the table below are:

• Limits encoder: Encoder readings at the limits (when the switch trips driving into the switch very slowly).
• Limits tape: The value measured (see illustration log section of td manual) with the tape measure when the td was at the final limit. The measured stop position for the final limit is a hardware stop (interlock opens). The measured stop position on the prelimit is the position where the software stopped it after seeing the digital bit change (and allowing for the slowdown).
• MiscLocations enc/tape . The encoder value, tape measurement at any other position.

• 17mar05. Changed the jack td12 for maintenance. Measured positions from bottom of jack to yoke.
• before:   after:
• measured the prelim encoder values with the vme. the final limits and the end of the jack travel were not checked. The final limit was computed from the prelim offsetkkj
• 28feb05. jack td4 broke. changed jack. Measured positions from bottom jack to yoke. difference before after was?? Looked at encoder values for prelims. Moved lower by about .08 inches. Did not measure the final limits or the end of jack encoder position.

    The software limits used to limit the requested positions are .2 inches inside the final limits. They are in the file /home/phil/h/tieProg.h
 

software request position limits.

start date	td12	td8	td4
08feb00	(22.29,1.43)	(22.87,1.93)	(22.20,1.19)
xxx	(21.79,1.2)	(22.14,1.52)	(23.21,1.95)

Tiedown power supply startup sequence:   (top)

1. the safety is closed.
2. the master contactor is closed.
3. there are no power supply faults.
4. you have requested the tiedowns to move.

1. POWER1 to energize the master contactor relay to startup
2. POWER2 to drive the master contactor relay during normal operation inline with the power supply fault contactor and the safety.

1. reset will close the safety if there are no safety problems (eg.blk liftoff, emg stop, etc.).
2. You must command the tiedowns to move (it can be to the current position) or use the pcu to turn the drives on.
3. The little star will driver 24 volts through POWER1  dio2 pin 2,3 for about 300 milliseconds. This provides power to the master contacter relay PS_MC_R if the saftey is closed.
4. PS_MC_R closes the master contactor and the 3 phase power is supplied to the power supply. The power supply will then close the power supply fault contactor (PSR_4_FAULT* goes high). 24 volts is wired through the power supply fault contactor, throught the POWER2 contactor in the little star, the safety, and then the PS_MC_R.
5. The little star loops up to 20 times checking to see if PSR4_FAULT* goes high (about 100ms/loop i think). This is pin DIO1 J3 pin4 --> lsPin03.  If after 20 times through the loop the contactor hasn't closed, then the little star will drive POWER1 to 0, open POWER2 and log fault 12 (PSR_FAULT psr4F).

Once the little star sees PSR4_FAULT* go high, it turns on (closes) POWER2. After one cycle it will drive POWER1. The PW_MC_R is now getting 24 volts through pwrsupply fault contactor, POWER2 and  the safety contact. If any of these go away, then PS_MC_R  will lose its 24 volts  and the master contactor will open (removing the 3 phase power to the power supply).

Load cell resistances measured at input to amp.  (top)

In the table below:
        amp 1 is the top    amplifier
        amp 2 is the bottom amplifier
        cable 1 normally goes to the top amp
        cable 2 normally goes to the bottom amp
see the drawing in the td manual for where the load cell is located on the yoke.

To do the measurement:

1. turn off amplifier
2. remove the 4 wires that go to the amplifier.
3. remove tension on the load cell by raising the  jack. Point the  dome point at the tiedown.
4. measure the resistance at the 4 wires that connect to the amp.
5. The sparcarrestor,and db25 filter should be in place.

The values with ** had bad filters in the db25 connector.
++ removed the filter because it was bad (and had no spares)

• 1. 09nov06. ld cell 1 td12 failed. replaced with spare loadcell

Load cell Info:locations,history,calib    (top)

• 147697
• 207629

Tiedown reference position:

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