As was reported before (91114) the JAC/HAM1 temperature has been drifting up and it's still changing. See the first attachment for the 8 days trend.
As the things heat up, the PZT has to compensate and hit the rail eventually, unlocking JAC. The second attachment shows that the JAC is unlocked repeatedly, most of the lock stretches chopped up to 30 to 40miniutes. See the top right that shows the JAC PZT voltage. If JAC happens to lock to the fringe at higher voltage the lock lasts longer, but the lock duration is limited by the temperature drift.
The temperature is leveling off slowly, and the last lock lasted for 4.5 hours.
But we need a temperature loop. Maybe we can start with maximum heat (right now we're pumping out 3W nominal into 25 Ohm but Daniel says the driver can handle +-18V 1A, so up to 13W seems to be possible), wait for half day or so until the effect of that mostly levels off, turn the servo on and see how far we can go.
TJ, Sheila, Jennie W
Summary: JAC HEATER guardian WIP.
With TJ and Sheila's help I wrote a guardian node called JAC_HEATER which is located in userapps/lsc/h1/guardian.
This uses the cdsutils Servo class to step the heater power based on the beckhoff readback for the JAC PZT. This will aim to keep the pzt voltage where it is once JAC is locked. The Beckhoff PZT offset voltage is only scanned on lock acquisition and after this the front-end servo does fast feedback to the PZT.
This temperature loop will step the DC offset voltage at the PZT using beckhoff at a very slow rate. I have set the UGF at 0.001 Hz for now.
We will test the guardian tomorrow morning but I have committed it to the svn.
We also need to determine the gain needed.
Masayuki last tested this here (LHO alog #89514) in March when HAM1 was last at vacuum.
Looking at his test data, (see pic) this gives 294.7 V change in the readback power going from 0 to 3W, which corresponded to a change of 0.044 K in thermistor 1 and 0.034 K in thermistor 2 before the cavity lost lock.
I tried to repeat this test with a smaller step but JAC still lost lock so I will step the requested heater power back to 3W, let the temperature settle, and redo this check with an even smaller temperature step in the morning.
