YamaT, Akutsu

Have got a lead on the problems of the PMC temperature control. Not yet solved.

Detail

The PMC temperature monitor does not vary despite varying heater input in these couple of days, while we surely saw this number had varied in response to the heater input some days ago. So strange. We inspected things one by one.

We measured the resitances of the heaters on the PMC to be 25.6 ohm. According to the LIGO document for the PMC assembly (Iguess this is it... but I am not too sure. Someone please confirm this), each heater would be IS250C50RKE by Ohmite, whose specification said 250W rating and 50 ohm resistance. Actually two of the heaters seemed to be used for our PMC, and they are connected in parallel. So the theoretical resistance shuold be 25 ohm, which is consistent with our measurement. Note that we turned off the PMC temperature controller and also disconnected the cable to the heaters (and the thermometer; they are combined in a single 4-pinn LEMO cable.) while our measurement.

We also measured the relation between the heater-in offset count K1:PSL-PMC_HEATER_OFFSET and the voltage drop due to the load by the heater pairs (corresponds to the pins-3 and -4 of the connector X5 in  the temperature controller.). This time the heaters (and the thermometer) were connected to the controller, of course. This will be reported later. Note that the output block of the temperature controller for the heaters is a transistor. Hope the power supply 24V to this controller can supply enouogh current without severe disturbance to the otherr cirucit. (For example, 10V to 25 ohm means 400mA, which should mean 4W.)

But, touching the thermometer did not vary the thermometer read value K1:PSL-PMC_TEMP_OUTMON.

Then, we started to suspect the electric-wise issue. By hand tweaking the 24V power supply cable to the temperature controller, we observed the thermometer read drastically varied! To confirm that the thermometer works better, I also touched the termometer on PMC and then the thermometer read varied. Nice. So the heart of this problem would be in electric-wise. By the way, the reason why we suspected the elecric-wise is that we noticed that the +15V LED was turned on when we sent large counts to the heater input, which is delived to the temperature controller via  the Dsub-BNC converter (see also 16245) even though we did not toggle on the switch of the 24 V power supply of the temperaturer controller.

Now, by laying the 24 V cable somehow "nicely", the thermometer read seems working. But we are not sure the circuit can bring proper signals; what should we believe? So this electric issue, and maybe surrrounding electric issues must be resolved later.