This morning I started driving OM2 T-SAMS heater.
Right now the voltage is 22.2V across the heater element (7.3V into the driver), which is close to the safe maximum drive at LLO that would result in 60 degC (for LLO T-SAMS). Since LHO T-SAMS seems to be more tolerant for higher temperature than LLO, and since we probably need more heating, I'll find a voltage that would give us 70 degC or so.
It seems that there's some outgassing from the heater. I'll be watching the temperature as well as HAM6 pressure.
Details:
Since we know that LHO OM2 will be a one-sided actuator if we don't go higher than 60 deg C (see G2201709 page 13), there's a strong motivation to go higher than that.
T-SAMS mirror is compression-fit into a ring. ROC of the mirror is a function of the tightness of the fit, which in turn is a function of the heater power, thermal environment and the tightness of the fit at room temperature. The last one, i.e. "cold" tightness of the fit, seems to vary from sample to sample.
We have evidences that LHO OM2 is much tighter than LLO OM2 at the same temperature. One example is that, unlike LLO unit, it was hard to fit the mirror and the ring at 80 degC, they had to go as high as 105 degC at the manufacturing stage. We should be able to go ~70 degC or a bit more.
The radius of curvature of the mirror standalone, with compression ring, is 1.5 m. Extrapolating the mesurements done at Caltech, this RoC would be reached for 88 degrees C. Meaning that close to that temperature there is a substantial risk that the mirror will fall off. Therefore we sure make sure that there is enough safety margin. I wouldn't recomment going higher than ~75 degreed C.
Thanks Gabriele.
So far, 7.3W request (7.5W measured, 26.8V across the load, 9V out of DAC into the driver) got us to 72.7 degC, it might reach 73 if we wait loooong enough (right 2nd from the top). It seems that 9V out of DAC is a good number to hard-code for our heating limit at LHO.
I'll change the request to get to ~56 degC where the T-SAMS ROC is supposed to be close to that of the old OM2.
Pressure at HAM6 (left top), BSC3 (left 2nd from the top) and BSC2 (left 3rd from the top) are already coming down.
Eventually reached 56.25 degC (right, 3rd from the top) with 4.4W of requested power (VSET=20.976V, VMON=20.8V, IMON=0.217A, PMON=4.5W). I'll just keep it like this.
