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Fri Sep 13 16:46:54 2019
Cavity heater resistances remeasured
was the last measurement of cavity shield heater resistances. These were reported as 85.6 Ohm and 156.8 Ohm.
So Andrew, undestandably, configured the EPICs channel such that to put in 1 W power on the south heater, more current was driven through it in comparison to North heater.
This should have worked well, but over the past year atleast, I have been noticing that south heater is much more effective than the north one.
I remeasured the resistances and they came almost same: South 88.4 Ohm and North was 159.7 Ohm.
It could have been the case that North side was some parasitic resistance (due to bad connection with the heater) in series, increasing its effective resistance to 159.7 Ohm.
This would mean that the heating part of the resistance is still almost same as South, but because we sense it larger, we send less current on this coil.
I assume Tara or whoever put on these heaters, they made sure the length of the wires were almost same, so it is a fairly good assumption that the heating part of resistance is same.
This also matches with the observation. North side is less effective in heating, because we send less current to it.
Changes made today
I changed the dB files for the EPICs channels, so that same 88.4 Ohm resistance is assumed for both North and South heaters.
From the performance so far, and looking at the
of the beatnote signal, I feel the heaters are more balanced now.
This should help the PID as the actuation is not biased now.
I have made the hard actuation limits same on both ends of PID at 1.1 W.
We might need to retune the PID to get new PID constants.