Abstract:

I measured proper comp offset values for IMC CMS IN1 gains.
Since I measured between -8dB and +24dB, it is necessary to measure it we use IMC In1 gain more than 24dB or less than -8dB.
After setting new values, IFO can be locked with 10W without IMC ASC saturation.

Detail:

Since comp offset values have not been changed since O3GK, I remeasured it and set new parameters.
Measurement procedure is as follows:

1. IR shutter was turned off.
2. Set In1 gain at -1dB and close IN1 switch.
3. Chaeck the signals of K1:IMC-SERVO_MIXER_DAQ_OUTPUT.
4. Increase/decrease gain by 1dB and change the value of K1:IMC-SERVO_IN1GAIN_OFS_COMP_GAIN(XX)_OFS((XX) should be the value of IN1 gain at that time) so that the signals of K1:IMC-SERVO_MIXER_DAQ_OUTPUT doesn't change.
5. repeart #4 until IN1 gain reaching 24/-8dB.

Figure 1 and 2 show the matrix elements before and after measurement, respectively.
Figure 3 and 4 show the IMC signals during increasing laser power before and after the matrix changes.
IMC offset change was reduced by a factor of 3.5 after the new parameter setting and DOF4_P drift becomes much smaller than before.