Previously, I hacked together a high power DCPD counts checker in the OMC whitening state that worked well for 20 mA. We have changed the DARM offset, so it no longer worked well, and we have nearly saturated the DCPDs when turning on the OMC whitening during lock acquisition.

What I failed to understand when I first designed the checker, and thank Jenne for patiently explaining to me: the OMC whitening is frequency dependent, so any DC offsets (like the DARM offset) should be factored out of the calculation and added back in later, after the high frequency portion of the DCPD counts is multipled by 10.

Using the DCPD min/max scope, I eyeballed what count offset corresponds to DARM offset. It appears that at 40 mA, the offset is about 110,000 cts. This lines up with the eyeballed value at 20 mA DARM offset which is about 55,000 cts.

Now, the math in the "check_for_violins_saturation" (ISC_library function) at power=high goes like this:

• overall_max is estimated by taking the maximum of the recent 30 seconds of DCPD data
• Expected_counts = 10 * (overall_max - 100000) + 100000
• If this number is greater than 2^19, the function returns false, and we hold 60 seconds before checking again. If the function returns true, we turn on the OMC whitening and proceed to NLN.

Note: I chose 100,000 instead of 110,000 to overestimate what the counts would be with whitening on. This value is hard coded, and must be updated every time we change the DARM offset.