[JimW, JeffK, Jenne]
Several times today we've had to hand-request the OMC guardian to go to ReadyForHandoff, after it fails to find the carrier during the PZT scan. I'm a little unsure why it sometimes works, and sometimes doesn't, since the scans look quite similar.
In the two attached screenshots, once the OMC scan worked, and once it didn't. The one that includes "succeed" in the filename starts at a slightly lower DCPD value (below 2mA), whereas the "failed" time the DCPD value starts at around 5mA, so maybe that's the difference in it recognizing that the first peak on the left is one of the 45MHz sidebands? I'll have to look at the OMC scan code, but if that's not it, then I'm certainly confused.
Okay, fixed.
Since the first 45MHz peak is so close to the start of the scan, the "pzt_diff" value that the OMC guardian is looking for isn't super accurate, so it's failing a test and returning the OMC to its Down state.
What the scan is doing is chunking the data into 7 pieces, and then finding the max value in that piece. It then compares the max DCPD value from each of those 7 chunks. It decides that it has found a pair of 45MHz peaks if the peaks are within 25% of the same height and are within 18V (where V are from the PZT2_MON_DC_OUT channel). Since we're at the beginning of a ramp, and it's the soft CDS ramp and not a sharp triangle ramp, I think that the peak location is maybe not getting mapped exactly correctly to the PZT value, so sometimes it looks like the 45MHz peaks are 18.03V apart, which causes the test to fail. However in some cases, like the "succeed" case from the parent comment, the difference is found to be something like 17.95V, which barely passes the test.
I have increased the acceptable peak difference to 20V. As you can see in the screenshots in the parent comment, the 45MHz peaks that are not a matching pair are more than 30V apart.
Upon our first try after this change, the pzt difference that it found was 18.05V, but kept locking happily since this is lower than the new threshold of 20V.