Richard, Fil, Rahul, Dave:

The EX hardware watchdog (HWWD) starting having periods of low led-monitor signal warning (STAT=8) starting 12th Nov 2019. The transitions between periods of low signal and normal signal occur mostly on Tuesdays. Attached plot shows a 6 month trend of the EX-HWWD STAT channel. Prior to 12th Nov there was little noise, on that date the signal went noisy. The transition back to no noise was Tue 19th Dec 2019, then noisy Tue 07 Jan 2020, then to a short period of low noise Tue 04 Feb 2020. For these transitions there is evidence that the monthly charge measurement may be the trigger. The only transition which does not fit this theory is on Wed 05Feb when it went noisy again at noon local, at this time H1 was in observe.

We will work with Rahul on the next charge measurement in March to see if the LED-mon voltage is indeed varying.

This is not a problem per-se (for example EY HWWD is much more noisy). However it would be nice to know why the HWWD changed its behaviour around 12th November 2020. A look at the alog says that NCAL and PEM PWR work was ongoing in EX at that time.