Attached is a two hour second-trend plot of the DAC drive  for the TCS ITMX temperature setpoint and the chiller water flow rate (which shows when the chiller tripped). The data is from Wednesday night, 10pm to midnight PDT.

At 22:42 PDT the IOP stopped driving the DAC outputs (presumably due to a FIFO error) with the user supplied signals and instead outputted zero volts.

At 23:32 PDT the chlller tripped (+50mins later)

Nutsinee says that the nominal driving temperature is around 20C, the trip point is 15C, and the maximum temperature rate-of-change is 0.1C/minute. The transition from 20C to 15C would then take 50 minutes, which agrees with the timing seen on Wednesday.

The plot shows that after the chiller tripped, the control room was alerted of the problem, the front end was restarted and the chiller was reset within 10 minutes.

Clearly if the verbal alert system warned the control room at the time the DAC output went to zero, in this failure mode we will have plenty of time to restart the OAF IOP model and recover chiller operations.