Cathode High Voltage - Troubleshooting

What to do if....

The voltage on the pick-off point changes

If the value changes to a new value like this:

Don't worry. This happens regularly:

HV Minor Alarms

The HV is set to Minor Alarm if the 5 second pick-off point average differs by more than 0.1 V from the 60 second pick-off point average.
This pick-off point average, the Blip Monitor (variable name uB_TPCDrift_HV01_keithleyPickOff/voltDiff5s60s), is the peach-toned parameter plotted on the DriftHV_Deviation Tab on the Slow Controls plotter.
Post a screen shot of this tab in the e log, similar to the screen shots inserted below, when you log the Minor Alarm (then acknowledge the alarm).

The vertical scale for the Blip Monitor parameter is frequently adjusted by Shifters to be way too sensitive, making every little noise twitch appear like a large blip.

The screen-shot below shows what happens when the Blip-Monitor scale is too sensitive -- it looks like a spike or blip - but the vertical scale is expanded so far that the trip level is outside of the view.

The screen-shot below is the same time-frame as the one above, with the Blip-Monitor vertical scale set more appropriately.
The apparent spike or blip is not a blip at all - just noise - and is well below Minor Alarm threshold.
The other values plotted on this Tab also tend to be adjusted to a too-sensitive level.
The screen shot below has reasonable vertical scales for all of the plotted parameters.

HV Major Alarms

The HV is set to major alarm in the case of a PS going to 0 V when it should be at a drift voltage, and also in the case of the pick-off point being more than 0.2 V from -216.86 V.
Call the Run Coordinator and the HV expert for any Major Alarm. They will monitor the situation.

The HV supply trips

Call the Run Coordinator.
If it is not between the hours of 10 pm - 7 am, also call the HV expert; otherwise, call them in the morning.
The detector will need a full system checkout before ramping the HV back on -- and generally we will not be ramping the voltage in the middle of the night.

Crash button

If the HV must be ramped down, it is best for an expert to use the expert GUI.

In the rare case where all else has failed and the HV must go down, the power button on the Glassman supply can function as a crash button.
This is not the default method to ramp down.
It will create a sudden drop in voltage in the entire system, stressing the TPC components. The power button is highlighted below.