Hi/Lo Pixel Anomaly

What is it?

Event data stops being reported for one CCD/FEP combination and the delta overclock values are peculiar, large and negative for the first three output nodes and large and positive for the fourth output node.

When did it happen before?

Twice:

  • March 7, 2011: obsid 12934
  • October 31, 2013: obsid 16496

Will it happen again?

It appears likely it could happen again.

How is this Anomaly Diagnosed?

Both of the following symptoms will be noticed:

  • One or more FEPs will stop returning event data.
  • The deltaOverclock values reported from these FEPs are large and negative for the first three output nodes and large and positive for the fourth output node.

Both of these symptoms can be observed from one of the PMON pages.

What is the first response?

Most likely we will be notified by CXCDS Ops that data ceased prematurely for a single CCD for an observation. But there is a chance we can catch this anomaly in a realtime contact during a long observation. If yes, we have a SOP written to intervene if the observation with the anomaly is still in progress to dump diagnostic data.

If not, we need to:

  • Send an email to the ACIS team (including Peter Ford, Bob Goeke, Mark Bautz, and Bev LaMarr)
  • Process the dump data and get access to the CXC products
  • Convene a telecon at the next reasonable moment.
  • Examine data from the next observation, because the setup for the next observation should clear the problem.

Impacts

  • The last portion of the science run for that particular CCD/FEP combination will be lost. The following science run should be unaffected.

Relevant Procedures