Reason for change

We request to put AlarmsCfg-06-03-02 in production. This implements the third round of tweaks to cope with the new rocking profile.

The detailed description of the changes is in the last section.

Test Procedure

We have processed monitoring products from real on-orbit data (LPA) locally with this version of AlarmsCfg.

Rollback procedure

The package can be rolled back to the previous version by flipping a soft link. Also note that the package is completely independent from any other package running in the pipeline and will not cause a version change of L1Proc.

CCB Jira

SSC-371@JIRA

Details (release notes for AlarmsCfg-06-03-02)

 

  • Upper limits on the digi_eor Tick20MHzDeviation_TH1 (x_average) moved from -176/-168 to -165/-150.
  • Upper limits on the fastmon_eor Tick20MHzDeviation_TH1 (x_average) moved from -176/-168 to -165/-150.
  • Upper limits on the digi_trend Tick20MHzDeviation_TH1 moved from -176/-168 to -165/-150.
  • Upper limits on the digi_trend OutF_Ratio_EvtSize_CompressedEvtSize changed from  5.75/6 to 5.85/6.25.

Relevant thread(s):

  • https://www-glast.stanford.edu/protected/mail/datamon/11758.html

 

Here is the time history of the deviation (in clock ticks) of the GPS internal clock wrt the 1 PPS. I haven't looked at the temperature profile in the same time period, but we know that the the crystal is a good thermometer and I will take for granted that the trend is entirely due to a temperature variation (at 0.5 ppm/degree 30 clock ticks at 20 MHz imply something like a change of 3 degrees in temperature).

 

 

And here is a plot from Eric Siskind, confirming that the clock drift is indeed due to temperature changes.


For reference, here is an excerpt from a related e-mail exchange.

Do we expect the temperature to continue to trend upwards (as it has been doing since December 20th)? At what point does overheating the battery become a concern?

-Alex

Hi Alex:

The answer to the first question is that it depends on whether the current GASU temperature rise is a result of the solar beta angle change (which goes through about 8 complete cycles per year) or the angle between the Sun and the IP target (which goes through one complete cycle per year).  We’re very close to a beta angle peak (which is one of the two largest negative excursions in the current year; both centered about the winter solstice).  If the current temperature rise is the result of the beta angle, then we should see the GASU temperature begin to fall about a week from now.  If it’s the annual cycle that is causing the temperature rise, then you really have to understand heat flow through the LAT in order to predict when that cycle will reach a maximum.  If you adopt a really simple model and neglect the heat that is flowing through the grid because of sunlight hitting the instrument at more positive Z values, then you might conclude that the maximum temperature will occur near the time of the year when the Sun is right along the +X axis during the IP portion of each orbit.  My understanding of the geometry is that those peaks will occur in March and September, but that understanding of the geometry is not exactly ideal.

As far as the battery goes, there we know that the problem will be worst when the Sun is near the –Z axis.  As Julie has just said, the battery is cold and happy right now (because the Sun is in the +Z hemisphere), but it definitely has become quite a bit warmer over the last few weeks.  Right now, it’s only about as cold as it was when we first started 50 degree sky survey, or certainly within a degree of that.  Again, I’m not certain whether the rise over the last few weeks is the result of the beta cycle, but I’m suspicious (and hopeful!) that this indeed so.  If it is so, then again we should start seeing the battery temperature drop within another week or so.  In fact, I certainly didn’t expect to see the battery temperature rise from the annual cycle until we get to the vernal equinox, and we certainly have seen the effects of the beta cycle in the past when we were observing in almost pure 50 degree sky survey mode.  If we hadn’t changed the observing strategy, then I would expect that the battery would be 5-6 degrees warmer than it currently is.

ejs


  • No labels