Detector 2 anneal 2012

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Latest revision as of 19:02, 25 August 2014

Notes

• Detector 2 has been unsegmented since the 2012 anneal. The entire detector volume is read out through the front segment electronics, so rates look higher for G2 (and also G4) than for the other detectors.

• Detector 2 is located in a position where it can receive light leak through a valve at the back of the cryostat. This problem occurs when the back of the spacecraft is pointed towards the sunlit earth, so it comes and goes with the orbital precession. Light leak only affects the rear sections of the detector, but since Detector 2 is unsegmented, the excess counts are seen in the front segment readout. Symptoms of this problem are enhanced reset rates and fast LLD rates, and the problem does degrade livetime. (Example) Raising the LLD level can ease the livetime problem, but this will have a negative effect on lower-energy spectroscopy. Light leak can be seen to a lesser extent in detector 3, and very rarely in 5 and 9.

• 2012 Feb 27 02:12: Small isolated spike in G2. No steps taken.

• 2012 March 30 17:53:27 UT: The front fast event threshold for detector 2 was raised by 0x10, from 0x60 to 0x70, to free up livetime (due to light leak problem)

• 2012 18 - 25 April:
  • Front slow threshold from 0x50 -> 0x60
  • Front fast threshold from 0x70 -> 0x80
    • /IDPUDUMPTABL DIBTBL2
    • /IDPUTABLE2 FRONTSLOWDAC  ;Load address 0x25B9
    • /IDPULOAD VALUE=0x60  ;Byte 7, Front Slow threshold
    • /IDPULOAD VALUE=0x80  ;Byte 8, Front Fast threshold

• 2012 August 1: In the past week detector 2 livetime has occasionally been compromised by the light leak problem. No action is being taken, since we do not want to impair low-energy spectroscopy.

• 2012 November 6: There was a bit of noise on detector 2, so the front slow threshold was raised from 0x60 to 0x78. This may help with the SSR fill level issues we have been seeing recently.

• 2013 January 8: At 07:26:26 UT the HV on Det 2 was raised by five steps (206 -> 211). HV is now at 4117 V.

• 2013 January 24: The high voltage of detector 2 was raised by five steps (211 -> 216). The voltage is now at 4215V.

• 2013 January 30: The high voltage of detector 2 was raised by five steps (216 -> 221).

• 2013 February 5: The detector 2 high voltage was raised by another five steps (221 -> 226). This increase puts G2 at 4411 V, which is now the highest voltage of all our detectors.

• 2013 February 13: The front slow event threshold for detector 2 was lowered from 0x88 to 0x58. This was done to see if the low-energy counts that troubled us before (at a lower HV) are still present or not.

• 2013 February 14: The front slow event threshold for detector 2 was lowered from 0x58 to 0x48 (at 044/19:08 UT) but was raised up again on the next orbit from 0x48 to 0x50 (at 045/20:47 UT).

• 2013 February 21: The front slow threshold for detector 2 was lowered from 0x50 to 0x44.

• 2013 February 22: The front slow threshold for detector 2 was lowered from 0x44 to 0x38.

• 2013 September 1: Spike in D2 at about 10:26UT.

• 2014 Feb 18: After signs of intermittent segmentation starting in mid-January, detector 2 finally has sustained stretches of segmentation. It still desegments during the SAA.

• 2014 Mar 17: Since the detector is mostly segmented now, the front and slow thresholds were lowered to nominal values. Behavior after lowering looked fine, at least from the monitor rates.

   14-076-20:38:58 /IDPUTABLE2 FRONTFASTDAC
   14-076-20:39:22 /IDPULOAD VALUE=0x22 ;was 0x80
   14-076-23:48:25 /IDPUTABLE2 FRONTSLOWDAC
   14-076-23:48:40 /IDPULOAD VALUE=0x0C     ;was 0x38

D2 front slow LLD threshold history

D2 front fast LLD threshold history

D2 rear slow LLD threshold history

D2 rear fast LLD threshold history