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February 2006 CDS Report (Error Messages & Efficiency)

Filter Usage

  Time (s) Cathode Time (%) Cathode
Num Description Pos Used Down Up Down Up
0 Blocked 2200 0 0.0 0.0 0.00 0.00
0 Blocked 0000 540 777042.9 51389.4 32.13 2.12
1 UV Grism Clocked 0160 0 0.0 0.0 0.00 0.00
1 UV Grism 0200 10 136.5 4867.2 0.01 0.20
2 UVW2 0400 873 90859.3 262800.0 3.76 10.87
3 V 0600 1025 78156.1 441898.8 3.23 18.27
4 UVM2 0800 831 21835.4 196944.8 0.90 8.14
5 Vis Grism Clocked 0955 6 4140.4 10801.1 0.17 0.45
5 Vis Grism 1000 12 166.9 7229.4 0.01 0.30
6 UVW1 1200 771 7842.1 136401.9 0.32 5.64
7 U 1400 698 8329.0 98391.4 0.34 4.07
8 Mag 1600 0 0.0 0.0 0.00 0.00
9 B 1800 707 24098.9 153791.0 1.00 6.36
10 White 2000 156 4690.2 36666.1 0.19 1.52
  Totals   5629 1017297.6 1401181.1 42.06 57.94

Observing Efficiency

Description Time (s) % Time
UNKNOWN 8848.25 0.37
BASIC 0.00 0.00
SAFE 0.00 0.00
SLEW 248749.70 10.28
SETTLING 132.93 0.01
FINDING 2598.52 0.11
AUTOMATED 342752.73 14.17
PLANNED UNBLOCKED 1008873.08 41.71
PLANNED BLOCKED CATHODE DOWN 399332.90 16.51
PLANNED BLOCKED CATHODE UP 41027.15 1.70
SAFEPOINT 10402.35 0.43
SAA UNBLOCKED NON AT 70369.13 2.91
SAA UNBLOCKED AT 12410.17 0.51
SAA BLOCKED 231021.58 9.55
IDLE 41633.37 1.72
UNPLANNED IDLE 444.72 0.02
     
TOTAL 2418596.58 100.0

Comments on Tables

~10% of the time was spent in SAA in a blocked position. These observations usually cause unnecessary movement of the filter wheel and would be better spent in PTNull, when implemented. (In this mode, no movement takes place of the filter wheel from its previous position whilst setting up for SAA).

A small amount of time (414 s) was spent unexpectedly in blocked idle as the exposure ran out just prior to a slew to the SAA - a 'Mode Exhausted' error. This is due to the SAA size used in planning - see discussion of errors below. Once PTNull is implemented, such errors would cause a unneeded move to blocked, with the attendant filter wheel wear issues.

~16% of the time the planned observations were spent in the blocked filter with the cathode down. This time would probably be better spent in engineering exposures, UV survey etc now that the new UVOT mode table is available.

As a result of the PT table change of release 12, more than 10 000 s were spent doing flatfields instead of nothing.

The time spent in 'UNKNOWN' state is due to data gaps in telemetry.

Comments on Errors

Note: a summary of the NHK messages encountered this month, listed in increasing frequency of occurrence, may be found at http://msslje.mssl.ucl.ac.uk/lists/nhklis_2006-02.txt

Exposure Reduction for a PT

There were 13 occurences where the UVOT had to reduce the exposure time for the same planned PT, which presumably should have been detected at the planning stage. The times were

2006-02-01 00:29:01.66
2006-02-01 02:06:02.88
2006-02-01 03:42:00.72
2006-02-01 05:16:18.75
2006-02-01 06:53:17.80
2006-02-01 08:29:17.53
2006-02-01 10:06:16.35
2006-02-01 11:42:35.63
2006-02-01 13:18:16.52
2006-02-01 14:55:18.69
2006-02-01 21:22:01.81
2006-02-01 22:58:00.64

The star was HD 32518 RA 05 09 36.72 dec +69 38 21.8 B=7.537 V=6.43 Sp=K1III which is half a mag brighter than the limit.

Possible Bugs

  1. There was also a reduction for an exposure at 2006-02-28 21:03:07.79 which was in blocked just as it switched to SAA and therefore this may be a bug to investigate.
  2. It was noticed that, when 'goto blocked failsafe' is run, the state goes briefly through SAA prior to reaching IDLE. A preliminary inspection of the relevant RTS indicated this should not occur and need investigating to see if this is a 'bug'.

S-0198 FONEXTOBSINFO DCS Event Timeouts

There were 6 occurrences of a DCS Event Timout awaiting a FONEXTOBSINFO record. Further examination of the logs reveals that on each occasion, the ICU sent a slew warning response twice (presumably to two spacecraft slew warning for one slew) for a single slew but we only received one FONEXTOBSINFO. This has been logged as anomaly S-0198.

S-0200 Total Exposure Time is Zero

2 occurrences of the error message 'Total Exposure Time is Zero' were received. These are caused by an attempt to divide by zero when calculating a scaled exposure time. Initial investigation indicates a race condition problem which arises when a slew warning comes in at the same time as the ICU is preparing for the next scaled PT observation. It has been logged as anomaly report S-0200. Although this is a 'bug' in the ICU code, the circumstances that revealed it appear to be a consequence of the uncertainties in the planning process. It would be prudent to remember that the last exposure in a multi-exposure sequence may be cut back by too much and this should be considered the next time UVOT modes are altered.

S-0206 Mode Exhausted Message

There were 25 occurrences of "Mode Exhausted" when the time supplied in the FONEXTOBSINFO was insufficient. Investigation indicates the need to improve the ground SAA model. This has been submitted as Anomaly Report S-0206.

Pointing Errors

Below are the small pointing position errors the ICU detected. The number immediately after the "Small...." text is the pointing or drift error in arc minutes.
2006-02-03 20:56:39.78 APID 375 ICU*ERR*pkg=24 err=d0 Small Differential Drift 0003 3b11 1047 d00003
2006-02-16 09:04:22.94 APID 375 ICU*ERR*pkg=24 err=d4 Small Settled Position Error 0008 2f9a 1fa5 d40008
2006-02-16 09:04:25.78 APID 375 ICU*ERR*pkg=24 err=d1 Small Absolute Drift 0009 2f9a 1fa5 d10009
2006-02-16 12:17:23.75 APID 375 ICU*ERR*pkg=24 err=d4 Small Settled Position Error 0008 2f9a 1fa5 d40008
2006-02-16 12:17:25.77 APID 375 ICU*ERR*pkg=24 err=d1 Small Absolute Drift 0008 2f9a 1fa6 d10008
2006-02-16 15:30:23.75 APID 375 ICU*ERR*pkg=24 err=d4 Small Settled Position Error 0008 2f99 1fa5 d40008
2006-02-16 15:30:25.78 APID 375 ICU*ERR*pkg=24 err=d1 Small Absolute Drift 0008 2f99 1fa5 d10008
2006-02-16 18:43:23.95 APID 375 ICU*ERR*pkg=24 err=d4 Small Settled Position Error 0008 2f99 1fa6 d40008
2006-02-16 18:43:27.79 APID 375 ICU*ERR*pkg=24 err=d1 Small Absolute Drift 0008 2f99 1fa6 d10008 

Justin Knavel reports (30 March 2006)

  • 2006-02-03 20:56:39.78 - During the previous target the Star Tracker was Not OK.

  • All 2006-02-16 - The Observation was GRB060206 and the previous target was GRB060213. None of the times were during a Star Tracker Not OK. But, there were 5 Star Tracker Not OKs while observing GRB060206 after slewing from GRB060213 on 2006-02-16. So, there was a Star Tracker issue on this day while observing GRB060206. The Slew had high roll (108 degrees) and this could be an anti-sun slew. We'll have someone run some CHILE plots to check it. If it was an anti-sun slew then this would explain the attitude and possibly the Star Tracker problems.

It is worth noting that, prior to release 12, the above small pointing errors would have caused UVOT to go to Safe. It will still do so for large errors.

Slew Aborts

There were no slew aborts this month (these are normally caused by UVOT not responding with an "OK to Slew" in time).


Last revision: r10 - 2006-08-10 - 16:27:16 - HowardHuckle
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Topic revision: r10 - 2006-08-10 - HowardHuckle
 
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