STIS Instrument Science Report STIS 98-03
MAMA Anomalous Recovery
Harry Ferguson, Mark Clampin, Steve Kraemer, and Vic Argabright
October 23, 1998
ABSTRACT
We specify the procedures for reactivating the MAMA detectors after an anomalous shutdown. These procedures provide (1) a test of the signal processing electronics, (2) checkout of the high-voltage by ramping up slowly to a setting 300 V below nominal, monitoring
the health of the detector at each voltage increment, and (3) final ramp up to the nominal
voltage setting, followed by dark and flatfield exposures and a fold analysis.
The procedures described here are identical to the those in the initial MAMA turnon (STIS
TIR 97-05), with the following exceptions: (1) The darks at the end of the HV check out
and the HV full ramp-up are 540s long to allow adequate time to check the different event
counters; (2) the yellow, red, and SGM limits are higher for the NUVMAMA to allow for
higher dark current; and (3) the flat-field exposure and fold-analysis have been kept modular (as part of proposal 7643), rather than as explicit exposure lines in the anomalous
recovery procedure proposals.
1. Introduction
T
The STIS MAMA detectors offer a relatively limited amount of telemetry information
for problem diagnostics when a high voltage shutdown occurs. Such HV shutdowns can
occur either as the result of a hardware problem, or a bright object violation which causes
either the Software Global Monitor (SGM) or the Bright Scene Detection (BSD) monitors
to shut down the detector’s HV. The Anomalous Recovery procedure should be used when
it is believed that there may have been damage to a MAMA detector, either as a result of a
hardware problem, or a bright object violation. The need for an anomalous recovery process should be evaluated on a case-by-case basis. For example, the anomalous recovery
procedure is not needed if a post-facto analysis of a bright object shutdown shows that the
count rates would have been safe for the detector. The anomalous recovery procedure is
also not needed for MCE resets due to charged-particle events in the opto-isolators.
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2. Anomalous Recovery Procedure
The procedure for the recovery of the MAMA from an anomalous shutdown has been
developed with the goals of maintaining the detector safety at all times, and avoiding the
need for real-time contacts with HST. Since a communication link can never be guaranteed, real-time operations with a MAMA detector involving decisions to proceed with a
test based on observed telemetry will always have inherent risk to the detector.
The Anomalous Recovery Procedure is comprised of three stages: a signal processing
electronics test, an intermediate HV ramp and then a full HV ramp. The procedure more
closely resembles the Initial MAMA Turn-on procedure (TIR-STIS-97-04) than that
described in earlier memos. Two procedures have been defined for high-voltage ramp-up
of each detector, an initial checkout procedure followed by the full high voltage ramp. The
procedure can run over a three day period, and requires an event flag to be set at each stage
to continue.
The anomalous recovery proposals associated with this ISR are 7719 for the FUVMAMA and 7725 for the NUVMAMA. The full HV ramp-up should be followed
immediately by a flat-field exposure and fold analysis using one of the ON-HOLD visits
from proposal 7643.
Initial requirements
A minimum wait period of 24 hours following the shutdown is required to ensure that any
gas generated in the MAMA has time to be reabsorbed into the MCP pores.
Signal processing electronics checkout
The signal processing electronics check is designed to verify that the charge amplifiers and
signal processing electronics are operating nominally. It should run as a self contained
procedure prior to the MAMA HV recovery stages and, since it requires no detector HV, it
can be run within 24 hours of the shutdown. The test procedure is to power on the charge
amplifiers and signal processing electronics, setting the amplifier thresholds first to the
nominal level (0.48V) to verify that no counts are seen, and then to a lower value of 0.28
volts. In this lower setting, amplifier noise should produce some counts, thus verifying that
the signal processing chain is responding.The OR count telemetry is then checked to see if
the ORCOUNT rate exceeds:
•
7000 counts/sec for the NUV MAMA
•
11000 counts/sec for the FUV MAMA
In the event of an anomalous result (i.e. count rates that exceed these levels, or are less
than these levels by more than a factor of 100), further electronic diagnostic tests would
have to be developed to characterize the problem, prior to attempting the HV ramp.
2
Intermediate HV checkout
The two checkout procedures are similar in design, and comprise a ramp-up in voltage
until the MCP voltage is 300 V below nominal, a 540 second dark image and then a ramp
down to 0 volts. A timetag dark exposure runs for the duration of the ramp-up procedure.
The ramp down uses the default voltage ramp down procedure. In the case of the NUV
MAMA, 50 volts is also applied to the photocathode (PC). Between each high voltage
increment, on the ramp-up, telemetry is collected to monitor the health of the detector. For
these procedures the monitoring limits are shown in Table 1.
Table 1: MAMA Monitoring limits during HV ramp up
FUVMAMA:
NUVMAMA:
Yellow limit
500 cts/s
Red limit
1000 cts/s
SGM monitor between voltage increments
100cts / 0.1s
Yellow limit
2500 cts/s
Red limit
5000 cts/s
SGM monitor between voltage increments
500 cts/0.1s
The NUVMAMA limits are set high on the expectation that the recovery may follow a
period of several days during which the detector was cool. The dark current will then be
unusually high as the increasing temperatures excite phosphorescent decays in the detector window.
The software global monitor is enabled between voltage increments while telemetry is
being collected. It is set to trigger on a OR count rate exceeding 100 counts per 0.1 sec
sample, which should be well above the expected dark count rates, with the MCP 300
volts below nominal, but low enough to shutdown the detector in case of problems. No flat
field images are taken during this procedure.
Full high voltage ramp-up procedures
The full high voltage ramp-up procedure is also similar in design for both detectors. It
comprises an incremental ramp-up to the nominal operating voltage, followed by a 540
second dark image. Once again time-tag dark exposures are obtained during the HV rampup. Between each high voltage increment telemetry is collected to monitor the health of
the detector. The monitoring limits to be used during HV ramp-up are shown in Table
1.The SGM is then set to its standard an operating level, and a fold-analysis visit from proposal 7643 is executed.
3
3. HV ramp-up telemetry
The MAMA HV turn-on proposal is primarily monitored via real-time STIS telemetry,
which can be viewed at PORTS pages, or dumped for analysis following execution of the
procedure. The relevant keywords for this procedure are those which provide information
on the MAMA detector’s voltages and event rate monitors. These keywords are summarized in Table 2. Examples of the FUV MAMA’s MCP voltage and repeller voltage during
the HV checkout and the full HV ramp-up are shown in Figure 2. These data were
obtained during SMOV. For this test the normal wait times between each ramp-up procedure was waived and so the full HV ramp-up immediately follows the checkout ramp-up
in the telemetry stream. During the HV ramp-up, the event counter is set to monitor the
OR count rate. which is shown in Figure 3. Similar telemetry for the NUV MAMA is
shown in Figure 4 and Figure 5.
4
Figure 1: A schematic flow chart showing the procedures for the a MAMA detector’s high
voltage ramp-up.
Event Flag
Stop
Do not proceed if event flag
is not set.
Proceed
Counts should be seen at
a threshold of 0.28 V
MAMA
Signal Processing test
1 Day Wait
Event Flag
Stop
Do not proceed if event flag
is not set.
Proceed
MAMA
Intermediate HV ramp-up procedure
Procedure aborts if
Red/Yellow limts exceeded
or SGM shuts down MAMA
Review the MAMA telemetry
and timetag/accum dark
count images.
MAMA
Telemetry and data analysis
2 Day Wait
Event Flag
Stop
Proceed
Do not proceed if event flag
is not set. This occurs if the
analysis results are
unsatisfactory.
Procedure aborts if
Red/Yellow limts exceeded
or SGM shuts down MAMA
MAMA
Full HV ramp-up procedure
Procedure leaves FUVMAMA
in normal operating state.
MAMA
Fold Analysis (ISR 98-02)
5
Table 2. MAMA detector diagnostic keywords
Keyword
Description
OMiEVQ
event counter
OMiEVX
event counter selected
OMiMCPV
MCP voltage
OMiMCPC
MCP current
OM1FLDV
Field voltage
OM2PCV
Photocathode voltage
OMiTHRV
Threshold voltage
OMiHBIAV
high bias voltage
OMiLBIAV
low bias voltage
OMiP8AV
+8V amp voltage
OMiP8VAC
+8V amp current
OMiP5DV
+5V Discriminator voltage
OMiP5VDC
+5V Discriminator current
OMiM2DV
-2V Discriminator voltage
OMiM2VDC
-2V Discriminator current
OMiP5V
+5V voltage
OMiP5VC
+5V current
OMiP15V
+15V voltage
OMiP15VC
+15V current
OMiM15V
-15V voltage
OMiM15VC
-15V current
OMiP2RFV
+2V Reference voltage
OMiP8RFV
+8V Reference voltage
Note: i=1 for FUV MAMA and i=2 for NUV MAMA
6
Figure 2: MCP and repeller field voltages versus elapsed time for the FUV MAMA detector. The telemetry data for the full ramp-up procedure shown.
Figure 3: Plot showing OR Counts versus elapsed time for the FUV MAMA detector. The
telemetry data for the full ramp-up procedure are shown.
7
Figure 4: MCP and Photocathode voltages versus elapsed time for the NUV MAMA
detector. The telemetry data for the full ramp-up procedure are shown.
Figure 5: Plot showing OR Counts versus elapsed time for the NUV MAMA detector.
The telemetry data for the full ramp-up procedure are shown
8
Table 3. FUV Intermediate voltage checkout procedure (proposal 7719, visit 3)
Step
Exposure
Action
Target voltage
Rate
1
1
Switch on Lower Voltage power supply
2
2
Initiate timetag exposure for duration of ramp up
3
2
Ramp MCP voltage to -500 V
-500 V/MCP
50 V/step
[10 sec between steps ]
4
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-500 V/MCP
240 sec
5
2
Ramp MCP voltage to -1000 V
-1000 V/MCP
6
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1000 V/MCP
50 V/step
[10 sec between steps ]
240 sec
7
2
Ramp MCP voltage to -1500 V
-1500 V/MCP
8
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1500 V/MCP
50 V/step
[10 sec between steps ]
240 sec
9
2
Ramp MCP voltage to -1950 V
-1950 V/MCP
10
2
Stop timetag dark exposure and dump image
-1950 V/MCP
11
3
Dark Accum image for 540 secs
-1950 V/MCP
12
4
Ramp down using special commanding MAMA
high-voltage ramp-down procedure
9
Pause
50 V/step
[10 sec between steps ]
600 sec
Table 4. NUV Intermediate voltage checkout procedure (proposal 7725, visit 3)
Step
Exposure
Action
Target voltage
Rate
1
1
Switch on low voltage power supply
2
2
Initiate timetag exposure for duration of ramp up
3
2
Ramp MCP voltage to -500 V
-500 V/MCP
50 V/step
[10 sec between steps ]
4
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-500 V/MCP
240 sec
5
2
Ramp MCP voltage to -1000 V
-1000 V/MCP
6
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1000 V/MCP
50 V/step
[10 sec between steps ]
240 sec
7
2
Ramp MCP voltage to -1500 V
-1500 V/MCP
8
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1500 V/MCP
50 V/step
[10 sec between steps ]
240 sec
9
2
Ramp MCP voltage to -1750 V
-1750 V/MCP
10
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1750 V/MCP
50 V/step
[10 sec between steps ]
240 sec
11
2
Ramp PC voltage to -50 V
-1750 V/MCP
-50 V/PC
12
3
Dark Accum image for 540 secs
-1750 V/MCP
-50 V/PC
13
4
Ramp down using standard MAMA high-voltage
ramp-down procedure
10
Pause
50 V/step
[10 sec between steps ]
600 sec
Table 5. FUV MAMA Full high voltage ramp-up procedure (proposal 7719, visit 4)
Step
Exposure
Action
Target voltage
Rate
1
1
Switch on low voltage power supply
2
2
Initiate timetag exposure for duration of ramp up
3
2
Ramp MCP voltage to -500 V
-500 V/MCP
50 V/step
[10 sec between steps ]
4
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-500 V/MCP
240 sec
5
2
Ramp MCP voltage to -1000 V
-1000 V/MCP
6
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1000 V/MCP
50 V/step
[10 sec between steps ]
240 sec
7
2
Ramp MCP voltage to -1500 V
-1500 V/MCP
8
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1500 V/MCP
50 V/step
[10 sec between steps ]
240 sec
9
2
Ramp MCP voltage to -2050 V
-2050 V/MCP
10
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-2050 V/MCP
50 V/step
[10 sec between steps ]
240 sec
11
2
Ramp field voltage to -100 V
-2050 V/MCP
-100 V/Field
12
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-2050 V/MCP
-100 V/Field
13
2
Ramp MCP voltage to -2150 V
-2150 V/MCP
-100 V/Field
14
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-2150 V/MCP
-100 V/Field
15
2
Ramp MCP voltage to -2250 V
-2250 V/MCP-100 V/Field
16
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-2250 V/MCP
-100 V/Field
17
2
Ramp field voltage to -1500 V
-2250 V/MCP
-1500 V/Field
18
2
Enable SGM @ 1000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-2250 V/MCP
-1500 V/Field
19
2
Stop timetag dark exposure and dump image
-2250 V/MCP
-1500 V/Field
20
3
Dark Accum image for 540 secs
Cycle through the W,X,Y,Z,OR,EV, and VE
counters collecting 5 samples of each
-2250 V/MCP
-1500 V/Field
11
Pause
50 V/step
[10 sec between steps ]
240 sec
50 V/step
[10 sec between steps ]
240 sec
50 V/step
[10 sec between steps ]
240 sec
50 V/step
[10 sec between steps ]
240 sec
Step
Exposure
21
4
22
Action
Target voltage
Reset SGM to nominal operating level and sampling rate. Leave HV on for fold analysis.
Execute fold analysis (ON-HOLD visit from proposal 7643). See ISR 98-02.
12
-2250 V/MCP
-1500 V/Field
Rate
Pause
60 secs
Table 6. NUV MAMA high voltage ramp-up procedure (proposal 7725, visit 4).
Step
Exposure
Action
Target voltage
Rate
1
1
Initiate timetag exposure for duration of ramp up
2
2
Ramp MCP voltage to -500 V
-500 V/MCP
50 V/step
[10 sec between steps ]
3
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-500 V/MCP
240 sec
4
2
Ramp MCP voltage to -1000 V
-1000 V/MCP
5
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1000 V/MCP
50 V/step
[10 sec between steps ]
240 sec
6
2
Ramp MCP voltage to -1500 V
-1500 V/MCP
7
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1500 V/MCP
50 V/step
[10 sec between steps ]
240 sec
8
2
Ramp MCP voltage to -1850 V
-1850 V/MCP
9
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1850 V/MCP
50 V/step
[10 sec between steps ]
240 sec
10
2
Ramp PC voltage to -100 V
-1850 V/MCP
-100 V/PC
11
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1850 V/MCP
-100 V/PC
12
2
Ramp MCP voltage to -1950 V
-1950 V/MCP
-100 V/PC
13
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-1950 V/MCP
-100 V/PC
14
2
Ramp MCP voltage to -2050 V
-2050 V/MCP
-100 V/PC
15
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-2050 V/MCP
-100 V/PC
16
2
Ramp field voltage to -700 V
-2050 V/MCP
-700 V/PC
17
2
Enable SGM @ 5000 counts/sec (0.1 sec sample)
Collect 4 telemetry samples
-2050 V/MCP
-700 V/PC
18
2
Stop timetag dark exposure and dump image
-2050 V/MCP
-700 V/PC
19
3
Dark Accum image for 540 secs
-2050 V/MCP
-700 V/PC
21
4
Reset SGM to nominal operating level and sampling rate. Leave HV on for fold analysis.
-2250 V/MCP
-1500 V/Field
13
Pause
50 V/step
[10 sec between steps ]
240 sec
50 V/step
[10 sec between steps ]
240 sec
50 V/step
[10 sec between steps ]
240 sec
50 V/step
[10 sec between steps ]
240 sec
60 secs
Step
22
Exposure
Action
Target voltage
Execute fold analysis (ON-HOLD visit from proposal 7643). See ISR 98-02.
14
Rate
Pause