Transcript ppt
GLAST LAT Project
IA weekly meeting , February 3, 2006
ACD Pedestals
ACD Team at Goddard: Alex Moiseev
Dave Thomspon
Bob Hartman
ACD subsystem
Alex Moiseev
GLAST LAT Project
IA weekly meeting , February 3, 2006
ACD Pedestals
Pedestals monitoring: we want them to be within ±5 ADC counts of
reference value (< ±1.25% of the mip, which is at minimum 400 ADC counts);
otherwise reference values have to be changed respectively. Another
variable is a temperature; pedestals vary with the temperature. Our tests at
Goddard demonstrated that pedestals variation is acceptable within ± 5C
temperature variation; thus pedestals are calibrated for 10C temperature
bins.
All results presented here assume ambient temperature (18C – 28C)
Summary:
• we found that pedestals stay stable within needed range for extended
period of time if there was no (known) external configuration changes made
• we found that some pedestals change by up to 40 ADC counts when:
- other GASU is used
- HV is applied or not applied to ACD (? – see below)
ACD subsystem
Alex Moiseev
GLAST LAT Project
IA weekly meeting , February 3, 2006
ACD Pedestals (cont.) Tests Compared
Mean of 3
runs
Prethermal
Thermal
1,
Thermal
10,
Postdelivery,
ACD
CPT 1,
ACD
CPT 2,
B13
ZS Off
B13
ZS Off
GSFC,
May 23,
2005
GSFC,
July 21,
2005
GSFC,
July 24,
2005
GSFC,
August
4, 2005
SLAC,
August,
2005
SLAC,
12/28,
2005
SLAC,
12/28,
2005
SLAC,
January
14 , 2006
SLAC,
January
14, 2006
GASU 1,
HV On
GASU 1,
HV Off
GASU 1,
HV Off
GASU 1,
HV Off
GASU 1,
HV Off
GASU 2,
HV Off
GASU 2,
HV Off
GASU 2,
HV Off
GASU 2,
HV On
Pedestals Difference mean and
01/14/06 B13 no HV on ACD
5
25
25
20
20
15
15
30
10
10
20
5
5
5
0
0
0
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
6
5
4
3
2
1
10
35
30
25
20
15
10
5
0
70
60
50
40
30
20
5
4
3
2
1
7
Blue frame and plot numbers – compared with ACD CPT 1 (new GASU)
7
Red frame and plot numbers – compared with “Mean of 3 runs”
0
-1
-2
-3
-4
-5
7
6
5
4
3
2
1
-1
-2
0
Bin
6
Bin
-3
-7
10
0
0
-1
-2
-3
-4
-5
7
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
Pedestals Difference CPT-1 and B13
with no HV
8
6
Bin
-6
-7
6.
5
5
3.
5
2
0.
5
7
6
5
4
3
2
1
0
-1
-2
Bin
Pedestals Difference CPT-1 and B13
with HV On
11
40
30
20
10
Bin
ACD subsystem
Alex Moiseev
5
4
3
2
1
0
-1
-2
-3
-4
-5
-7
0
-6
-3
-4
-5
-6
Bin
0
-1
0
0
-2
.5
5
5
-4
5
-7
10
25
10
-5
.5
10
6
-4
15
15
Pedestals Difference mean and
01/14/06 B13 with HV On
Pedestals Difference mean and ACD CPT-2
20
15
20
20
Bin
Bin
-5
4
25
25
10
Bin
Pedestals Difference mean and Postdelivery
2
30
-7
-6
Bin
Bin
50
0
-7
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
10
60
40
15
35
9
25
20
Pedestals Difference mean and
Thermal 1
Pedestals Difference CPt-1 and CPT2
7
30
-6
40
35
30
25
20
15
10
5
0
Pedestals Difference mean and ACD
CPT-1
3
-6
1
-7
Pedestal Difference mean and
Thermal 10
Pedestals Difference mean and Prethermal
GLAST LAT Project
IA weekly meeting , February 3, 2006
ACD Pedestals ( cont.)
• During a number of test runs at Goddard: Before and after
Vibration, Acoustic, and Thermal tests, as well as after delivery of
ACD to SLAC (in total over 3 months) – pedestals stay stable
within ± 5 ADC counts (plots 1 - 4)
• Pedestals shifted significantly – by 5 and more ADC counts –
when GASU was changed (ACD CPT, December 2005), 39
channels in total – plots 5 – 8. Channel-to-channel comparison with
data from Margin Test (performed at Goddard) is well consistent
with the assumption that FREE voltage changed to 3.25. This is
very marginal to ACD Performance. Needs attention from
Electronics Team!
• Pedestals again stay stable during CPT and full LAT B13 runs
(with HV Off by mistake) – plots 9 and 10
• But some channels shifted when HV was brought On (plot 11)! –
see next slide – new puzzle!
ACD subsystem
Alex Moiseev
GLAST LAT Project
IA weekly meeting , February 3, 2006
Sudden pedestals change during B13
• Found a fact that in two B13 runs,
separated by a few minutes, the first one
(135005319) was running with ACD High
Voltage turned Off by mistake.
• ACD High Voltage was turned On in all
next B13 runs.
Channel
Pedestal Position
difference, ADC
counts
0-002
-19
0-042
-15
•It appeared to be a luck for us to find a strange
thing: there are 12 channels where pedestals shifted
by more than 10 ADC counts between runs with and
without HV (PedestalHV On – PedestalHV Off)
1-124
-11
•All these changes have negative sign!
0-130
-23
1-222
-11
• All other channels stay stable, but with slight
negative difference (about 1 ADC count)
1-320
-20
0-230
-9
1-230
-18
0-330
-16
1-422
-17
0-430
-12
1-430
-18
ACD subsystem
• We have previously compared pedestals positions
with and without HV applied and FOUND NO
DIFFERENCE – “Mean of 3 runs” was taken with
HV On, and “Prethermal”, “Thermal 1, 10”, “PostDelivery” were taken with HV Off (ACD Long
Functional test, pedestal runs). This is a new
problem!
Alex Moiseev
GLAST LAT Project
IA weekly meeting , February 3, 2006
New Puzzle
Puzzle:
• All
that 12 shifted pedestals are from GAFEs with number 17 (last
on the board) – one per each (!) ACD FREE board! – discovered by Dave
Thompson
• All pedestals shifted in one direction – cannot be explained by voltage
change because it causes both direction change
• All other pedestals stay stable within 1-2 ADC counts. There was small shift
of all pedestals in the same direction by ~1 ADC bin. It is negligible, but the
fact itself can contain a hint.
• This pedestal shift happened during a few
Pedestals Difference CPT-1 and B13
with HV On
minutes – the only change made was applying
High Voltage – and pedestals changed!
40
• Pedestal change is significant to cause high
rate – more than Zero Suppression threshold
• Need to repeat this test to confirm the effect
30
20
10
• So far NO IDEA how to explain it
Alex Moiseev
NOTHING!
7
6
5
4
3
2
1
0
-1
Bin
SHIFTED CHANNELS
ACD subsystem
-2
-3
-4
-5
-6
-7
0
GLAST LAT Project
IA weekly meeting , February 3, 2006
Conclusions
Conclusions:
1. ACD Pedestals seem to be stable over time if no changes are made
2. We believe that pedestal change, when other GASU was installed, was caused
by slight change of low voltage (3.3 V) supplied by GASU to ACD FREE board
3. Our previous tests demonstrated that pedestals behave by different way with
variation of FREE voltage – some stay unchanged, some have changes in both
direction. The fact that ALL changes in B13 runs have negative sign, does not
agree with this
4. Our previous tests also demonstrated that pedestals do not depend on HV (On
or Off)
5. We request for additional pedestal runs, with HV On and Off
6. Until the behavior of pedestals is completely understood, pedestals runs have
to be run periodically
7. Would it be possible to run periodical trigger with switching to ZS Off mode?
8. The puzzle with “end” GAFE’s pedestal shift – needs explanation
ACD subsystem
Alex Moiseev