Protection and monitoring of Gas Detector Systems using optoelectronic devices

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DAE SYMPOSIUM ON NUCLEAR PHYSICSDecember 22
26, 2008Indian Institute of Technology, Roorkee,
India - 247667Sponsored by the Board of Research
in Nuclear Sciences, Department of Atomic Energy
Protection and monitoring of Gas Detector Systems
using opto-electronic devices M. R. Dutta
Majumdar Variable Energy Cyclotron Centre,
1/AF, Bidhan Nagar, Kolkata - 700064, INDIA
email mrdm_at_veccal.ernet.in
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Gas Detector operation problems

• Gas detectors as used in STAR1 and ALICE2 PMD,
  are an array of honeycomb cells.
• They operates in proportional region of gas
  ionization by avalanche multiplication.
• But sudden increase of leakage current or
  shifting the operating region above
• proportion region results abrupt discharge or
  spark in detector which creates major
• problems for detector operation.

• Reasons of increase of leakage current and
  sparks
• Gas impurity, change of gas proportion, gas leak,
  poor flow rate
• Surface impurity of detector cells, impurity in
  boundary of detector gas enclosure
• and anode wire distortion or its tension
• Formation of sharp edges in detector cells to
  distort electric field
• Sharp edge formation results some time
  microscopic in nature due to
• strong local vibration shock or thermal stress
  in honeycomb cell structure.
• Enclosing top bottom PCBs of detector module,
  used as extended cathode can
• develops sharp edges and leakage current path.
• Detector top PCB tracks going to readout
  connectors may develop leakage path.
• Improper grounding of detector HV and EMI also
  induce malfunction.

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High Voltage and Readout Electronics problem
Schematic HV FEE

• Causes of damage and remedy
• ESD and fast discharge case partially series
  resistance improves it. ESD protection upto HBM
  (Human body model) and partly MM (Machine model)
  also. ESD effects with in 1 mSec time of spark.
• EOS (electrical over stress) where slow (above
  1mSec to millisecond) discharge degrades FEE in
  the long run and may result occasional damage.
• So remedy should take care of Both ESD and EOS.

EOS protection may be taken care by crowbar
circuit as shown in guinea pig test using
opto-electronic devices
They are like detector capacitance (Cdet),
detector cell dynamic resistance (Rd), small
inductance L (due to track etc.) and possible
series resistance (Rext for ESD protection),
back to back fast diodes and finally to input of
readout chip.
Opto-electrical transformer opto-coupler
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Use of opto-electronic device Opto-Electrical
Transformer
Opto-Electrical Transformer where input/output
electrical power is transferred by the optical
coupling to change the voltage level up or down.
Alternately input/output is in optical form and
inside coupling or processing is done by
electrical means.
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Schematic circuit of crowbar for Gas Detector FEE
protection
Guinea pig test stage
Momentary sparks are sensed by low current
opto-coupler, which by using suitable gating
circuit drives opto-electrical transformers.
Outputs of opto-electrical transformers
simultaneously switch on all series connected
high voltage transistors to discharge the charge
of gas ionization detector capacitance to an
alternate path to reduce EOS damage.
http//www.veccal.ernet.in/pmd/ALICE/crwtest_0606
08.ppt
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Crowbar Testing with Guinea Pig (Dummy
electronics)
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Application in HV current monitoring
This setup is still under modification for
improving it to measure current below 1nA range.
Further this setup may be useful for measurement
in combustible gas environment also.
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• Summery
• Test result reveals ESD damage and EOS damage are
  less when
• both crowbar and Series resistance schemes are
  implemented.
• This experience may help in real case
  implementation or better understanding
• of gas detector problems in future.
• High voltage current measurement (1 to 100nA)
  work needs more work
• for calibration and over coming limitations of
  present setup.
• Present stage of opto-electronic work may have
  other new applications also.

References 1 M. M. Aggarwal et al, NIM A 499,
751-761 (2003). 2 S. K. Sidharth et al for
ALICE Collab. proc. NP Symp., 52B, P-651(2007).
3 M. R. Dutta Majumdar and Debasish Das, N.P.
Symp., 46B, P-522 (2003). 4 M. R. Dutta
Majumdar, Debasish Das and T. K. Nayak Photonics
2004, Cochin, Abs. P 369 (2004).
http//arxiv.org/abs/physics/0512227