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Gas detector Crowbar circuit: Present status and planning

Gas detector Crowbar circuit: Present status and planning . Contents: Principle of crowbar Some major sub systems and calibration Crowbar scheme circuit and design Testing performance and Observations Justification of location and scheme Justification of Appropriate Protection Scheme

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Gas detector Crowbar circuit: Present status and planning

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  1. Gas detectorCrowbar circuit: Present status and planning Contents: Principle of crowbar Some major sub systems and calibration Crowbar scheme circuit and design Testing performance and Observations Justification of location and scheme Justification of Appropriate Protection Scheme Implementation plane M. R. Dutta Majumdar 6th June, 2008

  2. Principle of crowbar Principle: whenever spark is sensed, quickly stored charge of the ALICE module may dumped outside using a crowbar system. This may help to reduce over energy dumping to FEE boards and save them due to slow discharge or Electrical Over Stress (EOS). • Causes of damage and remedy: • ESD and fast discharge case partially series resistance improves it and ESD protection upto HBM (Human body model) and partly MM (Machine model) also. • EOS (electrical over stress) where slow discharge degrades FEE • in the long run and may result occasional damage. • EMI (electromagnetic interference) results minor damage possibility during sparks lots of EMI produced and which may go through (as spikes) LV supply rail. This can damage any of surrounding channel or chip. Probability of this type of damage is less compare to other two above mentioned damages. • So remedy should take care of Both ESD and EOS.

  3. Some major sub systems and components 1- HV current sensor using opto-coupler LED and Photo transistor encapsulated inside light tight encolsure using otical glue. Bypass diode is used to protect LED from reverse voltage surge. 2- opto-electrical transformer current source High efficient photo diodes in series combination coupled with LED (parallel) in light tight enclosure. 3- HV transistor switchingin series Each stage HV transistor collector emitter is connected with high resistance (200 meg) to equalize voltage distribution during off condition. HV current sensor using opto-coupler -ve HV + LV Calibration: ~1volt/150mA LED Bypass diode PT 100K Limitation- low current (below 5ma) not available in market current Single stage of HV transistor switching using opto-electrical transformer current source to achieve isolation Calibration: at input 1 mA,output current nearly 20 mA -ve HV 1K 1M 1K 200M 1 ms perspex HV Tr Assembly of photo diode and LED Prev refhttp://arxive.org/abs/physics/0512227

  4. Calibration of opto-couplers OPC OPCF

  5. Schematic circuit of crowbar for Gas Detector FEE protection HV cable length Very small or 3.5m HV filter HVPS detector module Shorting connectors D.U.T comp 10M ref 1ms Mono shot Modification: Previous logic circuit modified to avoid multiple trigger during short interval, which was causing over discharge and tripping HV occasionally. Mono shot 500ms Previos refhttp://www.veccal.ernet.in/~pmd/ALICE/extprotection.ppt

  6. Present Fabricate Circuit size Device Under Test configurations A B Crowbar action with A&B used For data collection RS=1K 10M 10M 5 High voltage Transistors: Length =175mm, W = 125mm and H = 25mm C Feasibility of C also checked with limitations 2 High voltage Transistors: Length =125mm, W = 80mm and H = 25mm After getting few 800 volt HV transistors RS +3V 5 High Voltage Transistor configuration working nicely without damage of HV transistor, availability also good and voltage sustainability also good (2000V with 400X5). So this is preferred. 10M -3V

  7. Configuration of Crowbar System A B ALICE PMD Module OPC HV Filter HV Filter OPC ALICE PMD Module HVPS HVPS CB CB A&B: were initially thought of but later on found delay introduced due to HV filter. So less effective. C C: was tried out where signal of spark sensing time reduced using optical fibre based optocoupler. But needs additionalOptical fibre cable. So other right options also explored. HV cable=3.5m ALICE PMD Module HV Filter OPCF HVPS CB D E ALICE PMD Module ALICE PMD Module HV cable=3.5m HV Filter OPC HVPS HV Filter OPC HVPS CB D&E options are for implementation D:away from module by 3.5mHV Cable and works. Data shown. E: close to module and works much better. Data shown. CB

  8. Location of Crowbar in PMD stand Close to detector module: Present HV filter Box with extended length, if possible supply with +- 2.5 V LV or +3 V floating, needs SMD components and optimized space with HV transistor integration, HV filter + opto-coupler. This configuration is much faster as delay of filter capacitor combination avoided. Opto-coupler is between HV filter and detector HV wire. This circuit will sit on top of each module. Away from detector module: 1 to 5 meter from module, block of 24 circuit in a fox with separate LV supply. Delay may be introduce due introduction of inductance of 1 to 5 meter length of HV cable. Present way HV filter is near to detector module, but in principle HV filter can be placed inside crowbar PCB.

  9. Crowbar circuit PCB layout when circuit is on top of module (provisional) Proposed Box: L=190 mm H=25 mm D=12 mm Only length will Increase of HV Box. HV connector HV filter & optocoupler Optoelectrical transformers & HV transistors LV logic circuit

  10. Testing performance and Observations Crowbar circuit performance testing: Earlier reported circuit logic single retrigger mono-shot was used. So possibility of multiple triggering of crowbar was there. Now using dual single shot and AND gate possibility is completely removed. Once crowbar (duration 1ms) triggers that will not retrigger with in 500 ms time. This avoids false triggering and over discharge of detector capacitor charge which cause unnecessary tripping of HVPS. Present circuit working without any failour on LV circuit or HV part and major tests of guinea pig are done after new circuit. • Protection testing Guinea pig tests: • Guinea pig test seems good for under standing basic damage problem and help FEE boardtesting with crowbar later on. • ALICE module with shorting connector, DIP switch connected with D.U.T, this is a small signal low voltage diode (germanium) used in radio receiversor silicon diode. • High Voltage applied upto 1500V under gas flushing in PMD lab VECC using CAEN N 470 • The circuit does not trip with proper setting of HV current setting, trip time, crowbar trigger duration and drive current.Typical values are 15mA, 5 sec, 1 ms and 4 mA

  11. Guinea pig (germanium diode) test #01 Crowbar location in configuration A A Crowbar Passive Ratio of reverse resistance of D.U.T before and after use 10M More damage Crowbar in Action 26-4-08 & 27-4-08 Sample number of D.U.T tested in configuration A

  12. Guinea pig (germanium diode) test #02 Crowbar location in configuration A Crowbar + Resistance off (4) B RS=1K Only Crowbar on (3) Ratio of reverse resistance of D.U.T before and after use Only Resistance on (2) More damage Crowbar + Resistance on (1) 10M Sample number of D.U.T tested in configuration B

  13. Guinea pig test #03 Crowbar with cable length of 3.5 m using silicon signal diode as guinea pig Crowbar is close to detector module using silicon signal diode as guinea pig #01s #04s Procedure of testing: a) Sequence are HV on i) Crowbar on + Res on HV off measured ratio of resistance with previous value HV on ii) Crowbar off + Res on HV off measured ratio of resistance with just previous value. b) Repeated the sequence of operation 5 times for each sample. c) Resistance measured at Reverse mode of diode at 90 Volt, 10% below rating in test Jig. Ratio of reverse resistance of D.U.T before and after use Ratio of reverse resistance of D.U.T before and after use #02s #05 Ratio of reverse resistance of D.U.T before and after use Ratio of reverse resistance of D.U.T before and after use #03s #06 Ratio of reverse resistance of D.U.T before and after use Ratio of reverse resistance of D.U.T before and after use Number of operation done on each sample #diodes Number of operation done on each sample #diodes

  14. Guinea pig test #04 Crowbar is close to detector module using germanium signal diode as guinea pig Crowbar with cable length of 3.5 m using germanium signal diode as guinea pig #04g #01g Procedure of testing: a) Sequence are HV on i) Crowbar on + Res on HV off measured ratio of resistance with previous value HV on ii) Crowbar off + Res on HV off measured ratio of resistance with just previous value. b) Repeated the sequence of operation 5 times for each sample. c) Resistance measured at Reverse mode of diode with DVM. Ratio of reverse resistance of D.U.T before and after use Ratio of reverse resistance of D.U.T before and after use #05g #02g Ratio of reverse resistance of D.U.T before and after use Ratio of reverse resistance of D.U.T before and after use #03g #06g Ratio of reverse resistance of D.U.T before and after use Ratio of reverse resistance of D.U.T before and after use Number of operation done on each sample #diodes Number of operation done on each sample #diodes

  15. Summery of results observed • Initial tests done #01 and #02 are now carrying less importance due to improper location. Which is known after some studies performed. But have historical importance for further progress of the work. • Test plots of #03 and #04 shows comparison of performance of crowbar away • from module (3.5 m) and close to module using silicon diode, germanium diode. • Plots shows damage is less when crowbar and series resistance are both implemented. • Further close to module configuration seems more effective. • Some inconsistency are due to quick rise and fall of HV, which normally may • be absent with FEE board testing with seasoned and slow raising of HV.

  16. Justification of Appropriate Protection Scheme j • Resistance and crowbar, avoiding external diode. • Series resistance decreases substantially ESD and fast discharge • (ns to micro sec) as seen in FEE testing (refhttp://www.veccal.ernet.in/~pmd/ALICE/HV-problems-in-PMD.ppt ) • which supported by guinea pig test (crowbar operation) also. • Slow discharge remedy taken care by crowbar. • Additional external diode protection need not require as ESD and fast discharge • damage protection is taken care by series resistance and internal diode of Manas chip. • Putting external diode may not improve the situation very significantly and may increasenoise level also. • Implementation in kapton cable is difficult to accommodate and handle, powering of +- 2.5 V to diodes makes wiring cumbersome and may be another source of introducing EMI to LV line. • Lastly this is not cost effective as 48 modules for diode scheme needs nearly 80,000 CHF where as for crowbar scheme total cost may be 3,500 CHF for 48 modules.

  17. Implementation plane Design & fabrication- complete, needs more miniaturize and low power version, procurement of components can start. Over all testing- guinea pig test to real test with FEE board test and finally testing at CERN with HVPS SY1527 Real Location and final configuration – i) on module with HV filter or ii) few meters away from stand Whether needs integration with DCS: signal of sparks of each module can be Used for data cleaning and status of module during run time. Necessary logic out put provided for implementation. Review documentation for ALICE: need to convince collaboration before Final integration Time scale for implementation Online discussion

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