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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 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


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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.


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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



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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


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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


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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


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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.


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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


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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


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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


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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


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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


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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


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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.


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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.


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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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