Test bench of the barrel calorimeter modules

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HAL Id: in2p3-00010953

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Submitted on 17 May 2001

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Test bench of the barrel calorimeter modules

J. Boniface, H. Bonnefon, J. Colas, G. Dromby, M. Jevaud, B. Mansoulie, N.

Massol, F. Molinie, M. Moynot, P. Perrodo, et al.

To cite this version:

J. Boniface, H. Bonnefon, J. Colas, G. Dromby, M. Jevaud, et al.. Test bench of the barrel calorimeter modules. 2001, pp.22. �in2p3-00010953�

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ATL-LARG-2001-007

26/02/2001

Testbenchofthebarrelcalorimeter

modules

February20,2001 ATLASInternalNote

LARG-NO-xxx

February2001

writtenby 1

MassolN.

1

BonifaceJ., 1

BonnefonH., 1

ColasJ., 1

DrombyG., 2

JevaudM., 3

MansoulieB.,

3

MolinieF., 1

MoynotM., 1

PerrodoP., 2

SauvageD., 3

SchwindlingJ., 3

TeigerJ.,

1

ZolnierowskiY.

|||||||||

1

Laboratoired'Annecy-le-VieuxdePhysiquedesParticules,IN2P3-CNRS,Annecy-

le-Vieux

2

CentredePhysiquedesParticulesdeMarseille,IN2P3-CNRS,Marseille

3

CEA,DSM/DAPNIA,Centred'EtudesdeSaclay,Gif-sur-Yvette

Abstract

Asystematicproceduretoqualifythebarrelcalorimetermodules

isanessentialsteptoguaranteea0.7%constantterm,whichisthe

collaborationobjective.Theproceduredetailedinthisnoteconsists

ofqualitymonitoringduringmechanicalassemblingandofasetof

electricaltestssuchaselectricalcontinuity,cellandcross-talkcapaci-

tancemeasurement,andhigh-voltagebehaviour.Forthewholetest,it

hasbeennecessarytodevelopdedicatedelectronicboards,todevelop

measurementmethods,andthewholeoperationsoftware.Makingthe

procedureautomaticwillguaranteethequalityofeachmoduleduring

assembling,cabling,andtestinliquidargon.

1

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The ATLAS barrel calorimeter [1] is composed of two half-barrels, each of

them containing 16modules (gure1). Placed insidea cryostat, it works at

1 module

Figure1: Half-barrel calorimeter

the liquidargon temperature. Each module is made of 64 absorbers and 64

electrodes(gure 2),andweights 3.3tons. These moduleswillbeassembled

one by one, and only six of them will be fully scanned at CERN with an

electron beam. So to reach the goals driven by the physics requirements, a

complete test procedurehas to be developed to qualify allcalorimeter mod-

ules before starting the experiment. To guarantee a small overall constant

term in the energy resolution, the mechanical anelectricalcharacteristics of

the detector are carefully monitored. Similar tests are used to qualify the

end-cap calorimetermodules.

These tests run in three steps:

during assembling, we verify that the readout electrodes are not dam-

agedduetotheirhandling(TBF-1test),thenwemonitorthecleanness

of each component (HV test), and nally we check the mechanical as-

sembling quality (capagap test).

After cabling of the whole module, at room temperature, we check

connectics between HV bus and electrodes (TBF-2 test),we check ifit

holds high voltage (HV test),and weexercise each cell(TPA test).

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sampling 2 collision point

...

η r

sampling 2

1 2 3

sectors

sampling 3

Figure2: Readoutelectrode

Thesetestsarereproducedattheliquidargontemperaturetoeliminate

problems induced by the thermal contraction.

The qualication procedure of the electromagnetic calorimeter modules is

performed by a test bench to study the calorimeter behavior at room tem-

peratureand at liquidargon temperature, and toobtain amap of all cells.

All informationsconcerningthe modulesare saved inadatabase: itincludes

the measurementson the absorbers and onthe electrodes beforeassembling

and thetestsresultsduringassemblingandaftercabling. Moreoverwemake

the procedure automatic tominimize errors.

2 General description of the electrical tests

2.1 Test bench equipment

The test benchis composed of (gures3 and 4):

electronic boards to generate several test signals: a low frequency si-

nusod (TBF board [2] + MUXCAPA board) and step pulses (TPA

board [3]),

a set of multiplexers (MUX board [4] + MUXCAPA board) to drive

the output channels towards the readoutsystem,

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CCCCCC CCCCCC CCCCCC CCCCCC

PC

HH

HH VME Crate

5v,10 v BUS GPIB

HH VME Crate

BUS GPIB Power:+5v

GPIBmux

1 2

1 2 3 14

GGGGGGG

11 MUX Board

HT_3KV ^L^H^H

interface L

RS232/IEEE

HH

DIGITAL SCOPE 2 Channels

HH

VME Crate BUS GPIB Power:+5v 1 2 3 11

14 MUX Board .... ns

-40v,+40v

60v/1Hz

CALIB

.... mv

IGPIB

TPA TBF

MUX

IGPIB IGPIB

LABVIEW

Front 50 Ohms

Middle+Back 25 Ohms

MUX

mux

Figure3: Electrical test bench

an interface board between GPIB bus and VME-like crate (IGPIB

board [5]),

a digitaloscilloscope toproceed the output signals acquisition,

a high voltage module (1469 board [6]),

a precisioncapacimeter [7],

a PC to controlthe dierent boards and devices through a GPIB bus

(drivers written with LabVIEW [8] software), and to analyse all the

measurements.

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a set of cables for each test: lemo cables (10 m), HV cables (10 m),

25 and 50 Axon cables with ATI connectors (7 m for assembling

tests and 4m +2 mfor cabling tests).

2.2 Electrical continuity test (TBF test)

2.2.1 Principle

This test veries the continuity of the electrical circuit to be sure that the

high voltage is distributed everywhere. It checks connectors and resistors

chains on the electrodes outer layers. The principle is to send (gure 5)

a low frequency sinusodal signal on the high voltage lines and to read the

response from the signal layer by capacitivecoupling. The signal amplitude

collected oneachcelldependsonthe decouplingcapacitance. Thecapacitive

part ofthesignal isextractedbyacarefulchoice offrequenciestodetectany

damage inthe resistor chain.

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000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000

111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111

000000 000 111111 111

1 ΜΩ

00000000 0000 11111111 1111

TBF

Oscilloscope HV bus

S1 S2

C

S3

A P A K A P T O N

½ electrode Absorber

Figure5: Electrical continuity test

2.2.2 Hardware for this test

The sinusodal signal is provided by the MUXCAPA board. The frequency

is programmable between 0.1 Hz and 100 Hz, by step of 0.1 Hz, and the

amplitude is about 70 V. Another board, TBF, is used to distribute the

signal on the HV lines. It has 16 channels remote controlled by a PC via a

GPIB interface. Both boards use the VME mechanical standard. A digital

oscilloscope reads the signal coming from the electrodes via a multiplexer,

and a PC computes all parameters. The data are compared with reference

values.

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2.3.1 Principle

Thistestdetectsanyhighvoltageproblemlinkedtoacleannessproblem. For

this,the leakagecurrentofallchannelsismonitored. Itisatestofabsorbers,

electrodes,andhoneycombscleanness,oranysurfacedefault. Wecanchoose

the voltage ramp to adapt the charge current. It should not exceed a given

threshold (< 1 A per channel and per electrode) to avoid damage on the

electrodes.

The collaboration has chosen a high voltage board from Lecroy with the

characteristics given below:

programmableDC voltage between 0 and 3500 V,

independent current measurementfor each channelwith a precisionof

1% forcurrent higher than 10nA,

programmabletrip for each channel between 0 and 100 A.

This equipment is characterized by a current measurement threshold par-

ticularly low. It is controlled by a PC via a GPIB bus and a GPIB-RS232

convertor [9]. The high voltage cablesare connectedto aCQHT (SECUrity

HT) board to discharge rapidly the whole module in case of emergency.

2.4 Gap thickness measurement (capagap test)

2.4.1 Principle

The ATLAS goal is to obtain a constant term contribution of 0.15% from

the dispersionof the gap thickness, equivalent toa dispersion of 50 microns

for a4 mmgap. Totest the gap thickness uniformity duringassembling, we

want to measure the gap capacitance with a precisionof 0.1%.

We use a capacimeter controlled by a PC. It sends a sinusodal signal on a

cell, and it measures the current and the voltage at its terminals to deduce

the impedance module and phase. We deduce the distance between two

absorbers from the capacitance measurement. Tomeasure automatically all

the capacitances foranelectrode, we use the secondpart of the MUXCAPA

boardwhich multiplexes the dierent sectors.

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2.5.1 Principle

The purpose ofthistest istodetectcablingerrors,andtotestthe wholecal-

ibrationchain: boards,cables,connectors,... Todothat,wesend steppulses

on the calibration lines and we record the cells response. The ouptut signal

islteredbysoftware,and theresultingamplitude, linkedtothecapacitance

value, allows to detect the bad channels (grounded cells, short-circuits be-

tween channels, excessive cross-talk,...). The principle is described on the

gure 6.

injection resistor

TPA

detector capacitance

oscilloscope

50 Ω (1 ΚΩ)

resistor (50 Ω) adaptation

Figure6: Cell capacitance measurement

10Vstep pulseswitha2nsrisetimeare providedby theTPA board. It has

64 relays remote controlled by a PC via a GPIB interface in order to pulse

on calibration harness. The output channels are connected toa multiplexer

system, and only one channel atatime is analysedon adigital oscilloscope.

The ltering part is done by software. Multiplexers and pulse generator

modules use aVME mechanical standard.

3 Tests development and measurement results

A more detailed explanation about tests development and the results on

prototypes can be found in [10].

3.1 Electrical continuity test during assembling

The maindiÆculty forthis test comesfromthe outputsignalsummation on

the electrodes. Duringassembling,thechannelsare summedintodecrease

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channels from sampling1, for the back, we sum 4 channels fromsampling2

with 2 channels fromsampling 3. This summationimplies to distinguish an

output signal variationproportionalto the number of defective channels.

3.1.1 Test condition

Therststepistodeterminetheoptimalfrequencyforthistest. Weconsider

only the sampling1: it is the most complicated case, because this sampling

is excited via another sampling.

First we choose a high frequency to obtain a negligible impedance of

detector capacitanceincomparisontothe 1Mresistor onthe HV bus. We

obtain theconditions described on thegure 7. Wesuppose thatthe second

E S1

SIMPLIFICATION

E

R1

1 ΜΩ S1 1 ΜΩ Z <<1 ΜΩ

Ck1

Ck1 Ck2

Ck2 kapton layer 1 kapton layer 2

1 ΜΩ

negligible

Cki: kapton capacitance of sampling i negligible

1 ΜΩ

R

Oscilloscope R1

Figure7: TBFtest at \high"frequency (>1 kHz).

HV face is oating. This system issensitive onlyto the resistive part of the

electrode. However, if a resistor is broken (R1 on gure 7), the capacitance

between HV layer and signal layer must decrease. That is why we must be

sensitive tothe capacitivepart.

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E

S1

SIMPLIFICATION

R

Oscilloscope Ck1

Ck2

1 ΜΩ 1 ΜΩ

Ck1

S1 negligible

(compared to 1 Mohms)

E Zeq

1 ΜΩ

1 ΜΩ R

Figure8: TBFtest at low frequency with the other face grounded.

at atime, weneed tobe sensitive toonlyone HV layer. Todothat, the HV

bus of the otherouter layerisgrounded. Thetypicalvalue foracapacitance

of a front sampling channel is 8 pF 200. To neglect the 1 M resistor

in comparison with the impedance of the kapton capacitance, we choose a

frequency suchas:

1=C

k1

! >10 7

=)f <10 Hz

For the front, the output signalis given by the relation:

S

1

=

1

2+1=jR C

k1

! E

and after simplication:

S

1

=jR C

k1

!E

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1 capacitance which is proportional to the number of cells. So in these

conditions, we are able to distinguish adefective cell.

3.1.2 Signal variation versus the number of cells

For this measurement, we take the conditions of gure 8. We measure for

the sampling1the signalcorrespondingtoonestrip,then twostrips,...until

eight strips to reproduce the eect of summation boards in . The result is

given on gure 9. We obtain a linear variation between the output signal

Number of strips

0 1 2 3 4 5 6 7 8

Voltage (volts)

0 0.5 1 1.5 2 2.5 3 3.5

Amplitude versus the number of cells

Figure 9: Output signalamplitude versus the numberof cells at 5 Hz.

and the numberof connectedstrips, asexpected. In caseof problem,we are

able to determine the number of missing cells.

3.1.3 Final conguration

The prototype electrodes have highlighted a real problem concerning the

inked resistors. The dispersion of measured values is so high that it is im-

possibletowork withthe same frequency onthe whole electrode. Moreover,

if we use a very lowfrequency for all channels, the test length can strongly

increase. Thatis why it isnecessary to modifythe test tobeless dependent

to the electrode quality. Of course, we must keep the sensibility to the ca-

pacitive part but we use a couple of frequencies to extract capacitance and

resistance. Withsuchamethod,wedon'tmakeanyapproximationanymore,

and wekeep an automatic test.

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For this test, the inner layer of each electrode is grounded via a 10 M

resistor on the summation boards. the table 1 summarizes the main used

parameters.

Parameters Typical value

Nominal voltage 1800 V(in air,humidity <50%)

Voltage ramp 5V/s

Trip 17A for1 face (7sectors)

Charge current 0;5<I

avg

<1A per sector(/ surface)

Leakage current <200 nA after 30mn for a wholeelectrode

Table 1: Main parametersfor the HV test.

An exampleof charge currents on one electrode is given ongure 10.

2.0

0.02.0

0.0

240 0

secteur 1 secteur 2 secteur 3 secteur 4 secteur 5 secteur 6 secteur 7 courants HT2

2.0

0.02.0

0.0

240 0

µA µA

Figure 10: Chargecurrents for eachsector and foreach faceversus time.

These currents are dominated by the decoupling capacitance charge. We

have:

i

charge

=

"

o

"

r S

e

V

t

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The high voltage software uses a linear voltage ramp. Moreover, a feed-

back loop on the current of each channel avoidinopportune trips in case of

discharge. Aboveagiventhreshold,thevoltageisstabilizeduntilasignicant

decrease of the whole currents.

At the nominal voltage, we measure the leakage currents (gure 11).

0.1

0.00.1

0.0

1500 480

0.1

0.00.1

0.0

1500 480

µA µA

Figure11: Leakage currentsfor each sector and for each face versus time.

These currents decrease inabout one hour to the detection threshold of the

HV system (10 nA).

So this test veries not only the cleanness of the module (discharge or

shortcircuitduringtheramp),butalsotheelectrodeinnerstructure(leakage

current).

3.3 Gap thickness measurement

To dothis test, we must takeintoaccount several constraints:

thereisabigdispersionofresistorsvaluesontheelectrodesHV layers.

Sothe measuredcapacitance varies with the frequency. It isnecessary

to become independent of this resistors eect.

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solution impliesan increase of test duration and money.

we must use a long cable (' 10 meters) which introduce a parasitic

capacitance (100pF/m). This is not acceptablefor precisionmeasure-

ment oncells of several hundreds of pF.

To avoidthese problems, weadopt the principles given below:

we measure the three samplings in the same time (gure 12). In this

condition, we are not sensitive to the capacitance variation with fre-

quency.

CAPACIMETER

Absorber

C2

C3 C1

Borne Low

1 ΜΩ HV channel

High Borne 64 C1

8 C2 + 4 C3

Figure 12: Measurement of capacitance between electrode and absorber by

sector.

we measure the capacitance by sector of = 0:2 to decrease the

numberof cables.

we use a four terminal pair conguration to be insensitive to some

parasiticseects.

we choose a frequency of 100 kHz. A higher frequency is not a good

choice because our system becomes sensitive to the cables inductive

eect.

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3.4.1 Principle

In this test,we don'twant totest the electricalcontinuity onthe electrodes,

but the HV cables and boards. Moreover, in the liquid argon, it is impera-

tivetoverify the connecticsbetween electrodes and HV boards. Likeduring

assembling, we send a sinusodal signal on the HV channels and we anal-

yse signals induced by capacitive coupling. Nevertheless, several dierences

modify the test conditions:

one HV channelisconnected to32electrodesinonone faceand one

sector in.

anoutputchannelconcerns one cell, i.e. asum of4 electrodes infor

sampling 2. Soour system includes 4dierent resistors incomparison

to 1at assembling stage.

due tothe motherboard, each cell is connected tothe ground through

an injectionresistor and an adaptationresistor.

Weworkoncells ofsampling2becauseofthe summationinby groupof4

insteadof16onsampling1,andbecauseofthe littlecapacitancevariationin

incomparisonwiththecellsofsampling3. Weobtainthesystemdescribed

on gure 13.

Inthisconguration,theoutputsignalSdependsonkaptoncapacitances

and inked resistors. The maindiÆculty isdue tothe bigdispersiononthese

resistors value. We can't work with 2 frequencies to extract resistive and

capacitive parts like during assembling. So we must choose a frequency as

lowaspossibletoneglectthe resistances. But adecrease offrequency causes

a decrease of signal amplitude. The measured signals are very noisy and it

becomesdiÆculttodetect them. A solutionisto use anFFTtoextract the

fundamental amplitude.

3.4.2 Results

Withthis method,welook atthe linearity between the outputsignalampli-

tude versus the number of electrodes. We work at1Hz toobtain aphase of

=2. Weconsider a complete celland we disconnect successively the elec-

trodes. Weobtainthe resultgiven ongure14. We areable todistinguisha

missing electrode inside a cellwithout ambiguity. Moreover, on sampling2,

we have 8cellsin fora given sector,allof themconnected tothesame HV

channel. So for a given position in , we calculatethe mean value on these

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S

ρ =1 ΜΩ

(in phi) E

25 Ω R1

Ck R2

Ck R3

Ck R4

Ck

R5

Ck R6

Ck R7

Ck R8

Ck

Calibration Ri

50 Ω

terminated in MUX

x7

Figure 13: Electrical continuity test after cabling, for a cell of sampling 2.

The detector capacitancesare not represented.

8 cells. We obtaina dispersionof about 1-2%, excepted in case ofa bad cell

with a dispersion of 9%.

Withthe same test, thanks to its good sensibility, we are able todetect

a wrong cabling between the electrode outer layers. On gure 15, we have

the amplitude of the output signal versus the cell number in , for a given

sector. The cells

0 to

5

have 4 electrodes, while the cell

6

is empty and

the cell

7

has only 1 electrode. The two curves correspond to the two HV

layers. The observed dierenceis due to the dierence of the glue thickness

between the copperlayers.