The Volotek controller and its cable infrastructure in LHC: specifications, functional behavior, cable layout and results from cabling quality check

(1)

The Volotek controller and its cable

infrastructure in LHC:

specifications, functional behavior, cable layout and results

from cabling quality check

Benoit Rio

TE/VSC/ICM

(2)

Content

•

Introduction

•

Volotek specification

•

Functional behavior

•

Circuit overview

 Digital  Power Filament  Electrometer

•

Triax cable specs and connectors

•

Typical cabling layout in tunnel

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Introduction

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Volotek specification

•

Technical specification

Description

Specification

Pressure range 10-4_{Pa to 10}-11 _{Pa (10}-6 _{to 10}-13 _mBar)

Electron emission current

0.2mA to 10mA (until 70mA in degassing)

Grid Voltage +150 to 200Vdc (measurement)

+600Vdc fixed(Degassing) Filament

(with tranformer box)

50V (measurement) 5V (degassing)

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Functional behavior

Front view

Rear view

(6)

Functional behavior

•

3 modes of operation :

–

Measurement

Measure of the pressure by reading of ionization current

–

Modulation

Identification of residual current created by X-rays

–

Degassing

(7)

Functional behavior

•

Operation in measurement (Ie = 4mA)

Vfil 50V Ifil 3A Vgrid 150V Ic Ie 7

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Functional behavior

•

Operation in modulation (Ie = 4mA)

Ifil 3A

The modulator is fixed at the ground potential to attract the

ionization current

X-ray X-ray

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Functional behavior

•

Operation in degassing

Vfil 5V Ifil 5A Vgrid 600V

The modulator and the collector are fixed to the grid

potential

The grid is

cleaned by

bombardment of

electron

9

(10)

Circuit overview of Volotek

•

Block diagram

Digital

card

Backplane

Electrometer

Power

Filament

Power supply

Transformer

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•

Digital card

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(14)

Measure of emission current

(15)

Circuit overview of Volotek

•

Electrometer

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-AOP LMC6001 : Ultra Ultra-Low Input Current Amplifier with input current of 25fA.

-Adjustable gain between 106_{at 10}12 _{by command}

of relay.

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Circuit overview of Volotek

17 0 Ω 0 Ω 0 Ω Gain of 1.

This AOP is use for inverted the signal in input (First AOP is inverting amplifier).

ADC 14 bits with SPI communication. Sampling frequency is 1kHz.

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Circuit overview of Volotek

•

2 Versions of Controller :

–

Version B

–

Version C

The difference between versions are :

 Improvement of communication board (profibus signal amplification)

 Modification of power supply card (AC/DC power module)

 Modification of digital card (pinout connector, reference driver, layout, …)

 Modification of backplane card (pinout connector)

 Replacement of the second OPA in the electrometer (component obsolete)

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Distribution of Volotek

in the LHC

Version B

Version C

Version of controller

Quantity

Version B

128

Version C

40

Version B Version C Gauge 128 40 Noisy gauge 70 17 0 20 40 60 80 100 120 140 Nu m b e r of g au ge s

Version vs noise

Version of controller Noisy gauge (in %)

Version B 41 %

Version C 42.5 %

The percentage of noisy gauges between version B and C is the same.

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Triax cable specs

and connectors

•

Specification of the triax cable TCA3

Insulation Insulation Semiconductive layer Inner Shield 1 Wrapping Wrapping Inner shield 2 Sheath Inner conductor

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Triax cable specs

and connectors

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Triax cable specs

and connectors

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Triax cable specs

and connectors

•

Triax connector specification

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•

Wiring diagram

Controller in

the rack

Gauge in

the LSS

Transformer

in the LSS

Triax cable TCA3

Power shielded cable

between the controller

and the transformer

Power shielded

cable

between the

transformer and

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•

Cabling in the LHC

–

Controller in the UJ/US/UA

–

Transformer near the gauge in the LSS

–

Up to more than 300 meter of cable between

controller and the gauge

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Measurements and cabling quality check

•

Check of cable quality :

–

Measurement of shield continuity with ohmmeter

»

Identify the discontinuity internal shield

–

Measurement of cable quality with reflectometer

»

Identify the broken internal shield

»

Measure the cable length

»

Identify the number of broken cables and their lengths

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•

Distribution of inner shield continuity

14

2

18

5

12

4

18

6

13

4

2

16

7

6

16

5

Internal shield continuity ok

Internal shield continuity nok Don’t know (No access or other)

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Measurements and cabling quality check

68%

29%

2%

Inner shield continuity

Internal shield continuity OK

Internal shield continuity Nok

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•

Measurement of cable quality with reflectometer

(36)

Good cable

(Continuity between the shield)

Bad cable

(No continuity between the shield)

Example of graphic with reflectometer in P7

External shield Internal Shield External shield

Internal shield

End of cable End of cable

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Measurements and cabling quality check

P7 Reflectometer

VAC Name Shielding continuity

L ext shield L int shield diff L shield

[m] [m] [m] VGI.172.7L7.B NO 321.00 304.00 17.00 VGI.172.7L7.R NO 321.00 304.00 17.00 VGI.392.6L7.B NO 262.00 248.00 14.00 VGI.534.6L7.R NO 273.00 261.00 12.00 VGI.53.6L7.B NO 231.00 213.00 18.00 VGI.324.5L7.R YES 198.00 198.00 0.00 VGI.210.5L7.B NO 193.00 176.00 17.00 VGI.130.5L7.R NO 177.00 167.00 10.00 VGI.454.4L7.B NO (BNC+BNC) 142.00 125.00 17.00 VGI.456.4L7.R NO (BNC+BNC) 142.00 125.00 17.00 VGI.193.4L7.B NO (BNC+BNC) 172.00 127.00 45.00 VGI.193.4L7.R NO (BNC+BNC) 172.00 127.00 45.00 VGI.454.4R7.B NO 81.00 41.00 40.00 VGI.456.4R7.R NO 80.00 41.00 39.00 VGI.130.5R7.B YES 100.00 100.00 0.00 VGI.210.5R7.R YES (BNT) 108.00 108.00 0.00 VGI.324.5R7.B NO 161.00 118.00 43.00 VGI.53.6R7.R YES (BNT) 167.00 167.00 0.00 VGI.534.6R7.B NO 208.00 191.00 17.00 VGI.392.6R7.R NO 200.00 191.00 9.00 VGI.128.7R7.B YES (BNT) 244.00 244.00 0.00 VGI.128.7R7.R YES (BNT) 244.00 244.00 0.00

•

Length measurement at P7

37

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•

Why the internal shield is cut ?

During the building of the LHC, the cables were extended to match the machine

evolution.

The cable extension has been realized with the

BNC coaxial adapter.

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Measurements and cabling quality check

Repair the cables

•

Replace the cables.

•

Use triaxial adapter.

•

Mount a triaxial female

connector.

Mitigate the current in the shield

•

Use capacitor box to limit

the low frequency signal in

the external shield.

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The Volotek controller and its cable

infrastructure in LHC

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