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High precision vacuum measurement system based on Bayard-Alpert ionization gauge. System overview for LHC, system performance, first operational measurements and noise immunity (July 2009 – February 2010) G. Peñacoba 07/04/2011. Collector. Grid. I +. Filament. e -. e -. 10 V 5 A. - PowerPoint PPT Presentation
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High precision vacuum measurement system based on Bayard-Alpert ionization gauge
System overview for LHC, system performance, first operational measurements and noise immunity (July 2009 – February 2010)
G. Peñacoba 07/04/2011
G. Peñacoba 2
Nude UHV Ionization Gauge
• Down to 10 -4 mbar
Pirani Gauges
• Down to 10 -10 mbar
Penning Gauges
e-
e-
I+
Filament
GridCollector
10 V 5 A
4 mA1 pA
4/7/2011
• Down to 10 -12 mbar
Bayard-Alpert Gauges
G. Peñacoba 3
ProfibusCommunication Electrometer
Filament-gridControl
• Gauge controller
Volotek VGC1000
Cable multi-conductor, single shielding
Cable Triaxial(coaxial with double shielding)
4/7/2011
G. Peñacoba 4
• Point 1
Layout in LHC
200 m
4/7/2011
~ 20 / LHC point
G. Peñacoba
• PVSS• Oscilloscope
Noise figures
Electrometerhacked foroscilloscopeaccess
4/7/2011 5
4 hours 3 days
10 s
5 V
Gauge 5R3
10 s
1.5 V
Gauge 6L8Gauge 7R1
100 ms
2.5 V
Gauge 7R1
10 s
3.5 V
G. Peñacoba 6
Machine side
Rack side
•Hacked electrometer
Measures with stand-alone Volotek
Gauge 6L8Gauge 6L8
4/7/2011
Original
Gauge 6L8
- No Low Freq.- Stable reading
10 s
G. Peñacoba 7
Machine side
Rack side
•Hacked electrometer
Measures with precision current source
Double shielded Triax
Gauge 5R3
4/7/2011
10 s
Gauge 5R3
Original
The contact of shielding and GND brings in the noise
G. Peñacoba 8
•Noise basics•Ground current loop through shielding
Working hypothesis
Gauge 5R3(shield connected)
Gauge 5R3(shield disconnected)
4/7/2011
Disconnecting the shielding reduces the noise
10 s
10 s
5 V
1.5 V
G. Peñacoba 9
Gauge 7R1
Gauge 7R1
•Capacitor box on gauge
Shielding decoupling
Machine side
Rack sideGauge 5R3
Gauge 5R3
4/7/2011
The capacitor boxeliminates the noise
10 s5 V
10 s
0.5 V
0.5 V
10 s
10 s
3 V
10
Machine side
Rack side
•Capacitor box on current source
Shielding decoupling
1
2
Gauge 5R3Gauge 7R1
Gauge 5R3Gauge 7R1
4/7/2011 G. Peñacoba
Contact to GND: Position 1
Contact to GND:Position 2
5 V
10 s
10 s
0.5 V
3 V
0.5 V
Capacitor box within GND loopensures clean signal
G. Peñacoba 11
•Triax internal shielding discontinuity
Cabling non-conformity
Machine side
4/7/2011
Floating internal shielding
G. Peñacoba 12
• The dominant source of the signal degradation has been identified.
• The discontinuity of the internal shielding in some of the cables makes the acquisition system more vulnerable to noise pick-up.
• A possible solution implying a minor modification of the cabling infrastructure has been successfully tested.
• Systematic tests and detailed analysis are required for further conclusions.
Conclusions
4/7/2011
TO BE CONTINUED …