1. Irradiation test of Pressure Transducers for the LHC machine
Results from 2002 test-campaign in TCC 2.
Piezo resistive transducers

2. Poorly protected  high radiation dose
LHC requirements
Position
room temperature)
Purpose
Range (abs)
Accuracy
SSS
1.8 K phase separator
mbar
0.3 %FS
Cold mass
0..20 bar
0.5 %FS
QRL
line C
line D
DFB
Helium bath
0..4 bar
1.5 %FS 
Poorly protected  high radiation dose
RADWG Day, 9/
LHC/ACR/IN, T. Bager

3. TCC 2, Pneumatic and electric layout
Control room
Radiation zone
Vacuum pump
Vacuum pump
Transducers under test PT PT
GHe, bar
100 mbar pressure
reference PT TT
On-line data acquistion
RADWG Day, 9/
LHC/ACR/IN, T. Bager

4. Transducers under test
Membrane with 4 strain sensitive resistances moves with pressure.
Resistances can be either metallic or piezo resistive.
Bridge un-balance measured by remote electronic using either AC or DC excitation.
Excitation +
Excitation sense
Signal +
Signal -
In 2002 is only tested transducers based on piezo resistive technology.
3x Keller PAA 11 and 3x STS TM212
Excitation sense
Excitation -
RADWG Day, 9/
LHC/ACR/IN, T. Bager

5. On-line monitoring @ constant true pressure
Pressure = 16 mbar abs 2 1 1
: STS TM s/n
Courtesy S. Kaczmarek
Transducer 2
: Keller PAA11 s/n 47838
RADWG Day, 9/
LHC/ACR/IN, T. Bager

6. Evolution of transfer function
mbar mV dU
Gain shift dp
Offset shift
RADWG Day, 9/
LHC/ACR/IN, T. Bager

7. Piezo resistive transducers, evolution with dose
6 sensors of 2 types
Gain shift [%]
Offset shift [% of span]
A transducer type does not have a well defined drift with accumulated dose !
RADWG Day, 9/
LHC/ACR/IN, T. Bager

8. Piezo resistive transducers, gain and offset drift with radiation.
Gain drift [ppm/Gy]
Offset drift [ppm of span / Gy]
~ Gy
~ Gy
RADWG Day, 9/
LHC/ACR/IN, T. Bager

9. Estimated survival time in LHC tunnel
Requirement : radiation caused drift < 0.1 %FS
Transducer type
Arc (10-20 Gy/y)
DS ( Gy/y)
Piezo resistive strain gauge
~ 1 year
~ 1 month
Integrated electronic
< 1 month
< 1 week
Metallic strain gauge
> 60 years
> 6 years
RADWG Day, 9/
LHC/ACR/IN, T. Bager

10. Conclusion: the test facility
A facility allowing on-line monitoring of pressure transducers is operational in TCC 2.
Operation during radiation
Remotely controlled valves & vacuum pumps
10-2 mbar – 20 bar absolute
3 pressure reference instruments
Multimeters & scanners and voltage/current supplies
Possible improvement : better information on the spatial distribution of radiation in TCC 2 zone
RADWG Day, 9/
LHC/ACR/IN, T. Bager

11. Outlook High pressure range 100 mbar abs range
Pressure transducers for the 4 and 20 bar ranges are chosen => Based on metallic strain gauges with remote electronic.
100 mbar abs range
Presently the only potential suitable candidate refuses to cooperate with CERN allegating intellectual property issues.
Inductive, capacitive, Siemens piezo and vibrating beam technologies will be tested in All applying remote electronic.
A decision regarding the application of this transducer channel in the LHC control system shall be taken by the end of 2004.
RADWG Day, 9/
LHC/ACR/IN, T. Bager

12. Appendix : Calibration shift of metallic and piezo resistive sensors
RADWG Day, 9/
LHC/ACR/IN, T. Bager