1. Environmental Monitoring of CMS Tracker Volume
Michael Bloom: Kings College London
Supervisors
Paolo Petagna and Karl Aaron Gill
Special Thanks to Duccio Abbaneo
And all the CMS Tracker Team

2. Long term radiation damage
Due to radiation damage the silicon detectors become less effective. The effects can continue to get worse with time even when the detector is not in use (reverse annealing).
For this reason the tracker must be cooled during its operation, and also during maintenance.
It is thus necessary to keep the humidity low inside the tracker to avoid condensation (humidity can severely damage silicon detectors and electronics parts).
For this reason the tracker volume is sealed and flushed through with dry air or nitrogen.

4. Humidity Measurements
It is necessary to have accurate measurements of humidity inside the volume, to monitor the correct functioning of the dry gas ventilation.
So sensors were needed which were
Radiation Hard
Small in size and mass.
Due to these unusual requirements only one sensor was found which fitted the criteria (after a long search).

6. The HMX.
The sensors are Wheatstone bridges on a block of composite which changes shape with humidity.
There are hundreds of these throughout the tracker volume.
Usually each sensor has to be pre- calibrated. However this was not possible before the installation of the sensors.
For this reason a small number of calibrated non radiation hard sensors (Honeywell) where inserted into the volume to act as “standard candles” for the HMX’s (will be damaged after some irradiation).
Fig: Wheatstone Bridge.
My work has been to look through data taken over the past year during Tracker integration and find useful periods in terms of temperature and humidity and use the data from the Honeywell sensors to calibrate the HMX’s.

7. Conversion to Useful Values
ADC
BRIDGE
RELATIVE HUMIDITY
RELATIVE HUMIDITY
ABSOLUTE HUMIDITY
(DEW POINT)

8. The Calibration
Every moisture sensor must be coupled to a corresponding temperature sensor to apply the appropriate correction to its output.
The relative humidity Rh can be calculated from the DP measurement of the HIH’s.
Sets of values of
- Bridge (from HMX)
- Rh (from HIH)
- T (from dedicated sensor)
can be used to fit for the HMX calibration constants
Temperature(ºC) 20
Rh(%)
-20 10 20 30

9. Results HMX Name H1 H2 H3 Error in Rh 1 RH MONITOR_in_Zpf_TOP_1
HMX
Name H1 H2 H3
Error in Rh 1
RH MONITOR_in_Zpf_TOP_1
11.88% 2
RH MONITOR_in_Zp_Xm_BH_2
2.72% 3
RH MONITOR_in_Zpf_BOT_3
2.74% 4
RH MONITOR_in_Zp_Xp_BH_4
1.98% 5
RH MONITOR_in_Zmf_TOP_5
4.94% 6
RH MONITOR_in_Zm_Xm_BH_6
2.94% 7
RH MONITOR_in_Zpn_TOP_7
16.99% 8
RH MONITOR_in_Zpn_BOT_8
3.44% 9
RH MONITOR_in_Zmn_TOP_9
32.20% 10
RH MONITOR_in_Zmn_BOT_10
11.80% 13
RH MONITOR_in_Zmf_BOT_13
3.46% 14
RH MONITOR_in_Zm_Xp_BH_14
3.42%

10. Results HMX Name H1 H2 H3 Error in Rh 1 RH MONITOR_in_Zpf_TOP_1
HMX
Name H1 H2 H3
Error in Rh 1
RH MONITOR_in_Zpf_TOP_1
11.88% 2
RH MONITOR_in_Zp_Xm_BH_2
2.72% 3
RH MONITOR_in_Zpf_BOT_3
2.74% 4
RH MONITOR_in_Zp_Xp_BH_4
1.98% 5
RH MONITOR_in_Zmf_TOP_5
4.94% 6
RH MONITOR_in_Zm_Xm_BH_6
2.94% 7
RH MONITOR_in_Zpn_TOP_7
16.99% 8
RH MONITOR_in_Zpn_BOT_8
3.44% 9
RH MONITOR_in_Zmn_TOP_9
32.20% 10
RH MONITOR_in_Zmn_BOT_10
11.80% 13
RH MONITOR_in_Zmf_BOT_13
3.46% 14
RH MONITOR_in_Zm_Xp_BH_14
3.42%

11. Results
Before Calibration
After Calibration

12. Further Work Thank you for your time! Questions?
Analysis of more data to improve fitting.
The calibration of the Monitor HMXs were focused on but there are still many in the sub detectors which need to calibrated.
The calibration must be implemented in PVSS
The use of sniffer pipes to monitor humidity must finalised.
Thank you for your time!
Questions?