The SSD humidity, crucial for what concerns a good bias current behaviour, is always monitored usng dedicated sensors read via DCS. In the follwing picture, the humidity level measured, in 2011, in ALICE CR5 (where the ITS ventilation machine is located) and in SSD C and A side is shown.
On September 2012 a new ventilation machine has been installed. It was requested in order to achive the humidity values for a proper SSD working. Here below a report of the first machine working days is summarized.
04/09, 16:30 - Dessica started with this setpoints:
- RH: 15% (--> 2.03 g/kg)
- T: 19 deg (measured near the machine ~18.3 deg, decreased to ~16.6 in the following days)
- Flow measured ~314 m^3/h that increased to ~330 m^3/h in the following hours
- P measured ~1.5 kPa
- SSD C2-sensor RH (at the detector entrance): ~26%
- SSD A -sensor RH (at the detector exit): ~26%
We also monitored the leakage current of two SSD half ladders to see their variation. The leakage current value is the most important for the SSD and represents an absolute reference net of possible relative miscalibration between the machine and SSD sensors.
- A624: 195 uA
- C601: 400 uA
07/09, 09.30 - Flow reduced to ~ 300 m^3/h, other parameters fixed
- P measured: 1.26 kPa
- SSD C2-sensor RH: ~20.3%
- SSD A -sensor RH: ~21.5%
- A624: 180 uA
- C601: 375 uA
10/09, 09.30 - RH setpoint reduced to 10% (-->1.35 g/kg), other parameters fixed, RH and currents measured at 16.30
- SSD C2-sensor RH: ~16%
- SSD A -sensor RH: ~18%
- A624: 160 uA
- C601: 332 uA
11/09, 09.30 - Flow reduced to ~ 250 m^3/h (the nominal one), other parameters fixed, RH and currents measured at 16.00
- P measured: 0.864 kPa
- SSD C2-sensor RH: ~16.8%
- SSD A -sensor RH: ~17.9%
- A624: 157 uA
- C601: 327 uA
In the attached plots you can see the RH evolution as measured from the SSD sensors (to compare with the humidity values in CR5, i.e. more or less the external environment) together with the performed intervention. A real improvement in terms of RH measured and currents, in terms of stability was achived.