Temperature Sensor Calibration
The monitoring system of the AHCAL physics prototype comprises five temperature sensors inside the module cassettes. The sensors in modules 1 and 2 are placed in a diagonal line from the top left to the bottom right corner of the cassettes, while the sensors in the other modules are positioned along a vertical line in the centres of the cassettes. Counting from top to bottom, the sensors in each module are numbered from 1 to 5.
The temperature sensors measure absolute temperatures with an uncertainty of 0.5°C, i.e. each sensor has an offset on the centigrade scale and the distribution of the offsets of the whole sensor sample has a mean of zero and a width of 0.5°C. In order to improve the calibration of each individual sensor, their offsets can be determined and added to the readings. To do this, the temperature has to be the same throughout the whole prototype.
At the end of the CERN 2007 testbeam period, the prototype has been left off for some days. Afterwards the temperature should have been the same throughout the whole prototype, i.e. the mean of all sensor readings is the real temperature throughout all layers, without any offset. A series of temperature measurements has been performed in this state (measurements: CERN2007tempSensorCalibration.txt, file format: SCReadoutFormat.txt). note: The readout of several sensors seems to have malfunctioned during the first ~60 measurements.
The calibration offset Ci for each temperature sensor is obtained as the difference between its reading Ti from the average T of all sensors:
Ci = T - Ti.
Using temperature measurements 65-115, this procedure yields a calibration offset for 187 out of the 190 sensors. The offsets Ci (averaged over all 50 consecutive calibration offset determinations) are summarized in the following file:
calibration offsets: sensor_calibration.txt
format: <module> <sensor i (counting from 0 to 4)> <offset Ci> <error (= RMS / sqrt(entries))> <status (= # entries or 0)>