The FEE Server Control Engine of the ALICE-TRD - Westfälische ...

6 Temperature Monitoring of the Front End
Readout Electronics
6.1 Temperature Monitoring Inside the Supermodule
Monitoring the temperature inside the supermodule is important for different reasons.
First of all measuring the temperature is the only technically feasible solution to check
the proper cooling of all MCMs. The silicon hoses or the small aluminum tubes can be
blocked and in consequence the corresponding MCM column remains uncooled. Furthermore
a silicon hose can be laced up due to the under-pressure when not properly
routed. Especially in layer five this has happened several times. As long as these problems
are detected during supermodule integration they can be fixed. After a supermodule
is finished, it is very difficult if not even impossible to fix cooling problems in the
supermodule.
During normal TRD operation the most probable failure in the cooling system is a
breakdown of the cooling plant. Such a failure should be detected by the monitoring
software of the cooling plant and results in a shutdown of the TRD. However, monitoring
the temperature in the supermodules provides a good extension and a fallback system for
cooling monitoring. Lastly, the temperature inside the supermodule is also interesting
for physical reasons. The drift velocity in the Ar-CO2 gas mixture inside the chambers
depends on the temperature. Even though the thermal coupling between the gas mixture
in the chambers and the ambient air is weak and the drift velocity in the gas mixture is
monitored separately, measuring the temperature may give useful information about the
environment conditions.
Each ROC has three different types of temperature sensors. The first one is a dedicated
temperature sensor connected to the DCS board. It is placed about 2 cm away from the
DCS board. Therefore it measures the air temperature in the surroundings of the DCS
board. The sensor is a 10 MΩ NTC resistor. The voltage drop in the resistor is digitized
by an ADC on the DCS board. The FEEServer running on the DCS board reads out the
sensor in regular intervals, converts the sensor reading to a temperature measured in
degree Celsius and publishes the value via DIM.
The DCS board has a second temperature sensor directly mounted on the board. However,
this second sensor is not calibrated and measures the local DCS board temperature
only. Therefore this sensor is not used.
Finally, each MCM has an embedded temperature sensor which measures the temperature
inside the MCM. Therefore, these sensors give a very localized temperature,
in contrast to the temperature sensor connected to the DCS board which measures the
global air temperature. Since the MCM has six sensors in total (the temperature sensor
and five voltage sensors to measure different voltages in the MCM) but only one 10 bit,
80 kSamples/s ADC [A + 05] to digitalize sensor readings, an analog multiplexer is used
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