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6 Temperature Monitoring of the Front End Readout Electronics to connect one of the sensors with the ADC. Which sensor is connected with the ADC can be selected via an SCSN command. The sensor readout is done via the SCSN bus, too. The MCM temperature sensors are ideal to identify individual uncooled MCMs or blocked cooling lines. But using these temperature sensors contains some challenges. • Reliability Each time an MCM is powered up there is a certain chance that the embedded temperature sensor will not work. Reading out such a sensor results in useless values. Therefore a runtime identification of non-working temperature sensors is required. Since working temperature sensors remain working as long as the MCM has power the runtime identification has to be performed only after each power up of the MCMs. The procedure to identify non-working temperature sensors is described in section 6.2.1. • Cooling overview Each layer in the supermodule contains 656 MCMs. After a layer is installed and connected to the cooling system a quick overview about cooled and not cooled MCMs is required. But the conversion from the sensor readings to temperatures cannot be done very precisely due to calibration problems. Therefore a method was developed to generate a cooling overview of a layer without relying on calibrated temperature sensors (section 6.2.2). • Calibration The MCM temperature sensors are not calibrated. In principle each MCM requires an individual calibration to convert the ADC values to temperatures. As we will see, such a calibration is not feasible. Therefore only a global calibration was performed to get at least a rough estimate of the temperatures. Section 6.2.3 gives more details. 6.2 The MCM Temperature Sensors 6.2.1 Runtime Identification of Working Temperature Sensors The MCM temperature sensors do not work very reliably. Each time the MCMs are powered up some temperature sensors do not work. Detailed tests show that working temperature sensors remain working as long as the MCM has power. But if the power is switched off and on again later a previously working temperature sensor may not work afterwards and a sensor which did not work may deliver correct values now. Using a special power-off / power-on sequence it is even possible to increase the average number of working temperature sensors on a readout chamber (ROC): First the MCMs on the ROC are powered for more than two seconds. Then the power is switched off. If the power returns after about 0.5 seconds the number of working temperature sensors increased significantly. Without using this power sequence a ROC has 30 to 40 percent working temperature sensors and afterwards 60 to 70 percent of the temperature sensors do work. This power sequence is implemented in class TempControl and is executed each time the MCMs are powered on. 76
6 Temperature Monitoring of the Front End Readout Electronics The MCMs have a design error which causes timing problems in parts of the MCM. The exact mechanism is not known but probably the design error cause the observed behavior. ADC value (a.u.) 650 600 550 500 450 400 350 0 50 100 150 200 timebin (a.u.) ADC value (a.u.) 650 600 550 500 450 400 350 0 50 100 150 200 timebin (a.u.) Figure 6.1: Sensor readings of a working (left) and a non-working (right) MCM temperature sensor Figure 6.1 shows the readings from a working and a non-working temperature sensor. The data were measured in less than two seconds and therefore the temperature change is negligible. Consequently, the working sensor measured almost the same value each time. The small variations are caused by noise. In contrast the non-working sensor shows huge variations in the data. An analysis of the readings from working and non-working sensors revealed some characteristics of non-working temperature sensors. • The ADC values 361, 384 and 639 are measured frequently. Additionally, in consecutive measurements the reading often jumps between these values. • ADC readings are below 5 or above 1020. The ADC is an 10 bit ADC and therefor the possible values are between 0 and 1023. Extreme readings indicate a nonworking sensor. • Consecutive readings have exactly the same value. Usually the readings of two consecutive measurements varies by ±1 or ±2. • Large deviation of single readings from the average value. Based on these results criteria were defined to distinguish between working and nonworking temperature sensors. If one of the following criteria is fulfilled the temperature sensor is considered as non-working: • Equal or more than 20% of the readings are 384, and equal or more than 20% of the readings are 639. • The sum of number of samples with values 384, 639, 361, below 5, or above 1020 is more then 60% of the number of total samples. • More than 80% of the readings have exactly the same value. • At least one reading deviates by more than 10 from the average value of this MCM. The thresholds were adjusted iteratively to get no non-working temperature sensors marked as working and as few as possible working temperature sensors marked as nonworking. The above criteria were implemented in an algorithm in the class TempControl for runtime identification of non-working temperature sensors. In the final test a complete layer with 656 MCMs was read out. For each MCM a plot like the one in figure 6.1 was created to identify non-working temperature sensors manually. In parallel the algorithm 77
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1 Introduction The standard model o
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Temperature (MeV) 225 200 175 150 1
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