The problem with measuring Resistance
Respected,
We have a DT85 g series 2 on which all 23 temperature measurements have started to show a bag value compared to what it should be. An example is the air temperature is 9 degrees C outside and the logger shows 17 and all the others have been moved higher.
MU X Huggenberger 48 is connected to DT 85
example
1DBO(W)=1-1 1R(II,,MD100,ES10,GL300MV,S1,W,"Tb-2 ~0C",=115cv)
S1=0,30,27,5,31"C"

3W are probes PT30 , the resistance measurement at the sensor itself is 29.15 and 0.67 ohms, but at the MUx input it is 34.49 and 7.61 ohms due to the distance of the probe from the measurement location. Instead of around 14 degrees, it shows 20 or more degrees. and that for all 23 probes. What could be the problem.
thank you
Sorry for my English, I hope you understand the question.

Hi Bocac,

If the temperature sensor is a thermocouple, you need to check the wire layout of the thermocouple against any high-power equipment or cable since the wire can pick up electromagnetic interference and add a few mV to the sensor, which is equivalent to the offset.

If the temperature sensor is an RTD, you need to be aware of the wire length of your sensor. Your sensor has 3-wire; using the logger wiring can compensate for some of the wire resistance. The best type of sensor is only 4-wire, which can compensate both sides of the wire.

Can you share the RTD details and the reason for such scaling? Rather than using a resistance channel, you can utilize the RTD channel template. PT30 sensor means the sensor resistance is 30 ohms at 0 deg C. You can use PT385(3W,30) for example.

Best regards,
dataTaker Expert

Thanks for your reply and interest in solving the problem.
RTD probes were installed in 1975-1978 during the construction of the dam, for which there is no accurate data. Based on the monitoring of measurements, it was concluded that these are probes for which the relation T=20+(Ri-29.83)/0.117 is valid, where Ri is the measured resistance minus the compensation resistance.
It is clear to us that there is a length of cable from the probes to the logger itself, and depending on the place where the probes are located, those lengths range from 110 to 286 m, which can be seen when measured on the terminal strip before the entrance to the MUS. This system has been working happily since 2013.
For example, the measurement of the Tz-probe on the crown of the dam according to the calculation (T=20+(Ri-29.83)/0.117 measurement 06.02.2024) the calculated temperature is 14.0170C, and the thermometer at that moment on UG1 shows a value of around 14 0C while on the logger display it is a measurement above 20. The measured resistances at the outlet of the probe are 1-2.3=29.43 ohms, 2-3=0.29 ohms, and the measurements on the skirting board are 3.84 ohms and 33.04 ohms, the distance of the probe is about 200 m.
it is strange that the measurement was shown to be higher for all probes that measure temperature through resistance and use this scaling method.
Best regards,

Hi Bocac,

i working with Huggenberger equipment for 25 years. Please pull and push the switching card('s) in the MUX 3times and measure the resistance before and after the procedure. I hope it helps. Maybe you have also a 8-port Handswitch in the MUX, this card you must not pull and push, with it you can also handy readout the resistance with an ohmmeter from the frontside of the MUX.
Do you mean with skirting board the PCB on the backside of the MUX, where soldered all the wires of the temperature probes and so on?
Volker