Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question from 2020-10-22
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Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question No. 2020-10-22: Discussion question: 273. In thermocouple temperature measurement, if the indicated value is low, what could be the possible causes from the perspective of the thermocouple itself?
1. There is a problem with the cold-end compensation. 2. There is a problem with the temperature transmitter. 3. The core is corroded. 4. Moisture has entered. 5. The positive and negative poles are reversed
In thermocouple temperature measurement, if the indicated value is low, from the perspective of the thermocouple, this may be caused by the following reasons: leakage of current at the internal electrodes of the thermocouple (local short circuit)； Moisture inside the thermocouple ； Thermoelectric electrode corrosion or degradation ； The thermocouple is installed in the wrong position or not deep enough ； The temperature at the thermocouple reference terminal is too high, or the temperatures at the two contacts are different ； The type of thermocouple does not match the instrument’s calibration code ； Too much scaling on the surface area of the thermocouple protection tube.
1. No cold-end temperature compensation was performed； 2. The cold-end temperature is unstable and on the high side.
Short circuit of the thermoelectric electrode, short circuit between the compensation wires, deterioration of the thermoelectric electrode of the thermocouple, reversed polarity connection between the compensation wires and the thermocouple, insufficient insertion depth, and short circuit caused by dust accumulation on the terminals of the thermocouple.
In thermocouple temperature measurement, if the indicated value is low, from the perspective of the thermocouple, this may be caused by the following reasons: leakage of current at the internal electrodes of the thermocouple (local short circuit)； Moisture inside the thermocouple ； Thermoelectric electrode corrosion or degradation ； The thermocouple is installed in the wrong position or not deep enough ； The temperature at the thermocouple reference terminal is too high, or the temperatures at the two contacts are different ； The type of thermocouple does not match the instrument’s calibration code ； Too much scaling on the surface area of the thermocouple protection tube.
1. The compensation wire is connected in reverse. 2. The thermocouple is corroded, causing changes in its thermoelectric properties. 3. The thermocouple junction is fouled with dirt. 4. Water and dust accumulate at the connection points
Short circuit of the thermoelectric electrode, short circuit between the compensation wires, deterioration of the thermoelectric electrode of the thermocouple, reversed polarity connection between the compensation wires and the thermocouple, insufficient insertion depth, and short circuit caused by dust accumulation on the terminals of the thermocouple.
Possible reasons include: 1) Short circuit of the thermoelectric electrode. 2) Dust accumulation at the wiring connections of the thermocouple caused a short circuit. 3) Short circuit between compensation wires. 4) Degradation of the thermocouple thermoelectrode. 5) The compensation wire is not compatible with the thermocouple.