Regarding the resistance value of the thermal resistor and the display issue in the DCS
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It’s now the Endress+Hauser system; the thermal resistors on site are located in the cabinet room. The resistance values for A and B are over 130 ohms, while those for A and C are 7 ohms. However, the temperature displayed by the DCS shows negative values. Other temperatures displayed correctly when connected to this channel. Everyone, please analyze what the reasons are
Lines A/B/C might be connected incorrectly; also, consider the possibility of the wires being connected to the casing.
Check the wiring or replace the thermistor.
Disconnect the circuit at the site and measure the thermistor; if the thermistor is fine, then it’s a problem with the external circuit
If other temperatures are displayed correctly on this channel, on-site issues should be considered. Swap the on-site thermal resistor to another channel to see if it still reads a negative value.
For the other channels connected to the same card, as well as those connected to other good cards, if the value is 130 ohms then there’s no problem on site; check the three-wire and four-wire settings for those channels, along with the wiring.
The signal line should be connected in series with the voltage. Either there is potential interference. Also, B and C7Ω are a bit too high
Measure the voltage of the wire; short-circuit one end to measure the resistance of the wire