Questions about thermal resistors
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There is a thermistor in the factory; the resistance measured from the field location to the cabinet is 124 ohms. Based on calculations, the temperature should be 62 degrees. However, when it is connected to the terminal board, the DCS shows 44 degrees. It is suspected that there is a problem with the signal channel. By using a resistance box directly on the terminal board to set the values at 119.5 ohms and 129 ohms, the DCS shows 50 degrees and 75 degrees respectively, confirming that there is no issue with the channel. Then why does the signal coming from the field location read 124 ohms but still result in a temperature reading of 44 degrees? I hope someone experienced can help solve this problem
What wiring system are you using? If it is a three-wire system, and the two signals generated by the resistance box differ by 10 ohms, then there is a problem. 124 euros should work out to around 60; after deducting the inter-wire resistance, it should be in the 50s degrees. I really don’t understand what you’re describing
It’s usually a transmission issue. Check the wiring and wire type
The thermistor is broken; please replace it. I’ve encountered this issue before: the resistance can be measured without any problems when it’s not connected to the module, but problems arise as soon as it’s connected. Just replace the thermal resistor and it’ll be fine
There are two cases: 1 If it is a three-wire connection, the resistance value is not simply the resistance of two wires; the resistance of the two cables coming from the same terminal also needs to be subtracted. 2 The thermal resistor has a problem and needs to be replaced. Rule out the first possibility first, then consider the second.
Measure the resistance of the three wires coming from the thermistor element. Generally, for ABB components, two of the three terminals have the same resistance value; if the values differ, replace the thermistor – it’s not expensive
For the thermal resistors A and B themselves, the resistance values of A and B’ are the same; however, once they pass through the cable, both resistance values increase and become uneven. The difference between the resistance values of A and B, as well as between A and B’, is 4 ohms. Will an uneven reading be displayed as well when returning?
I changed it, but it still doesn’t work; once the cable is used, the resistance values for A and B, as well as for A and B’, are too high and uneven
It’s a three-wire system; the thermal resistor has been replaced, so it’s certain that the problem isn’t with the thermal resistor itself. After signal transmission via the cable, the resistance values between A and B, as well as between A and B’, are relatively high and uneven—the difference between these two sets of resistance values is 4 ohms. Normally, after signal transmission through the cable, the resistance should increase, which would mean that the temperature reading on the DCS should be higher. So why does the DCS display a lower temperature instead?
The channel is fine, the thermal resistor is fine; it must be a wiring issue. Check the wiring.