There is a resistance of 6 ohms between points b and c of the thermistor; this is a problem, right?
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This is the temperature of the front bearing bush of the compressor, measured at the field wiring box. The resistance is 124 ohms between a and b, 124 ohms between a and c, and 6 ohms between b and c. Compensation for all temperature points in the DCS has been applied. The problem is that the temperature shown on the DCS display keeps rising slowly until it reaches a maximum of 1300°. We tried re-wiring it, but while the resistance is 124 ohms on site, the temperature shown on the DCS is 43°. Where could the issue lie?
I think with a thermal resistor, when something like this happens, it can only mean it’s broken. ...What other reason could there be... Oh right, no temperature change, right? ?
You can check the temperature transmitter.
The calculated value is around 46 degrees; is that a problem?
Since there are 6 ohms extra, the temperature readings become inaccurate. Whether this has an impact depends on whether your team accepts it or not. But for compressors, the temperature of the bearing shells is particularly important; if spare parts are available, it’s better to replace them. Additionally, such equipment on-site usually has its own wiring box for the bearing shell temperatures, and the wires inside that box are usually very thin, as fine as hair strands. So the gradual increase in temperature is likely due to the vibrations of the equipment causing the connections to loosen. Also, what is the temperature range setting on your control cabinet – how is it possible to display 1300°C? ? ? ? At over 90 degrees, one would normally jump out of the car; a limit of 200°C is more than sufficient
If measured from the control room, 6 ohms should represent the wire resistance; the distance from the field site to the control room is likely not great. Using 124–6–100 and then dividing by 38.5 gives a value of over 40 degrees. If the measurement is 118 ohms when taken from the field site, that’s fine
Based on the phenomena described by the poster, it seems that there is poor contact at the connections; after addressing this issue, things return to normal. The 6 ohms value between B and C is likely the resistance of the wiring. Try checking the connections again – if such a high resistance still exists, it’s advisable to replace the wires...
Are you sure the 124-ohm resistor is over 40 degrees? Clearly around 62 degrees
124 minus 6 ohms of wire resistance gives 118
Interlocking is not activated; I’m making the measurements in my own junction box