Troubleshooting methods for abnormal readings on Rosemount multi-point thermometers
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The multi-point thermometers used in our tank area now show correct values after installation and configuration. The multi-point thermometer has a total of 14 measurement points from top to bottom; the temperature at the lowest point is 01, while it is 14 at the highest point. Our DCS displays the temperature at each of these points. The temperature at point 01 matches the actual measured temperature, while it decreases gradually from points 02 and 03 all the way to point 14 – a decrease of about 5 degrees over a height of 20 meters. The resistance values after unthreading the wires are fine; is there any expert with knowledge of multi-point thermometers who can explain this? Now the cause of the problem has been found.
This post was last edited by zzhzh on 2015-8-7 at 17:33. The longest length of these points is over 20 meters. Typically, a Pt100 sensor uses 3 wires; it’s possible that you only connected 2 wires when making the connections, which means that the resistance of the Pt100 leads (including the several meters within the protective covering) is also taken into account. As a result, the resistance value decreases from the lowest point (the longest length) to the higher points, and the temperature displayed also decreases accordingly
Water has entered the junction box and seeped into the sleeve.
If there is a temperature change, use a resistor to test the quality of that temperature change.
I’ve found the cause of the problem. I haven’t encountered a similar problem. I guess it’s because there is a heating coil at the bottom of the tank, so the temperature there is high, while it’s relatively lower compared to the upper part
I agree with the analysis in post 2; one wire was omitted for each temperature point, resulting in errors due to circuit resistance.
There shouldn’t be any issues with wiring as people mention it regarding the multiple temperatures of RMT. OP, please share your reasons
Rosemount multi-point temperature sensors are generally connected to 2240S or 2230; please check whether the two black wires of the sensor are properly connected
The actual measured resistance minus the wire resistance should be the value displayed on the DCS!
The original poster asks a question and then disappears. Actually, under normal circumstances, the temperatures with and without a dew point are different. I’d like to know what the reason for this is
The reason is actually quite simple: it’s a problem with the setting of the multiple temperature sensors. Since they are PT100 sensors, some of their leads use a common return path, while others use a separate return path. I guess you initially set them to use a common return path, which is why that error occurred. In TM, just change it to return separately. This fault is actually quite interesting.