Issues with on-site display and remote transmission errors in Hilscher control systems
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I’m currently using a three-wire PT100 sensor to measure low-temperature liquids. The multimeter shows that the resistance of the PT100 is 40 ohms; according to the calibration table, the temperature should be minus 159 degrees, while the control panel indicates minus 173 degrees. The wires used seem to be fine – so what could be causing this error? What should I do?
What is the resistance measured at the DCS card? What is the resistance measured on-site?
A change of 3–4Ω in the thermistor results in a temperature change of around 10 degrees. First, determine how accurate the multimeter is; if the multimeter is accurate, try using another meter or a different thermistor.
First, go to the control panel and locate the three wires connected to the thermal resistor; check the resistance value. If it differs from the actual resistance value on site, then there is a problem with the wires – inspect the wiring terminals. If it’s the same, it’s a problem with the card.
The resistance measured on the DCS card is 4 ohms higher than that at the site; all three wires show a value 4 ohms higher
Let me share a case with you. We installed a new DCS in our facility, and everything worked well at first. Suddenly, the temperature in one of the processing units increased by over 10 degrees. The process itself was fine; the on-site thermometers, sensors, and safety barriers were all in order. In the end, it turned out that the problem was related to grounding – the Allen-Bradley DCS requires three grounding points. You can take this as a reference