The actual resistance value of the PT100 thermistor does not match the temperature displayed by the DCS
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The workshop is equipped with PT100 thermistors, and it was found that the temperature readings displayed by the DCS were on the low side. Upon inspection, the resistance value of the thermistor was found to be 115 ohms; according to the PT100 calibration table, the actual temperature should be around 39 degrees. The range set for the DCS and temperature transmitter safety gates is -30 to 200 degrees; the measured output current of the safety gates is around 5.3 mA, while the temperature displayed on the DCS screen is around 12 degrees Celsius. I would like to ask the experts why there is a discrepancy between the temperature obtained by using a scale based on the measured resistance values and the temperature displayed by the DCS? Welcome everyone to leave comments and share your thoughts; thank you!
Is the temperature range setting on the DCS too low?
Could you be more specific? Is it a setting issue with that section?
The set range for both the DCS and the temperature transmitter safety barriers is -30 to 200 degrees. Is there any problem with this setting?
The safety barrier should output 8.8 mA. First, check whether an output of 4 mA is obtained at 100 ohms; I suspect that the safety barrier’s output range is set to 0–20
First, the measured resistance value includes the resistance of the two leads, so the value will be high; it is necessary to measure the resistance of those two leads and subtract it to obtain a more accurate value. Secondly, the range set for the safety barrier does not match the output mA signal: a current of 5.3 mA is generated for a temperature range of (-30-200)°C, which corresponds to -11.31°C; however, the DCS displays 12°C. If the range is indeed (-30-200)°C, the corresponding mA value should be 6.92 mA. Please check whether the range settings for the safety barrier and the DCS are consistent and correct.
First, the measured resistance value includes the resistance of the two leads, so the value will be high; it is necessary to measure the resistance of those two leads and subtract it to obtain a more accurate value. Secondly, the range set for the safety barrier does not match the output mA signal: a current of 5.3 mA is generated for a temperature range of (-30-200)°C, which corresponds to -11.31°C; however, the DCS displays 12°C. If the range is indeed (-30-200)°C, the corresponding mA value should be 6.92 mA. Please check whether the range settings for the safety barrier and the DCS are consistent and correct.
Okay, thank you! I’ll check it again using the method you suggested.
This post was last edited by li*ng419 on 2020-2-15 22:34. Which brand’s temperature-sensitive safety barrier?