Help from a layperson – Pt100 signal conversion issue
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Dear everyone: Here is a description of the situation: In a certain motor installation, a thermal resistor Pt100 is used to measure the temperature; this value is converted into a 4–20mA signal via a transmitter, which is then sent to the PLC. The temperature range displayed on the HMI is set to 0–200°C. However, it was found that the nameplate on the wiring box at the site indicated that the range of the thermal resistor was -40~+150°C. May I ask: Should the HMI range setting be changed to match the actual conditions on site?
The range is defined in relation to the transmitter; as long as the display shows the same range as that of the transmitter, it’s fine. You can use the 475 handheld device to check the range. The temperature range measured by a PT100 thermistor isn’t that limited, right?
The range of a thermal resistor indicates the range it can measure, while it is the range set on the transmitter that is displayed. For example, if the transmitter accepts inputs of 0~200°C and outputs (4~20) mA, then the displayed range will be 0~200℃
There are no 475 type controllers. In fact, in our industry, there are no positions or specialties related to instrumentation at all:D The thermal resistors are embedded in the motor stator windings; their range is indicated on the wiring box label, and it doesn’t match the specifications given in the manufacturer’s drawings. . .
Thank you to the people who replied above! What was said on the 3rd floor is right! I suddenly realized that the transmitter uses a Pt100 input, with 100 ohms at 0 degrees; the input and output should be matched accordingly.
Look at the transmitter; set the PLC value to match the transmitter’s range.
Just match the temperature variation with the range on the DCS
If the PT100 temperature variation cannot be adjusted, then the system needs to be modified to ensure that the measurement ranges at both ends are identical; otherwise, the display will be incorrect
Of course, it needs to match; otherwise, there will be discrepancies. The key issue is: who will set the range for the HMI in the instrument station?
Just match the temperature variation with the range on the DCS
Communication is required to check the specific range of the transmitter, which should be consistent with that of the DCS, rather than the range indicated on the nameplate.