Electrician Red Seal · Question
A plant technician notices that the temperature displayed on the HMI for a critical reactor fluctuates wildly, showing unrealistic values, even though the process temperature is stable. The temperature is measured by a PT100 RTD connected to an analog input card. What is the most likely cause?
Wild, unrealistic fluctuations in an analog signal often point to electrical noise or interference corrupting the signal before it reaches the input card. An in
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Question: A plant technician notices that the temperature displayed on the HMI for a critical reactor fluctuates wildly, showing unrealistic values, even though the process temperature is stable. The temperature is measured by a PT100 RTD connected to an analog input card. What is the most likely cause?
Answer options:
- The HMI refresh rate is too high. ✅ Interference or noise on the RTD signal wires.
- The PLC program is converting the temperature incorrectly.
- The RTD is designed for a much higher temperature range.
Correct answer: Interference or noise on the RTD signal wires.
Explanation: Wild, unrealistic fluctuations in an analog signal often point to electrical noise or interference corrupting the signal before it reaches the input card. An incorrect PLC conversion would result in a consistently offset or scaled value, not random fluctuations. An HMI refresh rate or RTD range mismatch would also not typically cause such erratic readings.
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