A plant technician notices that the pressure reading on the HMI for a specific vessel is consistently 15 kPa lower than the local pressure gauge. The pressure transducer producing the 4-20 mA signal was recently replaced. What is the most probable cause of this discrepancy?

Question: A plant technician notices that the pressure reading on the HMI for a specific vessel is consistently 15 kPa lower than the local pressure gauge. The pressure transducer producing the 4-20 mA signal was recently replaced. What is the most probable cause of this discrepancy?

Answer options:

• The HMI display resolution is too low.
• The PLC's analog input module is faulty. ✅ The transducer's calibration has drifted or its zero point was not correctly set.
• The communication cable between the PLC and HMI is damaged.

Correct answer: The transducer's calibration has drifted or its zero point was not correctly set.

Explanation: A consistent offset in a 4-20 mA signal usually points to a calibration issue, specifically the zero point or span calibration of the transducer itself. If the analog input module or communication cable were faulty, the readings would likely be erratic or absent, not consistently offset. Low HMI resolution would not cause a consistent offset.