The term “Bad PV” (Process Variable) typically refers to a situation where the process variable signal being received by the control system or operator interface is not reliable or valid.
Bad PV - Process Variable
This could occur due to several reasons:
- Sensor Failure: If the sensor measuring the process variable fails or malfunctions, it may send incorrect data. This could be due to mechanical or electrical issues, calibration drift, or damage to the sensor.
- Communication Errors: If the communication link between the sensor and the control system is disrupted or experiences interference, the PV may be lost or incorrect. This could be due to issues like network failure, wiring problems, or signal interference.
- Out-of-Range Values: If the sensor measures a value outside of its defined range, the control system may flag the PV as bad. This can occur if the process conditions exceed what the sensor is designed to measure.
- Invalid Data: If the data received does not conform to expected formats or seems implausible (like a sudden jump to an extremely high or low value), the control system might mark the PV as bad.
- Fault in I/O Modules: If the Input/Output (I/O) module of the PLC/DCS that communicates with the sensor is faulty, it may lead to a bad PV.
When a PV is flagged as bad, the control system typically takes a predefined action, like raising an alarm or switching to a failsafe mode, to prevent potential harm to the process, the equipment, or the personnel. It’s important to investigate the cause of a bad PV and resolve it promptly to ensure safe and efficient operation of the process.