A fiber optic sensor may fail to return to zero due to improper connections, environmental conditions, or incomplete calibration, and can often be corrected by following proper zeroing procedures.

Common Causes

1. Improper Connection: The sensor and calibration (CAL) key must be securely connected. Listen for two clicks to ensure a proper connection; forcing the connector can prevent zeroing and damage the sensor .
2. Environmental Conditions: The sensor electronics must reach normal operating temperature before zeroing. Extreme temperatures or vibrations can interfere with automatic zeroing .
3. Active Signal Interference: Automatic zeroing requires no active waveform detection. If the sensor is exposed to pressure or signal before zeroing, it may not return to zero .
4. Sensor or Cable Damage: Fiber optic cables are sensitive to bending, tension, or contamination. Damaged fibers or connectors can prevent proper light transmission, affecting zeroing .

Zeroing Procedures

Automatic Zero

• Ensure the FOS connector and CAL key are connected.
• Confirm data from the CAL key is downloaded to the system.
• Verify no waveform is detected and the electronics have reached operating temperature.
• The system will automatically zero the sensor when these conditions are met .

Manual Zero

• With the FOS and CAL key connected, select FIBER OPTIC on the system interface.
• Press the FOS ZERO soft key.
• A green indicator confirms the zero is complete, and a message will appear on the display .

Post-Insertion Calibration

• If zeroing cannot be performed prior to insertion (e.g., in emergent situations), the sensor can be calibrated after insertion by adjusting the measured value to a known reference .

Additional Tips

• Avoid forcing connectors; pull back slightly and reconnect if resistance is met.
• Tape the fiber optic cable securely to prevent movement during operation.
• Inspect for dirt, scratches, or bends in the fiber that could affect light transmission.
• If the fiber optic signal is lost, switch to an alternate measurement source as recommended by the system . By carefully following these procedures and ensuring proper environmental and connection conditions, most issues with a fiber optic sensor failing to return to zero can be resolved.