Proximity Probe - Eddy Current Probe - Calibration
Vibration Field Testing Prevents Cable Errors, Ensures Alarm Thresholds
Eddy current probes – often called proximity probes – are non-contact displacement sensors that protect some of the world’s most critical equipment like gas and steam turbines from critical failure. Technicians verify and calibrate these sensors to:
- Reduce perceived insurance risk
- Meet API 670 standards
- Promote safety
- Strengthen departmental relationships
- Improve peace of mind
- Eliminate downtime
- Bolster efficiency
Proximity probes can be calibrated both dynamically and statically against a 4140 steel target with the latter method described in Section 7 of the American Petroleum Institute Standard 670. Dynamic calibration allows technicians to simulate actual shaft vibration at turbine running speed, allowing for confirmation of alert and alarm thresholds in the machinery protection system.
Calibration and Troubleshooting Video
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Incorrect cabling is the number one cause of false or late vibration alarms tied to proximity probes.
The leading cause of failure in a machinery protection system relying upon Eddy current probes is cabling. The probe driver – also known as the proximitor – converts probe impedance to voltage and produces linear output. It requires precise cable lengths and types typically 1, 5 or 9 meters. Incorrect cabling causes dynamic output from the proximitor to be too high or low, leading to false or late alarm trips. Creating an amplitude linearity calibration certificate while confirming alert and alarm trips at running speed – as shown above – is the most effective method of ensuring correct operation of the machinery protection system.
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