Proximity Probe and Eddy Current Probe Troubleshooting

Prevent Cable Errors, Ensure 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

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.

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 (API 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.

Benefits of a Portable Shaker Table

The Modal Shop’s Portable Vibration Calibrator shaker table is often referred to as a wobulator or wobble plate. Although the Portable Vibration Calibrator is a useful tool for calibrating and loop-checking proximity probes, it is not actually a wobulator. The wobulator is a clever device that’s been around for decades. The Modal Shop's portable shaker is ideal for checking and calibrating accelerometers, velocity transducers, proximity probes, and more. Learn more about how a Portable Vibration Calibrator compares to a Wobulator.