SKF Condition Monitoring Eddy Probe Systems

Features:

• Non-Contact Vibration Displacement Measurement
• 80, 90, 160 or 300 mil ranges
• 5, 8 and 19 mm probes

Applications:

Often seismic transducers are not the best sensor for monitoring vibration on specific machines. Eddy probes offer a solution to most of the problems inhibiting the use of traditional seismic sensors. The most common use of eddy current probes is for journal type bearings. Journal bearings behave different than rolling element bearings in that they do not transmit the vibration of the shaft into the bearing cap due to the damping properties of this type of bearing. Another application for eddy probes, is where a high case to rotor weight ratio exists (turbines and compressors). In these applications most of the shaft's vibration energy is dissipated as displacement, which can only be measured by shaft relative motion.

Frequency considerations also exist with eddy probes. While eddy probes have no lower frequency limit, very high frequencies become a problem. An eddy probe senses displacement, and at high frequencies displacement is often quite small requiring the use of a seismic accelerometer.

How Eddy Probes Work:

An eddy probe system consists of a probe,  matched extension cable, and  driver (oscillator demodulator). The tip of the probe contains an encapsulated wire coil which radiates the driver's high frequency as a magnetic field. When a conductive surface comes into close proximity to the probe tip, eddy currents are generated on the target surface decreasing the magnetic field strength, leading to a decrease in the driver's DC output. This DC output is usually 200mV/mil or in a similar range. This signal is then sent to a CMCP500 Series Transmitter or Monitor for conversion into a 4-20 mA output relative to displacement (CMCP540 and 540A) or position (CMCP545 and 545A). The CMCP540A and CMCP545A Monitors allow programmable alert and danger alarms with relays for the eddy probe driver's signal.