SKF offers a selection of eddy probe systems, also called proximity probe systems, to ensure the most suitable transducer for machinery protection and monitoring. The simplicity and rugged design of SKF’s eddy probe systems enables them to withstand the temperatures and chemicals typically encountered in the harsh industrial environment.
Effective protection of rotating machinery requires that the proper type of measurement be performed. The most suitable type of transducer may then be defined. Finally, specific application circumstances (frequencies of interest, operating temperatures, mounting requirements) are considered to select the optimum transducer. The chart to the right provides general guidelines for determining the most effective type of measurement.
Eddy probe systems
An eddy probe measures radial or axial shaft motion. It mounts through or to the side of a bearing cap and observes the shaft's movement relative to its mounting position. An eddy probe system comprises a probe, a driver (oscillator demodulator) and an extension cable.
Eddy probe systems have excellent frequency response. They have no lower frequency limit and measure shaft axial position as well as vibration.
While eddy probe systems offer excellent high frequency response, displacement at typical blading and gear mesh frequencies is quite small (you may use an accelerometer to augment the eddy probe system when high frequencies are a concern).
Shaft relative motion
Shaft relative motion is the radial vibration of the shaft journal relative to the bearing. This method of vibration measurement is preferred for journal bearings, since it directly relates to permissible clearances. In machines with relatively light rotors and stiff heavy casings (turbines and compressors), almost all of the shaft’s vibration energy is dissipated as displacement (exhibit low transmissibility), which can only be measured as shaft relative motion. An eddy probe, mounted to or through the bearing, observes the shaft to provide this measurement. An additional eddy probe is often installed 90° from the first, in an orthogonal arrangement, to increase monitoring and diagnostic capabilities (voting logic and shaft orbit display).
API Standard 670
The American Petroleum Institute (API) has published Standard 670 as an aid to the procurement of standardized non-contacting vibration, axial position and temperature monitoring systems. The standard is based on the accumulated knowledge and experience of petroleum refiners and monitoring system manufacturers.
API Standard 670 is a valuable reference tool for all machinery users and manufacturers, and is highly recommended as a guide for defining, purchasing and installing machinery monitoring systems.
Selecting an eddy probe system
SKF eddy current probe systems are constantly temperature and performance tested in a continuing effort to improve what is already the best probe available for the measurement of vibration in rotating equipment. They are available with armoured and fibreglass sleeving, and may be offered ATEX (Sira)/CSA/FM certified.
SKF also offers a variety of accessories that are available for the eddy probe systems, including probes and drivers, mounting devices, housings, and much more. Reference the Eddy Probe Systems Catalogue for a description of the various accessories available for eddy probe systems.
The eddy probe is used to measure radial or axial shaft motion. It is mounted through or to the side of a bearing cap and observes the shaft’s movement relative to its mounting position. An eddy probe system comprises a probe, a driver (oscillator demodulator) and an optional extension cable.
Eddy probe systems have excellent frequency response. They have no lower frequency limit and are used to measure shaft axial position as well as vibration.
Eddy probes mounted to observe the shaft