Eddy current probes (a.k.a. proximity probes) are non-contact displacement sensors that protect some of the world's most critical rotating equipment, like gas and steam turbines, from catastrophic failure related to excess vibration. By measuring the distance between probe tip and shaft, using changes in the magnetic field, users can effectively plot the motion of the shaft and determine if fault conditions exist such as imbalance and misalignment. Keeping turbines running and properly scheduling maintenance during planned outages is paramount to the success of the plant.

The probe system consists of the probe itself with typical 5-, 8- or 11-mm encapsulated probe tip, an extension cable and a probe driver or signal conditioner. The probe impedance changes proportional to distance from the shaft or target, however, probe impedance alone is not linear. It is the job of the probe driver to linearize these impedance changes and produce a reliable voltage signal relating distance to voltage. Since impedance is critical to this measurement, cable length and type must be precisely matched to the probe driver.

Unfortunately, Eddy current probe cable installation error is one of the top reasons for failure of the vibration protection system. Making matters worse...