Proximity Measurements - GE Bently Nevada 7200 Series Installation Manual

14 mm Proximity Transducer System 7200 Series Installation Manual
The probe signal and the input power are transmitted between the Proximitor and a standard Bently
Nevada monitor through a 3-wire shielded signal cable (provided by the user in most cases). The
Proximitor can be up to 1000 feet (305 metres) from a monitor without degradation of performance.
Probes are compatible with most petrochemical environments. Strong acids with a pH of less than 4,
strong bases with a pH greater than 10, and some organic solvents may damage the probes. Contact
the nearest Bently Nevada Corporation office for details about probes that operate in harsh
environments.
Standard versions of the components of this system are shown in Appendix A. Specifications are
listed in Appendix B, and Appendix C shows scale factors and sensitivity curves.

1.2 PROXIMITY MEASUREMENTS

The probe radiates radio frequency energy from the probe tip coil. As a conductive material (such as
a machine shaft) approaches the probe tip, eddy currents are induced into that material. The closer
the conductive material comes to the probe tip, the greater the magnitude of the eddy currents. As
the eddy currents increase, the power energy radiated from the probe tip is absorbed and there is a
corresponding loss in power detected at the Proximitor. If the probe-to-shaft gap remains constant,
the Proximitor output signal remains constant; if the gap changes, the output signal changes
accordingly.
The 14 Millimetre Proximity Transducer System is primarily intended for measuring the axial thrust
motion of large machine rotors. Its relatively large linear measuring range may be required for
thrust position measurements on large machines. Probes mounted to measure thrust position should
be located within 12 inches of the thrust collar. Thrust position probes mounted at the machine end
opposite the thrust collar do not provide adequate protection since they also measure differential
expansion. Typically, two probes are used so that if one is damaged or fails, thrust position can
continue being monitored. See Figure 1-2.
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