What is the basic principle of vibration measurement by
BENTLY NEVADA vibration measurement system? and Why it
gives the -ve voltage output?

Answer Posted / sam

This is a very good, accurate writeup done by someone else
for a similar question earlier on. Hope it helps.


The vibration sensors used in turbine, generator etc are all
same type i.e proximity type of sensors. The sensor are
mounted at the proximity of the Turbine and generator rotor.
From the sensors one coaxial cable runs to the proximater,
which is mounted in a separate JB nearby. From TSI Monitors,
this Vibration probes gets +24 Volts DC. The proximater
gives a signal 0 to -22.4 Volts DC depending upon the
vibration measured by the sensor. Generally the distance
between the probe tip and the rotor is maintained such that
it gives -10 Volts DC when the turbine is not running.

The sensor works on eddy current principle. As the rotor
vibration increases, the eddy current generation remains
constant, but the absorption of power in terms of eddy
current increases. This loss of power is sensed by the
proximater and DC voltage signal is transmitter to TSI
monitor for Measurement, Controlling & Indication purpose.
Good luck

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