-
Does not actually
touch the shaft or bearing - it is mounted an exact distance from a clean,
smooth area of the shaft and fixed in place.
-
Externally applied
high-frequency carrier signal emits a magnetic field from a coil in the
tip of the probe towards the shaft.
-
The shaft absorbs
some of the magnetic energy present.
-
The closer the
shaft to the magnetic field source, the more it absorbs. The more magnetic
energy it absorbs, the more it uses up the carrier signal and reduces the
carrier signal strength.
-
The further away
the shaft is from the probe, the less it absorbs. The less magnetic energy
it absorbs, the less it uses up the carrier signal and the higher the carrier
signal strength remains.
-
The probe produces
2 signals:
-
AC signal proportional
to the vibration (shaft movement).
-
DC signal proportional
to the size of the gap.
Generally, the
applications are:
-
Relatively lightweight
rotors in massive housings and rigid (generally “sleeve” or “babbit”) bearings.
-
High speed rotors
on machines such as turbines, centrifugal compressors and pumps (where
shaft speeds can exceed 50,000 rpm).
-
Very slow speed
machines on which it is difficult to obtain reliable data with velocity
transducers or accelerometers.
Machines such
as these can fail catastrophically in an extremely short period of time
(hours, minutes or even seconds) from the initial onset of the problem
and on-line monitoring with permanently mounted proximity probes is essential
to both machine and human safety. |
