Differential Expansion
Shaft growth relative to the machine case.

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Ramp Differential Expansion
A differential expansion measurement
that uses a combination of two
probes observing a sloped surface on
the shaft to increase the
measurement range

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Ramp Differential Expansion
Composite: The axial position of the rotor relative to two proximity probes after
compensation for the effect of rotor radial movement. Composite is
calculated by the monitor using the Direct proportional value of the two
individual proximity probe channels. Composite is returned on both
channels of the channel pair in units of millimetres or inches.
2 General Information 3500/45 Operation and Maintenance
12
Direct: The axial position of the rotor relative to only one proximity probe. The
Direct proportional value is not compensated for the effect of rotor radial
movement. On the "flat" channel of a Standard Single Ramp Differential
Expansion channel pair the Direct value is actually radial movement
translated into an apparent axial position measurement.
Gap: The physical distance between the face of the proximity probe tip and
the observed surface. Gap is measured in volt units

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Standard Single Ramp
One proximity probe observes a ramp and the other observes the shaft. The probes
are mounted on the same side of the rotor and in the same axial plane