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The 330851-02-000-080-10-00-003300 XL 25 mm Transducer System consists of a separate 25 mm probe, an extension cable, and a 3300 XL 25 mm Proximitor Sensor. The 0.787 V/mm (20 mV/mil) output gives this system a linear range of 12.7 mm (500 mils). Based on this linear range, the 330851-02-000-080-10-00-00 3300 XL 25 mm Transducer System is suitable for measuring differential expansion (DE) on mid-size to large steam turbine generators caused by the difference in growth
rates between the turbine rotor and the machine stator
(casing).
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Measuring Differential Expansion (DE)
The Differential Expansion measurement is made by two
proximity transducers observing a collar or ramp some
distance from the thrust bearing. Typical transducer mounting
arrangements are:
-Two transducers observing the same side of a collar.
-Two complementary input transducers observing opposite sides of a collar, effectively doubling the measurable DE range.
Two transducers with at least one transducer viewing a ramp on a rotor and the second transducer viewing either a separate ramp or a different location on the rotor to compensate for radial movement. This arrangement adds some error to the measurement, but can measure a longer total DE distance than the complementary measurement.
The criteria for selecting a mounting method are the size of the available target, the expected amount of rotor axial movement and the type of DE target that exists in the machine (collar versus ramp). If sufficient collar height is available, two transducers observing the same side of a collar is the preferred configuration. These two transducers provide redundant measurements.
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