Meggitt vibro-meter VM600 - Shaft Collar Method

HARDWARE MANUAL Document reference MAMPS-HW/E
VM600 machinery protection system (MPS) Edition 18 - March 2022
7-16
Shaft relative expansion
PROCESSING MODES AND APPLICATIONS
7.9.1 Shaft collar method
(1) Description
Two probes are used in this configuration, with one probe placed on each side of a shaft collar
(see Figure 7-11). Two possibilities exist:
• Both probes are operating in their measuring range at the same time.
• The probes are operating alternately, with only one probe in its measuring range at a
given time. This doubles the measuring range that is possible with a single probe.
a. When both probes are in their operating range at the same time:
If GAP1
i
and GAP2
i
are the respective initial gaps, then:
ΔL = (GAP1 − GAP2) / 2 − (GAP1
i
− GAP2
i
)/2
If initial gaps are equal, the differential expansion is:
ΔL = (GAP1 − GAP2) / 2
b. When the probes are operating alternately:
ΔL = (GAP1
− GAP1
i
) in the operating range of probe 1.
ΔL = (GAP2
i
− GAP2) in the operating range of probe 2.
Figure 7-11: Two proximity probes mounted near a shaft fitted with a collar