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M9344 • REV K
(April 2022) Page
4 of 8
Scaling of the display is on the basis of the range of the transmitter. The measurement pa
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rameter name is “vibration” and the units are “ips” (inches per second) or “mm/s” (millime
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ters per second). The example below is based on a standard 1.0 ips transmitter.
To prevent nuisance alarms, due to transient operating conditions, program an alarm time
delay. Momentary “jolts” that can occur at start-up or during some operating condition
changes, do not reflect a machines steady state operating condition. The indicated vibration
level must cross the threshold level and stay above it for a preset time before any alarm ac
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tion is taken. A 2- to 3-second delay is normally applied to most machinery. Consult Metrix if
you have a question about your machines operating characteristics.
Some rough starting machinery may also need a start-up time lockout for alarms. A start-up
lockout is different than a time delay. Both may be needed.
TYPICAL TRANSMITTER PLACEMENT
The ST5491E measures seismic vibration at the attachment point on the machine. Its
sensitive direction is through its cylindrical body. It will not measure side to side motion. It
measures velocity vibration in ips (inches per second). Velocity vibration is a common mea
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surement for a large variety of machinery.
Figure 1 shows a typical transmitter mounting for casing vibration measurements is in the
horizontal direction at the bearing housings. Usually the horizontal direction is more sensi
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tive because of the way machinery is typically mounted. Figure 2 shows the flying leads be
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ing spliced in the conduit elbow. Please be aware the splice can not be made at this point if
in a hazardous area. In this case, make the splice in a second conduit hub (meeting splicing
requirements) at the end of the flexible conduit.
The standard lead length is 24 inches. We recommend using the “Y” conduit elbow because it
prevents the conduit from extending too far away from the transmitter, limiting the likelihood
of getting snagged while working near the machinery. If a 1 inch to 3/4 inch reducer is used at
the elbow, a smaller diameter flexible conduit can be used. It is always a good idea to limit
the mass that “hangs” on the transmitter. The flexible conduit should make a bend in order to
be sure any rigid conduit motion can not feed into the transmitter body.
Vibration Level
Transmitter Output
PLC (or other) Scale
None
4mA +/-0.1mA
0.00 in/s
1.0 in/s
20mA +/-0.4mA
1.00 in/s