Page 167 - Intro Predictive Maintenance

158 An Introduction to Predictive Maintenance

Figure 7–26 Permanent mounts provide best repeatability.

transducers, which is illustrated in Figure 7–26. This method guarantees accuracy and
repeatability of acquired data, but it also increases the initial program cost. The
average cost of installing a general-purpose accelerometer is about $300 per mea-
surement point or $3,000 for a typical machine-train.

Quick Disconnect
To eliminate the capital cost associated with permanently mounting transducers, a
well-designed quick-disconnect mounting can be used instead. With this technique, a
quick-disconnect stud with an average cost of less than $5 is permanently mounted at
each measurement point. A mating sleeve built into the transducer is used to connect
with the stud. A well-designed quick-disconnect mounting technique provides almost
the same accuracy and repeatability as the permanent mounting technique, but at a
much lower cost.

Magnets
For general-purpose use below 1,000Hz, a transducer can be attached to a machine
by a magnetic base. Even though the resonant frequency of the transducer/magnet
assembly may distort the data, this technique can be used with some success. Because
the magnet can be placed anywhere on the machine, however, it is difficult to guar-
antee that the exact location and orientation is maintained with each measurement.
Figure 7–27 shows common magnetic mounts for transducers.

Handheld
Another method used by some plants to acquire data is handheld transducers.
This approach is not recommended if it is possible to use any other method. Hand-
held transducers do not provide the accuracy and repeatability required to gain