Page 265 - Intro Predictive Maintenance

11

ULTRASONICS

This predictive maintenance technique uses principles similar to vibration analysis.
Both monitor the noise generated by plant machinery or systems to determine their
actual operating condition. Unlike vibration monitoring, however, ultrasonics moni-
tors the higher frequencies (i.e., ultrasound) produced by unique dynamics in process
systems or machines. The normal monitoring range for vibration analysis is from less
than 1Hz to 30,000Hz. Ultrasonics techniques monitor the frequency range between
20,000Hz and 100kHz.

11.1 ULTRASONIC APPLICATIONS
As part of a predictive maintenance program, ultrasonic instruments are used for
three primary applications: airborne noise analysis, leak detection, or material
testing.

11.1.1 Airborne Noise Analysis
All plants are required by Occupational Safety and Health Administration (OSHA)
regulations to meet ambient noise levels throughout their facilities. These mandates
have forced these plants to routinely monitor the noise levels within each area of the
plant and to provide hearing protection in those areas where the ambient noise level
is above acceptable levels.

Ultrasonic meters are the primary tool used to monitor the ambient noise levels
and to ensure compliance with OSHA regulations. In addition, some plants use
simple ultrasonic meters to survey noncritical plant equipment and systems for
unusual noise emissions. This latter application is limited to a simple “go/no-go” mea-
surement and has practically no ability to diagnose the root-cause of the abnormal
noise.

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