8
Fatigue
: repeated cycles of stress on a component. If you bend a part
back and forth enough times it will fatigue. As a general rule, fatigue
failures result from vibration frequencies 10 ‑2000 Hz and Velocity
measurements are used. Velocity will be the primary measurement taken.
Force:
mass x acceleration. Measured in Acceleration. Acceleration is
the rate of change of velocity. Acceleration is used for high frequencies
above 2000 Hz (120,000 RPM). Bearing defects and gear mesh
frequencies are usually found in this range.
Impact Forces
: the result of fatigue. Impact forces are cyclical events
which can be detected with Acceleration Enveloping. These are high
frequency‑low amplitude events and a filter in the EXAMINER 1000 is
set at 10-30 kHz to measure them.
7.3 Selecting Measurement Intervals
Measurement intervals are set based on the classification of the
machine, its repair history, and the amount of data required for a
detailed trend analysis. At the beginning of a Predictive Maintenance
Program, collect data frequently to build a rapid history of each
machine. Adjust your program as you go.
If measurement results are
indicating signs of change, measurements should be performed more
frequently.
8.0 TYPES OF MEASUREMENTS IN THE EXAMINER 1000
Velocity
— good for frequency ranges 10‑2000 Hz (600‑120,000 RPM)
Acceleration
— used for higher frequencies or speeds above 2000 Hz
(120,000 CPM)
Acceleration Enveloping
— uses a high pass filter to measure high‑
frequency, repetitive bearing and gear mesh vibration signals; used for
early detection of developing bearing or lubrication problems. Use this
type in combination with the other types to detect changes in machinery.
