Technical data are subject to change without notice.
© Copyright SPM 2002-04. 71650.B
SPM Instrument AB • Box 504 • S-645 25 Strängnäs • Sweden
Tel +46 152 225 00 • Fax +46 152 15075 • info@spminstrument.se • www.spminstrument.se
Excessive
play
Gear tooth
damage
Cavitation
Play,
scraping
Identify the shock pulse source
Shock pulses are strongest close to the source. They spread through the material of all machine
parts, but are damped (loss of signal) with distance and when passing through interfaces in the
material.
• Measure with the probe transducer on and near the bearing housing to find the strongest
shock pulse source.
• Listen for unusual noises.
Sources of interference
Any kind of metallic clatter, scraping or hard impacts produces shock pulses which may interfere
with the measurement on the bearings. Some of the more common sources of interference are:
• Shocks between poorly fastened machine feet and foundation.
• Rubbing between shafts and other machine parts.
• Loose parts striking the machine frame or the bearing housing.
• Excessive play and misalignment of couplings.
• Vibration in connection with loose parts and excessive bearing play (vibration alone does not
affect the reading).
• Cavitation in pumps.
• Gear tooth damage.
• Load and pressure shocks arising during the normal operation of certain machines.
Evaluation of SPM measurements 33
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