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Magtrol Hysteresis Dynamometers
4.1.6
f
riCTion
Friction of the shaft bearings is a measurable load, but some friction can exist in the carrier bearing.
When correctly loaded and lubricated, the friction is insignificant. The value may be quantitatively
established by the following procedure.
1. Remove all attachments to the dynamometer shaft.
2. Advance the torque control slightly, to obtain a small torque load.
3. Apply a small amount of torque (by hand) in one direction of rotation.
4. Carefully release the shaft, allow several seconds, and record the torque reading, if any.
5. Then, carefully re-apply torque in the opposite direction.
6. Slowly release the shaft as above, and compare the two readings.
The difference should be less than 1% of full scale. During actual motor testing there is usually
enough system vibration to "settle" negating frictional effects. If excessive drag is present, mechanical
realignment may be required, dependent upon dynamometer size. Certain mechanical factors need
to be determined before corrective action proceeds. Please contact Magtrol Technical Assistance.
4.1.7
V
iBraTion
All rotating dynamometer assemblies are precision balanced, however, the dynamometer shaft is
cantilevered. This may cause vulnerability to radial forces.
At high speeds, some vibration and noise are inevitable but not necessarily harmful. However,
excessive resonant vibrations, caused by bent shafts, poor alignment and out of balance couplings
will produce excessive data errors and are a safety hazard.
WARNING!
S H A F T C O U P L I N G S O P E R AT I N G AT S P E E D S
ABOVE THEIR DESIGN LIMITS ARE EXTREMELY
HAZARDOUS. MANY COUPLINGS CONTAIN SOMEWHAT
LOOSELY SUPPORTED FLEXURE ELEMENTS. WHEN
OVERDRIVEN, EXCESSIVE CENTRIFUGAL FORCE
MAY DISPLACE THEM OUT OF AXIAL ALIGNMENT.
AS THIS HAPPENS, THEY IMMEDIATELY BEGIN TO
ABSORB ENERGY RESULTING IN SEVERE VIBRATION
AND DESTRUCTION OF THE COUPLING.
49
Chapter 4 – Testing
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