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© 2022 S. Himmelstein and Company—all rights reserved. www.himmelstein.com
D. Operating &
Safety Considerations
D.1 Applicability
The following paragraphs apply to all MCRT
®
products.
D.2 Allowable Torque Loads
Operate an MCRT® torquemeter within its’ full scale; see
booklet cover for rating of this device.
D.2.1 Overload Considerations
The overload rating of an MCRT
©
Compact Digital Torque-
meter is 2 times full scale. This torquemeters’ overload is
listed on the cover sheet. The torquemeter will not yield
(evidenced by a non-return to zero) or fail if subjected to
an instantaneous peak torque up to its’ overload value.
Both the full scale and overload ratings are based on the
peak stress seen by the transducer. They are independent
of stress duration, except for cyclical (or fatigue) loading
considerations; see ¶D.2.2. Virtually all rotary power
producing and absorbing devices produce pulsating
rather than smooth torque and power.
Thus, in addition to its’ average torque and speed values,
the driveline torque usually includes a fundamental
(driving) frequency and superimposed harmonics.
Torsional vibration magnitudes can be amplified by the
driveline. See Bulletin 705 for further information. The
Figure 6 waveform is typical of what occurs in the real
world.
For these reasons, a conservative design approach
dictates the torquemeters’ overload => twice the probable
peak torque.
Reserve the region between the peak instan-
taneous torque and the torquemeters’ overload rating as
a safety margin for unexpected loads.
Do not knowingly
operate in the overload region. If you expect torques in
the overload region, then change to a torquemeter with a
higher overload rating.
D.2.2 Fatigue Considerations
If the peak torque seen by an MCRT
®
torquemeter is less
than half its overload rating, it can handle full torque
reversals with infinite fatigue life. When peak torques
are cyclical, and exceed 50% of the overload rating, then
fatigue failure can occur.
D.2.3 Starting High Inertias with Electric Motors
When started across the line, during the start, a motors’
developed torque can be several times its’ rated torque.
Thus, a Digital Torquemeter sized to handle the motors’
rated load torque, can be overloaded during starting.
Drivelines are particularly vulnerable when oversized
motors drive light duty, high inertia loads.
Load
J2
Driver
J1
J1 & J2 ARE ROTATING INERTIAS
Torquemeter
To avoid damage when starting high inertia loads, use
a torquemeter
rated for the starting torque
or,
limit the
starting torque to a safe value
. Techniques to limit electric
motor starting torques include:
• Use reduced voltage starting.
• Electronically limit the maximum motor current.
• Add inertia to the input side of the torquemeter.
Before operating,
verify the motor can safely start
the increased load inertia.
• Use “shock absorbing” couplings. Careful coupling
selection and thorough analysis is essential. Under
some conditions, such couplings can aggravate
rather than improve the situation.
Figure 6. Reciprocating Machine Torque Profile.
Figure 7. Motor Start Torque Profile.