Cleveland Motion Controls ULTRA ISC SERIES SLIM CELL TRANSDUCER REV AA - Manual (Page 36)

U LTRA ISC S ERIES S LIM C ELL T RANSDUCER MAN-70434-0 R EV AA
Examples of Force Loss due to Friction at Driven Roll
In this example, only a fraction of the test force is
transferred to the transducer due to drag from the
driven roll. In this example, by rearranging the anchor point
and the force location as well as utilizing the idle
roll, the frictional losses are minimized.
4.13 C ALIBRATION A CCURACY C ONSIDERATIONS
The application of an accurate calibration force requires careful attention to minimizing the non-
ideal effects of the real world. Keep the following points in mind:
When conducting a calibration that involves a large mass, it is often practical to use a series of smaller masses
added in succession. Consider performing an initial Zero and Gain adjustment when the first 20% of the
weights have been applied. By performing the calibration using this method, the Zero and Gain adjustments
can be made approximately correct earlier in the calibration effort (before many weights have been handled).
When the full calibration load is applied, there is a better chance that only minor adjustments will be needed.
 Allow the transducer and amplifier to reach thermal equilibrium before conducting
calibration. Ideally, the temperature should reflect the expected operating conditions.
 The test force should be a moderate percentage of the intended working force of the
transducer and never over the 100% Maximum Working Force (MWF) or, you risk
calibrating with an overloaded (“clipped”) transducer signal.
 Cycle the load on the transducer a number of times with the test force to pre-condition or
“set” the transducer prior to calibration. Repeat this procedure again before calibrating if
the transducer has been disturbed (i.e. roll remounted or any mounting bolts re-torqued).
 With very low force transducers consider that connecting a test mass involves some finite
cord mass.
 When two transducers support a roll, calibrate with the cord in the exact center of the roll.
 Passing a cord over a roll on its way to the transducer inevitably causes some amount of
friction. The worst case scenario involves passing the working part of a cord over a roll
that doesn’t readily freewheel. A test was conducted to determine the loss on a stationary
4” diameter anodized roll with a 90 degree wrap angle. It exhibited a 25 to 30% loss in
force due to friction!
 When all else is done correctly, the largest remaining contributor to error is friction. If
friction cannot be reduced, consider determining the magnitude of the friction through
measurement and then making first order corrections numerically.
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