Cleveland Motion Controls ULTRA ISC SERIES SLIM CELL TRANSDUCER REV AA - Manual (Page 37)

MAN-70434-0 R EV AA U LTRA ISC S ERIES S LIM C ELL T RANSDUCER
 Always apply and remove the test load in a continuously increasing or decreasing
manner, so that the force changes are monotonic. This helps to avoid disturbing any
hysteresis component of the transducers force signal.
 When calibrating for a particularly wide roll that will always have a narrower product
tracking to one side, consider applying the calibration force at the roll position that
represents the center of the product. This will automatically cancel some of the affects of
transducer gain imbalance without the need to actually re-balance the transducers gains
within the amplifier.
 It is a good practice to verify linear operation of the transducer and amplifier by applying
a final test force that falls somewhere between the zero and full-scale endpoints. The
intent is not to conduct calibration, but to confirm the hardware’s ability to accurately
report a measured force.
4.14 F INAL C ALIBRATION
Even though the ISC transducer is factory calibrated, calibration is still usually required to
accommodate application variables such as wrap angle and transducer orientation. The customer
then accesses these software parameters using an HMI, keypad, or other device. The transducer is
still calibrated using weights as is done currently.
Final calibration is usually required to take in to account particular application circumstances of
roll weight, wrap angle and loadcell orientation. The final zero and span calibration is most easily
accomplished by numerical scaling within the digital processor of the tension controller. Because
each ISC equipped tension transducer has been factory adjusted for uniform transfer function,
loadcell inter-changeability when calibrated this way is readily promoted.
Field calibration still consists of applying known force conditions in the web, but instead of
adjusting a potentiometer, the observed loadcell offset is determined at the controller and then
numerically subtracted from the reported loadcell signal.
In the case of Span calibration, a known web force (equal to a moderate portion of the expected
operational force) is applied using test cords routed through the expected web path past the
transducer pair. An appropriate numerical scaling factor is then determined and used as a scaling
factor within the tension controller.
Hint
An interesting approach to slightly attenuating the loadcell output by purely mechanical means can
be used with those loadcell styles which accommodate slight rotation relative to the bisector of the
wrap angle (i.e. Cartridge transducers and Slim Cells).
Consider taking advantage of the Cosine relationship (noting that a 10 degree mechanical shift
will reduce the output span by 1.5%). The deflection of CMC’s strain gage based loadcell is
sufficiently small that tracking will not usually be adversely affected.
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