Cleveland Motion Controls ULTRA ISC SERIES SLIM CELL TRANSDUCER REV AA - Manual (Page 41)

MAN-70434-0 R EV AA U LTRA ISC S ERIES S LIM C ELL T RANSDUCER
5.1 T RANSDUCER B ENCH T ESTING
Because the strain gage signal conditioning is completely internal to the transducer, it is impractical
to directly measure the resistance of the stain gage elements. This complicates the task of bench
testing.
However, there are measurable indications of the potential functionality.
1. Measure the DC load current powering the ISC. An in-line Digital Multi-meter (DMM) set up
to measure DC milliamps can be used. With a 24 VDC supply applied, the current into PIN 1
of the M12 connector should be between 25 and 45 milliamps. If no discernable current is
observed, check the applied polarity (the voltage to the ISC could be reverse, and the internal
polarity protection diode could be blocking current flow). Also check that the DMM is set for
DC and not AC milliamps.
2. If the current is reasonable, check the transducer output voltage for zero. Set the DMM back
to measuring voltage and amplified output voltage at PIN 2 with respect to PIN 4. With no
force being applied to the transducer, the voltage should be within part of a volt of ground.
For an un-mounted cartridge style transducer, the ideal “no force” condition can be
accomplished by orienting the loadcell so that the roll journal bore faces “skyward”. If the
transducer is still machine mounted, and there is a roll mounted, the dead-weight of the roll
can be negated by slightly loosening the mounting to allow the loadcell body to be rotated so
that the axis of loadcell force sensing is parallel to the ground. With heavy rolls, exercise care
before loosening any mounting so that an unsafe condition does not result.
3. If the transducer is of limited M.W.F. , it should be possible to apply forces by hand and
observe ( in a qualitative way ) the amplified output swing to different positive and negative
voltages.
If the transducer has a high M.W.F. capacity, the full amount of force may not by readily
applied “by hand”, and the following approach can be used to observe the capability of the
analog output stage.
It is generally not advisable to needlessly alter the factory calibration of the loadcell, but if
necessary, the ZERO potentiometer setting can be used as a way to temporarily drive the
transducer output to arbitrary positive and negative voltages to prove that the output stage of
the transducer is operational.
After changing the ZERO potentiometer, return it to the desired output voltage with no force
applied.
4. Because the ISC is a true analog design, there is no “quantization” of the analog signal and
the output has (theoretically) infinite resolution. It is therefore possible that high MWF
transducers can be checked with a DMM set to the millivolt scale and series of relatively
small test forces applied with either masses or a hardware store variety “fish scale”. For
example, a 1000 lb transducer should have a calibrated slope of 1.6 oz / mV. With just a
handful of appropriately weighted items (quantified using a shipping scale) it is possible to
conduct a crude test of a transducer to verify that it exhibits an essentially rational transfer
function.
5. Using a DMM set to measure high resistances, test between the M12-3 and M12-4 pins to
verify that the 24 VDC supply is galvanically isolated from the analog signal conditioning
stage as evidenced by a resistance above 20 Mohm.
6. As a final electrical test, a DMM should be used to check the resistance between each of the
M12 connector pins and the metallic case of the transducer. No pins should have less than 20
meg-Ohm (this is a typical measurement limit of most Multimeters). DO NOT use a high
voltage insulation tester (i.e. “megger”) to test for the high resistance, as this can cause
damage to the internal circuitry. Exercise care that ungloved fingers do not simultaneously
contact the two meter probes, or the resistance measurement will be falsely low due to the
conductance of human skin.
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