Cleveland Motion Controls ULTRA ISC CARTRIDGE TRANSDUCER REV AA - Manual (Page 39)

MAN-70430-0 R EV AA U LTRA S ERIES S TATIONARY S HAFT T RANSDUCER T ECHNICAL M ANUAL
5.1 Transducer Bench Testing
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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