4-WIRE LOAD CELLS TRIMMING
The figure below shows a diagram of three excitation trimmed load cells.
A temperature-independent variable resistor or potentio-meter of typically 20
n
is
inserted in the + excitation lead of each load cell..
__ ...,....,..... ____ ..... ______ ....,.._
,
,.
Exc tal D
""-!I!-------+--------• Outp t
--------------------
..
011.1tpu
There are two methods of trimming with excitation. The first method is to adjust the
potentiometers by trial and error whilst moving calibration weights around from corner to
corner. AII potentiometers should be adjusted to have the maximum sensitivity for each
cell by completely turning clockwise all them.
Then once the lowest output corner is located, the other cell are trimmed down to match
this lowest output.
This method may be very time consuming, particularly for high capacity scales, or vessel
scales where the use of test weigths at the corners is not practical. In these cases the
second and best method is "pretrimming" the potentiometers with the use of a sensitive
voltmeter (at least 4 1/2 digit). The following procedure can be used:
1) Determine the exact mVN rating of each load cell, which can be found on the load
cell's calibration certificate.
2) Determine the exact excitation voltage supplied by the signal conditioning
device/measurer (Z-SG for example) by measuring this voltage with the voltmeter (for
example 10.05 V)
3) Multiply the lowest mVN-value (step 1) by the excitation voltage (step 2).
4) Divide the trimming-factor found in step 3 by the mVN-value for the remaining load
cells.
5) Measure and adjust the excitation voltage of the three remaining load cells with each
respective potentiometer. Verify the results and make the final adjustment while moving
a testload corner to corner.
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ENGLISH - 5/7
MI00155-3-EN
Summary of Contents for SG-EQ4
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