Off-Center Load Compensation - HBM VKIA405 Montageanleitung

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Off-center load compensation

With weighing machines, mechanical imbalance may lead to off-center load
errors. According to the EN 45501 3.6.2 standard for non-automatic weighing
machines, specific values are to be maintained for eccentric loading. The
digital amplifiers provide an easy way to compensate for these errors
electrically. A binary-stepped network of 4 resistors is available for each load
cell, that is shorted at the factory via 0 ohm resistors (see Fig. 6.1). Opening
the vertical 0 ohm resistors activates the relevant resistances and thus
reduces the load cell signal.
Input: Load cells 1 4
0.39 Ω
0.82 Ω
1.50 Ω
3.00 Ω
Fig. 6.1: Resistor network for off-center load compensation of 4 load cells
Practical example using a platform with 4 load cells:
• When the four corners of the platform are loaded, note the scale signals in
order to assess the respective differences (in kg) to the corner of the scale
(load cell) with the lowest indication. This load cell is the reference load cell (4)
and does not need adjustment (in the example in Fig. 7.1, load cell 4).
• The chart (Fig. 7.2) is graduated in 7 test load ranges. Select the test loads
used (12.5 kg in the example) in the relevant line. Starting from the calculated
off-center load error difference on the X-axis, look for the intersection with the
test load and then, on the Y-axis, read off the resistance and the most suitable
combination. The resistance values here apply for 350 ohm load cells (see the
table in the lid of the VKIA405).
In our example, load cell 3 has an off-center load error of 80 kg, which
produces an adjustment resistance of 1.5 + 0.82 ohms (shown in Fig. 7.1).
HBM
4 3
0.39 Ω 0.39 Ω
0.82 Ω 0.82 Ω
1.50 Ω 1.50 Ω
3.00 Ω 3.00 Ω
Output: Amplifier
Sense (+)
Excitation (+)
2 1
Excitation (−)
Sense (−)
0.39 Ω
0.82 Ω
1.50 Ω
3.00 Ω
Signal (−)
Signal (+)
VKIA405
A2448-1.1 en/de/fr