Rice Lake Weigh Modules/Mount Assemblies - Manual (Page 76)

4-13
INSTALLATION & SERVICE TIPS System Calibration
Calibration Using A Load Cell Simulator
This is perhaps the simplest and fastest method of scale calibration,
particularly on large-capacity scales. It is less accurate than the
other methods described. A major disadvantage is that it doesn’t
test the scale mechanically or take into account the influence of
friction, piping, support deflection, etc. However, the method is
sometimes sufficient for process weighing applications that need
not meet legal-for-trade requirements.
To calibrate with a simulator:
1. Disconnect the cable from the junction box at the indicator.
2. Connect a load cell simulator to the indicator. The simulator
should have a vernier for fine adjustments.
3. Set the simulator to 0.0 mV/V and zero the indicator.
4. Set the simulator’s output (in mV/V) to simulate the output of
the load cells at full scale capacity (ignoring dead load for now).
To find the simulated full scale output, use the following
formula:
Total Load Cell mV/V Output = Simulator mV/V Setting
Total Load Cell Capacity
Displayed Weight
For example:
If four 5,000 lb 3 mV/V load cells are used for a 10,000 lb
capacity scale, the simulator setting expected when 10,000 lb
is placed on the scale can be determined by the following:
3.0 mV/V = Simulator mV/V Setting
20,000 lb 10,000 lb
Therefore, the simulator should be set to 1.5 mV/V.
5. Adjust the indicator to display the capacity of the scale (10,000
lb in our example) and set the indicator’s span.
6. Adjust the simulator’s output in steps (1.0 mV/V, 0.5 mV/V,
0.0 mV/V) and verify the indicator’s linearity and return to
zero.
7. Remove the simulator and reconnect the load cells. Recalibrate
the indicator’s zero point to take account of the actual dead
weight of the vessel.
8. The accuracy of this method can be greatly increased by using
a high-resolution 5
1 /
2
digit volt meter to measure the indicator’s
actual excitation voltage and to verify the actual mV output
from the simulator. Those more accurate figures can then be
used in the above procedure.