Specifications

METTLER TOLEDO Weigh Module Systems Handbook
(12/99)12-2
Calibration with Test
Weights and Material
Substitution
For large tank scales, it is often physically impossible to hang test weights equal to the
tank’s full capacity. In those cases, you can use a combination of test weights and a
material (such as water) to calibrate the scale.
1. For example, after taking a zero reading you might hang 500 lb of test weights and
take a reading.
2. Then remove the test weights and add water to the tank until the weight reading is
the same as that obtained with the test weights.
3. With the water still in the tank, hang the same test weights and take a second
reading.
4. Continue substituting water for the test weights and taking readings until you reach
the tank’s full capacity.
5. Once you have taken readings from zero to full capacity, use them to plot a graph
of the scale’s performance.
Calibration with
Material Transfer
When test weights cannot be used, you can calibrate a scale with material transfer.
Instead of hanging test weights, weigh a material (such as water) on another scale and
transfer it to the tank scale that is being calibrated. You can do this in a single transfer or
in stages until you reach the tank’s full capacity. This method yields only a rough
indication of the scale’s performance. It depends on the accuracy of the existing scale
and the integrity of the transfer process. Even in the best conditions, you will not know if
allowable errors are cumulative or compensating.
Electronic Calibration
When using the electronic calibration method, replace the load cell cables with leads
from a load cell simulator. The simulator sends out a signal equal to the signal the load
cells should produce. Electronic calibration is noted for its speed and simplicity;
however, it calibrates only the electronics. Because it assumes that the tank and all
mechanical connections are working properly, electronic calibration does not verify the
scale’s performance.
1. With the simulator adjusted to zero output, set the indicator to zero.
2. Adjust the simulator to full output (a signal equal to that which all the load cells
should produce at their rated capacity).
3. Adjust the indicator to show the total capacity of all load cells in the system.
4. Attach the load cell input to the indicator.
5. Set the indicator to read zero for the empty weight of the tank.