Specifications

Chapter 12: Calibration
Calibration with Test Weights
(12/99) 12-1
12
Calibration
When a weigh module system is installed, it must be calibrated so that the readings on
the indicator accurately reflect the amount of weight placed on the scale. METTLER
TOLEDO recommends calibrating a scale using test weights equal to the scale’s full
capacity. Specific instructions for calibration can be found in the technical manual for
the digital indicator that will be used with the weigh modules.
The design or size of a tank scale might make it impossible to hang test weights equal
to the scale’s full capacity. For those applications, there are several other calibration
options: calibration with test weights and material substitution, calibration with material
transfer, and electronic calibration.
WARNING
PERMIT ONLY QUALIFIED PERSONNEL TO SERVICE THIS
EQUIPMENT. EXERCISE CARE WHEN MAKING CHECKS,
TESTS, AND ADJUSTMENTS THAT MUST BE MADE WITH
POWER ON. FAILING TO OBSERVE THESE PRECAUTIONS
CAN RESULT IN BODILY HARM.
Calibration with Test
Weights
The most accurate, reliable way to calibrate a scale is with test weights. For this
calibration procedure, a tank scale needs to be equipped with some type of mounting
lugs for hanging test weights (see Figure 5-7).
1. Begin by taking a weight reading for the empty tank. Adjust the indicator so that it
reads zero when the tank is empty.
2. Check each load cell to make sure it is working properly. Hang a test weight near
one weigh module and take a reading. Move the test weight to a second weigh
module and take a reading. Repeat for each weigh module to make sure that all
load cells indicate the same weight.
3. Add test weights to the scale, taking a reading for each new weight that is added up
to the full capacity of the scale. At the very least, you should take weight readings at
one quarter of capacity, one half of capacity, three quarters of capacity, and full
capacity.
4. If the tank scale will be used to weigh its contents as they are being discharged,
you should also take weight readings as you remove the test weights.
5. Use the readings to plot a graph of the scale’s performance from zero to full
capacity (and from full capacity back to zero if those readings were taken).