Rice Lake Weigh Modules/Mount Assemblies - Manual (Page 75)

INSTALLATION & SERVICE TIPS
4-12
System Calibration
There are various methods available to calibrate a system. This
section outlines some of the more common. However, the following
recommendations apply regardless of the method adopted.
■ If the scale is to be used in legal-for-trade weighing, check with
the state or local Weights and Measures authority for specific
requirements in your locality.
■ The weight indicator should be switched on for 20 to 30
minutes (or as recommended by the manufacturer) before
beginning calibration.
■ The weighing system should be exercised several times by the
application and removal of weight before beginning calibra-
tion. This ensures that everything is seated properly in place.
■ While exercising the weighing system, check the return to
zero each time the scale is unloaded. Be certain to turn off any
Auto Zero function the indicator may have. If return to zero is
poor, check for mechanical binding before proceeding.
■ For best accuracy, use a weight of 80 to 100% of scale capacity
for calibration.
Calibration Using Certified Test Weights
This method will yield the most accurate results—however, it can
be difficult to place test weights in or on the vessel and attain
accurate readings. These difficulties have been overcome in some
installations by providing a means of hanging test weights from the
vessel by chains.
1. Remove all weights from the vessel.
2. Zero the indicator (follow the manufacturer’s instructions).
3. Place test weights on the vessel equal to 80 to 100% of scale
capacity, evenly distributed.
4. Adjust the indicator until it reads the weight applied to the
vessel.
5. Remove the test weights, check the return to zero, adjust if
necessary.
6. Reapply the weights once more to verify the calibration.
NOTE: This method cannot be used with vessels partially mounted
on flexures, since the weights cannot be placed accurately at the
center of gravity of the contents.
Calibration Using Weighed Material
This method uses a known weight of material (often water or sand)
as a test weight. This material is often loaded on a truck of known
tare weight, weighed on a truck scale, and transported to the job
site. It is important that material is not lost or altered in transit. Use
the same calibration procedure as described under Calibration
Using Certified Test Weights where the weighed material is used in
place of the certified test weights.
Calibration Using Material Substitution
Method
This method is used to accurately calibrate high-capacity scales
when a limited amount of certified test weights is available. It allows
you to substitute the known weight of material in a stepped fashion.
1. Remove all weight from the vessel.
2. Zero the digital weight indicator.
3. Place test weights on the vessel equal to at least 5% of scale
capacity.
4. Adjust the indicator until it reads the weight applied to the
vessel.
5. Remove the test weights and replace with material until the
indicator accurately displays the weight of the certified test
weights.
6. Again place the test weights on the vessel with the material.
Record the indicator reading of the total weight of material and
test weights.
7. Remove the test weights and replace with additional material
until the indicator reads the total recorded weight.
8. Again place the test weights on the loaded vessel. Record the
indicator reading.
9. Repeat this process until the applied weight (certified test
weights and added material) is between 80 to 100% of total
scale capacity.
10. The weight now applied to the scale is the weight of certified
weights plus material multiple. (For example, if the certified
weights total 5000 lb and 8 material substitutions were made,
then the total weight on the scale is now = 5000 + (8 x 5000)
= 45,000 lb)
NOTE: This method cannot be used with vessels partially mounted
on flexures.
Calibration Guidelines for Vessel Weighing Systems