Calibration of a Truck Scale

Now that you’ve bought a truck scale, completed the foundation, have the scale installed, what’s next?  Before your truck scale can be used for obtaining weight measurements, it must first be calibrated to your digital weight indicator and approved by your state. Your local scale service company will take care of this by bringing their test truck to the scale test site. The test truck holds certified calibrated test weights that are placed on the scale platform for testing and calibration. The test weights, usually in 1000 to 2500 pound blocks, are moved using either a hoist mounted on the back of the test truck or using a mobile test cart. Mobile carts are the preferred method. During testing, the individual load cells are adjusted and the scale sections are adjusted. A section is comprised of a pair of load cells on opposite sides of the platform. The test weights or test cart is placed over the section and a weight reading taken. This process is repeated for all of the scale sections and adjustments are made so that the weight indicator shows the same weight regardless of where the load is placed on the scale platform. (Also please note similar versions of these scale service tests are recommended periodically once your scale is in operation.)

Once the scale sections have been correctly adjusted, the final step in the calibration process is the span setting. Here the weight display is adjusted to read the exact value of the test load applied to it. Additional testing takes place by checking the weight display with increasing and decreasing loads to make certain the scale is linear. After successful completion of the calibration process, the scale service technician will apply security seals to all of the adjustment access points to prevent further adjustment. In the US, the scale will be tested to NIST Handbook 44 Class IIIL tolerances.

After the truck scale has been calibrated & sealed by the scale company, it will normally be tested in the presence of a state or local weights and measures inspector who will verify its proper operation and in-tolerance readings. In some states, the local scale service technician is licensed by the state to perform this function. In either case, once the scale has been officially tested and a report completed, a sticker will be placed on the digital weight indicator attesting to that fact and a copy of the test report sent to the state department of weights and measures for filing. You, as the scale owner, should also receive a copy of this test report for your records.