Keep the Cash Register Ka-Ching-ing
Bumper bolts minimize the momentum of the weighbridge as vehicles move on and off the scale. They are normally positioned at the ends of the weighbridge and are designed to bump the plates embedded in the end wall during scale movement. Bumper bolts need to be fastened in place and maintain clearance whether the scale is empty or loaded. Bolts should be adjusted with approximately 1/4-inch to 3/8-inch clearance from the end wall plates.
Seasonal weather changes can cause thermal expansion and contraction of steel and concrete in the bridge, resulting in potential binds. Bumper bolts that are too tight against the stops can result in errors that may go unnoticed for extended periods. Bumper bolts that are too loose can result in potentially damaging side loads to the load cells, or even, in some cases, a sudden collapse of the bridge structure. A bridge that does not swing freely or is noisy as vehicles enter and exit may require immediate attention from your scale service provider.
7. Grounding. To avoid the existence of multiple zero references that may create havoc with data lines and invite lightning damage, a single-point grounding system is recommended (see Grounding 101). Over time, this has proven to be a dependable means of lightning and transient protection for electronic scale systems.
Once the single-point grounding system is established, check the AC power supplied to other peripherals such as remote displays, printers, and computers. A remote device may not have the same AC power source as the digital instrument; therefore, each device may not be grounded to the same point. Again transient protection devices should be grounded to the same wire as the peripherals they are protecting. Measure the resistance between the AC-power ground points. The volt meter should read less than 1 ohm.
A copper transient bypass cable should be connected between modules and across each load cell mount to ensure transients pass through it instead of the load cells.
With proper maintenance and grounding, aggregate producers can extend the life of their truck scales and keep their operations’ “cash register” ka-ching-ing.
Checking a single-point ground involves two steps. First, verify the ground system of the AC power supply. Using a digital volt meter, check the resistance of the AC outlet ground to the actual ground rod of the AC power coming into the building. It should read less than 1 ohm. Then, measure the AC voltage across the ground and neutral of the AC outlet. The result should be 0 volts AC, not to exceed 0.5 volts AC. If you discover grounding issues with the AC power supply, notify the building owner or the power company.
Next, check the scale weighbridge grounding. Before this is done, make sure all peripherals are plugged into some type of transient protection device such as an uninterruptible power supply. Electronic scales are easily disturbed by any number of voltage distortions, so installation of power conditioning equipment is the best first line of defense.