4. Checking Devices: Some vehicle scales use suspension systems that don’t require checking devices. If your scale has checking devices, make sure they are working properly. Inspect check rods to make sure the attachment points are solid. Check for binding. If there is a problem, weight readings will be inconsistent from section to section. Inspect hardware to ensure jam nuts are tight, rods are level and free of foreign material, and washers are not rusted or distorted. Even if they are working properly, replace corroded hardware components so they don’t fail in the future.
Unlike check rod binding, bumper bolt displacement is easy to spot. Bumper bolts need to be tight so they don’t move on their own, yet maintain clearance when the scale is both empty and loaded. Seasonal temperature and weather changes can cause concrete and steel to expand, and bumper bolts can bind tight against the contact area. If binding occurs, adjust bumper bolts to maintain the proper amount of clearance for all conditions.
5. Load Cells: Examine load cells and the area surrounding them. The load cell area may contain dirt and debris that has built up since the scale’s last inspection. Load cells must have clearance to deflect through their capacity range. The same debris that can bind the scale deck can also keep the load cells and suspension components from moving freely.
Inspect load cell cables for damage. If damage is present, the seal is probably degraded as well. To combat this problem, some manufacturers offer rigid or flexible metal conduit to run the cable through, providing a layer of protection that’s nearly impervious to damage from rodents. Even though steel over braid cable provides more protection from damage than cable sheathed with polyurethane or plastic, they still need to be checked.
Weather is another enemy of load cell cables. When exposed to moisture, cables can become wicks. Water can be sucked through the cable’s length by capillary action until it enters the load cell or junction box. Once inside, it can damage components and seep into the inner layer of the cable. Wet cables may not cause signal distortion immediately, but they may slowly corrode the copper wires or shield beneath the insulation, eventually causing significant problems.
Corrosion of the shield limits the cable’s effectiveness in blocking electromagnetic interference (EMI) and radio frequency interference (RFI). Corrosion of individual wires will degrade the signal. If you discover a wet home run cable or load cell, replace it. To help prevent moisture from entering the cell from the cable, bend the cable or flexible conduit downward to create a drip loop at the location just before it enters the cell.
6. Junction Box: Check the junction box (j-box) for internal condensation; this is the most common moisture problem. It occurs from normal air exchanges from heating and cooling cycles, and from over-aggressive washing that damages sealing components that haven’t been properly maintained. If left unchecked, wiring terminals and other components in the enclosure will corrode. Due to its material properties, a stainless-steel j-box is more vulnerable to internal condensation. If stainless steel is not required, install a j-box with a fiberglass-reinforced polyester (FRP) enclosure. A desiccant bag in the enclosure will help control moisture.
7. Grounding: Scale manufacturers suggest a variety of grounding procedures. To avoid multiple zero references, which can create havoc with data lines and attract lightning damage, single-point grounding is recommended. Checking a single-point ground involves several steps.
• Verify the ground system of the AC power supply. 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.
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