Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/772143
34 AGGREGATES MANAGER / January 2017 EQUIPMENT MANAGEMENT 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, causing big trouble sooner or later. Corrosion of the shield limits the cable's effectiveness in blocking elec- tromagnetic 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 fl exible conduit downward to create a drip loop at the location just before it enters the cell. Bumper bolts Although there are truck scale designs that eliminate the need for bumper bolts, many manufacturers still require them. Frequent inspection is required on these models. 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 contrac- tion 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 damag- ing 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. Junction box Moisture caused from internal conden- sation is the most common problem for junction boxes. This occurs from normal air exchanges from heating and cooling cycles, and 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 junction box with a fi berglass-reinforced polyester (FRP) en- closure. A desiccant bag in the enclosure will help control moisture. Grounding Scale manufacturers suggest a vari- ety of grounding procedures including single-point grounding, AC transient protection, DC transient protection, deter- mining AC ground, and transient bypass cables. 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. 1. Verify the ground system of the AC power supply. Using a multi-meter, check the resistance of the AC outlet ground to the actual AC power ground Keep the scale foundation clean and well drained. Approaches to and from the scale should be level. Remove any debris around load cells and the surrounding area. Be sure to check cables for signs of damage.