Maintenance of Truck Scale/Weighbridge(2)
Author:jinmai Time:2017-09-13 10:34:24
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 check. 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 as well.
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, causing big trouble sooner or later. 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.
Check the junction box (j-box) for internal condensation, is the most common moisture problem. 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 j-box with a fiberglass-reinforced polyester (FRP) enclosure. A desiccant bag in the enclosure
will help control moisture.
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
1.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.
2.Install power conditioning. Electronic weighing systems are easily disturbed by any number of voltage distortions,
so installing power conditioning products should be your first line of defense against power problems. A braided transient
bypass cable should be used around load cells and between scale modules.
3.Check the ground again. Connect a bare 10 gauge copper wire to the frame of the scale platform and the grounding lug on the
j-box board. Then run the copper wire back to the ground rod provided by the power company. This wire can be buried in the soil
from the scale to the AC ground.
4.Check the AC power supplied to peripherals, such as remote displays, printers and computers. A remote device may not have
the same AC power source as the indicator; 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
No matter what type of scale you own: pit-type, above ground, side rail or portable vehicle scale, a portion of your preventive
maintenance plan has been dictated by the manufacturer. Many scale understructures are left untreated and vulnerable to
corrosion. Steel deck scales that have welded bottom plate harbor corrosion because water that seeps into the scale
cannot run aground and evaporate. In these cases one can protect the scale components mentioned earlier.
But the best protection of the under-structure comes from the manufacturer. Invest in a scale that does not
include a bottom plate and does include corrosion-resistant undercoating.Depending upon the scale's location,
special features, and the material it is weighing, your scale inspection may or may not require all of the steps mentioned.
But do them anyway. Your truck scale is a big investment, a mighty big ka-ching for any business. Keep 'em smooth.
Keep 'em shiny. Keep your 15-ton "cash register" ringing as long as you can.
If you are interested in our Truck scale, please visit http://www.jmscale.com/products/products_13_1.html