Central Carolina Scale
Truck Scales - Maintenance

Truck Scales - Maintenance

When you need accurate truck weights and unsurpassed durability, it only makes sense to call Central Carolina Scale, Inc.

Truck scales are available in either full-electronic or electromechanical types with either concrete or steel platforms. Low profile units offer simple installation with minimal foundation requirements while pit type installations are often the best choice for use in severe climates or when grain is to be discharged out of the truck onto a conveyor mounted beneath the scale platform. Multiple platform units are used to simultaneously measure the truck's axle weights while obtaining its total weight as well.

Vehicle scales may be equipped with many different options to increase their utility for both operator and driver. Options include traffic lights, truck management software, ticket printers, remote displays, intercom, video surveillance, automated systems, guard rails and so on.

 

Preventive Maintenance is Key To Truck Scale Performance

Installing a scale known for its structural integrity is the first step to ensuring dependable performance, but even a quality scaleís performance can slip if not maintained properly. Developing a thorough preventive maintenance plan can mean the difference between a scale lasting 2 years or a scale lasting 15 years.

Because all scales particularly those installed outdoors are subject to unique circumstances, itís impossible to cover every cause of trouble. However, regular checks similar to those described in the following paragraphs can help ensure a quality truck scale lasts for decades.

Scheduling Maintenance Checks

We suggest checking scales every six months at a minimum. A convenient time to run your PM inspection is during the scaleís regularly scheduled calibration check. Youíll also want to consider the location and circumstances of the application. Itís a good idea to inspect a scale just prior to peak usage times, such as harvest season in agricultural operations. In northern climates, the best time to examine a scale is in the spring after winter snow and ice have taken their toll, and again in the fall to remove dirt, grain and other debris that can hold water and later freeze.

Visual Inspection

The only tool youíll need for much of the inspection is a good pair of eyes. A scale is only as good as its foundation, so that should be the first element you examine. Cracks that lead to movement or settling will cause chronic calibration errors. For the scale to once again read accurately, the foundation will need to be repaired, which may require removing part or all of the foundation and pouring a new one.

Next, take a look at the deck. Rust or crumbling concrete can weaken the scaleís structure and cause problems if not addressed. You may want to clean and paint rusted steel, and repair or replace concrete as needed to maintain the scaleís structural integrity.

After examining the surface, look for debris such as gravel or crumbled concrete caught between the foundation and scale deck. Binding is a common cause of inaccuracies and can result from something as small as a single rock. Installing T-Strip molding between the deck and foundation can help keep debris from getting caught or falling down into the scale. In addition, some manufacturers of above ground scales offer the option of end cleanout plates that can be removed, allowing access to remove material that builds up on the foundationís surface closest to the scaleís end.

Once youíve cleaned out debris, be sure that the clearance between the walls and deck is even and consistent with manufacturersí specifications. Bowing and other irregularities caused by pit wall cracks, frost heaving, or poor concrete work on the deck or wall could result in future binding.

Next, examine the load cells and the area surrounding them. The load cell area may contain a rodent nest, dirt or other debris thatís built up since the scaleís last check. Load cells must have clearance to deflect through their capacity range. The same type of foreign materials that can bind the scale deck can also keep the load cells and suspension components from moving freely.

The performance of a load cell is often dependent on the condition of the attached cable, which should be the next stop on your inspection. Inspect the cable for rodent damage. If rodent damage is present, you can bet the seal is degraded as well. To combat this occurrence, some manufacturers offer rigid or flexible metal conduit to run the cable through, providing a layer of protection thatís nearly impervious to damage from rodents. Steel over braid cable provides more protection from rodent damage than cable sheathed with polyurethane or plastic, but is still vulnerable and will need to be checked more frequently.

Weather is another enemy of load cell cable. A damaged seal around the gland where the cable enters the cell can cause water infiltration. When exposed to moisture, cables can also serve as wicks. Water can move along the cableís length by capillary action until it enters the load cell or junction box. Once inside, it can not only damage these components but seep into the inner layer of the cable. Wet cables may not cause signal distortion immediately, but may slowly corrode the copper wires or shield beneath the insulation, setting the stage for future problems. Corrosion of the shield limits the cableís effectiveness in blocking electromagnetic interference (EMI) and radio frequency interference (RFI), and corrosion of individual wires will degrade the signal. If you discover wet home run cable, the best course of action is replacement. If moisture has infiltrated the insulation of cable running to a load cell, you will likely need a scale technician to replace the load cell. 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.

Now move on to the junction box with summing board, or j-box for short. Internal condensation is the most common moisture problem. This condition occurs from normal air exchanges from heating and cooling cycles, and over-aggressive washing that damages sealing components that havenít 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 promotes internal condensation and are therefore more vulnerable to this problem.

When a stainless j-box is necessary, the first line of defense is to minimize air exchanges by making sure gaskets are sealed tightly. When closing the back on an enclosure, tighten the bolts in an alternating pattern and to the exact torque settings specified. A desiccant bag in the enclosure will also handle some condensation, but must be changed often to be effective. In daily washdown applications, desiccant changes may be necessary several times per year.

Complete j-box submersion is a more drastic situation. If it has been underwater for any length of time and the operator has reported inaccuracies or lost calibration, water has probably gotten inside the enclosure.

Preventing Transients

Scale manufacturers suggest a variety of grounding procedures. To avoid the existence of multiple zero references that can create havoc with data lines as well as invite lightning damage, we recommend single-point grounding.

The first is to verify the ground system of the AC power supply. The second step is to check the scaleís grounding. But before you do that, make sure the scale and all peripherals are plugged into some type of transient protection device such as an uninterruptible power supply. 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.

Now 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.

Quality Counts

Whether you own a pit-type, above ground, siderail or portable vehicle scale, a portion of your preventive maintenance plan rests in the hands of the manufacturer. Itís not uncommon for scales that are functioning correctly to collapse without warning. The culprit? Rust. Many scale understructures are left untreated and vulnerable to corrosion. Steel deck scales that have a welded bottom plate also promote corrosion because water that seeps into the scale cannot run into the ground and is less likely to evaporate. In these cases you can and should protect the scale components mentioned earlier; however, there isnít a solution for protecting the understructure. If you are considering a truck scale purchase, you may want to consider a scale that includes a corrosion-resistant undercoating or does not include a bottom plate.

Depending upon the scaleís location, special features, and the material it is weighing, your scale inspection may or may not require all of the steps above. However, these guidelines should give you a good idea as to what to look for when looking over your truck scale and for interactively developing a preventive maintenance plan along with your local scale dealer (for customers in North Carolina, that would be Central Carolina Scale). Portions of this page are courtesy of Mark Johnson, Jr. Rice Lake Weighing Systems.

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