Purchasing the wrong truck scale can create expensive problems for years to come. The following illustrates six considerations that scale buyers in the cement and raw materials industries should examine when selecting a truck scale.
1. Weighbridge configuration
The physical configuration of the scale can be dictated by its intended use, but also by customer preference. A vehicle scale’s weighbridge is typically composed of one or more platforms, sometimes called modules. There are three common configurations for these platforms: axle scales, full-length scales and multi-axle scales.
An axle scale is used to weigh a single-axle group at once. Axle scales use a single platform that is large enough to accommodate the tyres of the axle group, but not the entire truck. They are intended to verify that axle loads are not over the legal requirements for roadways. These scales can be used to estimate gross vehicle weight; however, in most locations this method does not meet the standards for commercial use where transactions are based on weight values. That is why most vehicle scales in the aggregates and cement industries are designed to accommodate the entire vehicle at once.
A full-length vehicle scale weighbridge is typically composed of multiple platforms, or modules, placed end-to-end. This configuration captures the weight of the entire vehicle. If individual axle weights are also needed, the truck can be moved so that only the axles being weighed are on the scale. However, this can be challenging, or even impossible, depending on the axle configuration. Full-length vehicle scales capturing gross vehicle weights meet the requirements for commercial use in most areas.
To capture the weight of the entire vehicle, as well as the weight of each axle, another variation is a multi-axle scale, composed of an individual scale for each axle group. There, the scales can work together as well as independently and can simultaneously capture the weight of the entire vehicle along with individual axle weights. This configuration is also acceptable for commercial use; however, it requires additional components and has a higher cost.
A pit-style foundation is created by excavating an area where the scale will be installed. This allows the driving surface of the scale to be flush with the surrounding ground. It also requires a minimal amount of space, since the scale does not require ramps at each end. However, pits can accumulate debris and standing water, so pit foundations must incorporate a drainage system. Special safety permits may also be required when service personnel need to enter the pit.
Above-ground foundations may use a gradual ramp or elevated approach for vehicles to drive onto the scale. Local engineering codes often dictate the required grade for ramps and approaches to above-ground scales. This adds to the amount of space required for the scale, but above-ground scales have some benefits. This type of foundation provides easier access to clear debris and perform service activities.
Cement producers should be aware of the factors that can create problems for scale reliability. Scale downtime can result in production delays and lost business, as well as out-of-pocket repair costs. Fortunately, advances in scale technology can make newer scales significantly more resilient and reliable than their predecessors.
Typically, the main causes of scale downtime result from issues in the load-cell system and the challenges of outdoor environments. Load cells are the sensory components of the scale. A typical full-length truck scale has 6 – 10 load cells.
Cables connect the various components of the load-cell system, transferring the weight readings from each cell. These cables can be a point of weakness if they are not properly protected. Look for stainless-steel braided sheathing for effective protection from abrasion and even rodents. As opposed to cables that are permanently connected to the load cells, quick disconnects are now available that still meet water-resistant specifications, but make service much easier.
Junction boxes are part of the load-cell system on many scales. On these systems, the cables from each load-cell sensor make connections within a junction box, which is then connected to additional junction boxes, and eventually to the scale terminal. These connections are frequently compromised by moisture and corrosion, causing the terminal or indicator to receive inaccurate information from the load cell. Scale companies have continuously tried to seal junction boxes as effectively as possible, but they must still be opened periodically for servicing. To eliminate problems with reliability and junction boxes, look for load-cell systems without junction boxes.
Lightning strikes can do major damage to scale systems, requiring extremely costly repairs. Most truck scales are equipped with grounding features, but these offer only minimal protection. Locations that experience severe weather should consider scales that offer more substantial lightning protection.
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Written by Brad Hudson, Mettler & Toledo, USA. This is an abridged version of the full article, which appeared in the BMHR 2013 issue of World Cement. Subscribers can view the full article by logging in.
Read the article online at: https://www.worldcement.com/the-americas/29082013/considerations_when_selecting_a_truck_scale_part_1_114/