Your business has decided to purchase a truck scale in order to determine accurate and reliable vehicle weight for your application. Knowing fundamental truck scale basics will help you know which questions to ask your truck scale supplier to ensure you purchase the truck scale style that fits your needs with the options and accessories that can enhance your application.
Whether monitoring a vehicle’s weight for safety guidelines or to complete business transactions, you should know what the information determined by a truck scale means to your business.
Today, most scales are installed with aboveground or concrete pit foundations. Depending on state or regional requirements, scales can also be installed in a shallow pit, as opposed to the deep pit required by older mechanical scales. A pit installation requires less space than an aboveground scale since longer approaches are generally required for aboveground configurations. However, pit-styles require sump pumps and drains, and are generally more vulnerable to corrosion due to potential standing water.
The truck scale’s body and driving surface is called the weighbridge. Weighbridges are composed of steel or concrete decks, and are typically manufactured in modular designs that are placed together during installation.
The indicator, also called a controller or terminal, can display basic weight functions, as well as serve as the command center for a weighing system with advanced programming like truck in/out ID capabilities, and control for the entire truck scale system, including remote displays and printers.
High-quality load cells are vital to truck scale performance. There are various types of load cells, but they all have the same function—to accurately measure weight on the scale. All load cells take an analog measurement, and then that signal is converted to a digital output either at the load cell, junction box or in the scale indicator. Load cells are typically constructed of steel and are integrated within the weighbridge, usually at the corners of each module.
A junction box properly manages multiple load cells and weighing systems. By matching the signal of each load cell and summing them into a signal sent to the indicator, junction boxes equalize the system for accurate and reliable weight readouts.
Handwriting a ticket for each weighment is time consuming and tedious, and also leaves room for human error. Ticketing kiosks, scale data management software and printers eliminate both problems. Most states require ticket printers, and remote displays, gates, intercoms and other accessories increase truck scale efficiency and safety.
To ensure the longest lifespan and best performance for your truck scale, proper site planning is essential. Your truck scale supplier will help you select the best site, considering the traffic flow of your operation, the best location for a foundation, electrical and conduit requirements, soil conditions and drainage, ease of maintenance and accessory locations.
Before purchasing your new truck scale, it may be helpful to draw out a flow map of your current operations and determine if there are any areas for improvement. Creating an efficient traffic flow is important to keep operations running smoothly. Be sure there is adequate room around the scale to perform maintenance and to accommodate driver safety. Is there often a waiting line to use your truck scale? Consider the amount of space needed to accommodate a line of trucks, if needed.
Plot out traffic patterns on your flow map, marking where trucks enter the site, load and/or unload material, and exit the site. Make sure there is plenty of room for drivers to maneuver. Take a test drive with a full-size truck around your plotted traffic flow to test for any tight spots or potential safety issues. Note any special filling or dumping that must take place on site to accommodate for the space needed.
Even the toughest scales are put at risk with a poor foundation. Many factors, such as the slope of the site and soil conditions, must be considered prior to construction. The ground must also be free of any settling prior to scale installation. If the foundation is not properly constructed according to the certified drawing provided by your truck scale manufacturer, your truck scale foundation could shift, causing the scale to be outside acceptable calibration tolerance.
Concrete curing periods can vary depending on the type of concrete being used. Work with your scale supplier to integrate the foundation and approach design into your installation and site plan. Your scale supplier should also be able to recommend local contractors with truck scale foundation experience.
Until the early 1970s, all truck scales were mechanical and installed in expensive concrete pits. Today, most scales are installed aboveground or in concrete pits with floor foundations. With the benefit of new modular construction, scales can also be installed in a shallow pit, as opposed to the deep pit required by older mechanical scales.
One of the biggest reasons for choosing a pit-type installation is space—or lack of it. A pit installation requires less space than an aboveground installation since longer approaches are generally required for aboveground foundations. However, pit-type scales require sump pumps and drains, and are more vulnerable to accelerated rust and corrosion due to the potential of standing water in the pit.
|Cost||More expensive due to additional excavation, reinforcing steel and concrete.||Less expensive due to less construction work.|
|Service and Scale Repairs||In some cases, can be more costly due to confined area restrictions, which often require gas detection devices and operator safety harnesses to be used.||Less difficult/less costly and allows service from the deck of the scale.|
|Clean Out||Often done manually and can be very time consuming “bucket by bucket.”||Quick and easy—done with a water hose or air compressor from the side.|
|Scale Inspection||Must be done from inside the pit.||Can be performed by simply walking around the perimeter of the scale.|
|Restrictions or Hazards||Some states require specified clearances underneath the scale. Must also meet with OSHA and confined space hazards regulations.||Some states require specified clearances underneath the scale.|
|Approaches||10 feet flat and level.||Often 10 feet flat and level.|
|Ramps||Not required.||Typically 25 feet long on each end of the approach. Often requires more real estate to install and operate.|
|Electricity Needed||Typically has electricity for pit lights and sump pump if no gravity drain is present.||No pit light or sump pump required|
Typical for colder climates such as those found in northern areas of North America, the deep pier foundation places part of the foundation below the frost line to eliminate the negative effects that freeze-thaw conditions can have on foundations. Discuss with your scale supplier if a deep pier foundation meets your application requirements, or if a deep pier or other specific foundation design is required by your state and region. Similar to isolated pier foundations, the deep pier foundation also requires 2,500-3,000 PSF soil bearing pressure.
Shallow pier foundations are a cost-effective solution for truck scale sites with adequate soil compaction and a warmer climate that will not encounter frost line issues. Discuss with your scale supplier if a shallow pier foundation is best suited for your application and meets state and regional requirements.
A full slab foundation is a continuous or monolithic pour of concrete that runs the entire length of the weighbridge. This is the second most cost-effective type of foundation and is designed for ground that has a soil bearing pressure of at least 1,500 PSF. Discuss with your scale supplier if a floating slab foundation is ideal for your application and location, as well as meets state and regional requirements.
The pit foundation is available in numerous depths, from two to six feet. Your pit depth should best fit your needs as well as adhere to all federal, state and local requirements.
Efficient water drainage around the foundation is key to preserve scale components. The installation site should have adequate runoff, allowing water to easily drain away from the scale. Areas with heavy rain and melting snow should take extra consideration when planning site drainage.
Maximum weight regulations for on-road vehicles keep roadways structurally sound and ensure trucks are not overloaded which could cause damage to trucks as well as cause potential safety concerns. On-road weight regulations are determined on federal, state and regional levels to define the maximum allowed weight on public roadways. Discuss with your scale supplier all on-road vehicle loads your operation requires. Selecting the correct truck scale for your application will help assure your application’s on-road compliance.
If your truck scale is going to provide weight readouts for commerce, the scale will need to have a Legal for Trade approval to ensure the weight is within a certain degree of accuracy. Discuss with your scale supplier if you will need a truck scale that meets Legal for Trade approval, and which approval agencies, such as the National Type Evaluation Program (NTEP), Measurement Canada, or state and local approval agencies, need to provide certification for commerce in your area.
Each manufacturer has incorporated specific elements into their truck scale design to offer application advantages. However, most truck scales incorporate similar basic design elements and choices, such as deck and foundation types. Understanding the fundamentals of truck scale designs will help you and your scale supplier discuss which manufacturers offer the designs best suited for your operation and business needs.
Take time to and choose a scale supplier who will be able to provide the best services in your area. Ask potential scale suppliers about the products they sell and services they offer; some suppliers are exclusive to one manufacturer, which can work for your business, but it might also limit your choices. Choosing a scale supplier who also specializes in scale service can be an advantage. Having one contact for all your scale maintenance, service and replacement parts can help streamline your initial scale purchase and upkeep throughout its lifespan.
Before choosing a manufacturer, reach out to other truck scale owners, or ask your scale supplier to provide testimonials from similar businesses in your region. Knowing firsthand accounts about scale manufacturers and their reputation for quality products and services can be the deciding factor in your purchase.
Most truck scale manufacturers offer standard vehicle scales, but some will make custom designs to fit existing foundations, saving you time and money by eliminating site reconstruction. To ensure your scale is large enough for your application, plan your truck scale needs based on the largest truck you ever plan to weigh at your operation, including future trucks since truck scales should easily provide 25 years or more of dependable service with reasonable care.
A big consideration when choosing a truck scale is whether to select a steel deck or a concrete deck weighbridge. Both have advantages. Here are a few differentiating features that will help you choose the right type.
A concrete deck, which needs approximately 21 to 28 days to cure, is poured during installation and is usually done by an outside contractor—adding additional costs to your truck scale purchase at installation. Cured, factory-poured concrete decks may be damaged during transport and may have higher installation and transport costs due to the heavy weight of concrete.
Installation usually takes less than one day, and a steel deck scale weighs less, making it easier to relocate and expand if needed. Steel decks usually offer traction treads on the driving surface—beneficial in wet conditions due to rain or snow.
Weighing applications and process needs can change with the demands of commerce. As businesses grow and weighing requirements are expanded, additional modules may need to be added to an existing truck scale system. You need to be certain that your scale manufacturer can produce an additional module that fits perfectly with your current scale.
Some manufacturers design their truck scales with hinge fixtures that easily allow the addition of new modules to lengthen existing truck scales.
Quality truck scale accessories increase efficiencies and optimize the flow of trucks in and out of your plant. Knowing which accessories will complement your current operations can help you better select an overall truck scale system and manufacturer.
Refer to your site planning flow map to see where an accessory can speed up processes and reduce the risk of human error. Always consider the space an accessory will need prior to installing your truck scale system to ensure the best truck maneuverability and flow. Accessories include attended and automated ticketing kiosks, remote displays, traffic signals, printers, guiderails and more.
Guiderails offer drivers protection against accidental drive-offs. Many suppliers offer guiderails; make sure you examine the designs of each with your scale supplier closely, including the shape and strength of the rail. Some guiderails have open-ended rails, while others are sealed or plugged with an end cap. Open-ended rails can accumulate debris and moisture, and guiderails plugged with an end cap can corrode from the inside if moisture seeps past the cap. Caps with a welded seal offer the best protection, keeping debris and moisture build-up out of the rail.
From RFID truck identification to load assignment, weighing and ticketing, unattended automated ticketing kiosks optimize truck traffic and improve safety by keeping drivers behind the wheel. Many manufacturers’ kiosks can integrate with your central office and accounting systems.
Printers and printer kiosks improve more than just speed and accuracy. Many printer kiosk systems offer state-of-the-art features like RFID, vehicle recognition and durable weatherproof designs.
Truck scale data management software can print tickets or reports, as well as store information to a central database. Data management software enhances the functionality of automated ticketing kiosks by providing advanced data management and reporting capabilities. Most software systems are adaptable to a wide variety of industries and are compatible with many popular operating systems, streamlining your scale house or front office operations with your truck scale. Most manufacturers’ software allows you to generate reports, often broken down by a number of variables including customer, hauler, truck, product and vendor.
Whether you need to see weight readouts up close or messages at a distance, remote displays light up information to increase efficiency and provide direction to drivers. Many remote displays are customizable and feature stop/go red and green signal lights.
Industrial-strength stop lights professionally communicate the universal stop/go red and green signals at a distance, speeding up scale traffic and eliminating congestion.
Barrier gates block access at the entry or exit of your truck scale. Most gates are electronically controlled to open or close after a designated action is taken.
There are a variety of options in the truck scale market today and, to the casual observer, initial acquisition price may be the only differentiator. However, manufacturers promising great bargains are able to do so only because they’ve cut corners at some stage of the process—design, materials, components, finish or all of the above. While the price may seem attractive now, the eventual failure of a lower quality truck scale could mean a higher total cost of ownership from extensive downtime, increased maintenance costs, lost revenue and premature replacement.
A truck scale with a superior design and built-in protection features will save time and resources throughout its lifespan. A high-quality truck scale designed to last 25 years or more will require less repair and downtime due to maintenance or replacement. Your truck scale needs to meet the challenges of your application with long-term performance and accuracy.
Ask your scale supplier for information about various manufacturers and their design and testing procedures. Some manufacturers’ designs incorporate only high-quality parts, components and construction materials. The design and engineering involved in producing a truck scale are two factors that can have the most significant impact on the quality of your truck scale.
The decision to purchase a truck scale must be founded on long-range planning that takes into account all present and likely future uses of the scale system. Analyze your company’s needs for today, and project what you may need in the future. Consulting with a qualified project engineer familiar with your industry can help you determine the engineering specifications your truck scale will need to accommodate your operation.
A high-quality truck scale made with quality components and materials will help reduce scheduled and unscheduled scale maintenance. Many manufacturers incorporate features into their scales to help prevent component failure and damage to the scale or foundation, including transient bypass cables, diagnostic junction boxes, self-checking mounts, electrical component protection, single-point grounds and open-bottom designs on steel deck scales to allow moisture to evaporate.
Keeping the foundation clean and welldrained will help ensure a more accurate and dependable vehicle scale.
A preventative maintenance program is a key element in maximizing the life, performance and accuracy of your truck scale. Maintenance frequency is directly related to the daily truck volume and axle loads of the vehicles being weighed. Typically, inspections are recommended at least one to two times per year, depending on equipment usage. However, maintenance may be needed much more frequently depending on your application and the material being weighed. A comprehensive maintenance program consists of inspecting the weighbridge, foundation, load cells, junction box and grounding, and performing routine calibration and testing. More detailed information about maintaining these areas can be found in section 11-Maintenance.
When moisture or standing water seeps into the weighbridge, steel corrodes and the weighbridge can rust from the inside-out, often leading to accelerated corrosion, weakness and eventual failure. An open-bottom design on steel deck scales reduces internal corrosion. Steel decks with bottom plates trap moisture inside the weighbridge. An open bottom also allows maintenance crews to inspect the integrity of the weighbridge during scheduled maintenance, allowing you to plan scheduled downtime to repair, instead of making emergency service calls when the scale needs extensive repairs or component replacement.
Moisture and water can also wreak havoc on electrical components. A load cell and electronics pocket integrated into the weighbridge adds additional strength and protects electronics by keeping these sensitive components up off the ground and away from standing water. Quality component enclosures and environmental seals add extra assurance.
Protecting your truck scale from lightning and transient spikes is critical to prolonging its lifespan and reducing electrical component repairs and replacements. Many manufacturers provide lightning and transient protection packages that include the following features:
Proper lightning protection can mean the difference between emergency repairs and business as usual. Discuss with your scale supplier which manufacturers include the above protection features standard. Reputable manufacturers and suppliers will want to ensure your truck scale survives as long as possible, even in the harshest conditions.
The structural integrity of the weighbridge is the single most important consideration in the purchase of any truck scale. A failing weighbridge results in continued problems that can only be solved with replacement. Each manufacturer incorporates design elements into their weighbridge to distinguish it in the marketplace. Internal structural designs on the market include I-beams, lighter steel beams, C-channels, bent plates and steel tubing, among others.
One of the best ways to judge a scale’s strength and ability to withstand high-traffic volume is the weighbridge design and steel content. Ask your scale supplier to show you the advantages and disadvantages of each weighbridge design. Also, ask your scale supplier to provide the steel content of each manufacturer’s weighbridge so you can determine which scale is strong enough for your needs.
Two industry recognized terms often associated with weighbridge capacity and vehicle scale load ratings are concentrated load capacity (CLC) and dual tandem axle (DTA). These ratings define the maximum load the weighbridge is designed to support by a group of two axles with a center line spaced four feet apart and an axle width eight feet apart. A National Type Evaluation Program (NTEP) test records a truck scale loaded to CLC/DTA and the displayed weight. If the scale falls within acceptable testing tolerances, the scale has that CLC/DTA weight recorded on its Certificate of Conformance.
Closely examine each manufacturer’s truck scale specifications with your scale supplier and discuss what each specification means for your application. Note that load cell capacities do not directly correlate to the capacity of the scale, and always be mindful of the type of loads you will use on your truck scale. Depending on your average axle loads, a truck scale may need more strength to withstand fewer, heavy loads than the average scale designed for frequent, legal highway loading. If your application needs to process Legal for Trade transaction weighments, ask your scale supplier to discuss all scale options, including scales that can provide legal weights in as little as 10 pound increments.
Always discuss your Legal for Trade needs with your scale supplier and closely examine each manufacturer’s certifications to be confident your truck scale will meet your application’s needs. NTEP provides a set of procedures for the uniform testing and evaluation of weighing equipment. For more information on your region’s requirements for full scale capacity, CLC/DTA and NTEP Certification and guidelines, speak with your scale supplier and determine the best scale to meet those guidelines.
Ask your scale supplier to show you truck scales with a full scale capacity that exceeds the weight of a full-size loaded truck you currently use in your operation, and then discuss how heavy your trucks may weigh in the future if operations change. A high-quality scale should last 25 years or more with proper care and use. Ensuring your scale will last through changes in operational capacity is an important factor to consider before purchasing.
A load cell, also called a transducer, converts a mechanical force into an electrical signal. In its simplest form, the load cell bends when weight is applied. In a compression-mounted load cell where the load cell is beneath the weighing vessel, like a truck scale, the load cell compresses when a load is applied. The load cell produces an analog output signal proportional to the applied weight or force. The load cell transmits this signal to a controller that converts the signal into a digital weight measurement.
When an application requires multiple load cells, each load cell should measure the same proportion of the total load. So in a four-load-cell system, each load cell should measure exactly one-quarter of the load.
Many load cells are proprietary to a specific manufacturer, and may require additional maintenance and costs of ownership. Carefully discuss with your scale supplier all options for load cell systems.
The most common load cells on the market work on the strain gauge principle. All load cells need to convert their analog values to digital before the load’s weight reading can be displayed on an indicator. Some load cells are directly cabled to the digital weight indicator where the translation occurs. Other cells are connected to summing junction boxes on the scale where the box sums analog readings from multiple load cells, converts it to a digital signal and sends that signal to the digital weight indicator.
Unlike most other load cells, hydraulic load cells do not use strain gauges or internal circuitry. Instead, hydraulic load cells contain hydraulic fluid, and during compression, a change in pressure is created and transmitted via tubing to a summing system where the pressure is applied to an analog load cell to determine weight.
Some analog load cells perform the analog-to-digital signal conversion within the load cell housing. Although sometimes referred to as digital load cells, the cell still measures in analog. Making the conversion from an analog signal to a digital signal in the load cell allows the system to compare the output of individual load cells and perform a diagnostic analysis based on that information, but because the conversion happens in the load cell, sensitive electronic components are increased throughout the scale system, making them susceptible to damage from vibration, moisture and increased solder joints.
This is the most widely used vehicle scale load cell configuration in North America. A double-ended shear beam load cell is a compression load cell that offers a large capacity range from 1,000 to 200,000 pounds. The double-ended shear beam is secured at both ends with the load applied to the center of the load cell. As in all shear beam designs, the strain gauges are mounted on a thin web in the center of the cell’s machined cavity. The load cell also has the advantages of being less expensive in high-capacity applications than the canister load cell because it does not require checking, making it virtually a maintenance-free solution.
A canister load cell is the oldest load cell type. Also a compression device, it is shaped like a vertical canister and can handle loads from 100 to 1,000,000 pounds. It is either hermetically sealed or welded to protect the gauges. This load cell’s drawbacks include the fact that it requires checking—installing check or stay rods to hold the weighing vessel in place on the load cell’s top plate during weighing. For these reasons, many canister load cells on the market today are used to replace older canister load cells on existing weighing systems.
Some manufacturers prefer rocker column load cells because they are inexpensive. However, they require check rods and bumper bolts that require maintenance, increasing your cost of ownership. The cost saved by the manufacturer on the raw material is passed down the line to the end user in the form of additional maintenance.
Truck scale load cells are generally made of stainless steel or steel alloy, but most manufacturers offer a variety of load cell solutions that best fit your application needs.
Load cells manufactured from tool alloy steel elements are by far the most popular cells in use today. The cost to performance ratio is better compared to either aluminum or stainless steel designs. The most popular alloys are 4330 and 4340 because they have low creep (the change in load cell output over time while under load) and low hysteresis (the difference between load cell output readings for the same applied load).
Stainless steel cells are more expensive than tool alloy steel load cells. They are sometimes fitted with hermetically sealed web cavities, which make them an ideal choice for corrosive, high-moisture applications. Stainless steel load cells that are not hermetically sealed have little advantage over comparable cells constructed of tool alloy steel, other than a higher resistance to corrosion.
It may be necessary to trim the load cell outputs as a first step before starting the calibration process. Trimming is performed at the junction box to equalize the weight reading from all load cells in the truck scale system. This ensures that the scale weighs correctly regardless of where the load is applied to the scale. Load cell trimming and calibration should always be performed by licensed technicians. There are also multiple systems on the market to trim and calibrate a truck scale through a digital interface. Discuss each manufacturer’s calibration systems with your scale supplier to determine the best system for your application.
Every vehicle scale should be calibrated and tested frequently to ensure proper performance. Accurate truck scale calibration is vitally important to any operation, especially applications requiring Legal for Trade use. A truck scale should be calibrated and tested by a state-licensed service agency using no less than 12.5 percent of the scale’s nominal capacity, or 25,000 pounds of certified test weights. The scale’s calibration interval is determined by the frequency of use, individual application requirements, and federal, state and local guidelines. Each section of the scale should be tested and detailed test reports should be provided to the customer and government authorities.
A preventive maintenance program will help you maximize the life of your scale. Not only do regular inspections find repairs needed on the scale, they can also reveal potential component replacements before they cause emergency scale downtime. At a minimum, scale inspections are recommended every six months depending on equipment usage, scale type and application. If your truck scale is used to weigh material that can easily seep under the scale or cause potential bindings, regular scale inspections and cleaning between scheduled maintenance inspections are necessary to keep your scale’s high performance and accuracy.
Truck scale maintenance should include comprehensive inspections of the weighbridge, foundation, load cells, grounding as well as calibration and testing as required by your local weights and measurement authority.
Proper weighbridge inspections are essential to ensure accurate and consistent truck scale performance. Conduct visual inspections of the top deck surface, including welds, during every maintenance visit. Clean out areas beneath the bridge and inspect for potential mechanical bindings as a result of debris, loose bolts or misalignments. Debris, snow and ice between the approach bulkhead and the end of the scale should also be removed. Paint conditions should be examined and noted yearly.
Your truck scale is only as good as the foundation on which it rests. Keep the foundation clean and well-drained to maintain accuracy. Visually check sump pumps and drains at least once a month. Keeping the condition of concrete piers, slabs and concrete approaches maintained is very important for maximum scale performance. Any cracks in the concrete or evidence of heaving due to frost or poor soil conditions should be recorded and resolved immediately. Foundation issues are common causes of inaccurate scale performance.
Inspect load cells for cable damage and any loose or damaged connectors or fittings. Remove any standing debris around the load cells and check for moisture damage and standing water. All cable connectors should be checked and any corrosion should be removed.
Check the junction for any moisture or corrosion from moisture damage to internal circuitry. Air filters and desiccant packets should be inspected and exchanged on an annual basis. Cable connectors should be inspected and checked for tight fittings. Grounding Single-point grounding systems avoid multiple zero references that can create transient problems.
Quality doesn’t stop once the manufacturing process on your truck scale is complete. One of the most important factors to buying a truck scale, especially if time is a factor, is the ease of installation. Ask your truck scale supplier for the time commitments needed to install many different manufacturers’ models. Some scales can be installed in as little as one day, allowing you to start using your truck scale sooner than others. Models that incorporate boltless module fittings are often more user-friendly and timely during installation.
Some manufacturers use bolts to secure their modules together. Although bolting your truck scale together seems more secure, there are several negatives to this approach. Bolting each module together takes much more installation time. Also, depending on your geographic location, bolts could bind or freeze during freeze-thaw seasons or potentially corrode from the elements. Your scale supplier will be able to provide you with well-qualified contractors who have worked on truck scale installations before. Your foundation and installation is a large investment in your overall truck scale purchase.