Responsible for channeling both power and communication between the load cells and the indicator, load cell cables are an integral part of building a custom scale. Though not just any cable will work. See, load cell cables are selected based on the distance between the two parts, as well as certain environmental conditions like temperature, contact with abrasive or flammable materials, or even rodents.
Before you can know the right type your custom scale project needs, it is best to have an understanding of the different types of load cell cables available.
4-Wire Load Cell Cable
Perhaps the most common cable, the 4-wire load cell cable is used primarily for short distances. As its name suggests, this type consists of four wires:
Power (excitation) +
Signal (output) +
Once connected, the cable should run from the scale to the indicator display. These wires are calibrated and designed to handle the surrounding temperatures. Many custom scale projects use the 4-wire load cell cable since it is more affordable and suitable for most scales. However, should you need additional length or if your scale is in an unpredictable environment, you may need to reconsider the type of load cell cable you are using.
6-Wire Load Cell Cable
Designed for longer distances and more difficult settings, the 6-wire load cell cable offers a lot more options. Again, as the name suggests, these load cell cables have six wires. They contain the four found above, as well as positive and negative sense wires. The long distances that 6-wire load cell cables cover can subject them to changes in resistance, temperature, and dips in voltage. The addition of these two sense wires helps to keep things flowing steadily.
Because they are not thermally compensated as the 4-wire load cell cables are, the 6-wires can be cut and used alongside other cables with no issue – making them perfect for larger commercial custom scale projects.
Types of Load Cell Cable Shielding
While 6-wire load cell cables offer a lot of benefits when designing a project, it is important to note the surrounding environment and opt for shielding that will protect the cable from any outside environmental factors. Below are the most common types of load cell cable shielding.
Hostile Environment Cable
Hostile environment cable is best used in environments that are, well, hostile. Depending on where the scale is being used, the cables may come in contact with harsh or abrasive substances, such as fuel, ether, or even salt. Over time, these substances can damage the cables.
Hostile environment cables are created with a polyurethane jacket that acts as a barrier against these damaging substances, keeping the cable safe and the scale running smoothly.
Rodent Protection Cable
Rodents and their incessant chewing may seriously interfere with a scale’s functionality. If in an environment where there are rats, mice, or other pests, the load cell cable may become enticing – leaving you with hefty costs to replace some or all of the cable.
Rodent protection cable is a type of cable that protects against this pesky situation. The outside layer of the cable is a braided shield making it difficult to chew. And, as an added defense, it is coated with a chemical that will discourage them from wanting to ever take a second bite.
Intrinsically Safe Cable
Flammable gases or liquids or generally hazardous materials can be damaging to load cell cables, requiring added security in the form of a jacket. For intrinsically safe cables, industry-standard blue double jackets are used to protect the cables from exposure to these dangerous materials.
In environments where the temperatures fluctuate or reach extreme highs, load cell cables need an outer covering that will protect the wires regardless of how hot it gets. A high-temperature cable is designed with a fluorinated ethylene propylene (FEP) jacket that insulates the wires and can withstand the heat without getting damaged.
Should I buy a truck scale with weigh bar sensors? The Avery Weigh-Tronix Weigh Bar® was designed to overcome the shortcomings of the traditional strain gauge load cell and to provide the end user with a rugged, highly reliable and linear load sensing device at reasonable cost.
More than twenty years of extensive use in industrial, farm and transportation applications has demonstrated that the Weigh Bar has met these requirements. The unique, robust design of the Weigh Bar is the primary reason for this success.
The Weigh Bar has proven itself over the past 20 years to be one of the world’s most robust weight transducers manufactured today with over 500,000 installations world-wide.
The IP67 Weigh Bar design provides inherent strength and overload protection, while also providing accuracy and high reliability. A significant contributor for this is the positioning of the gauges on the outside of the Weigh Bar. More robust than a shear beam load cell for a given output – a shear beam load cell will reach its peak fatigue point much sooner than a Weigh Bar.
The unique design of the Weigh Bar allows simple calculations to be made by the indicator, eliminating several types of errors:
• End Loading – When an end load is applied to the Weigh Bar, it is subjected to a uniform compressive strain throughout its length – all sensors detect the same strain. • Torsion Effects – When torque is applied to the Weigh Bar, a uniform torsional shear strain is developed through the length of the bar – both sensors detect the same strain. • Side Loading – When a side load is applied to the Weigh Bar, it acts as a beam, but at a 90-degree angle. When this occurs, the neutral axis of the beam (the point in the beam where neither tension or compression occur) falls directly under the center of the strain gauges. No apparent strain is seen by the gauges. • Vibration –The fine grain structure of aircraft quality steel is resistant to vibration fatigue and induced error. The strain gauges and adhesive used are also vibration and fatigue proven.
Load Cells – The Avery Weigh-Tronix Weigh Bar® Weight Sensor
The exclusive Avery Weigh-Tronix Weigh Bar® is an extremely rugged, highly reliable, load sensing device. Over several decades, the Weigh Bar® has built a reputation for precision, reliability and durability that no other load cell can match.
Weigh Bar – Reduced cost of ownership
Precision machined from aircraft quality, alloy steel, the Weigh Bar® offers excellent repeatability and long-term durability, reducing cost of ownership and need for load cell replacement.
Rugged Weight Sensors
With up to ten times more steel content than shear beams or compression cells, it absorbs impact to minimize peak forces and is virtually fatigue-proof. The Weigh Bar® is proven to resist electrical surges and is protected by a limited warranty that includes coverage against lightning damage.
Accurate Weigh Bar
The sensor’s design automatically cancels the effects of side loading, end loading and twisting, resulting in quick, accurate readings which are achieved regardless of temperature change, vibration, and shock loads on the scale.
Sealed “Load Cell”
The standard alloy steel Weigh Bar® is well protected against harsh environments by an exclusive 5-layer, sealing process. For the most challenging locations hermetically sealed stainless steel weigh bars are available.
A lot of customers are curious about this question… how long should a truck scale last? Or perhaps it’s phrased like this… how do I know when my truck scale needs to be replaced?
The vast majority of truck scales are located outside. This means the scales have the hot sun blazing down on them all summer (every year). Then, they have the piles of snow on them in the winter (every year). In between all the hot and cold extremes, they have all the rain that you typically see fairly often.
So, with all the weather conditions, that means a truck scale must be able to withstand all the environmental challenges while working reliably and accurately…. For years and years! And, be able to handle 80,000 lb vehicles everyday!
So, how long can I expect my truck scale to last?
That’s a really good question and it’s a question that has a variety of answers.
Depending on the environment and application, most truck scale owners can typically expect a truck scale to last anywhere from 15-30 years.
If your location consistently has over 250 trucks a day going over the scale (or you project it will eventually have that kind of truck traffic) then you will need to choose a truck scale built for that kind of traffic. Choosing an “economy” or standard duty truck scale in that situation may be cost effective now… but will most likely lead you to have a shorter truck scale life and force you into looking for scale replacements or weighbridge repairs sooner than you would prefer.
Sometimes spending an extra few thousand dollars up front will allow you to purchase a heavier duty “HD” scale that will last you significantly longer than the “SD” model. What’s an extra few thousand dollars when you average it out over twenty-five or thirty years of use? Especially if the extra cost helps you gain an extra five or ten years of scale use?
Can I Repair My Truck Scale Instead of Buying a New One?
This is a good question and a common question that a lot of people ask when they have an old truck scale. In most cases, the answer is yes. Depending on the age of the truck scale and severity of the issues, repairing a truck scale can certainly work and be a cost savings.
However, once a truck scale has been in service for over 20 years or so… repairs may not be the best choice. Often you will hear people refer to the scale repairs as “band-aids”. We understand what they’re referring to, but the truth is that truck scale repairs on a 20+ year old scale weighbridge are just that, repairs…
A “band-aid” is supposed to heal your wound and help you get back to 100%. A “band-aid” on a 30 year old truck scale is not going to “heal” the scale. It is simply designed to get a few more years out of the scale before the scale will need to be replaced.
Unfortunately, truck scales that have been repaired often don’t last as long as you would like. One of the reasons is simply the age of the steel and the components. Often the areas that were repaired may be ok after the repair, but then the other areas that were doing ok before the repair, are now starting to fail.
When you think of a truck scale overhaul, the Truck Scale components can usually be replaced… things like load cells, junction boxes, summing boards, etc…, but the core weighbridge construction and integrity are sometimes challenging to rebuild in a cost effective & timely manner…. especially in a scale that’s 25 or 30 years old… or older.
It’s also important to look at the actual repair costs. Sure it can be overwhelming when you see a $50,000 quote for a new truck scale. However, if you attempt to repair and put “band-aids” on a 25 year old truck scale, how much money is that going to cost? Between materials and labor, we’ve seen these repair costs rise above $3000. Plus there is down time where the scale can’t be used.
And even after the scale is repaired, there really is no guarantee or warranty that the scale is going to last X number of additional years. So, in this example, you could spend several thousand dollars on scale repairs that may get you a few more years of service…. or, that $3000 could be used to help pay for a new truck scale.
Planning for Buying a Replacement Truck Scale on Your Terms
Here is one other scenario that we would like you to think about. Let’s say you have a 25 year old truck scale. It has some weighbridge issues and probably should be replaced. But, you and the scale company talk and decide that some weighbridge repairs could likely be made that might give the scale a little more life. Keep in mind at the same time this talk is taking place, new truck scales are readily available with a short 1 to 2 week lead time for fast delivery.
Well, the truck scale repairs take place and it turns out that you did in fact get an extra year of use out of the scale. Unfortunately, the scale now has more weighbridge issues and repairs will likely not make much sense at this point. And, as often happens, the scale failure has just happened right in the middle of your busiest time of the year! And, now it looks like the lead time on truck scales is closer to 14 weeks and there is a 8% steel surcharge now in place.
This scenario that we just mentioned above is all to real and can very well take place. Sometimes if your scale has lasted for two or three decades, it can be a smart move on your part to setup the replacement purchase on your watch (before the scale actually “breaks”). Maybe you talk with your scale company and decide the next time there is an incentive offered, you’re ready to purchase. This can be a wise decision because we all know that no one wants to be in a situation with a broken scale that must be replaced and then be facing extended downtime and a 14 week lead time before your scale can ship.
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.
One other note to mention on the subject of money would be taxes and leasing. This article is not going to be in depth on either of those subjects but if you purchase a new truck scale there can be tax advantages (see IRS section 179). We also have leasing programs which can make it easier to afford a larger purchase like a truck scale.
One other thing we wanted to mention on this subject is the overall trend for truck scale pricing. Generally speaking, the price for new truck scales is not going to get any less expensive in 2021 and beyond. In fact, at the time of this article in early 2021, we have received word from at least (3) truck scale manufacturers that there will likely be surcharges very shortly due to steel prices. (So if you’re in the market for a new scale, it might be time to act now!)
Believe it or not, the goal of this article is not to be completely gloom & doom about repairing a truck scale weighbridge. There are certainly situations where a truck scale overhaul makes sense. Most of the time, it makes more sense to upgrade components and less sense to try and do major weighbridge structural repair.
However, if you’re in the market for refurbishing a truck scale or purchasing a new truck scale… we encourage you to look at the entire picture and get a true understanding of the costs involved and the expected lifespan with each scenario. The fact is that many truck scale manufacturers are getting really good at building their truck scales to fit existing foundations. This can help to lower costs and lessen the down time when you’ll be without a scale.
Truck scales are important to the daily operations of the facilities that use them. That means that selecting a truck scale is an important decision. Whatever scale you choose (or have chosen), will likely be your scale of choice for possibly two or three decades! Often, a little extra thought or cost up front, can pay off down the road with a durable truck scale that can provide decades of service with proper scale maintenance.
If you have questions or would like to obtain a truck scale quote, please complete our RFQ form on our website or you can call our heavy capacity scales team at (919) 776-7737.
#1 IMMUNITY TO LIGHTNING DAMAGE Unlike other load cell technologies including both digital and analog strain gauge load cells, hydraulic load cells are immune to damage resulting from lightning strikes or other electrical surges. Hydraulic load cells have neither strain gauges nor wiring like other load cell technologies thus making them unaffected by lightning strikes; one of the most common reasons for load cell failure.
#2 IMMUNITY TO WATER DAMAGE Hydraulic load cells are constructed using stainless steel components welded together then pressure tested to ensure there are no leaks. Keeping the hydraulic fluid inside the load cell also keeps water out. Hydraulic load cells will operate when continuously submerged in water for an extended period.
#3 OPERATES OVER A WIDE RANGE OF TEMPERATURES Hydraulic load cells are capable of operating over a wide range of temperatures. Using proprietary grades of aircraft hydraulic fluid, hydraulic load cells can and do operate at temperatures of –60 degrees C (-76 degrees F). A number of hydraulic vehicle scales are located across Canada.
#4 HYDRAULIC LOAD CELLS NOT SINGLE SOURCE COMPONENTS Unlike digital load cells, hydraulic load cells are currently available from at least two sources. Because there is no standard protocol for digital load cell outputs, you cannot replace a digital load cell with another digital load cell from a different manufacturer. Each manufacturer of digital load cells have their own proprietary output for the cell that works only with their weight indicators and other digital load cells.
#5 CAN OFFER SAME ADVANTAGES OF A DIGITAL LOAD CELL One advantage of a digital load cell is its ability to display weight data from each load cell in a multiple load cell scale (like a vehicle scale). Digital load cell systems can also alert the scale operator or service technician of a potential problem before the scale weights are affected. Hydraulic load cell systems are available with load cell system controllers that perform the same functions as found in digital load cell systems. These controllers digitize each hydraulic load cell output independently allowing the operator or technician to view the outputs of each load cell. Further, software is included to alert the operator when an excessive shift in the no-load output of one or more cells is detected prior to affecting the accuracy of the scale. Automatic calibration can be another feature of hydraulic load cell systems provided with a load cell controller.
#6 MEETS THE SAME LEGAL & METROLOGY PERFORMANCE STANDARDS The hydraulic load cells available in today’s scales have been thoroughly evaluated and have been found to be in compliance with NIST Handbook 44 requirements for Class IIIL multiple load cells with 10,000 divisions, just like their digital counterparts.
#7 HYDRAULIC LOAD CELLS HAVE A LONG HISTORY OF USE Hydraulic load cells have a long history of being used in scales; much longer than either the strain gauge load cell or digital load cell. They have not been as popular as the less expensive strain gauge versions of the load cell but, when the costs of ownership including cell damage, the hydraulic load cell is clearly less expensive to own.
#8 HYDRAULIC LOAD CELLS COME WITH A LIFETIME WARRANTY Most manufacturers of hydraulic load cells offer a lifetime warranty on their load cells against damage from voltage surges (lightning) and water damage; the two most common reasons for failure of strain gauge and digital load cells.
#9 SAFE FOR OPERATION IN THE MOST HAZARDOUS AREAS Because hydraulic load cells contain no electrical circuitry, there is no source of ignition when used in an explosive atmosphere. Hydraulic load cells are regularly used in hazardous areas where explosive materials are present. Fuel or other flammable materials leaking from a vehicle and collecting in the scale pit cannot be ignited by hydraulic load cells making them a safer alternative than strain gauge or digital load cell.
#10 HYDRAULIC CELLS OFFER LOWEST POSSIBLE MAINTENANCE COST A lifetime warranty on impervious, non-conductive environmentally-sealed stainless steel hydraulic load cell that are waterproof, shockproof, explosion-proof, and resistant to both caustic and corrosive environments means we are extremely confident in Cardinal hydraulic load cells.
Lightning strikes are one of the most common difficulties that can affect a truck scale. SmartCell® digital load cells provide superior protection that protects against electrical uncertainties.
• Truck scales, due to their composition and size, are a magnet for attracting lightning. Many times, these scales are placed in an outdoor area that is exposed to the elements. The main front of protection against lightning strikes and power surges lies in the junction box. Unfortunately, if the junction box is compromised it can cause damage to the whole load cell weighing system. One or more of the load cells can be damaged in a traditional load cell arrangement, which can come at a great cost.
• The gas discharging tubes that divert excess voltage from lightning and power surges are normally placed inside the summing box of analog load cell systems. Cardinal’s SmartCell® digital load cells have the apparatus of discharging excess voltage placed in each load cell. This ability for each load cell to individually protect itself provides another line of protection for the whole load cell system. If a lightning strike or power surge happens, one load cell has the capability of preventing damaging surges from passing onto other load cells.
• Unfortunately, lightning strikes and power surges are commonplace. These occurrences have the potential to wreak havoc on truck scale electronics. Luckily, Cardinal’s SmartCell® digital load cells can protect individual load cells and the entire load cell system from excessive damage caused by freak electrical incidents.
• If you’ve experienced reoccurring problems with damaged load cells and repairs caused by lightning and power surges, SmartCell® digital load cells can help protect your truck scale electronics against severe damage.
Replacing the SmartCell® load cell is incredibly simple. Most importantly, it is a very fast procedure that gets your scale back to work in rapid time.
• Ease of use is also continued with installation or replacement of digital load cell (DLC) cards or 225D mainboards in the truck scale’s weight indicator. The 225D indicator can detect whether either option has been replaced using checksums and board identification numbers. The new DLC card or 225D mainboard will be reconfigured to the existing scale by the indicator acknowledging the new card and asking the user to verify if it is new. This simple reconfiguration process saves time and effort.
• One of the most important upgrades the SmartCell® digital load cell offers is the ability for truck scale dealers to change out the load cell in a matter of minutes. Normally, with analog load cells, dealers will have to check, replace, or pull a whole host of wires from the summing box when changing one out. Now, Cardinal’s digital load cells can be removed and replaced in as little as five minutes without any specialized equipment. It really is that short and simple!
• Electronic truck scales with analog load cells require many more moving parts. With an eight-cell system there are up to 100 wires that have to be prepared and terminated, up to 14 configuration jumpers to be set for proper operation, and sense lines must be utilized to regulate excitation voltage. This complicated wiring system lengthens time spent when trying to simply replace a load cell and calibrate it. This cumbersome process is no longer needed with the ARMOR® digital system.
• The ARMOR’s simple load cell connector design and the axis® frictionless centering system’s unique construction permit just a few steps for load cell replacement. After turning off power and jacking up the weighbridge a minimal amount, a single technician simply has to remove the dual load cell cables, remove two bolts that hold the cell to the weighbridge, and place a new load cell in its place. Next, after applying cleaner and Dielectric grease to the load cell cable connectors, the connectors are reconnected, and the load cell bolts are tightened. It’s just that simple—not another moment needs to be spared on time-consuming load cell replacements.
• If you have to spend large amounts of time dealing with wiring analog load cells, the SmartCell® digital load cell streamlines the tedious task of getting your new load cell in operation.
SmartCell® digital load cells provide many layers of protection against damage from water and debris. The SmartCell’s construction, placement, and ingress-blocking technology keep water and grime from damaging the load cells.
• As part of the axis® frictionless centering system that is provided, SmartCell® digital load cells are moved from an exposed area near the ground or beneath the deck to a placement above the bottom of the deck. Generally, most failures that are associated with debris and sediment build-up happen at the base of the truck scale near ground level, which greatly contributes to corrosion. SmartCell® digital load cells are given an extra layer of protection against the filth that typically accumulates under truck scales by being situated much higher in the scale weighbridge
• The orientation of the SmartCell® digital load cells in their load cell stand also provides the added bonus of selfcleaning. SmartCell® load cells rest on top of a cup-and-ball system that grinds up sediment and pollutants that might settle in the receiver cup from day-to-day operations. Normally this accumulation of pollutants would be left to build up and cause issues with load cell integrity or might cause inaccurate readings, but this self-cleaning feature can help protect the load cell modules from incorrect weighing.
• If, by chance, water levels rise high enough to expose SmartCell® digital load cells to moisture, their rating provides the highest level of protection afforded: IP69K. Their stainless steel casing and potting-filled cell body prevents water from entering the load cell and damaging valuable digital components that transmit weighing information.
• SmartCell® load cell cables are also placed above the load cell housing to keep wiring clear of exposure to sediment and water. Load cell cables include rat-proofing protection from nibbling rodents.
Over the next few blog entries, we are going to take a look at a few of the reasons why Cardinal’s ARMOR® Digital Truck Scale arguably provides the best return on investment.
Cardinal Scale’s all-around innovative truck scale and load cell design provides the most protection against circumstances—seen and unforeseen. The combination of Cardinal Scale’s SmartCell® load cells, ARMOR® weighbridge, and axis® frictionless centering system provide a well-rounded vehicle scale package that protects against the harshest conditions while transmitting valuable weight data digitally. Cardinal Scale provides customers with the versatility and efficiency required to fit their individual scale needs while saving valuable time and effort.
Cardinal Scale engineers, develops, and manufactures their truck scale hardware, software, and load cell technology in one location. Weighbridges, indicators, load cells, and related instrumentation are produced to meet the individual customer’s needs. Due to the highly-vertically-integrated nature of Cardinal Scale’s manufacturing processes, the company can easily modify and customize each truck scale they make to fit a customer’s application—a benefit that is becoming increasingly rare in today’s truck scale market.
Keeping with its visionary heritage, Cardinal Scale has again pushed the boundaries of truck scale technology by developing SmartCell® digital load cells. The added benefit of transmitting weight digitally is greatly augmented by Cardinal Scale’s iSite remote monitoring system. Dealers can now see, in real time, load cell issues as they happen. Most importantly, time spent checking load cell wiring is greatly reduced thanks to the streamlined, digital load cell diagnostics. Dealers can now quickly and remotely diagnose load cell issues and replace defective load cell elements in a fraction of what analog load cell diagnosis requires.
Carefully consider the following questions for the purchase of a truck scale to see if Cardinal’s ARMOR® digital truck scales will provide the best solution for your time and resource investment.
A couple of years ago we discussed the ever popular how much does a truck scale cost? Today, we answer a similar question. What factors impact the price of a truck scale?
When purchasing a large piece of equipment, such as a truck scale, it can be hard to look past the price tag. However, to ensure you are investing in quality equipment that will last your business a generation or more, it is important to understand the factors impacting total purchase price. Elements such as design, craftsmanship, components and foundation of a truck scale all impact the final purchase price.
The number and size of beams in a weighbridge can also impact steel content. Designs that place larger beams closer together offer more support for vehicles than designs with smaller beams placed further apart. The support from larger beams means the deck won’t bend as easily, so the truck scale will provide accurate weighments for a longer time.
To better understand the cost of the truck scale steel content, divide the cost of the scale by its shipping weight to get the price per pound of the scale. This can be used to compare the price per pound of similar scales from different manufacturers. You may find the scale with higher steel content actually costs less on a price-per-pound basis.
Value in Scale Quality
Quality craftsmanship also contributes to a truck scale’s integrity. Purchasing from a company that invests in engineering and manufacturing ensures that there is a highly skilled team behind each and every truck scale.
The components that make up a truck scale are just as important as the team behind it. Companies who take the time to source high-quality load cells, steel, cables and other components often have a higher quality product.
Truck Scale Installation
The installation of the truck scale will also impact the final price. Installation includes excavation, the cost to pour the concrete foundation, off-loading and positioning the scale, installing electronic components and performing the initial calibration of the scale.
The truck scale installation should be performed by professional scale technicians who have experience working with scales from the manufacturer you chose. This expert installation will ensure proper scale operation and reliable weighments over the life of the scale.
A truck scale is a significant investment, and design, quality and installation all impact the final price of a truck scale. Choosing a truck scale with a heavy-duty design, superior engineering and components backed by industry experts gives you a scale that will last for a generation or more.
For more information on purchasing a truck scale, please contact the Central Carolina Scale heavy capacity sales department by calling (919) 776-7737.
The majority of this article is provided by Rice Lake Weighing Systems. We have also added a few insights and thoughts of our own as well.
What is a Load Cell?
A load cell, also commonly referred to as a transducer, converts a mechanical force into an electrical signal. Basically, the load cell bends slightly 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. This would apply to scales like the Cardinal PRC which has the SCA load cells.
The load cell produces an analog output signal that is proportional to the applied weight or force. The load cell transmits this signal to a digital weight indicator 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.
Analog Load Cells
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.
Hydraulic Load Cells (pressure transmitters)
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.
The advantages of the hydraulic load cell typically relate to being resistant to lightning damage. The disadvantage of this type of scale and replacement load cell is the cost.
Analog-to-Digital Load Cells
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.
Some would say that 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.
Types of Load Cells Found in Truck Scales
Double Ended Shear Beam
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.
Load Cells Are Usually Manufactured as either Alloy Steel or Stainless Steel
Alloy Steel Load Cells
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 Load Cells
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.
We hope you enjoyed learning more about the different load cells found in the average truck scale. Since 1980 we have been providing customers throughout the central part of North Carolina with truck scale inspections, scale repair and calibration services. Our test weights and weight cart are certified by the state of North Carolina for accuracy. Our scale technicians are highly trained and knowledgeable when it comes to checking and installing various brands of truck scales.