Category Archives: Load Cells

Answering Your Questions About Truck Scale Load Cells & Mounting Systems

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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.

replacement rl75058-75k truck scale load cells

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.

Canister
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.

Rocker Column
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 

Truck scale load cells are generally made of stainless steel or alloy steel, but most manufacturers offer a variety of load cell solutions that best fit your application needs.

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.

If you need your existing scale checked or perhaps you’re in the market for a new truck scale, please give us a call today (919) 776-7737.

 

Brewery and Beverage Manufacturing Equipment Co. Uses Cardinal Scales in Process and Packaging

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In the case study below, we take a look at how a brewery and beverage company that manufacturers equipment for that industry, uses Cardinal Scale equipment in its process. The company that is featured in the case study chose Cardinal products for various reasons, one important reason was the wide range of products that Cardinal offers which allowed the company to utilize Cardinal Scale products throughout and not have to contend with multiple different brands of scales.

Cardinal 190 indicator

The systems provided by IDD provide answers for operations such as keg cleaning, sanitation and filling, flash pasteurization, bottling, and their HEBS (High Efficiency Brewing System). IDD manufactures these intricate and precise equipment systems to meet the distinct needs for their many customers in the beverage industry.

IDD’s reach extends all over the world. While primarily servicing America and Canada, IDD Process and Packaging, Inc. ships to Western Europe and as far as countries in the Oceania area, such as Australia. The burgeoning craft brewery and distillery movement in America and Canada provides IDD with a great deal of business opportunities; however, they are not limited strictly to beer and spirits. IDD delivers expertise in more traditional beverage production, such as grape juice, to more exotic and contemporary drinks, like kombucha and cold-brew tea.

To round out the design of a few of their systems, owner Jeff Gunn researched scale manufacturers to compare products lines and breadth of products. Cardinal Scale was capable of providing the load cells he preferred, along with the digital weight indicators meant to complete filling functions for keg, grain, and yeast managements systems, plus the scales themselves. “Cardinal Scale provided all of the implements that I needed within one company, and that influenced my decision to go with them,” said Gunn.

Cardinal Scale products are featured in Squire Keg Systems, Grain Handling Systems, and Yeast Management Systems. For the Squire Keg series, Cardinal Scale’s model EB-300 scale is coupled with the 190 STORM indicator. The EB-300 weighs the keg that can be moved on a roller platform, and the 190 provides the weight preset programming that is invaluable to precision filling. The Squire Series system can fill up to 30 kegs per hour.

The Grain Handling Systems and Yeast Management Systems utilize Cardinal Scale’s 825 or 225 weight indicator and the company’s TCBSS1KM-4 load cell kits. The TCBSS1KM-4 load cell kits provide the durability and precision needed to take on filling of grain augers, mills, and hoppers or multi-tank yeast propagation systems. The 825 or 225 weight indicator guides the more complex filling functions associated with the aforementioned tanking systems.

So as you can see, the robust product features of the Cardinal Scale Manufacturing lineup of products was a key ingredient in the success of the featured company in the case study. With more than five years of business between the two entities, both the companies are poised to achieve even more success in the beverage industry.

You too can enjoy this same level of success for your business. Contact our sales department to discuss adding load cells under your tanks or adding digital weight indicators to your scales that can collect data that you can then analyze in a spreadsheet on the computer.  Call (919) 776-7737 to get started.

Food Safety Modernization Act (FSMA) and Digital Scales

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Food safety is extremely important to all of us. In today’s ultra competitive and fast paced world, it’s imperative that we have laws in place to ensure that the food we eat is as safe as possible.

We hope the article below helps you better understand information about the Food Safety Modernization Act (FSMA). Ultimately we think this information will highlight the ability of Rice Lake’s washdown products to meet your requirements of commercial processing industries. The FSMA info below not only informs producers about how to meet compliance laws, but demonstrates how Rice Lake scales can help prevent food contamination by the integrity of their construction and design.

For all producers, from the farm to the table, purchasing equipment that meets Sanitary Design Principles (SDP) is considered a mandatory preventative measure by the FDA. Our product offerings that are microbiologically cleanable, hermetically sealed and compatible with hostile environments can greatly assist you in adhering to these strict guidelines.

On January 4, 2011, President Obama signed the FDA Food Safety Modernization Act (FSMA) into law. The FSMA brought a much-needed focus of food safety laws into the food processing industry as well as to consumers, and the general public as a whole.

The signing of the FSMA was arguably the largest reform to food safety in the previous 70 years. According to the U.S. Food & Drug Administration (FDA), the FSMA “aims to ensure the U.S. food supply is safe by shifting the focus from responding to contamination to preventing it.” The key focus being prevention versus reaction in regards to food safety, from all aspects and stages of food—from the farm to the table.

The FSMA was spurred into action from an increase in foodborne illnesses in the U.S. The Centers for Disease Control and Prevention report almost 1 in 6 Americans fall ill to food borne diseases each year. Foodborne illness became an issue of public health in the early 2000s, enabling the FDA to set higher preventative standards for food safety and elicit enforcement agencies to hold companies to these standards and contain any potential problems before they become a widespread risk of foodborne illness. To do this, the FDA under the FSMA can order companies to recall when needed.

The primary role of the FSMA is prevention. As noted by the FDA, “for the first time, FDA will have a legislative mandate to require comprehensive, science-based preventative controls across the food supply.” This legislative power ensures all U.S. companies that contribute to the food supply, no matter their size, are subject to the authority of the FDA and their preventative and responding agency.

Under the Prevention section of the FSMA, controls are given to the FDA for the following:

• Mandatory preventive controls for food facilities
• Mandatory produce safety standards
• Authority to prevent intentional contamination

These measures need to be qualified by scientific justifications by the FDA and are enforced by legislation. Under the mandatory preventative controls for food facilities is the addition of a preventative control plan that includes the following:

1 ) Evaluating the hazards that could affect food safety
2 ) Specifying what preventive steps, or controls, will be put in place to significantly minimize or prevent the hazards
3 ) Specifying how the facility will monitor these controls to ensure they are working
4 ) Maintaining routine records of the monitoring
5 ) Specifying what actions the facility will take to correct problems that arise.

Purchasing and using equipment that meets the Sanitary Design Principles (SDP) falls under these mandatory preventative measures as a control to prevent or minimize the possibility of foodborne contamination and disease. Continue reading →

Benefits of Cardinal Digital Truck Scales

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Cardinal Armor series Smartcell digital truck scales have several distinct benefits to you, the customer. First there is the heavy duty weighbridge design the Cardinal Armor digital truck scale uses. For example, the steel deck has (12) 12 inch eye beams across the scale but most important is there’s no moving parts under the scale.

ADVANTAGES OF A DIGITAL TRUCK SCALE

With a traditional truck scale, when it comes to debris build-up under the scale, that you typically see in landfills, quarries, sand and gravel businesses; all of that debris can cause problems under the scale and cause binding. Then you will be forced to have folks out there power washing the truck scale, trying to get the scale to work properly because safe linkage systems or load cells that are mounted to piers; the debris impedes on that critical weighing process.

This can often lead to down time for cleaning and can also lead to your scale being rejected when being tested by the State weights and measures inspector.

Another key element of the Cardinal Armor digital truck scale is simple connections which can also lead to limited downtime. Most important there is no power running to the scale other than the home run cable, that’s very important. Do you know what lightning, rain, and snow can do over time to the junction boxes of a traditional truck scale? There’s over a hundred and eight connection points in many standard analog truck scales.

digital truck scales

But, with the armor digital system, there’s ten. There’s five wires that plug into the terminal connector to go to the first load cell and there’s five that you simply wire into the weight indicator in fact Cardinal chooses 225 and the 825 as indicators of choice but most important for you; you want limited downtime for the life of the truck scale. Continue reading →

I Want To Buy A Scale That Is Made In The United States of America.

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The title of this blog post sounds simple enough, right? Many customers are interested in purchasing lots of different items that are made in America versus buying items made in China and other countries. But, I would like to ask you a question…

What exactly do you consider “Made in America”?

The reason I bring this up is that it’s really difficult to find certain types of scales that meet a certain definition.

According to the FTC, for most products there is no law requiring manufacturers and marketers to make a “Made in USA” claim. But if a business chooses to make the claim, the FTC’s Made in USA standard applies. Made in USA means that “all or virtually all” the product has been made in America. That is, all significant parts, processing, and labor that go into the product must be of U.S. origin. Products should not contain any – or should contain only negligible – foreign content. The FTC’s Enforcement Policy Statement and its business guide, Complying with the Made in USA Standard, spell out the details, with examples of situations when domestic origin claims would be accurate and when they would be inappropriate.

For simplicity, let’s look at an industrial floor scale as an example.

Ok so you’re looking to buy an American Made floor scale. Did you know that almost every floor scale that is built in the USA utilizes (4) load cells that were made in China? With that being the case, let’s say your floor scale was built in Rice Lake, Wisconsin but uses load cells from China.  Do you still consider this scale an American Made item?

industrial floor scale

Did you also know that many of the junction boxes and summing boards are made overseas? Finally, did you know that the home run cable, the fifteen foot long cable that connects the scale to your digital weight indicator is probably constructed overseas? And, what about the steel used in the floor scale? Was it purchased domestically?

Sticking with the floor scale example, next area to consider is the digital weight indicator. Is it one hundred percent made in the USA? Were all the boards and components made in America? How about the display board? The plastic or stainless steel enclosure? Was the AC adapter made in the USA?

These are some interesting things to consider. I know of many people who can justify buying a scale that was constructed and calibrated in the USA but does utilize some Chinese components. However, there are some who absolutely want their products to be 100 % made in America.  Are there any scales that can one hundred percent meet that?

From our standpoint as a distributor it can be quite tricky since we are not involved in the actual manufacturing process. We have had numerous scale manufacturers tell us over the years that they build Made in the USA weighing equipment and then over time they slowly start substituting Chinese parts or in some cases, send all the manufacturing over to China. Unless the scale manufacturer tells us, sometimes we are not even aware that anything has changed in the manufacturing process.

So if buying a Made in the USA scale is important to you, contact us and we can help you. Just be sure to specify to us up front how flexible you wish to be when it comes to things like Chinese components such as load cells being a part of the final product.

In our experiences, many customers may originally start a transaction as a “Made in the USA” fanatic but once they discover certain prices and lead times for domestic components, they become a fanatic of “Made in U.S. from Imported Parts” or “Assembled in U.S.A.”.

Installing Load Cells on Suspended Hoppers or Tanks

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If you have a hopper or tank in your facility, one great way to accurately keep track of its contents is to weigh it. The ITCM Series modules utilize several Rice Lake Weighing Systems components (mounting hardware, load cells, junction box) to provide an unmatched level of performance in suspended tank and hopper weighing applications and mechanical scale conversions. The ITCM HE incorporates clevis and unique rod-end ball joint assemblies to reduce the overall length to less than half of the traditional tension cell mounts, while providing correct load alignment.

In addition, the load cell is completely electrically isolated from stray currents, which are a major cause of load cell failure. To complete the design, a grounding strap connects the two clevis assemblies to further provide safety to your load cells. As always, the installation should be planned by a qualified structural engineer. Each installation is unique, and this manual is meant to serve only as a general guideline for installation.

The ITCM Weigh Module provides excellent performance in suspended tank and hopper weighing applications. The ITCM reduces the overall assembly length to less than half of traditional tension cell hardware arrangements and offers correct alignment of the assembly. The combination of clevises and rod end ball joints isolates the load cell from extraneous forces detrimental to accurate system performance.

suspended hopper load cell mount for scales

The ITCM incorporates an insulating system which resists the flow of stray currents through the load cell. To insulate the load cells from the clevises, the clevises incorporate nylon insulating washers, and the rod end ball joints are lined with Teflon®. A parallel grounding strap connects the two clevis assemblies to provide an alternate path to ground, preventing load cell damage from electrical spikes or stray currents.

The ITCM modules feature RL20000 series S-beam load cells and are available in a variety of capacities, ranging from 100 to 20,000 pounds per module. A single ITCM module is often used to convert a mechanical scale to electronic operation, allowing for the added benefits of an electronic signal for process control or data collection. When an ITCM module is inserted into the steelyard rod, the mechanical beam or dial is still functional and can serve as a backup indicator.

General Installation Guidelines for Tension Cell Mounts

Depending on the weighing application, ITCM modules may be used in single or multiple load cell configurations. Single cell suspension configurations are relatively simple and work well in low capacity applications which have minimal disturbance from mixers, materials flow, or other agitators.

For best results, the vessel should be symmetrical with respect to the suspension point and used to weigh only self-leveling materials, such as liquids.

This allows the center of gravity to rise along the same vertical line each time and minimizes the tendency of the vessel to bind against the bumpers. The bumpers only serve to limit sway caused by accidental contact or other external forces. Erroneous scale readings result if the vessel contacts the bumper. Instead of bumpers, horizontal stay rods may be used to rigidly hold a vessel which has a tendency to sway sideways. Also, note that single cell systems must be restrained from rotating to prevent the suspension hardware from coming unscrewed.

single load cell tank hopper mount

Multiple cell suspension configurations commonly involve three or four load cells. One advantage to using three suspension points is that even weight distribution is inherent in this configuration. Support points should be equally rigid and deflect by the same amount when loaded. Otherwise, one or more of the cells may be overloaded.

For maximum stability, attach suspension rods at or above the filled vessel’s center of gravity. In situations where there is a potential for vibration, agitation, wind, or seismic activity, install bumpers or horizontal check rods to check the sideways motion of the vessel.

3 and 4 load cell hopper scale mount

We always like to mention that all suspended vessel weighing systems must be protected by safety check rods, chains, or other means to prevent damage or injury in the event of a failure.

If piping or conduit is required, make sure that it runs horizontally and verify that the distance from the vessel to the first pipe support is 20 to 30 times the pipe diameter. If necessary, incorporate flexible sections into the pipe. Suspension rods should be as long as possible to minimize the introduction of side forces.

Use only hermetically sealed load cells in washdown applications. Environmentally protected load cells are not suitable for such applications and will eventually be damaged. If tanks and surrounding equipment are frequently steam cleaned, or if the load cell might be subjected to direct washdown pressure, a protective shroud for the weighing assembly is recommended.

It is important that the S-beam load cells are properly oriented with respect to the load. The cable must emerge from the dead, or fixed, end of the cell. If it emerges from the live end, it will restrain the movement of the cell. This orientation must be followed with low capacity S beams.

correct way to use a s-beam load cell

Installing the ITCM suspended weighing modules

1. Select a suspension rod of the appropriate diameter. Use a safety factor of at least 4, based on the yield strength of the rod material. If vibration or shock loads are common, then a higher factor of safety should be considered. Commercially available threaded rod is made from a low yield strength material and will not provide an adequate safety factor in many applications. When determining the rod length, subtract the length of the ITCM module from the overall suspension length, making allowance for complete thread engagement in each clevis.
2. Making certain to provide adequate thread for the jam nut, cut the suspension rod near its center point and thread the ends that screw into the ITCM module.
3. Making sure to put the jam nut on first, assemble a clevis to the top and bottom rods. Screw the rod in sufficiently so that all threads of the clevis are engaged. Lock each clevis in place using the jam nuts. The clevises should be rotated 90° relative to each other.
4. Initially, the lined rod end ball joints are stiffer than regular rod end ball joints. This is normal. Verify that all threads of the load cell are engaged by the rod end ball joint, then lock in place with the jam nuts provided. Screw the rod end ball joints into the load cell. Align one so the flat face is in the same plane as the load cell. Turn the other to 90°.
5. Insert the rod end ball joint into the upper clevis. Place a nylon washer on each side of the rod end and insert the shoulder screw. Secure the shoulder screw with the lock nut provided. Repeat the procedure on the lower clevis.

Note: The 15K and 20K ITCM models use plain pins secured with washers and cotter pins, rather than threaded shoulder screws and lock nuts.
6. Remove the 1/4” machine screw and lock washer from each clevis. Fasten the bonding strap in place as shown in the illustration below. Make sure to connect the vessel or the support structure to a single system-wide ground.
7. The attachment points on the structure and vessel should be rigid to minimize deflection. Add gusset plates if necessary. Spherical washers help to minimize bending of the suspension rod due to structure or vessel deflection under load. They can also compensate for initial misalignment.
8. In multiple cell applications, adjust the length of each assembly to level the vessel. If the system consists of more than three cells, you must be sure the load is evenly distributed. This may be done by lifting or prying on the vessel at each support point, checking for even load, or by reading the dead load output from each cell. The variation in load among the cells should be no more than 20%.

Load Cell Wiring

1. Route the load cell cables so they will not be damaged or cut. Cables should not be routed near heat sources greater than 150 °F. Do not shorten any load cell cable. The load cell is temperature compensated with the supplied length of cable. Cutting the cable will affect temperature compensation. Coil excess cable and protect it so it will not be mechanically damaged or be sitting in water.
2. Provide a drip loop in all cables so that water or other liquids will not run directly down the cables onto either the load cells or the junction box. Attach load cell cable to the dead structure, not the vessel.
3. If conduit protection is necessary against mechanical or rodent damage to the load cell cables, use flexible conduit and conduit adapters at the load cells.
4. Connect cables for the load cells to the summing board in the junction box according to the load cell calibration certificate provided with the load cell and the labels on the terminal strips of the junction box.
5. For better performance, use positive and negative remote sense lines if the wiring run from the junction box to the indicator is longer than 25 feet.

Junction Box Connections, Adjustments & Calibration

• Refer to junction box manual for trimming details.
• Refer to indicator manual for system calibration details.

Scale Troubleshooting

If the system powers up and gives some type of stable digital readout that varies with the load on the system, the system problems are probably caused by factors other than the load cells. Often, load cells are blamed for a malfunctioning system and the majority of the time, the problem lies elsewhere.

Look for mechanical causes first. If the system can be calibrated but doesn’t return to zero, loses calibration, or demonstrates non-linearity or non-repeatability, see the following chart for possible causes and refer to the following list of checks.

No return to zero
Mechanical binding or debris in seals or under load cells; may have lost system calibration

Non-linearity
Thermal expansion or deflection under load causing binding or side load

Non-repeatability
Loose load cell mount; drifting caused by moisture, load cell overload or shock damage; mechanical binding

Lost calibration
Out of level or plumb; moisture problem; mechanical binding

Drifting readout
Moisture in junction box, cables, or load cell; mechanical binding

1. Check load cell mount for debris restricting load cell movement or debris between scale and structure.
2. Check that tank/vessel and mounts are plumb, level, and square at the critical areas.
3. Check piping and conduit for connections that restrict vessel movement.
4. If check rods are used, loosen connections to finger tight only for testing.
5. Check load cell cables for physical or water damage.
6. Check all electrical connections, especially in the junction box.

Contact the scale sales and service team at Central Carolina Scale today for hopper scale load cells and weigh bars. Nobody stocks more load cells in North Carolina than we do. We can put together a quote for the ideal system for your weighing needs. And when it comes to digital weight indicators, we can meet just about anyone’s requirements for specifications like analog output or a certain price range. We can also repair or calibrate an existing hopper scale. We feature many of the top scale manufacturer product lines to choose from. Call us at 919-776-7737 or complete the Request a Quote form on our website.

Load Cell Repair Service

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We can offer you load cell repair services with fast turnaround times and affordable pricing. Our load cell repairs come with a one year warranty and flat rate pricing to help make the repair process easy and worry free.

Our repair service has experience repairing all types of load cells and even offers a load cell Exchange Program. Calibration work and repairs are traceable to the National Institute of Standards and Technology (NIST).

truck scale load cell repair

We offer no hassle load cell repairs with:

  • Fast Turnaround Times
  • Low Repair Rates
  • Long Repair Service Warranties
  • High Temperature Option Available!

Fill out our Request for Quote button on the website and include the manufacturer, model number, capacity, etc… and we can get an estimated quote sent to you.

Load Cell Kit For Weighing Tanks and Vessels

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Cardinal Scale Manufacturing has a wide variety of Made in America load cell kits which allow you transform almost any vessel or platform into an integrated weighing system. A few simple things need to be considered when choosing the right system. We’ll also discuss the proper installation and setup methods to use.

Whether utilizing beam, tension, or compression cells in either analog or hydraulic configurations, Cardinal load cell kits give you flexible options to help solve many weighing applications.

To determine the total capacity of the system, you first need to know the total weight of the structure that the load cell stands will be supporting (dead load).

Add the anticipated maximum system live load to the actual dead load, and that total will be the necessary minimum system capacity. Normally, you want to divide this total by the number of load cells and then go up to the next largest size available load cell.

For example, let’s say a tank has an empty weight of 22,000 lb and an anticipated live load of 100,000 lb for a total combined load of 122,000 lb. Using four load cell stands, each cell will be seeing 30,500 pounds of anticipated weight. We would normally use a 50,000 pound load cell in this application. Since many times these systems are under a continual long-term load it is not uncommon for load cells to be almost twice the necessary capacity in order to help reduce signal creep.

load cell kit for weighing tanks

Installation of load cell kits begin by determining if the floor (in the case of stand assemblies) or the building structure (for tension systems) is strong enough to bear the anticipated load. If not, piers or footings may be needed or additional support structures added. For all overhead suspension type systems, safety chains must be provided locally to bear any anticipated load due to component failure.

After the system is assembled, it is necessary to make sure that all of the load cells are taking equal dead load to the extent that it is possible. After the millivolt readings are as close as possible, secure the load cell stand assembles. Grouting the stands in place is the preferred method for long-term accuracy.

Most Cardinal Scale load cell stand kits come with checking designed into the stand itself. Depending on the device, some applications may require additional checking. Mixers and blenders are examples of devices that may need additional checking. Also, very tall tanks or hoppers may require additional restraints due to wind load on the structure.

Many systems using load cell kits require the connection of electrical supply or control wiring, as well as pipes and supply augers. Discharge chutes or pipes are used to get material out of the tank or hopper. It is very important to understand that anything connected to the scale structure must be installed with flexible couplings so that no path is present for force to be shunted off to ground during the weighing process. The more items that are connected to the structure the harder it is to get accurate weights.

For more information, contact the sales team at Central Carolina Scale (919) 776-7737

Common Issues Found on Tanks with Load Cells For Weighing

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It’s fairly common to see tanks used in various industries that have load cells or weigh bars underneath, connected to a digital weight indicator. This is a great way to keep track of how much product is inside the tank. These systems generally work very well but every now and then you will find a system that has some errors. Below is a list of problem areas to consider when it comes to tanks and hoppers that have load cells. The information applies to tanks and hoppers currently in operation and also if you’re thinking of putting load cells under one of your existing tanks the information below could help you make a better decision as well.

Probably the number one issue we see is binding. It could be due to something like rigid piping or some kind of attachment that has been added or modified since the scale was put into service. Whatever the case may be, the tank needs to be free and able to get an accurate and consistent weight. We typically see either three or four module systems and that is usually what we recommend.

What type of load cell should you choose? Talk with your scale company to determine what load cell will work the best. The single-ended shear beam cell is designed for low-profile scale and process applications. The shear-beam cell strain gauge cavity contains a thin metal diaphragm onto which the strain gauges are mounted. Typical shear beam capacities range from 1,000 lbs through 20,000 lbs, although some manufacturers offer shear beams up to 40,000 lbs. One end of the shear-beam contains the mounting holes while the opposite end is where the cell is loaded. The cell should be mounted on a flat, smooth surface with high strength hardened bolts. The larger shear beam cells have more than two mounting holes to accommodate extra bolts and keep the hardware from stretching under stress load. The double ended shear beam characteristics are similar to those of the single-ended shear beam. The most common bridge resistance for this load cell is 700 ohm. It is most commonly used in truck scales and tank and hopper applications. Instead of being secured at one end with the load applied to the other end as in the single-ended shear beam, 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. S-Beam load cells derive their name from their shape which is the shape of the letter S. The S-beam is normally used in tension applications. However, there are S-beams available which are bidirectional. They are primarily used for mechanical-to-electronic scale conversions, platform scale and general purpose weighing applications. They vary in size from as low as 25 lbs to as high as 20,000 lbs. When mounting an S-beam, remember to include the side from which the cable extends is the dead portion of the system. Movement of the cable in the live part of the system can be a source of weighing errors.

Aluminum load cell elements are used primarily in single point, low capacity applications. The alloy of choice is 2023 because of its low creep and hysteresis characteristics. Aluminum load cells have relatively thick web sections compared to tool steel cells of comparable capacities. This is necessary to provide the proper amount of deflection in the element at capacity. Machining costs are usually lower on aluminum elements due to the softness of the material. Single point designs can be gauged for costs similar to those of bending beams. Load cells manufactured from tool steel elements are by far the most popular cells in use today. The cost to performance ratio is better for tool steel elements compared to either aluminum or stainless steel designs.  Stainless steel load cells are made from 17-4ph, which is the alloy having the best overall performance qualities of any of the stainless derivatives. Stainless steel cells are more expensive than tool steel load cells. They are sometimes fitted with hermetically sealed web cavities which makes 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 steel, other than a higher resistance to corrosion.

Environmentally protected load cells are designed for “normal” environmental factors encountered in indoor or protected outdoor weighing applications. By far the most popular type, these load cells may employ strategies like potting, rubber booting, or redundant sealing to afford some protection from moisture infiltration. Potted load cells utilize one of several types of industrial potting materials. The liquid potting material fills the strain gauge cavity then gels, completely covering the strain gauge and wiring surfaces. While this may significantly diminish the chance of moisture contamination, it does not guarantee extended waterproof performance, nor does it withstand corrosive attack. A second method of protection uses an adhesive foam-backed plate. This protection affords some moisture and foreign object protection. In many cases, manufacturers will use a caulking material to seal the plate to decrease the potential for cavity contamination. A common approach among manufacturers to further decrease the entry of moisture to the strain gauge combines both a potted cavity and a foam-backed plate, in a process called redundant sealing. Yet another strain gauge cavity protection strategy is the rubber boot. Commonly employed with cantilever and bending beam models, the boot covers the cavity and is secured by clamps. While this provides easy access for repairs, the boot may crack if not lubricated regularly, allowing contaminants into the load cell cavity. Lubricating the rubber boot during routine inspections will contribute to the long-term durability of the load cell. Protecting the strain gauge cavity is just one consideration in protecting a load cell from contamination. Another susceptible area is the cable entry into the body of the load cell. Most environmentally protected load cells incorporate an “O” ring and cable compression fitting to seal the entry area. This design provides protection only in applications with minimal moisture. In high-moisture areas, it is safest to install all cabling in conduit, providing both a moisture barrier and mechanical protection. Although environmentally protected load cells keep out unwanted contaminants, they are not suited for high moisture, steam, or direct wash down applications. The only long-term strategy for these applications is to use true hermetically sealed load cells.

Hermetically sealed load cells offer the best protection available for the weighing market. Using advanced welding techniques and ultra-thin metal seals, these load cells handle the extremes of harsh chemical and washdown applications. What makes the seal unique is the process of laser-welding metal covers to protect the strain gauge and compensation chambers. The cavities are then injected with potting or, in the case of glass-to-metal seals, filled with a pressurized inert gas, providing a redundant seal. As a final assurance of the integrity of the seal, a leak test is conducted to reveal any microscopic flaws in the sealing weld. True hermetic protection addresses both the strain gauge cavity and cable entry area. The most advanced cable entry design employs a unique glass-to-metal bonding seal which makes the cable termination area impervious to moisture. Cable wires terminate at the point of connection to the load cell, where they are soldered to hermetically sealed pins that carry signals to the sealed strain gauge area through a glass-to-metal seal. Water or other contaminants cannot “wick up” into the load cell, since the cable ends at the entry point. This design allows for field-replaceable cable, since the connection is outside the load cell. Note, stainless steel load cells are not synonymous with hermetically sealed load cells. While environmentally-protected stainless steel load cells may be suitable for dry chemical corrosive environments, hermetically sealed stainless steel models are the appropriate choice for high-moisture or washdown applications.

It is vital to the performance of a weighing system to select load cells of the correct capacity. Here are some guidelines, all load cells selected must be of the same capacity. Estimate the vessel dead weight, including all piping, pumps, agitators, insulation and vessel heating fluids. Add the maximum live weight of product to be weighed to the dead weight. This is the gross weight of the vessel and contents. Divide the gross weight by the number of legs or support points. This is the nominal weight which will be carried by each load cell. Select a load cell with a capacity somewhat greater than the nominal weight. The following should be considered when determining how much greater the load cell capacity should be; is your dead weight accurate? Will the load be evenly distributed on all cells? Is the vessel fitted with an agitator or subjected to shock loading? Is it possible the vessel will be overfilled, exceeding your live weight value? Will the vessel be subjected to wind or seismic loading? A good rule of thumb is to select a load cell with a capacity 25-50% in excess of the calculated nominal load per cell. Once the load cell capacity has been determined, check that the live weight signal is adequate for the instrumentation selected.

weigh bar kit for tanks

If you’re designing your tank you will want to make sure that you provide an easy way for scale companies to hang test weights evenly all around the tank for testing and calibrating your system. Also, don’t forget to take safety into consideration. Our scale technicians are fairly agile but a little planning up front can make the tanks much easier to test and work on. If you’re in the planning stage, make sure you work with a scale company to ensure that you spec the right parts for your application. For example, we look at several factors such as the weight of the tank, number of legs, and the expected amount of product the tank will hold to determine what capacity of load cell or weigh bar to place underneath.

Finally, you need to think about the environmental conditions such as extreme temperatures, moisture, vibration, and corrosive substances. If any of these elements take place, adjustments such as digital filtering or different products such as hermetically sealed load cells may be recommended.

If you’re looking to place load cells under your tank or add load cells to your hopper, contact us at (919) 776-7737 and we can discuss the options that are available.

What Does The Arrow On A Load Cell Mean?

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One question we are asked occasionally is what does the arrow on my load cells mean and what direction should it be pointing?

As you can imagine, correct load cell orientation is necessary for your scale to function properly. Most load cells have an arrow that tells you the direction of the load. When weight is applied to the scale, the load cell will deflect in the direction the arrow is pointing. When installed correctly, this deflection provides a positive output (based on the load cell color code) which is then interpreted as weight. If the load cell is installed incorrectly, you won’t get a positive weight reading on your scale.

Also, make sure you know your load cell’s color code. They can vary by manufacturer, but don’t worry we have a web application to alleviate any confusion. Just visit the link above and enter the load cell’s manufacturer and model to see the correct color code.