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What is Moment Compensation?

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Moment compensation refers to a process of adjusting or counterbalancing the effects of an external force or torque, known as a moment, on a system or object. This is often done in engineering or physics contexts where precise control and stability are required, such as the design of force measurement applications.

Moment compensation is often used to prevent unwanted movements or deformations in systems, to ensure precision and accuracy in measurements, or to maintain stability and control during operation. Moment compensated load cells improve accuracy by compensating for the impact of external forces and moments on the measurement, allowing for more precise and reliable measurements.

Most load cells are sensitive to orientation and loading concentricity. When external forces or moments are introduced, measurement errors are more common and reduce the accuracy of the readings. These external forces or moments can come from various sources. Examples of external forces or moments that can affect the accuracy of load cells and require moment compensation:

  • Off-axis loading: When the load is applied off-center to the load cell, it creates a moment that can introduce errors in the measurement.
  • Temperature changes: Changes in temperature can cause thermal expansion or contraction of the load cell, which can introduce measurement errors.
  • Vibration: Vibrations from nearby equipment or processes can cause the load cell to vibrate, creating measurement errors.
  • Changes in orientation or position: Changes in the orientation or position of the load cell can cause gravitational forces or other external forces to act on the load cell, affecting the measurement.
  • Torque: When a load cell is subject to torque, such as twisting or bending forces, it can introduce measurement errors.
  • Wind or air currents: Air currents or wind can create external forces on the load cell that can affect the measurement

A load cell that is moment compensated can minimize or eliminate these errors, resulting in higher accuracy. Load cells with moment compensation can be more sensitive to slight changes in the load, as it can compensate for any external forces or moments that might affect the measurement.

Moment Compensation is an Interface Differentiator

Interface’s moment compensation process reduces force measurement errors due to eccentric loads by deliberately loading cell eccentrically, rotating load, monitoring and recording output signal, and then making internal adjustments to minimize errors. Every product we ship must pass moment compensation specifications and performance requirements. Every Interface LowProfile™ load cell is moment compensated to minimize sensitivity to extraneous loads, a differentiator from other load cell manufacturers.

When load cells are moment compensated, they can be used in a wider range of applications, including those with complex or dynamic loads, which might be difficult or impossible to measure accurately using a load cell without moment compensation. Interface’s LowProfile Load Cell models have the intrinsic capability of canceling moment loads because of its radial design. The radial flexure beams are precision machined to balance the on-axis loading.

Moment compensated load cells are designed to counteract the external forces or moments by using a configuration of strain gages and electronics that can detect and compensate for these forces. The strain gages are arranged in a way that allows the load cell to measure the force applied to it in multiple directions, and the electronics can then use this information to calculate the impact of external forces and moments on the measurement.

Interface uses eight gages, as opposed to the four used by many manufacturers, which helps to further minimize error from the loads not being perfectly aligned. Slight discrepancies between gage outputs are carefully measured and each load cell is adjusted to further reduce extraneous load sensitivity to meet exact specifications.

Moment compensation improves the stability of a load cell, particularly in situations where the load is off-center or subject to torque. This can prevent the load cell from shifting or becoming damaged, leading to more consistent and reliable measurements. It also improves the durability of a load cell, as it can help protect it from the impact of external forces or moments that might cause damage or wear over time.

ADDITIONAL RESOURCES

Addressing Off-Axis Loads and Temperature Sensitive Applications

Contributing Factors To Load Cell Accuracy

Off-Axis Loading 101

How Do Load Cells Work?

Load Cell 101 and What You Need to Know

Get an Inside Look at Interface’s Famously Blue Load Cells

Strain Gages 101

 

Off-Axis Loading 101

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Off-axis loading refers to a situation where a load cell, which is a device designed to measure force or weight, is subject to forces that are not aligned with its primary sensing axis. Load cells are typically designed to measure forces that are applied along a specific direction or axis, which is known as the primary sensing axis. When forces are applied to the load cell in other directions, this is referred to as off-axis loading.

Off-axis loading can affect the accuracy of load cell measurements, as the load cell may not be able to accurately distinguish between forces that are applied along the primary sensing axis and forces that are applied in other directions. This can result in errors in the measured weight or force.

To minimize the effects of off-axis loading, load cells are often designed with measures to reduce sensitivity to forces applied in other directions. These may include mechanical features such as strain relief structures or specialized materials that are more resistant to off-axis loading. Additionally, load cells are often installed and used in ways that minimize the likelihood of off-axis loading, such as aligning the primary sensing axis with the direction of the applied force. Be sure to carefully follow all Force Measurement Installation Guides provided with sensor.

What can be done to protect from off-axis loading?

Off-axis loading can affect the accuracy of load cell measurements, so it is important to take steps to protect against it. Here are a few ways to do so:

  • Use proper mounting and alignment: Load cells should be mounted and aligned in a way that ensures that the primary sensing axis is aligned with the direction of the applied force. This helps to minimize off-axis loading and ensure accurate measurements.
  • Use appropriate accessories: Using accessories such as adapters or mounting bases can help to ensure that load cells are properly aligned and oriented, minimizing the potential for off-axis loading.
  • Use anti-rotation features: Many load cells are equipped with anti-rotation features, such as bolt-hole patterns or keyway slots, which help to prevent the load cell from rotating around its mounting point. This can help to maintain proper alignment and reduce the effects of off-axis loading.
  • Use overload protection: Overload protection features, such as limit switches or stoppers, can be used to prevent load cells from being subjected to excessive forces or moments. This can help to prevent damage to the load cell and ensure accurate measurements.
  • Use a protective enclosure: Load cells can be placed in protective enclosures that shield them from external forces and environmental factors. These enclosures can help to protect against off-axis loading, as well as other types of interference.

By taking these steps, load cell users can help to protect against the effects of off-axis loading and ensure accurate and reliable measurements.

Product designs that mitigate off-axis loading

Engineers are constantly working to design new load cells that are more resistant to off-axis loading.  In fact, Interface product engineers have several products that are designed to protect from off-axis loading, including:

  1. ConvexBT Load Button Load Cell
  2. SuperSC S-Type Miniature Load Cell
  3. MBP Overload Protected Miniature Beam Load Cell
  4. MRTP Miniature Overload Protected Flange Style Reaction Torque Transducer
  5. MBI Overload Protected Miniature Beam Load Cell
  6. LBMP Overload Protected Compression Load Button Load Cell
  7. SMT Overload Protected S-Type Load Cell
  8. WMCP Overload Protected Stainless Steel Miniature Load Cell with Male Threads

By optimizing the mechanical design of load cells to minimize their sensitivity to off-axis loading this can include use of materials, such as composites or alloys, which are more resistant to deformation and strain. It also includes the use of specialized geometries that can help to distribute forces more evenly and reduce the effects of off-axis loading.

As well, engineers utilize built-in electronic compensation to correct for the effects of off-axis loading. This may involve using additional sensors or feedback loops to monitor the load cell’s response to external forces and adjust the output accordingly.

Interface engineers use a multi-disciplinary approach to designing load cells that are more resistant to off-axis loading. By combining advances in mechanical design, electronics, manufacturing, and simulation, they are creating load cells that are the most accurate in by classification in the world.

ADDITIONAL RESOURCES

ConvexBT – The Most Innovative Load Button Load Cell

Eccentric Loading Analysis for SuperSC S-Type Miniature Load Cell White Paper

Addressing Off-Axis Loads and Temperature Sensitive Applications

Benefits of Proof Loading Verification

How Do Load Cells Work?

New Technical White Paper Analyzes SuperSC S-Type Miniature Load Cells

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Interface recently introduced a revolutionary new miniature load cell, the SuperSC. The extremely compact design makes it an ideal all-purpose load cell with high accuracy measurement in an exceedingly small form factor.

The SuperSC (SSC) models are part of the Interface product line of shear s-cells. They are specifically designed as environmentally sealed and insensitive to off axis loading. This product is available in capacities ranging from 25 to 1000 lbf (100 N to 5 kN). The new SuperSC force transducer easily fits requirements for a high accuracy sensor that can be designed into components, equipment, and end products.

In our new technical white paper, Eccentric Loading Analysis for SuperSC S-Type Miniature Load Cell, Interface’s Raymunn Machado-Prisbrey, Design Engineer for OEM Solutions, provides an extensive review of the performance and capabilities of the new SuperSC.

The paper details FEA analysis performed on spring elements of equivalent capacity, in this case 250 lbs. Two eccentric load scenarios were considered: a full scale axially applied load with three degrees of misalignment and a full scale load applied to the edge of the element loading surface. Results of this analysis are available in the new white paper, available for download here.

Additionally, the new technical review highlights SuperSC data, misalignment analysis and edge loading, providing results and images of each test.

The Eccentric Loading Analysis for SuperSC S-Type Miniature Load Cell conclusion sums it up clearly. The Interface SuperSC S-Type Load Cell outperforms traditional s-type bending cells in output consistency and safety factor stability when loaded at three degrees of axial misalignment.

The SuperSC has a higher output change under edge loading conditions than the s-type design; however, linearity is much better and safety factor remains acceptable. S-bending cells are not capable of withstanding this level of edge loading from a mechanical standpoint.

You can also watch the recorded online seminar below to get the inside scoop on this revolutionary new product.

ADDITIONAL RESOURCES

Interface Introduces SuperSC S-Type Miniature Load Cell

Superior S-Types Webinar Recap and New SuperSC

 S-Type Load Cells 101

Interface OEM Solutions Process

 

Strain Gage Design Under Eccentric Load WRSGC Presentation

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By Ashlesa Mohapatra, product design engineer, Interface

In the global marketplace, Interface is well known as providing the force measurement industry’s most reliable and accurate products. One of the key reasons that Interface consistently earns this recognition is because we manufacture our own strain gages. Products engineered and manufactured at Interface use our proprietary strain gages, and each designed for the specific transducer model based on the application type and environment for use.

As an example of our dedication to quality and excellence in performance as it pertains to strain gages, I recently shared a technical presentation on the negative effects of eccentric load and how strain gage design can reduce these challenges.

Below is a brief recap of this presentation made to the attendees of the Western Regional Strain Gage Committee meeting that took place in Tempe, Arizona in October 2022. The summary explains why strain gage design can make all the difference in quality versus poor performance with load cells.

Interface redesigned the strain gages on one of our mini load cells, the LBSU Miniature Load Cell Load Button, also known as our ConvexBT – The Most Innovative Load Button Load Cell. Our goal in the redesign was to create more controlled and repeatable loading, in turn creating a more predictable output. Our research focused on strain gage designs for load cells where mechanical moment compensation is not feasible.

The main challenge with this initiative was overcoming the errors associated with eccentric loading by making the installation process smoother through a redesign.  This is difficult because strain gages are very small in size and therefore more difficult to work with, in addition they are extremely sensitive to the environment with factors like temperature, humidity, cleanliness and electric interference all potentially effecting performance.

Before diving into the redesign, I would like to touch on eccentric loading and the errors it will cause, as well as the varied factors in strain gage manufacturing that can lead to errors causing eccentric load. There are two types of eccentricity: loading and mounting. Eccentric load results from improper loading or mounting of the strain gage, which leads to off-axis loads and bending. This causes several problems including distorted measurement results, decreased load cell accuracy, and diminishing life of the load cell.

When a strain gage is mounted on the load cell incorrectly or gages are badly bonded, it will almost always be an error source and contribute to mounting errors. Also, when strain gages are not bonded to the load cell at appropriate temperature and humidity, it leads to bubbles under the gage. Chemical composition of the strain gage is critical, such as the adhesive between the foil and backing, based on the application in which load cell will be used in a lab, machine, or testing program.

With these factors in mind, we set out on a redesign continuous improvement project. The previous design of this products strain gages was rectangular in shape. So, when the load cell was loaded, eccentrically or not, the strain field would not pass through because of shape. Therefore, we began to look at other shapes for our strain gage design, ultimately landing on a circular “diaphragm” style strain gage that allow strain fields to pass through.

One of the features of this newly designed strain gage is the proprietary adhesive foil we used to adhere the foil to the backing. This adhesive provided a great deal of benefit including a lower modulus of elasticity making it resilient to adhesive failure, and the elasticity also allows for better flow.

Another feature is the full bridge gage pattern we used that provides three key advantages. This includes fewer solder joints and reduced risk for electrical shorts due to simplified wiring, reduced symmetry error, and consistent thermal performance.

One process improvement we wanted to point out was that in our calibration process we only used 5V excitation voltage. Most manufacturers use 10V to calibrate their load cells. Due to lack of thermal mass in the thin diaphragm design of our strain gage, the zero will shift due to high voltage and low poor heat dissipation with 10V. We use a 5V excitation voltage to calibrate these miniature load cells instead of the alternative to prevent overheating of the cell.

To further improve the design, we enhanced the inspection process. Our diaphragm gages are quality inspected for accurate mounting with visual and electrical testing. Visual testing includes checking for air bubbles under the gage, badly bonded edges, unreliable solder connections and flux residues. Electrical tests include checking for electrical continuity and insulation resistance.

We then moved our attention to the circuit board. Some manufacturers use a circuit board in the cable due to the limited space within the cell to improve zero balance zero balance and to better compensate for temperature. However, bending or moving this cable would put pressure on the board and shift the zero. Therefore, we elected to install an abradable compensation resistors inside the flexure instead of the cable. This keeps the compensation resistor close to the gages and is intimately bonded to the body of the sensor to improve the reaction time of the cell to temperature.

To evaluate and confirm that our design was superior, we assessed three different strain gage styles: the rectangular gages (discreet gages), patch gages, and our diaphragm gage. Each of the gage styles were placed on three different load cells and loaded at one degree centricity. This test was run at 45 degree increments eight times. The results showed diaphragm style provided more reproducible result under eccentric load compared to other gages.

This was an interesting undertaking that taught the project team a lot about strain gage design and eccentric load. What I took away from this experience, other than a superior design for our ConvexBT Load Button Load Cells, is that any commercially successful product has a strong process behind it. You also need to have a clearly defined process that includes a continuous improvement plan. Interface Minis are a popular product line that has been around for many years. As soon as a product like this hits a point of stagnation, it will lose its hold on the market. I am proud of our team’s ability to avoid stagnation by taking critical steps to improving the Mini product line, maintaining our reputation for having the best quality, accurate and reliable products no matter the capacity available for precision force measurement.

Western Regional Strain Gage Committee (WRSGC), a technical division of the national Society for Experimental Mechanics (SEM), was established to promote a free interchange of information about strain measurement techniques using strain gages.

Interface is a proud member and sponsor of WRSGC. Our engineers participate in the technical conferences, in both presentation and attendance. Interface’s Product Design Engineer Ashlesa Mohapatra presented at the event held in Arizona, October 17-19, 2022.

The Five Critical Factors of Load Cell Quality

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Accurate data and high-quality test and measurement programs have many contributing factors. None are more important than the devices and equipment used on the test line. At Interface, we understand this better than anyone else.

Quality is why our force measurement products are used and known across multiple, highly regulated, and complex industries for providing the most reliable and accurate data anywhere. It is also why Interface is recognized as the preeminent leader in load cell quality.

How do we reach this high standard that we continue to hit with every product that leaves our facility? It is our overriding commitment to quality and consistency. The most important aspect of this is the fact that Interface controls the entire manufacturing process of our load cells. Many providers outsource certain components like that strain gages. We build the strain gages, the load cells, integrate the strain gages into the load cells and we do our own test, calibration, and quality inspection on each device.

Through our development process, which has been created and perfected over 52 years, we have learned what makes a great load cell. To start, Interface Chief Engineer Ken Vining outlines the top factors in load cell quality.

Five Most Critical Factors of Load Cell Quality

#1 Repeatability

Repeatability is first on the list and it is what our customers consider the most important aspect of buying an Interface load cell. Anyone can develop a load cell that is accurate for the first 10 to 15 measurements, but as environmental factors and stress are inflicted upon the load cell it needs to last. Due to our experience in this industry, we understand how certain temperatures, loads and other factors can diminish the accuracy of a load cell. This is one of the reasons we work so closely with our customers. Every application is different, and if we understand the application, we can deliver a custom load cell that withstands the various stressors over time without providing diminishing returns. This ensures that our customers receive the same, high-quality data after 10 years of use that they received on day one.

#2 Longevity

Like repeatable data accuracy over time, the load cell also needs to feature a high-quality and ruggedized build to last physically. Constant application of weight, pressure or torque can diminish the build quality and strength of a load cell if it does not meet the material requirements of the application. This can also reduce accuracy and lead to higher costs if customers must replace their load cells regularly. Interface has worked across a wide variety of industries and we understand the materials necessary for nearly any environment. With proper use, build quality and routine maintenance, load cells should last a very long time. In fact, Interface still has load cells in use in the field from when we started building quality product more than five decades ago.

#3 Accuracy

Data accuracy is affected by a litany of factors in load cells. In fact, we wrote an entire white paper on this very topic called, “Contributing Factors to Load Cell Accuracy.” Once again, the application of the load cell is what determines the conditions that affect accuracy. These conditions include creep, side and eccentric load, temperature, humidity, the mounting process and more. Interface can customize each of our load cells to ensure these conditions are accounted for to maintain premium accuracy.

#4 Sensitivity to Off-Axis Loads

A typical load cell is designed to measure load in one direction. However, nearly any project using force measurement test processes is going to introduce an off-axis load. If the load cell is not designed to adjust for this and compensate for what is called moment, the data output will be skewed. This is another reason that customers need to be extremely specific when discussing the application of the load cell. There are several ways to compensate for moment; however, most of these adjustments are physical and occur in the design and manufacturing process. With a correctly calibrated and designed load cell, off-axis loads will be eliminated and will not affect the accuracy of the data.

Special Note: Our recent release of the new ConvexBT product, the first to market miniature load button load cell that is designed to solve for off-axis (eccentric) loading. Read more here.

#5 Access to Prominent Force Measurement Experts

Every factor of quality listed above is realized and accomplished through a close and transparent relationship between customer and force measurement provider. Every application dictates a different force measurement solution. When we understand the application, we can select the right type of load cell or customize an off the shelf load cell to meet the quality and accuracy needs necessary for any project. This is why a customer’s access to a force measurement expert is an integral part of load cell quality.

Every force test and measurement project can create a different challenge and developing an accurate and reliable load cell to meet those challenges can be tough. Therefore, Interface considers these five factors, and hundreds more, for every product we engineer and build. This is our unwavering commitment to quality and customer satisfaction.

Contributor:  Ken Vining, Chief Engineer and Head of Quality

Advancing Load Button Load Cell Capabilities with ConvexBT

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Demands for high precision testing utilized for compact designs and in confined spaces is growing. The requirements for quality, accuracy and most importantly reliability are what has driven the experienced engineers at Interface to create the newly released ConvexBT™ Load Button Load Cell product line.

The revolutionary design of the ConvexBT is a first of its kind load button load cell, providing better temperature resistance and more enhanced eccentric load rejection. Miniature load cells categorized as load buttons have been sensitive to off-axis, eccentric or misaligned loads. This means if the load is not exactly perpendicular to the surface it is resting on, the data could become skewed or inaccurate.

Interface designed the ConvexBT™ Load Button Load Cell to confine misaligned loads to the primary axis of the cell providing superior performance in comparison to similar products on the market in repeatability, better data and reproducible results.

“As technology advances, there is a growing demand to make devices and products more compact and convenient. This trend is happening across industries and is especially prevalent in medical, industrial automation and products reliant on advanced communications technology. To design and validate these products, our customers need force-sensing solutions that can fit in confined spaces and provide extremely accurate data. This is the driving force behind the development of ConvexBT, the next generation in force measurement device.” – Ted Larson, VP product management and marketing, Interface.

CONVEXBT FEATURES AND SPECIFICATIONS

The newly released ConvexBT product comes in two different sizes: 3/8-inch, and 1/2-inch, which are all manufactured using 17-4 PH heat treated stainless steel. These options provide a wide measurement range from 10 to 250 lbf, a compensated temperature range of 60° to 160°F, and an operating temperature range of -40° to 175°F.

Additional specifications for ConvexBT include:

  • 2.00 ± 20% mV/V rated output
  • ± 0.25 non-linearity as a percentage of full scale
  • ± 0.25 hysteresis as a percentage of full scale
  • ± 0.50 static error band as a percentage of full scale

Other load cell load buttons designs have also been extremely sensitive to temperature conditions. Interface has redesigned its ConvexBT ultra-precision product line of load buttons to ensure that this is no longer something the user has to account for by taking the sensing technology disrupted by temperature out of the cable, and designing it directly into the load button.

The new available ConvexBT models include the following capacities:

  1. ConvexBT Model LBSU-10 lbs 3/8″
  2. ConvexBT Model LBSU-25 lbs 3/8″
  3. ConvexBT Model LBSU-50 lbs 3/8″
  4. ConvexBT Model LBSU-100 lbs 1/2″
  5. ConvexBT Model LBSU-250 lbs 1/2″

Additional model capacities will be available this year.  You can view the complete product specifications as well as technical guide by visiting the product page here.

“ConvexBT was developed through a combination of intense research into growing technology trends in force measurement and actively collaborating with our customers to understand their unique challenges, By introducing the industry’s most advanced and versatile ultra-precision load button load cells, we are solving the test and measurement challenges associated with miniaturization of existing and new technologies.” – Greg Adams, CEO at Interface

The revolutionary ultra-precision line of ConvexBT™ Load Button Load Cells uniquely uses multi-point calibration for testing force on miniaturized products and within confined spaces where accuracy is paramount to success and safety. The requirements are critical to common buyers of miniature load cells, especially for use in medical devices, robotics and in industrial automation applications

In addition to its ability to solve test and measurement challenges with compact devices, another key benefit of ConvexBT is its versatility in that it can be used as a traditional test and measurement solution. It can also be installed into OEM components and devices as an advanced miniature sensing solution to collect accurate real-time force data on the product as it is in use.

ConvexBT is available now under the product family of Interface Mini® Load Cells. The product is part of a growing line of Interface Load Button Load Cells. The new ConvexBT model LBSU specifications are available here: /product-category/load-button-load-cells/.

Read more about Off-Axis Loads and Temperature Sensitive Applications here.