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Bending Beam Load Cell Basics

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Bending beam load cells are a versatile and cost-effective solution for many weighing and force measurement applications. These types of miniature load cells are small in dimension, which makes them ideal solutions for compact testing environments and for embedding into machines or products for continuous performance measurement.

The use of bending beam load cells expands across industries and applications, for weighing scales, medical devices, industrial process controls, robotic designs, packaging machinery and civil engineering projects.

How Bending Beam Load Cells Work

A bending beam load cell converts a force applied to it into an electrical signal by measuring the flexure of the beam. This is done by attaching strain gages to the beam. When the beam bends, the strain gages change their resistance, which is then converted into an electrical signal by a Wheatstone bridge circuit. The output signal is proportional to the applied load.

The bending beam load cell is bolted to a support through the two mounting holes. Under the covers, you can see the large hole bored through the beam. This forms thin sections at the top and bottom surface, which concentrate the forces into the area where Interface’s proprietary strain gages are mounted on the top and bottom faces of the beam. The gages may be mounted on the outside surface, as shown, or inside the large hole.

The compression load is applied at the end opposite from the two mounting holes, usually onto a load button that the user inserts in the loading hole.

MB Miniature Beam Load Cell

MB MINI BEAM LOAD CELL

The Interface Model MB is a miniature beam load cell used in test machines and a variety of low capacity applications.

  • Standard Capacities are 5 to 250 lbf (22.2 N to 1.11 kN)
  • Proprietary Interface temperature compensated strain gages
  • Performance to 0.03%
  • Low height – 0.99 in (25.1 mm)
  • Eccentric load compensated
  • ±0.0008% /˚F – max temperature effect on output
  • Low deflection

MBI Overload Protected Miniature Beam Load Cell

Interface’s Model MBI Overload Protected Miniature Beam Load Cell has better resistance to off-axis loads then other similar load cells and is fatigue rated.

  • Standard capacities from 2 to 10 lbf (10 to 50 N)
  • Proprietary Interface temperature compensated strain gages
  • Performance to 0.03%
  • Low height – 1in max
  • ±0.0008% /˚F – max temperature effect on output
  • 10x overload protection

MBP Overload Protected Miniature Beam Load Cell

Our Model MBP series Mini load cells provide a similar performance to Model MB series with the added safeguard of internal overload protection. This patented overload protection is accomplished via hard stops that are EDM machined into the load cell flexure. This provides a greater overload protection (2.5-10lbf ±1000% of full scale capacity, 100 N ±500% of full scale capacity), giving the user added protection in more severe applications.

  • Standard capacities from 2 to 10 lbf (10 to 50 N)
  • Proprietary Interface temperature compensated strain gages
  • 10x overload protection
  • Low height – 0.99 in (25.1 mm)
  • ±0.0008% /˚F temp. effect on output
  • 5′ Integral Cable (custom lengths available upon request)
  • NIST Traceable Calibration Certificate

MBS Parallelogram Load Cell

The Interface MBS Parallelogram load cell is made of lightweight aluminum construction and highly suitable for medical and robotics applications.

  • Capacities from 2.2 to 10 lbf (9.8 to 44.5 N)
  • Lightweight
  • Nonlinearity error 0.02% FS
  • Ideal for OEM applications

Double Bending Beam Cells

A very useful variation on the bending beam design is achieved by forming two bending beams into one cell. This allows the loading fixtures to be attached at the threaded holes on the center line, between the beams, which makes the sensitive axis pass through the cell on a single line of action.

Bending Beam Load Cell Applications

Material testing is a common application for bending beam load cells. This type of miniature load cell measures the forces applied to materials with a high degree of accuracy to determine stiffness, strength and durability of the specimen.

It is quite common to find bending beam load cells in industrial automation machines and robots to precisely measure the forces required for control, safety and efficiency. In robotics specifically, bending beam load cells will measure the force applied to the robot’s arms and grippers. The data is used to control the robot’s movements and to ensure that it is not damaging the objects it is handling.

Aerospace engineering have long used bending beam load cells in design, testing and manufacturing of aircraft and spacecraft. Automotive engineering use bending beam load cells to design and test vehicles for safety and reliability.

Due to Interface’s ability to custom design bending beam solutions that meet strict size, capacity and accuracy requirements, our products are commonly used in medical and healthcare applications.

Bending Beam Application for Medical Device Testing

In this application, the medical device product lab needs to apply known forces to stent and catheters to ensure they pass all necessary strength and flexibility testing. MBP Overload Protected Beam Miniature Load Cell is placed behind the guide wire for the stent or catheter. The motor will spin the linear drive, push the load cell, and guide the wire through the testing maze. The bending beam load cell connects to the DIG-USB PC Interface Module to record and store testing data for analysis. Read more.

Bending Beam Application for Vertical Farming

Vertical farming is the production of produce in a vertical manner using smart technology systems, while indoors using an irrigation system. A wireless force measurement solution is needed to monitor the amount of water being used, to ensure the produce is being watered just the right amount. Interface suggests installing four MBI Overload Protected Miniature Beam Load Cells under each corner of the trays of the produce to accurate measure the weight during watering. A JB104SS 4-Channel Stainless Steel Junction Box connects to each bending beam cell and to a WTS-AM-1E acquisition module. The device wirelessly transmits the sum weight to the WTS-BS-1-HA Wireless Handheld Display for multiple transmitters, and the WTS-BS-6 Wireless Telemetry Dongle Base Station. Interface’s Wireless Telemetry System monitored and weighed the amount of water being used on the produce in this vertical farming system to increase yield and conversation. Read more here.

Additional Resources

How Do Load Cells Work?

The Basics Of Shear And Bending Beams

Interface Mini™ Load Cell Selection Guide

Introducing Interface Load Cell Selection Guides

The Anatomy Of A Load Cell

Mini Load Cells 101

Load Cell 101 And What You Need To Know

Rod End Load Cells 101

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Rod end load cells are designed to measure the tension and compression forces applied to a rod or similar structure. This type of load cell consists of a rod with a threaded connector. The load cell’s strain gage measures the deformation caused by the applied force. As the force is applied to the rod, it deforms slightly, causing a change in the electrical resistance of the strain gage.

To provide a complete analysis of the forces being applied to the structure, rod end load cells are often used in pairs, with one load cell measuring tension and the other measuring compression.

Interface Rod End Load Cells utilize proprietary temperature compensated strain gages for high-accuracy measurement. For example, our popular REC Rod End Load Cell is fatigue rated and designed to go up to 100,000,000+ fully reversed cycles which makes them ideal for test article failure tests. Our REC models are resistant to off-axis and impact loading with performance to .04%. They are environmentally sealed and made of stainless steel. They are easy to integrate in actuators.

Rod end load cells are commonly found in test labs and used in industrial environments, mechanical systems, and testing machines. They are adaptable and reliable force measurement devices utilized for applications in various industries.

Common Rod End Load Cell Use Cases

  • Material Testing: Rod end load cells are widely used in material testing applications, such as tensile testing, compression testing, and fatigue testing. They help measure the applied forces accurately and provide data for analyzing material properties, structural integrity, and performance.
  • Machine Force Monitoring: Rod end load cells are used in industrial machinery to monitor and control forces applied to rods, shafts, or other structural components. They help ensure that the machinery operates within safe load limits, preventing overloading and potential failures.
  • Hydraulic and Pneumatic Systems: Rod end load cells are employed in hydraulic and pneumatic systems to measure the tension or compression forces experienced by cylinders, pistons, or actuators. This enables accurate force control and monitoring for proper system use.
  • Robotics and Industrial Automation: Rod end load cells are integrated into robotic systems to measure the forces exerted by robotic arms or grippers. This allows for precise force control, feedback, and safety features in tasks such as assembly, material handling, and force-sensitive operations.
  • Calibration and Test Lab Equipment: Rod end load cells are utilized in calibration and testing equipment, such as force testers and dynamometers. They provide reliable and traceable force measurements, ensuring the accuracy and calibration of the testing instruments.
  • Aerospace and Automotive Industries: Rod end load cells find application in both aerospace and automotive industries for various purposes, including component testing, structural analysis, quality control, and safety testing. There are many use cases to rod end load cells for multiple industries, as found in our application solutions.
  • Research and Development: Rod end load cells are used in research and development activities across different fields, enabling precise force measurements for studying material behavior, product development, and prototype testing.

Drone Fireworks Rod End Load Cell Application

Drone fireworks have become increasingly popular in recent years. During drone firework and light shows, drones are equipped with LED lights, flying in synchronized patterns to create displays in the night sky.  Four rod end styled Interface WMC Sealed Stainless Steel Miniature Load Cells  are installed to the necessary propeller motors measure the attached LED lights. Each are connected to a WTS-AM-1E Wireless Strain Bridge Transmitter Modules. The WMC’s measure the weight of the LED lights to monitor weight shifting or any uneven weight distributions. Data results are wirelessly transmitted through the WTS-BS-4 Wireless Base Station.

Interface offers a wide range of rod end load cells. The following highlights our standard models for this type of load cell. Customization is an option if a rod end load cell is needed to be designed into machines or used as a component within a specific product.

Interface Standard Rod End Load Cells

REC Rod End Load Cell stainless steel mini with capacities from 1K to 50K lbf (5 kN to 220 kN).

WMC Rod End Load Cell industrial grade rod end type has capacities 15K to 200K lbf (65 kN to 900 kN).

WMC Sealed Stainless Steel Miniature Load Cell environmentally sealed in capacities from 5 to 500 lbf (22 to 2200 N). Submersible versions also available.

WMC Sealed High Capacity Stainless Steel Miniature Load Cell ranging from 1K lbf to 10K lbf (5 kN to 45 kN). Submersible versions also available.

WMCP Overload Protected Stainless Steel Miniature Load Cell With Male Threads is an excellent safeguard in rugged applications with capacities 1.1 to 2.2 lbf (500 to 1000 gmf).

WMCFP Overload Protected Sealed Stainless Steel Miniature Load Cell With Female Threads in 1.1 to 2.2 lbf (500 to 1000 gmf) capacities are stainless steel, sealed, and environmentally protected.

WMCF Miniature Sealed Stainless Steel Load Cell is an industrial design with capacities from 5 to 10 lbf with female threads.

MTFS Miniature Tension Force Load Cell is a small sized tension load cell available in capacity ranges from 1 kN to 100 kN (224.8 to 22.5K lbf).

NEW! ITCA Tension And Compression Load Cell is ideal for measuring both tensile and compressive forces 2.2K lbf to 330.6K lbf (1 MT to 150 MT). The standard metric threads at each end of the load cell are designed to accept standard spherical seating rod-end bearings. Customization is available.

Benefits of Interface Rod End Load Cells

#1 High accuracy: Our rod end load cells provide high accuracy in measuring the tension or compression force applied to a rod or similar structure. They are capable of measuring very small changes in force, making them suitable for precise measurement requirements and applications.

#2 Range of measurement and dimensions: Interface rod end load cells are available in a wide range of measurement capacities and compact size making them suitable for use in a variety of industrial and mechanical applications.

#3 Durability: Rod end load cells are designed to withstand harsh environments, high loads, and repetitive use. They are made from ruggedized materials, stainless steel or aluminum, so that can withstand exposure to moisture, dust, and other environmental factors.

#4 Versatility: Rod end load cells can be used in a variety of applications including material testing and manufacturing processes. They can be easily integrated into existing actuation systems and are compatible with a variety of instrumentation and control systems.

Rod end load cells, as highlighted in our recent Testing Lab Essentials Webinar, are used in applications that involve the measurement of tension or compression force on a rod or similar structure, such as in material testing or in the calibration of testing machines.

Load Cells Versus Piezoelectric Sensors

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Load cells and piezoelectric sensors are used in all types of measurement applications. While both types of sensors are used to measure similar physical quantities, they work on different principles and have distinctive characteristics.

By simple definition, load cells measure the amount of force or weight being applied to them. The amount of force a load cell is engineered to measure is numerated by the capacity of the model specification and design, such as 50lbf (pounds-force) or 5kN (kilonewton). When a force is applied to the load cell, the metal body deforms slightly, which changes the resistance of the strain gages. This change in resistance is then measured and used to calculate the amount of force being applied to the load cell.

Piezoelectric sensors work on the principle of piezoelectricity. They are made of materials that generate an electric charge in response to mechanical stress, such as pressure or vibration. Piezoelectricity is a property of certain materials that allows them to generate an electric charge in response to applied mechanical stress, such as pressure or vibration. The word “piezo” comes from the Greek word for “squeeze” or “press,” which refers to the fact that these materials generate an electric charge when they are squeezed or pressed. When a force is applied to a piezoelectric sensor, it generates a voltage proportional to the amount of force being applied. This voltage can then be measured and used to calculate the force or weight being measured. Piezoelectric sensors are most often used in vibration and pressure tests.

Load cells are more suitable for applications where high accuracy is required, as they are more sensitive than piezoelectric sensors in detecting smaller changes in force. Load cells are characteristically more robust and can withstand higher loads without being damaged. Piezoelectric sensors, on the other hand, can be more fragile and may require more careful handling to avoid damage.

Load Cell Advantages

  • Higher accuracy: Load cells are more accurate than piezoelectric sensors, especially when measuring low loads. Load cells can provide precise and reliable measurements with minimal error, making them ideal for applications that require high accuracy. Read: Specifying Accuracy Requirements When Selecting Load Cells
  • Lower sensitivity to temperature changes: Load cells are less sensitive to temperature changes than piezoelectric sensors. This means that load cells can maintain their accuracy even when the temperature changes, while piezoelectric sensors may need to be calibrated frequently to maintain accuracy. Read: Understanding Load Cell Temperature Compensation
  • Better linearity: Load cells have a more linear response than piezoelectric sensors, which means that their output is more predictable and easier to calibrate. This is particularly important in applications where accurate and repeatable measurements are critical.
  • Higher durability: Load cells are more robust and can withstand higher loads without being damaged. This makes them suitable for applications where high loads are present, such as in heavy machinery or construction.
  • Lower cost: Load cells are often less expensive than piezoelectric sensors, making them a more cost-effective choice, especially for OEM use cases.

Piezoelectric sensors are used in a wide range of applications that require the measurement of vibration or acceleration. For example, piezoelectric sensors can be used in machinery and equipment to monitor vibrations and detect potential problems, such as imbalances or misalignments. They are the sensors used in cars to measure pressure, such as in tire pressure monitoring systems or fuel injection systems. Piezoelectric sensors are found in ultrasound imaging to generate and detect sound waves and in musical instruments, such as electric guitars or electronic drum kits, to convert vibrations into electrical signals for amplification.

In selecting the right load cell for any project, check out our new Load Cell Selection Guide. It is a useful resource to determine the capacity, capability and design features that are best suited for your applications. You can also check out How to Choose the Right Load Cell.

Load cells and piezoelectric sensors have distinctive characteristics and advantages, thus specific application requirements will determine the choice of sensor. For questions about selecting the right sensor for your application, contact our solutions engineers.

Additional Resources

How Do Load Cells Work?

LowProfile Load Cells 101

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

Load Cell Basics Sensor Specifications

Interface Load Cell Field Guide

 

 

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

 

How Do Load Cells Work?

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What is the most frequently searched question searched related to Interface and the products we manufacture? It may seem overly simple to test engineers and frequent buyers of Interface force measurement solutions, but to many it is an important question. What do inquisitive users of the internet want to know? They want to how load cells work.

Diving into this question, we learned that many understand the purpose of a load cell. A load cell converts an applied mechanical force, whether that is tension, compression, or torsion, into a measurable electrical signal. Any change in force, increases or decreases the signal output change in proportion.

There are fewer people that understand how a force transducer works. After 55 years making load cells, we thought we should help provide an answer to an incredibly good question. Here is a quick technical brief on how a load cell works.

Interface Tech Talk Answers How Do Load Cells Work

A load cell has two basic components. It has a spring element that is often known as a flexure that mechanically supports the load to be measured and a deflection measurement element that responds to flexure movement resulting from the application of force.

In simpler terms, there is a bending beam under the load and when weight or force is applied, the change in bend (deflection) results in change in output.

A load cell’s basic function is to take applied force and convert it into an output signal that provides the user with a measurement. This process of converting a force into data is typically completed through a Wheatstone bridge that is comprised of strain gages.

Strain Gage Load Cells: A strain gage is typically constructed of an exceptionally fine wire or metal foil that is arranged in a grid-like pattern. Strain gages are strategically placed on the load cell flexure and bonded securely, such that the force induced deflection of the flexure causes the gages to stretch or compress. Thus, when tension or compression is applied, the electrical resistance of the strain gages changes and the balance of the Wheatstone bridge then shifts positive or negative. Fundamentally, the strain gages convert force, pressure, or weight into a change that can then be measured as an electrical signal.

Why use strain gages in load cells? Strain gage characteristics include thermal tracking, temperature compensation, creep compensation, frequency response, and non-repeatability. The major advantage of the strain gage as the deflection measuring element is the fact that it has infinite resolution. That means that no matter how small the deflection, it can be measured as a change in the resistance of the strain gage.

The strain gage is the critical foundation of a load cell and the most vital component for accurate and reliable measurements. One thing to understand about Interface load cells is that we develop our own strain gages in-house using a proprietary manufacturing process to ensure premium performance.

In addition to strain gage load cells, there are also two different less common load cells that use a diverse types of data collection method. This is defined as pneumatic and hydraulic methods.

Pneumatic: These load cells are typically used for measuring lower weights with high degrees of accuracy. They measure weight in terms of force-balance, meaning that weight is reported as a change in pressure. Key advantages of pneumatic load cells are their resistance to electrical noise and inability to spark, in addition to their low reactivity to temperature changes.

Hydraulic: As the name suggests, these load cells utilize fluid pressure for measurement. Like pneumatic load cells, hydraulic load cells balance force by measuring weight as a change in pressure, and the pressure of the fluid rises because of an increase in force. These load cells have no electric components, allowing them to perform well in hazardous conditions.

How to choose the right load cell?

Load cells seem like an extremely basic piece of equipment used to measure different forces such as weight, compression, tension, torsion, or a combination of these. It can be on a single axis or across multiple axes. However, there are many distinct types of strain gages and load cells that are designed for a variety of environments and force measurement testing requirements.

Specifications of a measurement sensor validate the design capabilities and capacities, including the amount of measurement that can be used for a particular device before you exceed the limits.

The field of force measurement has the same types of constraints as any other discipline. It starts with considerations of weight, size, cost, accuracy, useful life, and rated capacity. This also means considerations for extraneous forces, test profile, error specifications, temperature, altitude, pressure, and environment are particularly important when choosing a load cell.

The major difference in strain gages is the base material used in the manufacturing process. Varied materials are used when a load cell needs to perform optimally in a variety of temperatures, humidity levels, and elevations. Matching the correct strain gage and a load cell to the customer’s needs is critical to accuracy. It is why Interface has excelled in building precision load cells for five and half decades and continues to be a trusted supplier to industry market leaders, innovators, engineers, and testing houses around the world. It is what we do best. It is what we know.

Our team of engineers and manufacturing experts use expertise that has built over time, applications, and load cell experience. A load cell starts as a raw piece of steel, aluminum, or other metal. It is machined, gaged, wired, finished, and calibrated by experts in load cell production, machinists, and quality engineers.

If you are just beginning to work with products that require accurate force measurement, we would suggest that you speak with an application engineer who can help you understand the load cell that will fit best for your use case.

When shopping for a load cell it is important to know the type of force that you need to measure, the size of the application, the environment in which you will be measuring the application, the accuracy of data needed, the type of communication output that will work with your current test system and if there are any unique details about your application, like extreme or hazardous conditions.

ADDITIONAL RESOURCES

Interface Load Cell Field Guide

Interface Presents Load Cell Basics

LowProfile Load Cells 101

Load Cell 101 and What You Need to Know

Technical Library

LowProfile Cutaway

Extending the Calibration Range of a Transducer

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Interface has added a new technical white paper to our library, Extending Transducer Calibration Range by Extrapolation. This detailed engineering report delves into the concept of extrapolating the partial capacity calibration to full capacity, possibly thereby providing an increase in confidence in the extended range. The following is a brief introduction to the white paper and explanation of how extrapolation can increase confidence in your data.

Introduction

Force and torque transducers must be calibrated in a laboratory in order to be useful in their intended application. Applications of the transducers range from relatively basic process measurements to relatively critical calibration of other transducers or equipment. The laboratory calibration consists of loading the transducer with known masses and lever arms or using a comparison method where load is generated by hydraulic or pneumatic means and the transducer under test is compared to a reference transducer. In either method, the cost of calibration equipment rises rapidly with increasing capacity.

Many calibration laboratories have means to calibrate force up to about 10,000 lbf and torque up to about 20,000 lb-in. But capability for higher ranges is scarce. In fact, there are a very limited number of laboratories in the United States that have capability for force over 200,000 lbf and torque over 100,000 lb-in.

There has been some practice in the past by some manufacturers of transducers to calibrate a high capacity transducer at partial capacity and leave the owner to go on hoping and guessing for the sensitivity of the upper end of the capacity. This gives rise to the concept of extrapolating the partial capacity calibration to full capacity, possibly thereby providing an increase in confidence in the extended range.

When Full Capacity Calibration is Not an Option

Strain gage transducers are basically linear. That is, the output follows the input at a near constant ratio. The nonlinearity is routinely measured and typically is in range of ± 0.10%FS or less. This provides for the ability to interpolate values between calibration points with near zero error. But the same is not true for extrapolation which is really estimating values that are beyond the observable range. Conventional wisdom has it, and logically so, that extrapolation is not a valid method of calibration.

Extrapolating is similar to forecasting and that idea helps one realize the liability of it. But the various methods of extrapolation are not all equal. The purpose of this paper is to explore a method that has reasonable validity when economic considerations do not permit a full capacity calibration.

Extrapolation Methods

There are multiple methods of extrapolation. In the white paper, we outline three methods: Linear (0 and last point), Linear (last 2 points) and Poly (calibration points). We also expand upon the best methods for extrapolation by comparing these three methods, as well as demonstrating how to conduct the various methods. The goal of the white paper is to explain how to use extrapolation for best results.

The white paper goes into in-depth details on extrapolation, providing our customers and partners with a blueprint for extending transducer calibration range. If you’re interested in seeing the results and learning more, download the whitepaper here: Extending Transducer Calibration Range by Extrapolation.

For technical questions about Interface transducers and calibration, contact our applications engineers.

You can find additional technical white papers here.

Understanding Load Cell Temperature Compensation

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The performance and accuracy of a load cell is affected by many different factors. When considering what load cell will work best for your force measurement requirements, it is important to understand how the impact of the environment, in particular the temperature impact on output.

An important consideration when selecting a load cell is to understand the potential temperature effect on output. This is defined as the change in output due to a change in ambient temperature. Output is defined as the algebraic difference between the load cell signal at applied load and the load cell signal at no load. You can find more detailed information in our Technical Library.

Temperature affects both zero balance and signal output. Errors can be either positive or negative. To compensate for this, we use certain materials that are better suited for hot or cold environments. For instance, aluminum is a very popular load cell material for higher temperatures because it has the highest thermal conductivity.

In addition to selecting the right material, Interface also develops its own proprietary strain gages, which allows us to cancel out signal output errors created by high or low temperatures.

In strain gage-based load cells, the effect is primarily due to the temperature coefficient of modules of elasticity of the force bearing metal. It is common in the industry to compensate for this effect by adding temperature sensitive resistors external to the strain gage bridge which drop the excitation voltage reaching the bridge. This has the disadvantages of adding thermal time constants to the transducer characteristic and of decreasing the output by 10%.

Our load cells are temperature compensated for zero balance. By compensating for zero balance, we can flatten the curve in the relationship between temperature and zero balance. An uncompensated load cell has a much more severe curve, which ultimately affects accuracy and performance.

Interface offers thousands of load cell designs, for standard use and for use in hazardous environments. For instance, rocket engine tests subject our load cells to extremely high temperatures. For use in various maritime industry projects, they can be used in very cold coastlines and even submerged in cold water. No matter where you are, environment influences the load cell’s performance.

If you are concerned about temperature, Interface provides specifications for every load cell we manufacture. The Interface specification datasheet, as referenced here, is available for download by product. It always includes all the necessary data required to understand the load cell’s ability to perform at the highest-level including compensation range, operating range, effect on zero balance and effect on span.

One thing that is also unique about our products is that while most competitors only compensate for hot temperatures (60 to 160 degrees Fahrenheit), Interface covers both hot and cold thermal compensation from 15 to 115 degrees Fahrenheit, including adjust and verify cycles.

Watch our recorded webinar Load Cell Basics, where Keith Skidmore discusses temperature compensation.  He notes during this informative presentation that if the temperature is changing during a test, it can affect the zero and the output of the load cell. How much effect depends how much temperature is changing and how well the load cell is compensated against the errors, which can be either positive or negative. Good news is they are repeatable from test to test, so if you have large temperature swings you can characterize the system and then subtract out the shift if you know the temperature effect on zero.

Interface Application Engineers are available to answer questions regarding the effect of temperature on force measurement data, or the different ways we can help design a solution to compensate for your environment.

The Anatomy of a Load Cell

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Have you ever stopped to think about what makes the things we use everyday work? At Interface, our engineers think about what makes up an Interface load cell on the production floor and in our design lab every day.

Whether we are manufacturing a new load cell or speaking to a customer about how it can help solve their test and measurement challenges, we are always thinking about what a load cell can do and how to perfect the process of building one that exceeds all customer expectations in performance, reliability and accuracy.

One thing that people ask us about all the time is, what does it look like inside the pioneering Interface blue load cell? In the photo below, you have a cross-section of a basic load cell identifying each of the components and how it all comes together to provide industries around the globe world-class force measurement solutions.

The first component to understand is the strain gage. This mechanism is embedded in the gage cavity and is a sensor that varies its resistance as it is stretched or compressed. When tension or compression is applied, the strain gage converts force, pressure, and weight into a change that can then be measured in the electrical resistance. You can read more in our recent strain gage 101 blog. Here at Interface, we manufacture our own strain gages in-house to ensure premium quality and accuracy.

The main features of a strain gage are illustrated in the following image:

  1. Grid Lines – strain sensitive pattern
  2. End Loops – provide creep compensation
  3. Solder Pads – used to solder interconnecting wire to the gage
  4. Fiducials – assist with the gage alignment
  5. Backing – insulates and supports foil and bonds the strain gage to the flexure

There are also multiple gage configurations depending on the type of load cell. These include:

  • Linear – measures the strain under bending (used in mini beam load cells)
  • Shear – measures strain under shear force (used in low-profile load cells)
  • Poisson – measures strain under normal stress (used in the Interface 2100 Series Column Load Cells)
  • Chevron – measures strain under torsion (used in the Interface 5400 Series Flange Load Cells)

The next component to understand is the load bearing component of the load cell. It is made up of the hub, diaphragm, outer ring, inner ring and base. This component deflects under load to allow the strain gages to send a signal through the connector to the data acquisition device. Customization can include changing the metal materials used to meet environmental or strength concerns and designing the beam height and thickness to meet certain size and stress considerations.

The mounting ring and connector are also incredibly important to the proper use of a load cell and accurate data collection. The mounting ring is the area in which the load cell is mounted to the test rig to measure force and collect data. It is important to pay attention to mounting instructions because an improperly mounted load cell can cause inaccurate results, as well as damage to the load cell. There are also mounting adapters available to fit a wide variety of test rigs.

The connector is the component that allows the load cell to connect to a data acquisition device. The connector is attached via a wire to the data acquisition device and force data is sent through this device to the user through ethernet or Bluetooth® depending on the load cell and data acquisition device configuration. Interface also sells a wide variety of data acquisition devices.

Load cells have many configurations and capacities. In fact, we have made tens of thousands of them over the years to meet standard, modified and engineered to order specifications. The load cell diagram above represents a popular low profile “pancake” load cell.  There are many other styles including miniature load cells, bending and dual bending beams, column-style, S-beam and load button load cells. However, even as the shapes and uses change, the anatomy remains relatively similar, with these main components acting as the workhorse of the load cell and providing accurate force data to the user.

For more information on Interface and our wide range of load cells, torque transducers and data acquisition devices check out our product categories on our site or download our product literature here.

Interface Differentiator is Proprietary Strain Gage Manufacturing

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Interface products have been heralded for their accuracy, reliability, and quality for more than 50 years. We credit our vertically integrated approach to manufacturing as the most significant factor in our development of industry-leading force measurement products, meaning we control every part of the design, manufacturing and testing of our products before they are shipped to our customers.

The process for how we differentiate ourselves begins with Interface strain gages. By manufacturing our own proprietary strain gages here at our headquarters in Scottsdale, Arizona, we can optimize our load cells to a quality level very few providers can match.

Think of strain gages as the heart and soul of a load cell. These components power every aspect of the device and their quality dictates a significant portion of the load cells’ overall quality. In addition, customization of the strain gages is a critical factor in ensuring the load cell is meeting the specific requirements of a customer’s project.

The last point is critically important because Interface does not just provide one size fits all products. Yes, we have a large standard product line ready to ship. There are many times when we collaborate directly with our customers to understand their application and the challenges that may be present during a force measurement testing program or OEM design. This allows us to offer modified and custom products that are engineered to order.  Whether that comes in the form of an off-the-shelf product within our catalog of more than tens of thousands of options, or a new model using our strain gage technology to meet the needs of a unique application.

An example of our commitment to meeting customer needs is the way we develop our strain gages to compensate for temperature, an environmental factor that can drastically affect the accuracy of force data. Our strain gages are designed and manufactured to counteract the temperature characteristics of the modulus of the load cell structural material.

The benefit to this is that our load cells are temperature-insensitive and do not require modulus compensation resistors, ultimately producing a simpler and more reliable circuit with higher output signal. It also means no dynamic thermal mismatch errors from modulus compensation resistors which cannot be thermally connected with the load cell’s surface at the strain gage location.

In addition, our proprietary strain gages provide several key benefits. Included below are a few of the differentiators available with Interface strain gages:

  • A higher output of 4mV/V, while competitors provide 3mV/V or less, which provides superior performance, flexibility, and accuracy.
  • The ability to perform hot and cold thermal compensation, from 15˚ – 115˚F, while competitors typically only provide heat compensation (60˚ – 160˚F).
  • Eight strain gages per load cell compared to our competitors four gages, which provides superior compensation of eccentric loads to further minimize resulting errors.
  • Our strain gages also offer:
    • Higher signal-to-noise ratio
    • Higher resolution in precision measurement applications
    • Superior fatigue life

Another factor in the development of our strain gages is our expertise and knowledge of the manufacturing process. We have always developed our own strain gages going all the way back to 1968. Therefore, we have learned everything there is to know about it and can guarantee the quality of our load cells in any environment based on this tenured expertise and having manufactured and calibrated millions of force measurement devices.

To learn more about our vertically integrated manufacturing process and the various forms of product and system customization we offer, contact our specialized application engineers.