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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

Weighing Your Options Webinar

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Interface force measurement experts detail solutions used for all types of weighing and lifting applications. We discuss sensor models, capabilities, features and tips using various load cells, load pins, shackles, tension links, weighcheck systems and instrumentation. Learn about use cases, FAQs, measurement applications, options for harsh environments and OEM products. If you are exploring quality measurement solutions that provide high accuracy and reliability for scales, cranes, lifting equipment or tools, join us.

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New Interface Case Study Exams Weighing and Scales

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Test and measurement are used in the development and monitoring of manufactured goods across all industries. With a history of producing force measurement solutions for more than five decades, Interface has supplied a myriad of sensor devices for hundreds of thousands of different use cases and applications.

From the scales we use in packaging centers to the enormous weigh check equipment used in transportation, weighing and scale measurement solutions are instrumental in the successful design, engineering, launch, and maintenance of products and components.

Many of the earliest force sensors were designed for the purpose of weighing objects, and they continue to be a large part of test and measurement today. As products evolve and new inventions enter the market, sensors must maintain their durability, quality, and accuracy for large and miniaturized uses. Therefore, you see inventors and innovators turn to Interface today for sensors that are designed for use in robotics, IoT, and factory automation equipment used for weighing.

Historically, the only difference between now and then is that Interface has perfected accuracy in measurement across with an extensive range of force sensors models, configurations, sizes, capacities, and specification requirements that can measure weight at “jumbo” scale, as well precisely measure exceedingly small, minute forces as an embedded sensor.

Determining accurate weight is a key data point manufacturers need throughout a product lifecycle. Whether they need the information for transporting an object, lifting the object, or just creating a specification sheet, accurate data for weight measurements is fundamental for safety and function. This includes weighing single and combined parts in early design, weighing the manufactured equipment during assembly and production, using scales for weighing output with exact measure, as well as obtaining real-time weight in distribution and transport.

To accomplish this, Interface provides a host of load cells and instrumentation devices. Since our first load cells were designed in 1968, we have built millions of these products for engineers and designers that require the highest precision force sensors for accurate and reliable data collection in test and measurement (T&M). Our customers represent a wide swath of industries, products, equipment types, tools, and electronics that depend on us for proving accuracy, consistency, and reliability in performance in T&M.

In our latest case study, we outline four weigh and scale use cases that utilize Interface sensor technologies. Defined weight as a product specification requires extreme accuracy in measurement. Utilizing precision force sensing solutions and instrumentation enables product engineers and manufacturers to collect data and use it as part of the product design.

Accuracy Matters for Scales and Weighing focuses on weighing and scale applications used with heavy machinery, medical devices, operational containers, and distribution solutions. In each of these instances, utilizing weight in the design, build, and supply of these products is fundamental to each use case and the success for the product.

Weighing and Scales Case Study

 

Interface’s Steering Role in All Types of Transportation

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Interface serves a wide variety of industries that design and manufacture movers of people and objects. The transportation sector consists of companies that assist in the movement people or goods, as well as supporting infrastructure. Whether it is automobiles or planes, trains or helicopters, spacecraft or water vessels, Interface provides solutions to help test and measure force, weight, torque, lift and more.

The safety, quality and reliability of the overall transportation industry are all important considerations in design, build and performance. Human safety being the most critical requirement of any transport vehicle or structure.

This means that stringent testing is necessary to confirm the design of every part and system on a vehicle. Force measurement sensors can used to test a wide variety of factors on every type of invention that moves or transports a person or thing. From the torque of an electrical vehicle engine to the weight distribution of an aircraft, these types of tests help to refine the designs of components, vessels, and vehicles, confirming safety and dependability.

All Interface product categories have a role in the testing of all these transportation entities.  Many of our sensor technologies are also ideal for performance monitoring and integration into product designs, whether it’s for ongoing measurement of weighing ship cargo with load pins, load shackles and tension links or using our torque transducers for engine testing on e-bikes, automobiles, trucks, buses, and other transport vehicles.  If it moves, it needs to be measured. Our force and torque solutions are ideal for every segment of this market sector.

Let’s take a quick tour of a few application examples that demonstrate the different products we provide that are helping get people and objects safely moving down the road, on the rails, in the air and even into space.

Wind Tunnel Testing

A major aerospace company was developing a new airplane and needed to test their scaled model for aerodynamics in a wind tunnel, by measuring loads created by lift and drag. Interface offered a Model 6A154 6-Axis Load Cell which was mounted in the floor of the wind tunnel and connected to the scaled model by a stalk. A Model BX8-AS was then connected to the sensor to collect data. The wind tunnel blew air over the scaled model creating lift and drag, which was measured and compared to the theoretical airplane models. Software in the PC converted raw data signals to actual force and torque values at the stalk. Using this solution, the company was able to analyze the collect data and made the necessary adjustments in their design to improve the aerodynamics of their theoretical airplane models. Read more.

Garbage Truck On-Board Weighing

A garbage disposal company wanted to test the load capacity of their garbage truck bins so they know when it reached maximum capacity. Interface’s solution was to customize and install 4 SSB Sealed Beam Load Cells under the garbage box body, on either side. When trash continues to be piled inside the box body, it will push more force down onto the SSB Sealed Beam Load Cells. When maximum load capacity has been reached, the results can be reviewed and displayed when connected to the 482 Battery Powered Bidirectional Weight Indicator in real time. With this system, the customer was able to test the maximum load capacity of the garbage bin attached to the truck, so they know when to empty the truck’s garbage at the transfer station. Read more.

Engine Head Bolt Tightening

 

 

 

 

 

An industrial automation company was building an automated assembly machine for an auto manufactur­ing plant. They needed to tighten all head bolts on an engine on their assembly line to a specific torque value. Having the head bolts precisely and consistently tightened to the engine block is critical to the operation of the engine. Several Interface Model T33 Spindle Torque Transducers were installed in their new machine to control torque, angle, and ensure the head bolt was properly tight­ened. The square drive of the T33 allowed the customer to fix their tool directly to the end of the torque sensor, streamlining the installation. When the machine comes down and screws on the engine head bolts the torque and angle profile are sent to the customer’s machine controller. Based on the feedback received by the machine controller, the automation will pass the engine to the next step in the assembly line or fail and have the engine evaluated further. This allowed the customer to ensure the head bolts were correctly installed according to manufacturer specifications, producing an engine that meets performance and reliability expectations of the auto manufacturing plant. Read more.

Bicycle Load Testing

A mountain bike manufacturing company wanted a system that measures their bike frames load capacities and vibrations on the frame. They also want to ensure the bike’s high quality and frame load durability during this final step of the product testing process. Interface suggested installing Model SSMF Fatigue Rated S-Type Load Cell, connected to the WTS-AM-1E Wireless Strain Bridge, between the mountain bike’s seat and the bike frame. This will measure the vibrations and load forces applied onto the bike frame. When a heavy load is added to the seat, the SSMF Fatigue Rated S-Type Load Cell measures the vibrations and load forces applied to the bike to indicate any stress points through a number of cycles. The results will be captured by the WTS-AM-1E and transmitted to the customer’s PC using the WTS-BS-6 Wireless Telemetry Dongle Base Station. This solution helped the mountain bike manufacturing company gather highly accurate data to determine that their bikes met performance standards through this final testing cycle. Read more.

These are just a brief example of the work we do in transportation. Interface systems have been involved in projects with boats, races cars, construction vehicles and even rocket ships. Manufacturers turn to Interface because of our track record for accuracy and the transportation industry relies on this data to keep its customers safe.

For additional insights and ideas related to transportation solutions, here are a few more posts to read.

Interface Plays a Role in Testing Bicycles

Evolving Urban Mobility Sector for Test and Measurement

Interface’s Crucial Role in Vehicle and Urban Mobility Markets

Measurement Technologies for Boats, Yachts and Watercraft

Interface and The Race to Space

Driving Force in Automotive Applications

To review more application notes pertaining to transportation or to talk to an application engineer about your next project, contact us or call us at 480-948-5555.

Tension Links 101

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A tension link load cell is commonly used in lifting, both for short and long distances, and weighing applications. This type of load cell sensor generally has capacities ranging from 2.2K lbf to 1.1M lbf (5 to 500 metric tons). All tension links are available in custom versions and large capacities based on the customer’s project requirements.

Interface’s Tension Link series is manufactured from high tensile aluminum and stainless steel. Matched to shackle sizes, the load links have a rugged design for uses in harsh environments on the surface and in water. The tension links are environmentally sealed to IP65, IP66 or IP67. There are higher ratings available upon request.

A major benefit of Interface tension links is the option for custom designs in dimensions, ratings and capacities. The tension links are easy to install and are highly accurate.  They are compact in size and light weight. Another benefit is the options available, which include standard, wireless and self-indicating, giving the operator a variety of application use cases for quick measurement readings.  Self-indicating tension links have a built-inaudible alarm, which can be set by the operator to warn when an applied weight or force is met.

Often, customers will integrate the tension links with an Interface Crosby styled load shackle for robust applications that require accurate and reliable force measurement used for lifting, weighing, hoisting or towing apparatus that need sensors for safety and monitoring.

Wireless options are growing in acceptance for all types of uses. Interface provides wireless tension links that are compact and reduce the overall product weight based on the casing used to house the small alkaline batteries, which can be easily accessed by removing the telemetry housing cover while the internal electronics remain completely sealed. The antenna is also internally mounted, protecting it from accidental damage during use and handling, which is ideal for harsh environments.

Watch this discussion to learn more about the wireless features of the Interface Tension Links and Load Shackles.

Interface’s most popular tension links include:

WTSTL Wireless Tension Link Load Cell – Designed for lifting applications requiring short or long distances. This product can transmit wirelessly up to 600 meters in distance (clear line of sight) to a handheld display or USB base station. Model WTSTL is available in capacities ranging from 11K lbf to 220K lbf (5 to 100 metric tons). Custom versions and larger capacities are available upon request.

ISITL Self-Indicating Tension Link Load Cell – Manufactured from high tensile aluminum to minimize weight, the ISITL is great for lifting and weighing in rugged or harsh environments.  The self-indication tension link load cell is ideal for mobile use cases.  It is simple to install and is matched to standard shackle sizes. They have a built-in display for applied weight or force in tons, kgs, lbs or kN. Interface can also offer a custom software to meet any specific application requirements for digital display or readouts.

ITL Tension Link Load Cell – This basic tension link can be amplified with 5VDC, 10VDC or 4-20mA Outputs. It can also be made to meet ATEX requirements. Model ITL is available in capacities ranging from 11K lbf to 220K lbf (5 to 100 metric tons). Custom versions and larger capacities can be requested at no additional charge, based on the exact specifications needed by the customer.

To learn more about our wide variety of load pins, load shackles and tension links, please visit www.interfaceforce.com/product-category/load-pins-tension-links-and-load-shackles/.