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Interface Load Cells 201 General Procedures Guide

The Interface Load Cells 201 Guide is an extract from our comprehensive go-to for the force measurement industry, the Interface Load Cell Field Guide.

This shortened reference zeros in on general procedures for using load cells. With in-depth explanations, illustrations, practical procedures, and insightful tips, this Interface technical support resource is a helpful guide to have on hand. It is designed to support general procedures using load cells, optimize your processes, and achieve exceptional results in any force measurement application.

Interface Load Cells 201: General Procedures Guide topics include:

  • Excitation Voltage: Understand the crucial role of voltage in powering your load cell and learn techniques for remote sensing, ensuring accurate readings every time.
  • Physical Mounting: Master proper mounting with detailed instructions for both “dead” and “live” ends, ensuring maximum precision and optimal cell life.
  • Mounting Procedures for Different Load Cell Models: Whether you’re working with beam cells, mini cells, low profile cells with or without bases, or any other type, the guide provides clear, step-by-step instructions for a perfect setup.
  • Mounting Torques and Fixtures: Get the torque values right for your specific transducer, ensuring secure mounting without compromising performance.

This quick guide eliminates errors and ensures reliable data with expert mounting techniques. It helps to extend the life of a load cell, protecting your investment with proper installation practices that maximize cell longevity. A complete copy can be found below.  To save a copy, go here.

Looking for even more in-depth support? Interface offers additional resources, including installation manuals, video tutorials, technical support, and a complete library of Interface 101 articles.

VIDEOS TUTORIALS AND RESOURCES

 SUPPORT REFERENCES

 TECHNICAL INFO AND GUIDES

If you have questions about any of these topics, need help selecting the right sensor, or want to explore a specific application, contact Interface Application Engineers.

Interface Load Cell 201 Guide- 2024 Edition

What is Proof Testing and Why Does it Matter?

Proof testing determines that the failure of critical components and parts could result in costly damage to equipment and even injury in severe cases. Our measurement products are designed to be used in proof testing applications.

In proof testing applications, testing and measuring an object’s performance under extremely intense conditions, often above the specified operational use, is critical. This allows testing engineers to ensure the object can handle its rated load and go above and beyond to understand maximum performance and failure.

Interface load cells and data acquisition systems are frequently used for proof testing, which determines the strength and integrity of a test subject by applying a controlled, measured load to it. It is commonly used for general test and measurement applications for stress, fatigue, and materials testing. It is frequently used by industries such as construction, natural resources, infrastructure, heavy machinery, and manufacturing to verify the strong point and durability of objects and structures.

Top Three Reasons Why Proof Testing Matters

#1 Safety: Proof testing qualifies and quantifies the safety of equipment and structures that sustain substantial loads. Identifying weaknesses or defects is preventative, as failure can result in catastrophe. Proof testing for safety is standard for applications that include lifting equipment, rigging gear, structural supports, and components in aircraft or spacecraft.

#2 Quality: Proof testing is common during quality control to verify that equipment or materials meet the required specifications. Whether it is the equipment used in manufacturing equipment or the materials used to construct a building, proof testing is essential in defining and measuring adherence to quality standards.

#3 Reliability: Proof testing provides accurate data on the performance and trustworthiness of the tested objects. By understanding how it reacts under stress, product engineers and testing labs can validate the lifespan of a specific component or product. It is also used to define preventative maintenance requirements. It impacts production lines, product versioning, inspections, and, ultimately, the customer’s user experience.

Proof tests provide vital safety and performance measurements for equipment or structures with significant loads. It helps to prevent accidents, improve reliability, and ensure the quality and integrity of the tested item. Consult Interface Application Engineers to determine the best measurement devices for proof testing.

Proof Testing Using Load Cells

Step One: Load Cell and Set-Up

The starting point is selecting the proper measurement tool, in this case, a load cell. Consider the object’s size, expected load range, and accuracy requirements. Choose a load cell with a capacity slightly exceeding the maximum anticipated load during use.

TIP! Use Interface’s Load Cell Selection Guide

Mount the load cell and object in a stable, controlled environment. Ensure proper alignment and distribution of force on the load cell. Connect the load cell to the data acquisition system with a dedicated readout unit, computer software, or data logger, depending on your needs.

Step Two: Pre-Test and Zeroing

Most test engineers will run a pre-test at low load. This is done by applying a small force and monitoring the readings to ensure everything functions correctly and there are no extraneous signals. Zeroing the load cell to set the baseline measurement without any applied force is important. READ: Why Is Load Cell Zero Balance Important to Accuracy?

Step Three: The Test

When you start the proof test application and data recording, most technicians will increase the load gradually. As defined in a test plan, follow a preset loading schedule, typically in increments, until reaching the desired test load. This could be a static load held for a specific time or a cyclic load simulating real-world conditions. Next, using your load cell measurement instrumentation, monitor the load cell readings, object behavior, and any potential visual deformations throughout the test.

Step Four: Analysis

The proof testing provides data that can be used to analyze the load-displacement curve, identifying any deviations from expected behavior, excessive deflections, or potential failure points. Based on the data, determine if the object met the strength and performance requirements or exhibited any unacceptable flaws. This is why a high-performance, accurate load cell matters in proof testing. It determines the quality of your analysis. As with any testing, it is valuable to maintain records of the test procedure, data, and conclusions for future reference or further analysis. This step is crucial for regulatory and product liability requirements.

The specific requirements and procedures for proof testing will vary depending on the product, equipment, structure, industry standards, and regulations.

Proof Testing Example

The most straightforward solution, where it is necessary to measure the load in a tension cable subject to safety considerations, is to enclose the load cell in a compression cage, which converts tension into compression. The compression cell is trapped between the two plates. Thus, the load cell’s only overload failure mode is in compression, allowing a motion of 0.001″ to 0.010″ before the load cell becomes solid. Even if the load cell is destroyed, the compression cage cannot drop the load unless it fails. Therefore, the cage can be proof-tested with a dummy load cell or an overload-protected cell, and the risk of injury to personnel is avoided.

TIP! This example is detailed in our Interface Load Cell Field Guide. Get your copy here.

The nature of proof testing applications requires a diverse line of performance measurement tools. Interface products extend from overload capabilities for our precision LowProfile load cells to complete DAQ systems. These options provide perfect testing solutions when necessary to push the limits on a product, component, or part.

ADDITIONAL RESOURCES

Enhancing Structural Testing with Multi-Axis Load Cells

Fatigue Testing with Interface Load Cells

Load Cells Built for Stress Testing

Benefits of Proof Loading Verification

Manufacturing: Furniture Fatigue Cycle Testing

Data AQ Pack Guide

Interface Solutions for Consumer Products

Load Cells Built for Stress Testing

Stress testing with load cells is an integral part of research, design, and manufacturing processes for various products and components. It helps to ensure that material, equipment, and final products can withstand the stresses they will be subjected to in regular use.

Stress testing with load cells involves applying a known load to a test specimen and measuring the resulting strain. The strain is then used to calculate the stress, which measures the force per unit area.

For destructive stress testing, the test specimen is loaded to failure. The failure load is then used to calculate the ultimate tensile strength (UTS) of the material. In non-destructive testing, the test specimen is loaded to a predetermined stress level and then unloaded. The stress-strain curve is then plotted to determine Young’s modulus and the yield strength of the material.

Selecting the right load cell for any stress testing protocol is important. A detailed review of the sensor’s performance specifications is where to start. Consider the quality of the load cell, along with the materials used to build the testing device and the strain gages.

In designing and building load cells, material composition and build quality play a critical role in the quality, accuracy, and overall lifetime of a load cell. This is especially true when testing involves long, stress-test cycle testing. Interface load cells are designed for optimum fatigue life.

Built for Stress

When looking for a load cell that needs to go the distance over long periods, it’s essential to understand the difference between sensors built for stress and those not. In materials science, the S-N curve is a well-known tool. It is a graphical representation of the number of load cycles required to break a specimen at the range of peak cyclic stress levels.  S-N curves for the high-quality materials used in Interface load cells determine the stress level.

Commonly selected load cells used for high-stress level testing are known as fatigue-rated. Fatigue-rated load cells are designed explicitly for component durability and fatigue test machines where highly cyclical loading is present. These quality load cells resist extraneous bending and side-loading forces.

The table below outlines a load cell strain and safety factor comparison chart, which shows how Interface load cells, including our  1000 Fatigue-Rated Universal LowProfile® Load Cell and 1000 High Capacity Fatigue-Rated Universal LowProfile® Load Cell stack up against generic competitive load cells.

This table compares actual strain levels in Interface LowProfile Load Cells versus generic load cells. The safety factors are a means of visualizing the merit of the various designs. The value of fatigue-rated load cells for fatigue applications is evident from the safety factor data. It is also apparent that Interface load cells with 4 mV/V output have lower stress levels and, therefore, more fatigue resistance than other cells, even though their output is only 3 mV/V or less.

Lower Stress by User Limits

Note that the tests in the safety factor comparison are based on fully reversed load cycles. This type of loading cycle is considerably more stringent than unidirectional loading, which is the more common application of load cells. Suppose a fatigue load cell is repeatedly loaded in only one direction. In that case, the Goodman Law predicts that it can be loaded to about 133% of the bidirectional fatigue-rated capacity with no degradation of its fatigue rating. Conversely, unidirectional loading to a fatigue cell’s rated capacity is much less stressful on the cell than bidirectional. It can be expected to yield a fatigue life well beyond the number of cycles that could be reasonably and economically applied in a verification test program. For additional information on this topic, please refer to Interface’s Load Cell Field Guide under Fatigue Theory.

ADDITIONAL RESOURCES

Fatigue Testing with Interface Load Cells

Beam Stress Test

Force Measurement is Fundamental in Material Testing

Test and Measurement Solutions

LowProfile Load Cells 101

Stainless Steel Load Cells 101

Excitation Voltage 101

Excitation is an electrical signal. The excitation voltage is represented by the volts direct current (VDC). The direct current flows in one direction only. Alternating current (AC) changes direction at times.

Load cell excitation provides a voltage to generate an output signal, sometimes referred to as ‘powering’ the load cell. An output signal from a load cell is typically minimal, so an excitation voltage is needed to power the load cell and ensure the output signal is accurate. The magnitude of the output signal is proportional to the amount of force applied to the load cell. The greater the force, the greater the output signal.

Interface load cells contain proprietary strain gages applied to a Wheatstone bridge, essentially an electrical circuit that changes resistance when subjected to strain. The Wheatstone bridge is comprised of strain gages that are arranged in a specific configuration. When a load is applied to the load cell, the strain gages deform, and their resistance changes. This change in resistance causes the output voltage of the Wheatstone bridge to change.

Interface provides electrical performance data on all specifications represented as VDC MAX, when applicable.  The data for excitation voltage is listed under the electrical section of a transducer model’s specification datasheet, along with other factors, including rated output, bridge resistance, and zero balance.

Sensor Power and Excitation Tips

Load cell excitation is necessary to ensure the accuracy and reliability of load cell measurements.  Here are a few tips to consider regarding excitation and power signals when designing a force measurement system:

  • The output signal from a load cell is expressed in millivolt output per Volt (mv/V) of excitation at capacity.
  • The excitation voltage also affects the magnitude of the output signal. A higher excitation voltage will produce a higher output signal.
  • The output signal is directly affected by the input voltage. It’s essential to maintain a stable excitation voltage.
  • Interface load cells all contain a full bridge circuit. Each leg has a typical bridge resistance of 350 ohms, except for models like our 1500, which have 700 ohm legs.
  • The preferred excitation voltage is 10 VDC, which guarantees the closest match to the original calibration performed at Interface before it is shipped from our factory.
  • A DAQ system won’t always provide stable excitation voltage. Consider using a signal conditioner or DAQ with specific bridge inputs.

Why Load Cell Excitation Matters

Excitation matters in force measurement applications because it provides the power needed to operate the load cell and ensure an accurate output signal. The load cell cannot generate an output signal without excitation, and the force measurement will be inaccurate. In addition, it does influence accuracy, noise, and range.

Accuracy: The excitation voltage powers the load cell and ensures an accurate output signal.

Noise Reduction: The excitation voltage can help to reduce noise in the output signal.

Range: The excitation voltage can help extend the load cell’s measurement limit.

The excitation voltage should be applied to the load cell in a balanced manner. This means the excitation voltage should be applied to both sides of the load cell. The excitation voltage should be stable. This means that the voltage should not fluctuate or drift over time. The excitation voltage should be filtered. This means that any noise in the excitation voltage should be removed.

Excitation 101 in Force Measurement

The excitation voltage determines the sensitivity of the load cell. A higher excitation voltage will result in a more sensitive load cell, which means it can measure smaller forces.

The excitation voltage influences the frequency response of the load cell. A higher excitation voltage will result in a broader frequency response, meaning the load cell can track changes in force more accurately.

Linearity measures how accurately the load cell converts force into an electrical signal. A higher excitation voltage will result in a more linear load cell, meaning the output signal will be more proportional to the applied force.

The excitation voltage is well-regulated to reduce measurement errors. Variations in excitation voltage can cause a slight shift in zero balance and creep. This effect is most noticeable when the excitation voltage is first initiated. The solution is to allow the load cell to stabilize by operating it with a 10 VDC excitation for the time required for the gage temperatures to reach equilibrium. The effects of excitation voltage variation are typically not seen by users except when the voltage is first applied to the cell.

For tips like this, please consult Interface’s Load Cell Field Guide. We also detail remote sensing of excitation and temperature. Download your copy for free here.

It is essential to carefully select the excitation voltage for a load cell application to ensure that it can provide accurate and reliable measurements.

Understanding One-Cell Force Measurement Systems

When it comes to load cells and force measurement systems used to test and validate product designs, the options for different configurations is nearly endless. In fact, Interface has tens of thousands of force measurement products in standard, modified and custom-made configurations.

In our recent post, Considerations for Steel, Stainless Steel and Aluminum Load Cells, we detailed materials used in load cell construction. These considerations are important based on the project specifications for accuracy, quality and reliability in test and measurement.

Similarly, understanding the system configuration is another critically important factor to setting up the correct test for receiving accurate data.  A simple system configuration used for less-complex testing is known as one-cell or single load cell system.  They are popular for performance and durability testing.

How do one-cell systems work and what are the benefits and trade-offs?

One-cell systems are developed by using a tension cell and mounting it through a rod end bearing and clevises. If the cell is properly oriented with the dead end going to the support, the only other major consideration for this system is the elimination or reduction of possible parallel load paths. This type of simple system is attractive to some testing engineers and product designers because it is cost effective and can provide very accurate measurements when using Interface precision load cells.  It is important that the load meets the criteria for the test system.

In this figure, it shows a high-impact one-cell system platform. This one-cell system can withstand the high impact of rough treatment from certain applications such as large drums, LPG tanks and more.

The downside to using a one-cell system is that the center of gravity of the load must be placed directly on the mark for the system to work properly. However, this can be accounted for by positioning the fences as shown in the high-impact one-cell platform diagram, so that the center of gravity is located properly when the application you are measuring is shoved up against fences.

The actual load at the center of gravity for your application will be factored by the lever arm (as shown below):

The one-cell system works simply because the location of the center of gravity is under control. If the force on the primary axis of the load cell bears the same relation to the location of the center of gravity and the load under all conditions, the scaling will be correct. Whether using a one-cell or two-cell system, the system must be designed to retain its integrity.

This has been a brief overview of a one-cell system, which is detailed in Interface’s Load Cell Field Guide.

To learn more about these systems and to determine if your application test can utilize the simplicity and cost savings of a one-cell or two-cell system, contact our systems experts and application engineers.

Introduction to Interface Application Notes

Interface has a long history of sharing valuable resources to help our fellow colleagues and customers with various use cases for test and measurement applications. Whether it be with our in-depth technical library, the Interface Load Cell Field Guide, free access to design files for our breadth of products, or industry case studies highlighting how our customers use Interface products. Access to all of these resources is available on Interface’s website www.interfaceforce.com.

A frequently visited area of these online resources is our Interface Application Notes archive. These resourceful explainers are of interest to engineers, new product designers, metrology and engineering students, as well as T&M industry professionals.

Interface created a large collection of App Notes to showcase how Interface load cells, torque transducers, accessories and instrumentation are used by OEMs and for various test and measurement projects across all types of industries.

Each Interface App Note has the following details:

  • Name of the App Note with Primary Product
  • Industry
  • Summary of the Application Use Case Need or Challenge
  • Interface Solution
  • Results
  • Materials
  • How it Works
  • Visual Representation of the Application

Interface App Notes are great conversation starters. They help to showcase how various Interface products and systems are used across all types of industries including medical, automotive, energy, industrial automation, consumer products testing, and aerospace. Additionally, several application notes highlight specific test and measurement lab projects.

Interface Top 10 Application Notes

  1. Race Car Suspension Testing
  2. Aircraft Wing Testing
  3. Surgical Stapler Force Verification
  4. Drone Parcel Delivery
  5. Bluetooth Brake Pedal
  6. Medical Bag Weighing
  7. Seat Testing Machine
  8. Industrial Automation Friction Testing
  9. Vascular Clamp Testing  
  10. Bolt Fastening and Torque

We have many more for you to check out. Visit the entire library of Interface Application Notes here. We are adding new application notes on a regular basis, so check back frequently.

Be sure to check out the full line of Interface solutions here. If you have questions or would like to talk with our application engineering experts, drop us a note or give us a call.

Interface 2019 Load Cell Field Guide Now Available on Amazon

The Interface Load Cell Field Guide, the most thorough guide in the industry for understanding and utilizing load cells and strain gages, has been updated for 2019 and re-released on Amazon. The popular primer from leaders in force measurement solutions provides in-depth information for understanding and using load cells and strain gages to accurately measure force.

The 2019 Load Cell Field Guide is the ultimate tool for engineers and students who are learning about and using load cells for test and measurement projects and products. The book is available today in paperback on Amazon and can be ordered for $15 here.

“The creation of this instructional guide was driven by a value included in Interface’s mission to always go above and beyond,” said Joel Strom, CEO, Interface, Inc. “We believe this informative reference is a helpful resource for engineers, STEM students, and universities around the world because it comes from a company that’s recognized as the pioneer in load cell design and manufacturing. Sharing our knowledge benefits all industries testing force.”

The “Interface Load Cell Field Guide” was first published in 2014 and has been distributed throughout the world. In the newly released 2019 edition, Interface updated the book to include more than 120 pages of instructive content that covers force measurement topics including types of load cells, general uses of load cells, load cell characteristics and various test application use cases. This type of essential information provides value to all load cell users and force measurement enthusiasts.

Science, technology, engineering, and math (STEM) is a strategic focus of the 51-year-old load cell manufacturer. The introduction of Interface’s University Program earlier this year provides the Load Cell Field Guide to support global education and STEM programs. The guide was authored, edited and published by a team of expert Interface engineers with deep experience in the force measurement industry.

For more information on the “Interface Load Cell Field Guide” or University Program, please call 480-948-5555 or visit /the-load-cell-field-guide/.

Press release: https://www.prnewswire.com/news-releases/new-2019-load-cell-field-guide-from-interface-now-available-on-amazon-300911460.html 

Interface Launches New University Program

Interface is investing in the engineers of tomorrow with our new Interface University Program.  The new STEM-focused initiative promotes innovation and education by providing access to the best force measurement products, services, and experts in the industry.

As the world’s leader in force measurement solutions, Interface created the specialized Interface University Program to provide discounted products and services, educational materials and access to renowned test and measurement expertise.

The distinct Interface University Program offers higher education institutions and students reductions on the industry’s most accurate and reliable force measurement standard products and calibration services to accelerate research and development, advance science, perform accurate testing, and promote exploration.

Through the unique program, Interface is also providing educational support in the form of internships, R&D projects, sponsored test and measurement class projects, grants, and community STEM program support.

“Our goal is to empower engineering students to achieve their educational and career goals with the help of our exclusive Interface University Program,” said Joel Strom, CEO, Interface. “The program will make critical engineering tools, services and professional support more accessible to universities and colleges faculty and engineering students. This program provides best in class test and measurement products, specialized solution bundles and discounts on products and services that will enrich engineering and metrology program experiences.”

The Interface University Program

Interface Standard Products:

  • Get Started Bundle with Interface LowProfile®, Sealed S-Type and Mini Beam Load Cells, Torque Transducer, Indicator and more at 25% off
  • Load Cell 101 Field Guide by Interface Engineers
  • 10% off all standard products and additional loyalty program discount programs

Interface Calibration and Repair Services:

  • Tiered Calibration Services Program discounts
  • Expedited repair services with special discounts
  • 25% off 3-year annual calibration services programs for maintenance

Education Support and Resources:

  • Internships for R&D at Interface HQ in Arizona
  • R&D projects
  • Sponsored test and measurement class projects or challenges
  • Failure testing projects
  • Onsite engineering hours: class, speaking, events

Interface provides force measurement solutions and services to hundreds of universities coast-to-coast and around the world every year. The company’s founder, Richard F. Caris, was a major proponent of charitable giving to STEM-focused institutions and programs. In 2015, Caris donated $20 million to the University of Arizona Richard F. Caris Mirror Lab to support the construction of mirrors used for the Giant Magellan Telescope. The Mirror Lab has utilized Interface products in its mirror polishing process for the past twenty years.

“Interface has been a long-time partner of the University of Arizona,” said Buell Jannuzi, Ph.D., Steward Observatory director and head of the Department of Astronomy, University of Arizona. “Their commitment to STEM and support of the Mirror Lab has been critical to our efforts, as well as the education of our students.”

For more information on the program and for a detailed breakdown of special offers, services, and educational support, please visit /university-program/ or contact our Application Engineers at 480-948-5555.

PRESS RELEASE

University Program Overview

University Program 2 Page