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Load Cell Basics Technical Q&A Part One

Interface recently hosted a webinar, Load Cell Basics, where our experts answered a series of questions from event attendees.  In the interest of sharing what we know and addressing some frequently asked inquiries, we are offering a new series in our Interface IQ blog entitled Interface Technical Q&A.  At the conclusion of our presentation, we had several questions related to the basics of load cells.  We will be answering them in two posts.  Here is the first list.

Why Does Interface Use Proprietary Strain Gages?

Strain gages are a key component to any load cell. Making our own strain gages gives Interface full control over our design and production, ensuring we can meet our specifications with certainty in quality, accuracy, and dependability. Interface strain gages are precision matched to the load cell material to counteract the temperature effect on output. We have different load cell materials and that means we use different strain gages for each type.

Our strain gages are simple in design, and we don’t use compensation resistors making them a more reliable circuit.  They don’t have to go through resistors; thus, the accuracy and precision measurement is more reliable and capable of faster thermal and higher outputs.

What Type of Temperature Testing Do You Do on Interface Load Cells?

Interface performs both hot and cold thermal compensation from 15˚ – 115˚F, including adjust and verify cycle. Most other manufacturers of load cells provide only the hot side (60˚ – 160˚F) testing. The slope of the curve is much flatter near room temperature and identical at both ends of the slope.  The result is minimal variation across the entire thermal range.  We also offer custom calibrated ranges by request. Read more about temperature compensation here.

Is Temperature Compensation Achieved Using Dummy Gages?

The simple answer is no. Interface does temperature compensation of output by matching the strain gage to the material temperature compensation of zero. This is achieved by using a wire in the circuit that opposite resistance changes to the circuit.

Do You Have Software to Read TEDS Available to Use with Interface Load Cells?

Interface does offer instruments that can use the TEDS data and instruments that can write the TEDS data to the chip. Interface has software that hooks up or attaches to the TEDS chip reader writer so that when we program a chip during manufacturing of load cells in our factory, we have software we use to complete this function.  We also do offer this software for commercial use.

Is it Acceptable to Regularly Use a Load Cell Above Its Specified Capacity?

The short answer is no.  You want to reserve the “above capacity” for accidents. We are aware that people will do this in practice and the load cell will typically work reasonably well above capacity.  The problem is you want to handle that the answer is no you’re consuming your safety factor and you don’t have any extra head room for something that goes wrong.  Also, using the load cell above capacity doesn’t exactly follow the same calibration curve.  As an example, if you are using a 10k load cell with a 10k calibration and you are running tests at 12k, you may have higher errors.  You can ask us to calibrate the load cell to the 12,000 lbs.; however, you must note this can reduce the safety factor and that is why we do not recommend it.

Does Variable Altitudes Impact Performance?

Interface does have the ability to handle different pressure scenarios. Interface sends our products out ventured, if necessary, to be able to tolerate pressure change without causing any zero shift. If you do have applications where you will have either high pressure requirements or pressure change throughout the test, we certainly have solutions that can accommodate that requirement.  Work with your application engineer to ensure you have the exact testing requirements detailed when you are ready to buy your next load cell.

Can Cables Influence Temperature Errors?

If you’re adding cable to the load cell and for example, you have a 10-foot cable you want to add 100 feet more of cable, that adds resistance. The lower gauged cable, the better. A 22-gauged cable is better than a 28-gauged cable, so use a thicker cable and it will have less resistance impact on the measurement.

Is Creep Due to Material or Strain Gages?

Essentially all the elements in the sensor and everything mechanical will respond to creep.  The goal is to match the creep behavior of the bridge to the creep behavior of the load cell material or the flexure. Yes, creep affects both, but you want the result to trend in the same direction so that you get minimal error or change in the signal because of creep.

Are All Load Cells Intrinsically Safe?

They are intrinsically safe devices; however, anytime there is a hazardous environment or intrinsic safety requirements, please contact an application engineer to review the sensor use case and to factor in all aspects of your testing and use environment.  The load cells are typically working off 5-volt 10-volt and you need to look at all aspects of the location. For more information about our specialized line visit load cells for harsh environments.

This is the first in a new series of Interface Technical Q&A.  Do you have a question for our technical experts?  Send an email to digmktg@interfaceforce.com and we will add it to a future post.  If you have an immediate question, be sure to contact us today and let us know how we can support you.  You can also reference our technical support resources online for help.

Contributors:  Keith Skidmore and Brian Peters

Additional Resources

Load Cell Basics Webinar Recap

Interface Load Cell Field Guide

How to Choose the Right Load Cell

Load cells are used to test and confirm the design of hardware, components, and fixtures used across industries and by consumers. From the structural integrity of an airplane to the sensitivity of a smartphone touchscreen, there’s a load cell available to measure force. In fact, here at Interface we have over tens of thousands of products used in force measurement, for all types of different applications.

How do engineers and product designers go about choosing the right load cell for a specific application or testing project?

Have no fear, Interface has put together a short guide on choosing the load cell that is right for you. This blog will cover the basic questions to answer when selecting a product, as well the most important factors affecting load cell choice.  Be sure to watch the online video, Load Cell Basics, that highlights key factors of consideration when choosing the right load cell for additional insights.

The basic questions you need to consider when selecting a load cell include:

  • What are the expected loads? What is the minimum and maximum load you’ll be measuring?
  • Is there any potential for higher peak loads than what you intend to measure? What are these expected peak forces?
  • Is it tension, compression, or both?
  • Will there be any off-axis loads? If so, what is their geometry? Do you want to measure them too?
  • Will it be a static, dynamic or fatigue measurement?
  • What is the environment in which you’ll be conducting your test? Will the load cell need to be sealed?
  • How accurate do your measurements need to be? Do they need to be at the highest accuracy of ±0.02-0.05% or within ±0.5-1%?
  • What additional features, accessories and instrumentation does your application require to complete a test?
  • Do you need standard electrical connectors or customized options? What about additional bridges or amplifiers?
  • How are you planning to collect and analyze the data output from the load cell?

Next, these are the most important factors affecting accuracy, which will have a heavy influence over the load cell you choose. It’s important to understand how your application and the load cell will be affected by each of the factors, which include:

  • Mechanical – Dimensions and Mounting
  • Electrical – Output and Excitation
  • Environmental – Temperature and Moisture

One of the most important factors in choosing the right load cell is understanding how it will be mounted for testing or as a component within a design. There are a wide variety of mounting types including threaded connections, inline, through hole or even adhesive. Understanding the mounting type that suits your application is critical to getting the correct data because a poorly mounted load cell will distort the results and can damage the load cell.

The mounting process also requires you to understand which direction the load is coming from, in addition to any extraneous loads that may be present. The load cell mating surface is also an important factor. For example, when using our LowProfile® load cells without a pre-installed base, the best practice is to ensure that the mating surface is clean and flat to within a 0.0002-inch total indicator reading and is of suitable material, thickness, and hardness (Rc 30 or higher). Also make sure that bolts are torqued to the recommended level.

If you’re conducting a fatigue measurement, it’s also important to address the frequency and magnitude of load cycles with your load cell provider. Factors to address include single mode versus reverse cycles, deflection versus output resolution, and material types. Interface offers a wide variety of fatigue-rated load cells that are perfect for these types of applications.

Another consideration in choosing the right load cell is the electrical signal. Load cells work by converting force into an electrical signal. Therefore, it’s important to understand the electrical output type necessary for your application, which could include millivolt, voltage, current or digital output. You can find the excitation voltage data on our website for each of our load cells. Additional considerations include noise immunity, cable length and proper grounding.

The environment is also a critical factor in ensuring accurate performance of your load cell. Interface provides load cells in a variety of material types including aluminum, steel, and stainless steel. Each material has a variety of properties that make them more suitable for different environments. For a more in-depth perspective on the different strengths and weaknesses of materials, please read our blog titled, Considerations for Steel, Stainless Steel and Aluminum Load Cells. For applications where load cells need to be submerged in liquid or enter an explosive environment, we also have a variety of harsh environment and IP rated load cells, in addition to load cells suitable for high humidity or splash resistance. Learn more about our intrinsically safe load cells here.

Learn more about choosing the right load cell in these online resources:

WATCH: Load Cell Basics with Keith Skidmore

WATCH: How to Choose a Load Cell with Design Engineer Carlos Salamanca

READ: Load Cell Field Guide

VISIT: Interface Technical Library

To learn more about choosing the right load cell for any application, connect with our applications engineers about the force measurement needs for your next project at 480-948-5555.

Hazardous Environment Solutions from Interface

There are hundreds of thousands of engineers and manufacturers that spend their days working in hazardous environments. Whether its operating inside of facilities with large machines with intricate moving parts, working hundreds of feet in the air repairing a bridge, or deep within a mine shaft, these professionals put themselves in danger every day by the nature of their work. As engineers and manufacturers, many of us are also tasked to solve for safety challenges and keep these professionals protected in any environment.

At Interface, one of the ways we contribute to industrial safety is with the development of our Interface Ex Rated Load Cells, also known as Interface Intrinsically Safe Products. These specialized load cells and force measurement solutions are designed and manufactured so that the materials and electronic components are safe for use in hazardous gas and dust environments when installed per applicable installation instructions. These components play an integral role in the safety of the men and women working in dangerous environments in particular industries like oil and gas, mining, aerospace, automotive and more.

These hazardous environments are categorized by the amount of explosive risk that is present in the environment. These levels include:

  • Zone Zero – explosive presence is always there
  • Zone One – explosive presence is close and is sometimes there
  • Zone Two – explosive presence is nearby, but is rarely present other than in some type of leak or other catastrophes

In order for force measurement products to operate safely in these environments, companies must design the devices in accordance with a regulatory body. These products must also be inspected for approval and then it is marked with the certification code that displays the zone and temperatures it’s safe to operate in. In addition, the manufacturing process needs to be highly controlled. Manufacturers must keep documentation for each product, which includes how the product was made and where it went. And they are required to keep that documentation for 10 years in case of a product recall.

There are a number of different regulatory bodies focused on product safety throughout the world, and each has different specifications for explosiveness that need to be met based on the area in which the product is sold. Locations in which Interface can sell its Ex Rated products include countries in North America, Europe, Asia, and Brazil in South America.

The regulatory bodies that develop the specifications and approve products include:

  • International Electrotechnical Commission Explosive Atmospheres (IECEx) is given after a manufacturer proves compliance through a quality assessment report (QAR).
  • ATmospheres EXplosible or ATEX is a European Union(EU) examination certification. In order to receive ATEX certification, the manufacturer must obtain a quality assurance notification (QAN) to sell products in certain EU areas.

Interface develops a host of Ex Rated force measurement products that are certified by both IECEx and ATEX. These products have been used in a wide variety of applications within the energy and automotive industries. Included below are a few examples of the products we sell and the applications using our Ex products

ATEX 3400 Series Load Cells

The 3400 series of load cells are rated for Zone 1 and include the 3416 and 3430 Coil Tubing Intrinsically Safe Load Cells, the 3420 Coil Tubing Intrinsically Safe Load Cell and the 3410 Intrinsically Safe LowProfile® Load Cell. These products are hermetically sealed and have been used in the oil and gas industry to measure the force of coil tubing as it goes down an oil well. The 3400 Series is used in the space industry to help develop hydrogen-powered vehicles because of the threat of explosion with hydrogen power. The 3400 Series Load Cells have also been used in a distillery for a custom whiskey-making application.

ATEX, IECEx, ETL, Inmetro 1923 Series

The 1923 Series Load Cell is used in the oil and gas industry. These load cells include designs rated for both Zone 0 and Zone 2 applications. This load cell measures the force in which the pump jack is operating to avoid allowing the pump to go too fast and interrupt the capillary flow of oil. We also recently developed and released the 1923 Wireless Series load cell. Our 1923 Wireless Series innovation provides the same accurate, real-time data readings with little to no fuss over wires, which can create more hazards for the user.

ATEX SSMH Sealed Hazardous Environment Intrinsically Safe S-Type Load Cell

Our Zone 1 rated SSMH S-Type Load Cell is our only load cell that is certified for dust, so it is most often used in mining operations. This product is a tension and compression load cell that is environmentally sealed at an IP65 rating. It also has a high-temperature rating of up to 290° F for dust environments.

ATEX IECEx Bow Type Crosby™ Cabled Load Shackle

The Interface range of ATEX IECEx load shackles is designed for lifting and weighing in rugged or harsh environments, and also meet the requirements for operation in Zone 1 and 2 hazardous areas. The shackle pins are forged from high tensile stainless steel and are machined to an exacting specification. This range of load shackles is proof loaded to 150% of the normal rated load and is available in a range from 3.25 to 400 MT (7.17K to 882K lbf). The product is internally gaged and the whole instrumented area is sealed to IP67 to protect it in service.

When operating in explosive environments, our customers need to know that their products are safe and reliable. Here at Interface, we stand by the quality of our work and the safety of our Ex Rated products. For more information on Interface’s Intrinsically Safe and Ex Rated products, please visit /product-category/intrinsically-safe/.

Contributor:  Ken Vining, Chief Engineer at Interface

Interface Most Promising Energy Tech Solution Provider

Interface is proud to be recognized as one of the ‘20 Most Promising Energy Tech Solution Providers” of 2020 by CIO Review Magazine.

As a pioneer of load cell technology, Interface has long been recognized around the world for providing the most accurate and reliable force measurement solutions on the market. Accuracy matters for safety and reliability in test and measurement projects, engineering and product design and in the original equipment manufacturing of products that require precision sensor technology capabilities.

“The key ingredient to our product’s quality is our more than 50 years of experience and the fact that we have vertically integrated the entire manufacturing process from design to production. Because of this, we have a deep understanding of the materials and product capabilities necessary to suit every industry, application and customer need.” Brian Peters, Director US Sales, Interface

One of the industries where our knowledge of force measurement is vertically integrated processes is in the energy industry. The conditions energy professionals work in can be harsh. They’re often in dangerous environments extracting oil and natural gas, wind, or coal to fuel our nation’s need for power. The equipment our energy sector customers use must be ruggedized and provide the most accurate results possible. If the equipment fails, our customers risk steep financial losses and their staff is more exposed to safety hazards.

Interface has a special line of intrinsically safe solutions for harsh environments. These low profile load cells with loop-powered intrinsically safe amplified output are designed for use in the oil field and other hazardous locations. These load cells are specifically designed from Interface models by adding high resistance strain gages for low-current loop power and shielded internal amplifier for extra low emissions and minimal EMI susceptibility. Interface’s S-type load cell provides a suitable force measurement sensor for applications in coal mining and transfer and other heavy industries where explosive dust and environment conditions are potentially explosion-hazard rated.

Often times, our energy customers come to us needing a custom force measurement solution to deal with these unique challenges for all energy types including thermal, radiant, chemical energy, nuclear, electrical, motion, sound, elastic, and gravitational energy. Innovation in the energy is also heavily dependent upon accuracy in performance, whether it is advancing in the capabilities in the extraction of oil or measuring forces in solar and geothermal. Interface is relied upon by the energy industry leaders and OEM solution providers for their vast ranges of standard and customized load cells, torque transducers, digital instrumentation products and expanding wireless technologies. Read more here about our innovative solutions for the energy industry.

Upon selection for this recognition, Interface application expert Brian Peters contributed to an article for CIO Review Magazine detailing our work developing a custom downhole rig solution for an oil and gas customer. He also explains how Interface has evolved to meet the rising challenges of an industry that is addressing the need for more sustainable energy sources. Click this link to be redirected to Brian’s article online to share.  If you would like to speak with Brian or an application engineer about your test and measurement project or requirements for sensor technology, contact us here.

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