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Calibration Curve 101

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Calibration curves are essential for ensuring the accuracy of force measurements. They are used in a wide variety of test and measurement applications, including quality control, research, and engineering.

A calibration curve is a graph that shows the relationship between the output of a measuring instrument and the true value of the quantity being measured. In force measurement, a calibration curve is used to ensure that the force measuring device is performing accurately. In the context of load cell calibration, a calibration curve is a graphical representation of the relationship between the output signal of a load cell and the applied known loads or forces.

The load cell user will use a known force standard to create the calibration curve. The known force standard is applied to the force measuring device and the output of the instrument is logged via the supporting instrumentation. This process is repeated for a range of known forces.

The calibration curve for a load cell is created by plotting the output signals (typically in voltage or digital units) on the y-axis against the corresponding applied loads or forces on the x-axis. The resulting graph is the calibration curve.

Test and measurement professionals use the calibration curve to convert the load cell output to the true value of the force being measured. The curve helps to establish the relationship between the load and the output signal, and it provides a means to convert the load cell’s output into accurate force or weight measurements. For example, if the output is 100 units when a known force of 100 N is applied, then the calibration curve will show that the measurement using the load cell is accurate to within a certain tolerance.

Benefits of using a calibration curve in force measurement:

  • It ensures that the force measuring instrument is accurate and dependable.
  • It provides a way to convert the load cell output to the true value of the force being measured.
  • It can be used to identify and correct errors, including drift, sensitivity, overload and hysteresis.
  • It should be used for traceability and to track the performance of the measurement device over time.

Why does a calibration curve matter when calibrating load cells?

Load cells can be affected by a range of factors, including temperature variations, drift, and environmental conditions. The calibration curve helps identify and compensate for these factors. By periodically calibrating the load cell, any deviations from the original calibration curve can be detected, and appropriate corrections can be made to ensure accurate and reliable measurements.

The calibration curve for a load cell should be linear, indicating a consistent and predictable relationship between the applied load and the output signal. However, load cells may exhibit non-linear behavior, such as sensitivity variations or hysteresis, which can be accounted for and corrected through calibration.

The calibration curve allows for the determination of the load cell’s sensitivity, linearity, and any potential adjustments or corrections needed to improve its accuracy. It serves as a reference to convert the load cell’s output signal into meaningful and calibrated measurements when the load cell is used in practical applications for force or weight measurement.

Calibration curves are an essential tool for ensuring the accuracy of force measurements. They are used in a wide variety of applications, and they offer several benefits. If you engage in using load cells, it is important to understand the importance of calibration curves and how they can help you ensure accurate measurements.

Find all of Interface 101 posts here.

Interface recommends annual calibration on all measurement devices. If you need to request a service, please go to our Calibration and Repair Request Form.

ADDITIONAL RESOURCES

Interface Calibration 101

Interface Guides

Load Cell Sensitivity 101

Interface Force Measurement 101 Series Introduction

Extending Transducer Calibration Range by Extrapolation

Top Five Reasons Why Calibration Matters

Accurate Report on Calibration

Introducing Interface Load Cell Selection Guides

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When it comes to breadth and depth of sensor solutions, Interface has more than 35,000 products and countless options for customization. This can make choosing a specific load cell, torque transducer or instrumentation device for your next test project seem like a daunting task.

Our goal is to make your selection process easier. In addition to our global network of partners and team of Interface applications engineers, our online Interface Guides are resources designed to help you find the right measurement solution based on your exact requirements.

Recently, we have released two new selection guides to assist you in choosing the best load cell products, the Interface Load Cell Selection Guide and Interface Mini™ Load Cell Selection Guide. The two new Interface load cell selection guides offer a simple drop down menu for filtering the characteristics and model options of our extensive line of load cells. In addition, we provide a checklist for specific features that are best suited for your application and the environment in which you are utilizing the devices for testing and monitoring.

If you are not sure of what you need, we also include a helpful guide below each selection guide to walk you through the distinct types of load cells and their capabilities. Each selection will provide references to existing standard products that meet your criteria with easy links to additional specifications.

INTERFACE LOAD CELL SELECTION GUIDE

The Load Cell Selection Guide begins with criteria that will help you to narrow your options, including load cell types, options, features, and capabilities. Once you have selected one or more of the types to explore, each option will provide you a quick view of the product, capacities, and a link to detailed specifications, drawings, and datasheets. Start by selecting the model that provides the best fit based on the following types:

  • 2-Axis
  • Amplified
  • Axial Torsion
  • Calibration Grade
  • Canister
  • Column Rod End
  • Compression Only
  • Eccentric Load Compensate
  • Fatigue-Rate
  • Flange Mount
  • Intrinsically Safe
  • Moment Compensated
  • Overload Protected
  • Sealed
  • Stainless Steel
  • Submersible
  • Tension and Compression
  • Wireless

With every guide, Interface provides several technical references that are helpful in learning the ins-and-outs our load cells. As part of the Load Cell Selection Guide, you can review the technical make-up of our load cells, details about our proprietary strain gages, calibration insights, plus critical high-accuracy and quality performance parameters that set our products apart from the competition. You can also learn about the effects of temperature, moment compensation, and options available to support a variety of applications.

INTERFACE MINI LOAD CELL SELECTION GUIDE

For the Mini™ Load Cell Selection Guide, we provide a list of our popular miniature load cells with a detailed explanation of each model group. These descriptions provide an overview of the various features and capabilities of our mini products to help you choose the best solution for your use case. The products included in the Mini Load Cell Selection Guide include:

  • Load Cell Load Buttons
  • Load Washers
  • Bending Beam Load Cells
  • Double Bending Beam Load Cells
  • Sheer Beam Load Cells
  • S-Beam Load Cells
  • Overload Protected S-Cells
  • Single Point Impact Load Cells

These guides provide you with a solid baseline of information for making the right selection for your next project or for designing a sensor into your machine, product, or component. If you need further help or require an engineered-to-order or custom product, reach out to our experts. We are here to help!

For an all-time great load cell 101 reference, listen in as our top engineers detail load cell basics in this Interface Classic Series recorded webinar.

Additional Resources

How Do Load Cells Work?

Interface Load Cell Field Guide

Torque Transducer Selection Guide

Contributing Factors To Load Cell Accuracy

LowProfile Load Cells 101

Webinar Recap of Taking Measure of Miniature Load Cells

Interface Presents Load Cell Basics

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

 

 

Tension Load Cells 101

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A tension load cell is a type of force sensor used to measure tensile forces in materials, structures, or machines. It is used to measure the maximum load that a material can support without fracture when being pulled or stretched under the applied load. A strain gage manufactured inside the load cell sensor measures the deformation and converts it into an electrical signal.

The main difference between a tension load cell and a compression load cell is the direction in which they measure the force being pushed or pulled. Though most Interface high performance load cells are designed for both tension and compression, specific load cells are calibrated in tension only to measure forces that pull or stretch a structure. As the load cell stretches, it measures the resulting force.

It is customary practice for most labs to use tension and compression load cells, then determine its specific tension use case based on the requirements of a test project or product design. Tension and compression load cells are easily used for tension only but will measure both. Load cells can be calibrated in either tension or compression, and both tension and compression. The combined is more economical for test labs and most use cases.

Benefits of Tension Load Cells

Load cells that measure tension are preferred over other types of load cells when the force being measured is tensile in nature. They are accurate, reliable, and can be calibrated to suit different applications and environments. Additionally, they are easy to use and require minimal maintenance.

Accurate measurement of tensile forces: Tension-only load cells are specifically designed to measure tensile forces accurately, without being influenced by compressive or bending forces. This makes them ideal for applications where the force being measured is purely tensile, such as in the testing of cables, wires, ropes, or chains used in lifting applications and equipment. Interface Tension Links are preferred for these types of lifting and weighing use cases.

High sensitivity and resolution: Tension-only load cells typically have high sensitivity and resolution, meaning they can detect slight changes in the applied force. This makes them useful in applications where precise measurements are required, such as in the testing of materials with low tensile strength.

Easy installation: Tension-only load cells are typically easy to install and use, requiring minimal setup time and equipment. They are often designed with attachment points or hooks for attaching to the load being measured, which makes them convenient for use in the field or in a testing lab.

Durability and reliability: Tension-only load cells are often constructed from durable materials, such as stainless steel, which makes them resistant to corrosion and wear over time. They are also designed to provide reliable and consistent measurements, ensuring accuracy and consistency in test results.

Tension Load Cell Applications

Tension load cells are standard and their versatility in application use makes them popular in test and measurement. Tension load cells are used for test and measurement industry applications including in manufacturing, automotive, energy, aerospace, and infrastructure. For example, the transportation sector uses load cells to measure the tension in cables, wires, ropes, and chains. They are used in a diverse range of testing equipment to measure the strength and durability of materials. They are designed to provide accurate and reliable measurements of tensile loads and can be calibrated to suit different applications and environments.

Tension load cells are commonly used in applications for material testing to evaluate the tensile strength and elasticity of varied materials, such as metals, plastics, and composites. Tension testing is a valuable tool in materials science and engineering, as it provides valuable information about the tensile properties of a material. Some examples of tension testing include:

  • Determining the strength of a material: Tension testing provides a way to measure the maximum load a material can withstand before it breaks or fails. This information is crucial in determining the strength of a material and its suitability for different applications.
  • Understanding the ductility of a material: Tension testing can also be used to measure the amount of deformation a material can undergo before it breaks. This information is important in determining the ductility of a material and its ability to withstand bending and stretching without breaking.
  • Identifying defects or weaknesses in a material: Tension testing can help identify defects or weaknesses in a material that may cause it to fail under stress. By subjecting a material to increasing levels of tension, engineers can pinpoint the point at which the material fails and investigate the cause of the failure.
  • Comparing the properties of varied materials: Tension testing can also be used to compare the tensile properties of different materials. This information is useful in selecting the best material for a specific application and designing structures that can withstand the required loads.

Tensile Testing For 3D Materials

A customer wants to conduct a tensile force test on different 3D printing materials until failure. These different 3D printing materials being tested included PLA, PETG and ASA to see how they performed. The customer wanted to test the materials quality, strength, ductility, and stiffness. Interface recommended using our 1200 Standard Precision LowProfile™ Load Cell be installed into the customer’s test frame. The tensile test is conducted, and force results captured by the load cell are synced through the INF-USB3 Universal Serial Bus Single Channel PC Interface Module. These results can be displayed on the customer’s computer with supplied software.

Tension load cells are used in structural testing to measure the tension in structures used in construction, aerospace, maritime, and infrastructure. For example, tension load cells are commonly used for bridges, buildings, and towers, to ensure they can withstand the forces in their design and application.

Tension load cells are often used within manufacturing machines and equipment for monitoring and real-time force measurement. For example, in a facility they are used to measure the tension in cables or wires during production, to ensure they meet the required specifications and are safe for use.

Research and development for all types of applications need to assess the tensile properties of new materials or structures, to assess their suitability for different applications, from medical devices to product simulations.

If your next project needs an accurate tension load cell, contact our application experts to see which model best fits your exact requirements.

ADDITIONAL RESOURCES

Interface Solutions for Material Testing Engineers

Tensile Testing for 3D Materials App Note

Testing Lab Essentials Webinar

Bolt Tension Monitoring

Mooring Line Tension Testing App Note

Tension Links 101

Load Cell Stiffness 101

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Load cell stiffness refers to the ability of a load cell to resist deformation when a load is applied to it. It is a measure of how much a load cell will deflect or bend under a given load. Stiffness is an important specification of load cells, as it affects their accuracy and sensitivity.

Load cell stiffness is typically conveyed as the ratio of the load applied to the deflection of the load cell. For example, if a load cell deflects 1mm when a load of 100N is applied, its stiffness would be 100N/mm.

The selection of a load cell with an appropriate stiffness is critical to ensuring optimal performance in each application and should be carefully considered in the design and implementation of any measurement system. Load cell stiffness can significantly alter the performance.

High stiffness load cells are preferred in applications where high accuracy and precision are required, as they provide greater resistance to deformation and are less susceptible to measurement errors. High stiffness provides more precise and consistent measurements. They are the preferred choice for many applications, including in aerospace, robotics, material testing and of course calibration and metrology.

Low stiffness load cells may be used in applications where flexibility and compliance are necessary, such as in weighing systems that must accommodate vibration or movement. Load cells with low stiffness may be more suitable for applications where flexibility and compliance are important, such as in dynamic force measurement or shock testing.

The determination of load cell stiffness requires consideration of several key factors, including:

  • Load capacity of the load cell should be considered when determining its stiffness. Load cells with higher load capacities typically require greater stiffness to maintain their accuracy and precision under load.
  • Sensitivity of the load cell, or the amount of output change per unit of input change, should also be considered. Load cells with higher sensitivities may require greater stiffness to maintain their accuracy, as they are more sensitive to changes in the applied load. Read more in Load Cell Sensitivity 101
  • Environmental conditions in which the load cell will be used should also be considered, such as temperature, humidity, and vibration. In some cases, load cells with lower stiffness may be necessary to accommodate for environmental factors such as thermal expansion.
  • Application requirements specific to the use case, such as the required measurement range, accuracy, and resolution, will define the success of our project or program. Load cells with higher stiffness may be necessary for applications requiring high accuracy and precision, while load cells with lower stiffness may be more suitable for applications requiring greater flexibility and compliance.
  • Natural frequency, which is the frequency at which it oscillates when subjected to an external force is a consideration. Load cells with high stiffness have a higher natural frequency, which allows them to respond more quickly to changes in the applied force, resulting in faster and more accurate measurements.

Load cell design plays a critical role in controlling load cell stiffness. There are several key design factors that can affect the stiffness of a load cell, include material selection, geometry, strain gage placement and mechanical configuration. Read Get an Inside Look at Interface’s Famously Blue Load Cells to review our precision design features.

The choice of materials used in the load cell construction can have a significant impact on its stiffness. Load cells made from materials with higher Young’s modulus, such as stainless steel, are stiffer than load cells made from materials with lower Young’s modulus, such as aluminum.

Load cells with thicker walls, larger cross-sectional areas, and shorter lengths are stiffer than load cells with thinner walls, smaller cross-sectional areas, and longer lengths.

Strain gages placed closer to the neutral axis of the load cell will experience less strain and deformation, resulting in a stiffer load cell.

The mechanical configuration of the load cell, including the number and arrangement of its sensing elements, can also affect its stiffness. Load cells with more sensing elements arranged in a parallel or series configuration can be designed to be stiffer than load cells with fewer sensing elements.

Load cell design plays a critical role in controlling load cell stiffness to ensure that it meets the stiffness requirements of the application. If you have questions about the load cell that best fits your application, please contact us. Our experts are here to help.

ADDITIONAL RESOURCES

Interface Load Cell Field Guide

How Do Load Cells Work?

LowProfile Load Cells 101

Load Cell Basics Sensor Specifications

Load Cell Basics Webinar Recap

Interface New Product Releases Spring 2023

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Interface continues to expand our product offerings of force measurement solutions. We have added new high-accuracy load cells, Bluetooth data loggers, indicators and load cell base kits. The following product summaries highlight the latest additions, along with product features for each model.  We also have a new torque couplings technical guide.

In our Interface New Product Releases Winter 2023 updated, we featured our Pillow Block Load Bearing Load Cells (PBLC).  We are excited announce that our PBLC series are now available in multi-axis options. Reach out to our application engineers to learn more about Pillow Block Load Bearing Load Cells 2-Axis custom options.

If you have questions about our new products, capacities, capabilities, or application uses, please contact our application engineers.

SSLP STAINLESS STEEL LOW PROFILE UNIVERSAL LOAD CELL

The Interface Stainless Steel Low Profile Universal Load Cell SSLP model is a low profile, pancake-styled load cells. The internal construction is a diaphragm design, offering a lower cost solution with high natural frequency, low deflection and excellent resistance to side and torsion forces. There is an optional mounting base available, required if used in tension testing. It provides high stability and low height. The SSLP can be supplied calibrated as a complete system with associated instrumentation. View: SSLP Stainless Steel Low Profile Universal Load Cell

Primary SSLP features and benefits:

  • Capacities from 2.5 to 5000 kN (562 to 1,124K lbf)
  • Low profile with stainless steel construction
  • Environmentally sealed to IP67
  • Hose and conduit fitting at cable exit
  • High thermal stability
  • Base options, including custom bases and custom top plate
  • Load cap assembly optional
  • TED options
  • ATEX and submersible versions available
  • Options for internally amplified and multiple bridges

BX6-BT PORTABLE 6-CHANNEL HIGH-SPEED BLUETOOTH DATA LOGGER

Interface’s digital instrumentation data acquisition system BX6-BT Portable 6-Channel High Speed Bluetooth® Data Logger is a multi-channel measuring amplifier that offers a multitude of features in a convenient compact package. The BX6-BT first channel is for full-bridge strain gages, channels two through six are individually configurable as voltage input (single-ended) or strain gage bridge input, including half and quarter bridge configuration. View: BX6-BT Portable 6-Channel High Speed Bluetooth Data Logger

Primary BX6-BT features and benefits:

  • Simultaneous zeroing of all channels can be triggered via a digital input (tare)
  • Measurable temperature in the device and the battery voltage
  • Protected against vibration by full encapsulation housing
  • Configuration and acquisition of measurement data with BlueDAQ in the mode “BT Classic” with Serial Port Profiles (SPP)
  • Integrated Bluetooth module has its own microcontroller.
  • Connected 3.7V lithium-ion battery can be charged by an integrated charging circuit.
  • Power supply via a Li-Ion battery from 3.6V – 4.2V

9840C TEDS READ WRITE INTELLIGENT INDICATOR

Interface’s new digital instrumentation 9840C indicator is a CE compliant and versatile precision instrument intended for the digital readout of strain gage sensors, which includes load cells. It is TEDS Plug and Play Ready and IEE 1451.4 Compliant. View: 9840C TEDS Read/Write Intelligent Indicator

Primary 9840C Intelligent Indicator features and benefits:

  • Reads and writes calibration data and coefficients to the load cell
  • Stores load cell information and calibration data and coefficients for use with up to 20 load cells
  • 10-point linearization
  • Adjustable calibration curve
  • Bipolar and accepts 2, 3, and 4 mV/V load cell inputs
  • Remote sense excitation (6-wire load cells)
  • Fast direct analog output with +/-10 VDC scalable analog output — 16 bit
  • Full duplex RS232C communication
  • Eight selectable digital filters
  • Front panel shunt calibration with two selectable resistors

LOWPROFILE™ LOAD CELL BASE KITS

Interface’s standard LowProfile Load Cells are offered with bases. The base is a flat surface, guaranteed to provide optimum support for the flexure. Use of the base, or a support surface with its equivalent flatness and stability, is required to ensure the exceptional performance of the LowProfile® Series. Note that the threaded hole in the base is on center, and a plug is permanently installed to seal dirt and moisture out of the space between the bottom hub of the flexure and the flat surface of the base. Read more about the basics of base kits. View: LowProfile™ Load Cell Base Kits

Primary LowProfile Load Cell Base Kits features and benefits:

  • 14 model options in both U.S. and Metric thread
  • 15 stainless steel model options
  • Bases are all heat treated
  • High strength materials, including stainless steel options
  • Available in LowProfile standard sizes for Interface load cell models 1000, 1200, 2400, 3200
  • Standard thread size is the same as the mating load cell
  • Custom base options available
  • When the base and load cell are ordered together, a plug is supplied in both the cell and the base to prevent damage or errors caused by over engagement of mating parts

TORQUE COUPLINGS PLUS NEW TECHNICAL GUIDE

Interface is excited to introduce a complete summary catalog and technical guide of our extensive line of Torque ROBA® DS Couplings. These Interface torsional rigid shaft coupling transmits drive torques up to the nominal torque completely backlash-free and with permanently high torsional spring rigidity. Problems to be found on other commercially available couplings, such as denting the disks or overcoming the frictional locking, are not an issue when using our couplings. The specified shaft misalignments can be 100% utilized without affecting the transmittable torque. This guarantees unlimited use. View: Torque Couplings Technical Guide and Summary Catalog for all sizes, technical details, and installation instructions.

Primary Torque Couplings options and features:

  • Non-sensitive to alternating loads of up to 100% of the nominal torque
  • Low mass inertia due to high performance density
  • Completely backlash-free up to nominal torque
  • High misalignment compensation capability at low restoring forces
  • High torsional rigidity up to nominal torque
  • Completely wear and maintenance-free
  • Optimum construction shape due to large variant range

There are two main categories of couplings used in force measurement and the biggest difference in the two is the degree of freedom needed for the application. The categories are single-jointed and double-jointed. Read more in our Couplings 101 Series.

INF4-POWERLINK TWO, THREE, AND FOUR SENSOR WEIGHT TRANSMITTER AND INDICATOR

Expanding our INF4 series, we introduced the Interface INF4-POWERLINK Two, Three, and Four Sensor Weight Transmitter and Indicator. It has a six-digit red LED display (8 mm height), space saving compact design, four buttons for the system calibration. You can store up to 50 events, use multiple load cells in parallel and set alerts for value deviations. View: INF4-POWERLINK Two, Three, and Four Sensor Weight Transmitter and Indicator

Primary INF4-POWERLINK 2, 3 and 4 features and benefits:

  • Four independent channels for monitoring and direct management of individual load cells
  • Digital equalization
  • Four channel load distribution signaling with archive
  • Automatic diagnostics comparing recorded values plus alerts
  • Event log archives for calibrations, zero settings, errors, and equalizations
  • Excitation remote sense
  • 16 load cells in parallel
  • Tare weight zero setting, semi-automatic tare (net/gross weight) and predetermined tare
  • Connections to PLC via analog output or fieldbus and PC/PLC via RS485 up to 99 instruments with line repeaters, up to 32 without line repeaters
  • Direct connection between RS485 and RS232 without converter

INF1-POWERLINK SINGLE SENSOR WEIGHT TRANSMITTER AND INDICATOR

The INF1 series added the INF1-POWERLINK Single Sensor Weight Transmitter and Indicator. Like the version above, the options for this include a compact design, use with multiple load cells (up to 8) in parallel. View: INF1-POWERLINK Single Sensor Weight Transmitter and Indicator

Primary INF1-POWERLINK Single features and benefits:

  • Connection to PLC via analog output or fieldbus
  • PC/PLC via RS485 up to 99 instruments with line repeaters, up to 32 without line repeaters
  • Remote display via RS485
  • Excitation remote sense
  • Eight load cells in parallel
  • Digital filter to reduce the effects of weight oscillation
  • Theoretical calibration and real calibration with the possibility of weight linearization up to five points
  • Tare weight zero setting and automatic zero setting at power on

SPECIAL EVENT ALERT!

We are hosting Testing Lab Essentials: Today + Tomorrow on Thursday, April 6. We are diving into products and solutions used in all types of testing labs, along with tips and best practices for modernizing your test lab. Join the conversation.  All Interface webinars are recorded if you are not able to attend the live event.

ADDITIONAL PRODUCT RESOURCES

Interface is ready to help you get the exact product based on your unique requirements.  For engineered to order or custom solution options, please contact our experienced applications experts.

Load Cell Sensitivity 101

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Load cell sensitivity refers to the relationship between the input force applied to a load cell and the output signal it generates. It is a measure of the load cell’s responsiveness to changes in the applied force and is expressed in units of mV/V (millivolts per volt) or micro-volts per volt.

When determining the accuracy of a load cell, load cell sensitivity is an important parameter. A higher sensitivity means that even small changes in the applied force will result in a larger change in the output signal, making the load cell more sensitive and accurate.

It is critical to understand that load cell sensitivity and accuracy are closely related. A high sensitivity load cell will generate a larger output signal for the same applied force, which can increase the accuracy of the measurement. In general, the accuracy of a load cell is a combination of its sensitivity and the quality of its design and construction. Interface specializes in precision accuracy, which is important when considering the use case for your load cell.  As defined by the specifications, a high-quality load cell with appropriate sensitivity will provide accurate and consistent measurements, while a load cell with low sensitivity or poor quality may provide less accurate measurements.

Most load cells are designed to measure force in one certain direction, which is determined by the way the load cell is mounted. Inappropriate loading will cause side and eccentric load, which risks reducing the life of load cells and distorting measurement results.

Eccentric load sensitivity is measured by eccentric load, which is any load applied parallel to but not concentric with the primary axis. Side load is any load at the point of axial load application at 90 degrees to the primary axis.

To achieve a desired level of accuracy, it is important to choose a load cell with the appropriate sensitivity for the application. Load cell sensitivity can be affected by factors such as temperature, temperature gradients, and environmental conditions, so it is important to take these factors into account when selecting a load cell.

What conditions impact load cell sensitivity? Load cell sensitivity can be impacted by several factors, including:

  • Temperature: Changes in temperature can cause thermal expansion or contraction of the load cell material, affecting the output signal and reducing accuracy.
  • Temperature gradients: The presence of temperature gradients within the load cell can cause differential expansion or contraction of different parts of the load cell, further affecting the output signal and reducing accuracy.
  • Environmental conditions: Exposure to harsh environments, such as moisture, vibration, and shock, can cause damage or degradation to the load cell, reducing its sensitivity and accuracy.
  • Load cell orientation: The orientation of the load cell can impact the output signal, especially in applications where the load is applied at an angle.
  • Mechanical stresses: The presence of mechanical stresses, such as bending or twisting, can affect the output signal and reduce accuracy.
  • Aging: Over time, the load cell may experience degradation or wear and tear, reducing its sensitivity and accuracy. This is where regular calibration plays a role in the lifetime of your load cell.

It is important to consider these factors when selecting a load cell and to properly maintain and calibrate the load cell to ensure optimal sensitivity and accuracy over time.

Calibration is a process that involves adjusting the output signal of a load cell to ensure that it accurately reflects the applied force. Calibration improves load cell sensitivity by correcting for any errors or inaccuracies in the output signal, ensuring that the load cell provides accurate and consistent readings over time.

During calibration, a series of known loads are applied to the load cell, and the corresponding output signals are measured. These measurements are used to create a calibration curve that represents the relationship between the applied force and the output signal.

Calibration helps to correct for various factors that can affect load cell sensitivity, such as temperature, environmental conditions, and mechanical stresses. By adjusting the output signal to accurately reflect the applied force, calibration helps to ensure that the load cell provides accurate and consistent readings, even in challenging conditions. Interface recommends calibration of every load cell at least once a year for regular sensitivity maintenance.

Interface engineers design high accuracy, quality load cells with appropriate sensitivity that provides accurate and consistent measurements. It is important to consider both sensitivity and accuracy when selecting a load cell for an application and to regularly calibrate the load cell to ensure that it continues to provide accurate and reliable measurements over time.

Mechanical Installation Load Cell Troubleshooting 101

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The performance of a load cell force measurement system is dependent upon the reliability of the physical installation, correct interconnection of the components, proper performance of the basic components which make up the system, and calibration of the system.

Interface provides installation instructions for our products. Review the installation guide and keep on hand for installation and troubleshooting. Load cells not mounted in accordance with the manufacturer’s recommendations may not perform to the design specifications.

Always start any troubleshooting with a physical inspection of the load or weighing sensor. Resistance results from numerous factors, creating an inaccurate reading of the measurement and potential overload. If there is any appearance of dents, bending, cracks or deformation it is likely the device will need to be repaired or replaced. If none of these conditions are visible, the next step is to troubleshoot the mechanical installation.

The following is a quick checklist to reference for mechanical installation troubleshooting:

  • Check the mounting surfaces for cleanliness, flatness, and alignment
  • Check the torque of all mounting hardware
  • Check the load cell orientation
  • Check use of proper hardware as required to connect the load to the load cell
  • Check cables or output devices

Orientation is of a load cell is defined by the “dead” end on mechanical reference or load forcing source and the “live” end connected to the load to be measured by the cell. Dead end is the end closest mechanically to the cable exit or connector. A fundamental requirement is that there be one, and only one, load path.  This load path must be through the load axis of the load cell. This may sound elementary; however, it is a commonly overlooked problem.

Check all hardware and accessories when troubleshooting during mechanical installation, including all connectors, cables, thread sizes, jam nuts, swivels, mounts, and bolts. It is always important to also thoroughly inspect the cables used in a system. Evaluate the cable to ensure there is no crimping, cuts, or exposed wires. This is a common cause of mechanical installation failure.

For a quick reference, here is a discussion about what a healthy load cell should look like, and any visual clues that may potentially be a sign for an improperly working load cell.

For more helpful guides and troubleshooting tips, please visit the Interface Technical Library. Interface provides technical support for additional questions related to installation or if there is help needed in troubleshooting any of our products. Contact us here and let us know how we can help.

Additional Resources

Force Measurement Installation Guides

I’ve Got a Load Cell, Now What Play List

Force Measurement Accessories 101

 

Strain Gage Design Under Eccentric Load WRSGC Presentation

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By Ashlesa Mohapatra, product design engineer, Interface

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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