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Why Is Load Cell Zero Balance Important to Accuracy?

Several factors go into the accuracy and consistent performance of a load cell. These factors include non-linearity, hysteresis, repeatability, creep, temperature, environmental effects, and zero balance.

Every Interface load cell’s design and specifications account for all these factors. Understanding each of these factors is important, especially considering the use case.

Specifications are detailed descriptions that outline the characteristics, features, and qualities of our products, systems, or services. Product specifications detailing performance, capabilities, capacities, and dimensions are included on all datasheets. Products have internal specifications tested during manufacture, typically with full traceability.

Zero balance is considered an electrical load cell specification value. It is essential to consider when selecting the type of load cell for any application.

Load cell zero balance is the signal of the load cell in the no-load condition. It is defined as the output signal of the load cell with rated excitation and no load applied. It refers to the amount of deviation in output between true zero and an actual load cell with zero load. It is usually expressed in the percentage of rated output (%RO). Zero balance is a test that can be done to understand calibration on a load cell.

Load cells constantly reset to zero after every measurement to maintain accuracy. If it does not, then the results will prove to be inaccurate. The zero balance must be within the error margin indicated on the calibration certificate. Interface sensors are typically +/-1.0%.

This is important to test because zero balance will tell you if a load cell is in working order or has been damaged or overloaded. A computed zero balance of 10-20% indicates probable overload. If the load cell has been overloaded, mechanical damage has been done that is not repairable because overloading results in permanent deformation within the flexural element and gages, destroying the carefully balanced processing that results in performance to Interface specifications.

While it is possible to electrically re-zero a load cell following overload, it is not recommended because this does nothing to restore the affected performance parameters or the degradation of structural integrity. If the degree of overload is not severe, the cell may sometimes be used at the user’s discretion. However, some performance parameters may violate specifications, and the cyclic life of the load cell may be reduced.

To perform a zero balance test, The load cell should be connected to a stable power supply, preferably a load cell indicator with an excitation voltage of at least 10 volts. Disconnect any other load cell for multiple load cell systems. Measure the voltage across the load cell’s output leads with a millivoltmeter and divide this value by the input or excitation voltage to obtain the zero balance in mV/V. Compare the zero balance to the original load cell calibration certificate or the datasheet. Every Interface product has a detailed datasheet available on the product page of the sensor.

ADDITIONAL TECHNICAL DEFINITIONS

Zero float is the shift in zero balance resulting from a complete cycle of equal tension and compression loads. It is normally expressed in the units of %FS and characterized at FS = Capacity.

Zero stability is the degree to which zero balance is maintained over a specified period with all environmental conditions, loading history, and other variables remaining constant.

Learn more about the specification values that define load cell accuracy in this short clip from our  Demystifying Specifications Webinar.

Get your free copy of the Interface Load Cell Field Guide to learn more about factors affecting load cell accuracy. If you are concerned about the zero balance of your Interface load cell due to inaccurate results or recent damage, please get in touch with us at 480-948-5555.

ADDITIONAL TECHNICAL RESOURCES

Interface Technical Support Information and Troubleshooting

Interface Product Selection Guides

Interface Installation Guides and Operation Manuals

Interface Software and Drivers

Interface Product Catalogs

Interface 101 Blog Series and InterfaceIQ Posts

Interface Industry Solutions and Applications

Interface Recorded Webinars

Demystifying Specifications Webinar Recap

Interface recently hosted an online technical seminar that detailed product specification basics, key values, terms to know, how to read a datasheet, what specs matter most in force measurement applications.

For Interface, specifications are detailed descriptions that outline the characteristics, features, and qualities of our products, systems, or services. Product specifications are included on all datasheets, detailing product performance, capabilities, capacities and dimensions. Products have internal specifications that are tested against during manufacture, typically with full traceability.

Throughout the webinar Demystifying Specifications, Brian Peters and Jeff White offered important tips on what to consider for high-speed, durability, precision, and specialty product requirements. They highlighted what to look for on the product datasheet when choosing a load cell or instrumentation device. This includes variables in specifications related to expected performance of transducers and instrumentation based on frequency, environment, and other critical testing application considerations. They also answered the most frequently asked questions of our applications engineers related to specifications and datasheets.

Demystifying Specifications Webinar Topics

  • Specification Basics
  • Specifications and Values in Force Measurement
  • Decoding Datasheets
  • Detailing Product Specs for Load Cells
  • Detailing Product Specs for Instrumentation
  • Detailing Product Specs for Specialty Sensor Products
  • Applying Specifications to Applications
  • Specification Tips
  • FAQs and Resources

The entire webinar, Demystifying Specifications, is now available to watch online.

Four Types of Specifications

Interface provides four types of specifications for every product we make and sell: functional, technical, performance and design.

  1. Functional specifications describe the intended functionality or behavior of a product, whether a sensor, instrument or accessory.  They outline what the product or system should do and how it should perform its tasks. Functional specifications typically include applications, product requirements, and expected use case results.
  2. Technical specifications provide detailed information about mechanical aspects of a product or system. They may include information about the materials, dimensions, technical standards, performance criteria, capacities, and other technical details necessary for the design, development, and implementation of the product or system
  3. Performance specifications define the performance requirements and criteria that a product or system must meet. This is critical in force and measurement. They specify the desired performance levels, such as speed, accuracy, capacity, efficiency, reliability, or other measurable attributes. Performance can be defined by a specific range, with maximum standards for peak performance. Performance specifications help ensure that the product or system meets the desired test and measurement goals.
  4. Design specifications outline the specific design criteria and constraints for a product or system. These specs provide guidelines and requirements related to the visual appearance and can also reference the model details found in a product’s engineering CAD STEP file. 

Specifications Commonly Found on Interface Product Datasheets

  • Models based on Form Factor
  • Measuring Range (Capacity)
  • Measurement Units: US (lbf) Metric (N, kN)
  • Accuracy (Max Error)
  • Temperature: Operating Range, Compensated Range, Effect on Zero and Effect on Output (Span)
  • Electrical: Rated Output, Excitation Voltage, Bridge Resistance, Zero Balance and Insulation Resistance
  • Mechanical: Safe Overload, Deflection, Optional Base, Natural Frequency, Weight, Calibration and Material
  • Dimensions
  • Options
  • Connector Options
  • Accessories

Key Force Measurement Specification Terms to Know

Nonlinearity: The algebraic difference between OUTPUT at a specific load and the corresponding point on the straight line drawn between minimum load and maximum load.  Normally expressed in units of %FS.

Hysteresis: The algebraic difference between output at a given load descending from maximum load and output at the same load ascending from minimum load. Normally expressed in units of %FS.

Static Error Band (SEB): The band of maximum deviations of the ascending and descending calibration points from a best fit line through zero output. It includes the effects of nonlinearity, hysteresis, and non-return to minimum load. Expressed in units of %FS.  SEB Output is a best fit straight line output at capacity.

Nonrepeatability: The maximum difference between output readings for repeated loadings under identical loading and environmental conditions.  Expressed in units of %RO. In practice there are many factors that affect repeatability that ARE NOT included in the nonrepeatability specification.

Creep:  The change in load cell signal occurring with time, while under load and with all environmental conditions and other variables remaining constant. Expressed as % applied load over specific time interval. Logarithmic effect that is also symmetric on load removal. Stated specifications may differ and are not for the same time interval.

Eccentric and Side Load Sensitivity: Eccentric Load – Any load applied parallel to but not concentric with the primary axis. Results in moment load. Side Load – Any load at the point of axial load application at 90° to the primary axis. Error influences are reported in terms % and %/in.

Watch the event to understand why these specification details matter and some of the important variables to consider when comparing, using or troubleshooting different measurement products.  During the event, we provided a list of resources that are helpful when looking for specification information or definitions. The complete list is below.

ADDITIONAL RESOURCES

Interface Product Selection Guides

Interface Technical Support Information and Troubleshooting

Interface Load Cell Field Guide (Free Copy)

Interface Installation Guides and Operation Manuals

Interface Software and Drivers

Interface Product Catalogs

Interface 101 Blog Series and InterfaceIQ Posts

Interface Industry Solutions and Applications

Interface Recorded Webinars

Understanding Cable Length and Temperature Effects

Interface offers several different accessories, from interconnect cables and mating connectors to base kits and TEDS. Cables and connectors are used to attach the sensor equipment to a multitude of components and systems including data acquisition systems, power amplifiers, test stands and other instruments.

Consideration of the cable and connectivity are important when selecting any transducer. Interface has several standard cable options based on the type of measurement device, the instrumentation, the pinout, type of connector and length required for the testing use case.

Find a range of all standard cable assembly options listed here, such as:

  • Interconnect Cable from Bayonet-Type Load Cell Connector to Pigtails, 10-foot in length
  • Amplified Load Cell Bayonet-Type Connector to Pigtails
  • Screw-type Load Cell (non-TEDS) Connector to Model 9860 Indicator 10-foot in length
  • Interconnect Cable from Model TS-type Torque Transducer to Pigtails, 10-foot in length
  • Interconnect Cable from Pigtails to Pigtails, 10-foot in length
  • Interconnect Cable from TX Torque Transducer 8-pin Connector to Pigtails, 6-meters in length
  • Interconnect Cable from Model WMC/2420/2430 Bayonet-type Load Cell Connector to Pigtails, 10-foot in length

Interface uses the highest grade mating connectors to ensure that the performance of your force and torque solutions are not compromised during use. We offer options for standard connectors based on the receptacle and plug type requirements, as well as custom solutions. Our mating connectors include:

  • Bayonet-Type Mating Connectors
  • Screw-Type Mating Connectors

Cable Length and Temperature Considerations

For high accuracy force measurement, the effects of the cable on the measurement must be considered for any testing program. For constant voltage excitation there are two significant effects:

  • An effect on the sensitivity due to voltage drops over the cable length.
  • An effect on the thermal span characteristics of the load cell due to the change of cable resistance with temperature.

If the Interface load cell is purchased with a cable of any length, the sensitivity is determined with the installed cable in calibration. Always consider your cable options when buying a new sensor.

TIP: For load cells with connectors, or if a cable is added that is not designed for the exact use, there will be a loss of sensitivity of approximately 0.37% per 10 feet of 28 gage cable and 0.09% per 10 feet of 22 gage cable. This error can be eliminated if a six wire cable is run to the end of the load cell cable or connector and used in conjunction with an indicator that has sense lead capability.

Since cable resistance is a function of temperature, the cable response to temperature change affects the thermal span characteristics of the load cell cable system. For 6-wire systems this effect is eliminated and is a non-issue in performance. For 4-wire cables the effect is compensated for in the standard cable lengths offered with the load cells if the load cell and cable are at the same temperature at the same time.

There are cables designed for hot temperature or corrosive environments that can not only withstand those conditions, but also provide accurate data despite environmental challenges.

TIP: For non-standard cable lengths, there will be an effect on thermal span performance. The effect of adding 10 feet of 28 gage cable is to cause a decrease in sensitivity with temperature equal to 0.0008%/°F. For an added 10 feet of 22 gage cable the effect is to decrease sensitivity by 0.0002%/°F. In some cases, it is tolerable to degrade performance since Interface standard specification is extremely tight. However, for long cable runs or high accuracy applications, this can be a significant factor. The best approach to eliminate the problem is to run six wires to the end of the standard cable length and sense the excitation voltage at that point.

Our customers in the oil and gas industry often need force measurement solutions that can perform under extreme heat and pressure, such as in a downhole application. The cables and connectors needed for this type of project often need custom braiding and coating to ensure the wiring will not melt or corrode in this environment. Read more in Interface Pressure Compensated Downhole Load Cell White Paper.

Interface also provides our maritime and off-shore testing customers with submersible solutions in which the connection between the submersible load cell and the connector must be sealed tightly to prevent water damage to the components.

We develop all our products and accessories using only components and materials that are engineered to perform for precision testing applications. Find all the accessories here. Our engineers will also work with your directly to find the accessories that fit your specific needs. If we do not currently offer the necessary connectors and cables in house, we can work with you to create a custom solution. We also provide a variety of options depending on the data requirements, whether it is permanent monitoring, as well as different cables based on instrumentation interconnectivity.

The best option is to always purchase the cable and any mating connector at the time you choose your load cell or torque transducer. This ensures it is calibrated with the cable and performs to the exact specifications as it was designed and guaranteed by Interface.

ADDITIONAL RESOURCES

Demystifying Specifications Webinar

Force Measurement Accessories 101

Accessories

Interface Guides

TEDS 101

Basics on Load Cell Base Kits

Mating Connectors

Interface Load Cell Field Guide

How Load Cells Can Go Bad

Load cells are electronic devices that measure the force applied to them. Interface products are made to last, in fact we have many load cells that are in-market and being used for high-accuracy testing that were manufactured decades ago. Why do they last? Quality of design, material construction, build process, calibration, and regular maintenance prolong the life of a load cell.

Like any electronic device, load cells can go bad for a few reasons. It is also important to know that load cells can be repaired. Outside of complete destructive testing, the following issues are most common for how load cell can go bad.

Overloading: Load cells have a maximum capacity, and if they are subjected to a force beyond that limit, they can get damaged. Overloading can cause the load cell to deform or break, resulting in inaccurate readings or complete failure. Preventative options are to use overload protected load cells.

Mechanical and physical damage: Load cells are sensitive devices and can be damaged by impact, vibration, or shock. Mechanical damage can cause the load cell to deform or lose its calibration, resulting in inaccurate readings. Physical damage to devices is often because the load cells are dropped or mishandled during use.

Moisture: Load cells are often used in damp or wet environments, and prolonged exposure to moisture can cause corrosion or damage to the internal circuitry. Environmental exposure to moisture can also cause electrical shorts or create a conductive path between the components, resulting in inaccurate readings or complete failure. Review submersible options if testing in these environments is common.

Temperature: Load cells can be sensitive to temperature changes, and extreme temperatures can cause damage to the internal components. Thermal expansion or contraction can cause mechanical stress, resulting in deformation or damage to the load cell. Interface offers high-temperature and low-temperature load cells options.

Electrical noise: Load cells are susceptible to electrical noise, which can cause interference in the signals and result in inaccurate readings. Electrical noise can be caused by electromagnetic interference (EMI), radio-frequency interference (RFI), or other sources of electrical interference.

Aging: Not all load cells are made the same way. Interface load cells are designed to outlast any testing use for long-periods, we are talking millions of cycles. However, some load cells can wear out over time due to repeated use, exposure to the environment, or other factors. Aging can cause a decrease in sensitivity, accuracy, or stability, resulting in inaccurate readings or complete failure. All load cells need good health checks to stay working at optimal performance.

To avoid load cell failures, it is important to use them within their rated capacity, protect them from mechanical damage, and provide adequate protection from moisture, temperature, and electrical noise. Regular maintenance and calibration services, preferably every year, can also help ensure accurate and reliable performance over time.

What is the best way to determine if a load cell is bad or not working?

There are several ways to determine if a load cell is bad or not working. Here is a reminder of five quick checks:

#1 Visual Inspection: Start by visually inspecting the load cell for any signs of physical damage, such as cracks, deformations, or loose connections. Check for any corrosion or signs of moisture, as well as any visible wear and tear.

#2 Zero Balance Testing: A zero balance test is a quick and straightforward way to check if a load cell is functioning properly. With no weight applied, the load cell should read zero. If it does not, there may be an issue with the load cell or its connections.

#3 Load Testing: Load testing involves applying a known weight to the load cell and checking the reading. If the load cell is accurate, the reading should match the known weight. If there is a significant discrepancy, the load cell may be faulty.

#4 Bridge Resistance Tests: Load cells are typically constructed with a Wheatstone bridge circuit, which can be assessed for proper resistance values. If there is a significant deviation from the expected resistance values, there may be an issue with the load cell or its connections.

#5 Temperature Tests: Load cells can be sensitive to temperature changes, and extreme temperatures can cause damage to the internal components. Evaluating the load cell at different temperatures can help to identify any issues with temperature sensitivity.

Interface provides complete evaluations of any product we manufacture, to determine if the load cell is working properly. To request services, go here.

How does calibration help load cells from going bad?

Calibration is the process of adjusting a load cell to ensure its accuracy and reliability in measuring weight or force. Regular calibration is essential for maintaining the accuracy and reliability of load cells. Interface recommends annual calibration services as a preventative measure and for good maintenance of your force measurement devices.

Calibration helps to ensure that a load cell provides accurate and consistent readings. Over time, load cells can drift from their initial calibration due to environmental factors, wear and tear, and other factors. Regular calibration ensures that any deviations from the standard are detected and corrected, preventing inaccurate readings that can lead to errors in weighing and other measurements.

Load cells that are not calibrated regularly may experience premature wear and tear due to repeated use, leading to damage or failure. Calibration helps to identify any issues early on and prevent further damage, extending the lifespan of the load cell and saving on replacement costs.

Many industries and applications have strict standards and regulations for measuring weight and force. Regular calibration helps to ensure that load cells meet these standards and regulations.

Regular calibration can help load cells from going bad in multiple ways. It can help to prevent inaccurate readings, extend the lifespan of load cells, improve efficiency, and ensure compliance with standards and regulations. Accurate measurements are critical, and calibration helps to ensure that load cells is working properly. Request a repair or calibration service online.

ADDITIONAL SERVICES

Load Cell 101 and What You Need to Know

Load Cell Sensitivity 101

Can Load Cells Be Repaired?

Services & Repair

Mechanical Installation Load Cell Troubleshooting 101

How Do Load Cells Work?

Regular Calibration Service Maintains Load Cell Accuracy

Load Cell Sensitivity 101

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.

High Temperature Load Cells 101

The temperature rating of a strain gage type load cell is primarily dependent upon the materials selected for its construction. While the load bearing element is normally good for a wide temperature range, the non-metallic materials in a load cell are quite sensitive to temperature extremes and must be carefully selected to ensure they can withstand high or low temperatures.

Considerations in designing the right solution for high temperatures includes understanding requirements for the strain gage materials, adhesives, and insulations. With any set of materials, performance at temperature extremes is frequently compromised, relative to performance at nominal temperatures.

Most Interface standard load cell models are rated for an upper operating temperature limit of 200°F. Special models can be engineered to operate as high as 500°F by request for customization. We also carry a line of intrinsically safe load cells that are designed and used in harsh environments.

Interface offers a range of high temperature load cells in different form factors, from miniature to jumbo, including:

Compensated temperature range is the range of temperature over which the load cell is compensated to maintain output and zero balance within specified limits. Operating temperature range is the extremes of ambient temperature within which the load cell will operate without permanent adverse change to any of its performance characteristics.

There are four parameters to consider when examining temperature performance of high temperature load cells.

  • Temperature Effect on Zero: The change in zero balance that is due to a change in ambient temperature. It is normally expressed as the slope of a chord spanning the compensated temperature range.
  • Temperature Effect on Output: The change in output that is due to a change in ambient temperature. It is normally expressed as the slope of a chord spanning the compensated temperature range. Note that output is defined as a net value, as the zero-load signal is always subtracted from the loaded signal.
  • Creep: The change in load cell signal that occurs with time while under load, and with all environmental conditions and other variables remaining constant. It is normally expressed in units of % of applied load over a specified time interval.
  • Zero Return: The degree to which the initial zero balance is maintained after application and release of a load, while environmental conditions and other variables remain constant.

Interface load cells are temperature compensated for zero balance. By compensating for zero balance, we can flatten the curve in the relationship between temperature and zero balance. An uncompensated load cell has a much more severe curve, which impacts the accuracy and overall performance. Read more in Understanding Load Cell Temperature Compensation.

Another consideration for utilizing load cells in high temperature environments or exposing load cells to high temperatures is the use of cables. Since cable resistance is a function of temperature, the cable response to temperature change affects the thermal span characteristics of a load cell cable system.  Interface recommends consulting with your application engineer to see if a 6-wire system can eliminate concerns. Also, for non-standard cable lengths, there will be an effect on thermal span performance. For long cable runs or high accuracy applications, this can be a significant factor.

Additional Resources

Hazardous Environment Solutions from Interface

Ruggedized Test and Measurement Solutions Webinar Recap

Coil Tubing Load Cells

Load Pins, Tension Links, & Shackles

 

Announcing the Launch of the Interface Pressure Compensated Downhole Load Cell

Interface is excited to announce the release of a new downhole solution for the energy industry, the Interface Pressure Compensated Downhole Load Cell (IPCD).

The IPCD is a Wheatstone bridge foil-gaged-based force measurement solution using proprietary compensation methods and designed to provide highly accurate force data in harsh environments, like those found in the oil and gas industry, while requiring limited maintenance compared to similar solutions on the market. This is a product line that is many years in the making, as we’ve offered it as a custom solution. In fact, it has been developed across multiple applications to meet the needs of the oil and gas industry.

Interface’s new IPCD product is best suited for tension head applications of wireline services, particularly useful in deviated or horizontal wells where topside measurements are no longer reliable. Many applications include conveyance, pump down, perforating, tractor, and high pressure high temperature deep offshore use.

The key benefit the IPCD provides over existing solutions, commonly referred to as “wet” load cells, is its method of compensation. Wet load cells have a hydraulic compensation mechanism that uses pistons and seals, requiring frequent maintenance. Hydraulic compensation is complex for smaller tool providers and performance was suboptimal. For the IPCD, Interface developed a proprietary technology that compensates for that pressure influence and allows for bridge isolation. This means that the IPCD is far more rugged, needing little to no repairs, and it can be used downhole without risk of damage, a first of its kind in the industry.

It provides accurate measurement of downhole tension conditions in both vertical and horizontal wells and the proprietary internal compensation actively measures only the portion of the load caused by axial force, ignoring the portion of the load caused by pressure. Since it is an inherently passive system with no active pressure measurement being made or using a separate transducer, it is a completely analog solution for reliability and temperature stability.

We also test the IPCD heavily before it leaves our doors. The oil and gas industry can be extremely volatile, so we understand that our load cells need to be at peak performance for every use. Each load cell is tested individually on force, creep, temperature and pressure.

Advantages of the new proprietary Interface Pressure Compensated Downhole Load Cell include:

  • IPCD is a standard product from Interface and available today
  • IPCD offers maintenance-free service with significant long-term payback by eliminating disassembly, downtime, calibration, and instrumentation configuration
  • Interface’s new product is a precision with unmatched performance
  • IPCD has minimal thermal and pressure error, combined with world class linearity and hysteresis
  • It has field proven reliability and was designed based on a decades of engineering and force measurement experience

To learn more about the IPCD, we recently published a white paper that goes deeper into how the unit works, the specifications of the solution, as well as providing additional information on our testing process. You can read more about the IPCD in our new technical overview, Interface Pressure Compensated Downhole Load Cell White Paper available online for download.

We also issued a press release announcing the launch of IPCD.

This new product launch is a collaborative effort involving many of our team members in engineering, production and sales.

 

Understanding Load Cell Temperature Compensation

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

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

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

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

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

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

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

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

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

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

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

Load Cell Basics Sensor Specifications

When selecting a load cell, it’s critical to understand the major factors impacting sensor accuracy. These factors are determined by the materials and components used in the construction of the load cell, the calibration, instrumentation, the accessories such as cables, and mounting installation. Each must be considered in the specific use cases for the load cells.

During our virtual event, Load Cell Basics, applications expert Keith Skidmore detailed everything you need to know about load cells and how to choose the right load cell.  First, Keith highlighted four vital application considerations:

Mechanical – Dimensions and Mounting

Electrical – Output and Excitation

Environmental – Temperature and Moisture

Performance – Accuracy and Thermals

Taking a deeper dive into performance, an important consideration when selecting your load cell are the sensor specifications and how they impact accuracy. The sensor specifications relate to the max error of various parameters. The specifications are always included in product spec sheets and are expressed using the following values – %FS, %RO, %, %/°F, time-related. Specifications listed relate to the max error for accuracy and temperature.

Interface provides all sensor specification data for our load cells in the product datasheets found on each product page for easy download.

The information we provide for every load cell typically includes:

Accuracy:

  • Static Error Band
  • Non-linearity
  • Hysteresis
  • Non-repeatability
  • Creep
  • Side Load Sensitivity
  • Eccentric Load Sensitivity

Temperature:

  • Compensated Range
  • Operating Range
  • Effect on Zero
  • Effect on Span

Further definitions can be found in our online technical glossary.  Here are a few that we highlighted in the Load Cell Basics webinar.

Static Error Band: A band encompassing all points on the ascending and descending curves centered on the best fit straight line. It is expressed in units of %FS.

SEB Output: The output at capacity based on the best fit straight line.

Non-repeatability: The maximum difference between output readings for repeated loadings under IDENTICAL LOADING AND ENVIRONMENTAL CONDITIONS. In practice, there are many factors that affect repeatability that ARE NOT included in the non-repeatability specification. It is normally expressed in units of %RO.

Non-linearity: The difference in the output from a straight line. It is normally expressed in units of %FS.

Hysteresis: The difference in the ascending versus descending curves. This is normally expressed in units of %F.

Understanding these factors and the maximum error for your specific project is critical to selecting a load cell and getting the best possible data out of it.

To learn more about sensor specifications for load cells, review the product specs on each datasheet or in our product catalogs. For additional help, call to speak with our application engineers at 888-557-2533.

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