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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

Load Cell Simulator 101

A load cell simulator is a device that mimics the electrical signal of a load cell. This allows technicians to test and calibrate measurement systems without applying physical force or weight to the load.

By generating a range of input signals using a load cell simulator, technicians can assess the instrument’s linearity, sensitivity, and accuracy, ensuring it meets the required specifications.

The two most common uses for load cell simulators are troubleshooting and calibration. Load cell simulators can effectively troubleshoot force measurement systems, detecting and isolating faults or malfunctions. By simulating various load conditions and injecting fault conditions, technicians can pinpoint the source of the problem, such as a broken wire or a faulty load cell.

Load cell simulators are essential for calibrating force measurement devices, ensuring they accurately translate applied force into a measurable electrical signal. By generating a controlled force signal, technicians can compare the displayed value to the known input signal, identifying discrepancies and adjusting the device accordingly.

Interface load cell simulators are part of our accessories product line. They are an essential accessory and valuable investment for any testing lab or research facility frequently using load cells. These simulators can help to improve safety, reduce downtime, improve accuracy, lower costs, and increase convenience.

Why Use a Load Cell Simulator?

  • Testing and monitoring force measurement systems: Load cell simulators can test instrumentation performance used in force measurement systems, such as hydraulic presses, assembly machines, and material testing machines. By simulating forces that the system would typically encounter, the simulator can help identify potential problems with the instrumentation, ensuring that the system operates safely and efficiently.
  • Verifying proper indicator setup: Load cell simulators can be used to verify that an indicator is configured correctly for the type of load cells being used. This includes checking the scaling and the instrument’s linearity.
  • Cable checks: One of the first troubleshooting tips for any load cell application is to check the cables and connectors. A load cell simulator is valuable for checking cables.
  • Scaling: Load cell simulators are crucial for scaling force measurement devices, enabling precise calibration, troubleshooting, and testing. They play a vital role in ensuring the accuracy and reliability of force measurements across various industries.
  • Calibrating scale indicators: Load cell simulators can generate a precise mV/V signal corresponding to a specific weight. This allows technicians to calibrate scale indicators to ensure that they are displaying accurate weight readings.
  • Application evaluation: Load cell simulators can be used to develop and troubleshoot force-related applications, such as medical devices, prosthetics, and exercise equipment. By simulating forces that users would typically apply, the simulator can help to ensure that the application is safe, effective, and operational.
  • Research and product development: Load cell simulators can be used to research new force measurement applications.
  • Technician training: Load cell simulators can educate and train technicians on the proper use and calibration of load cells.

Interface Load Cell Simulators

CX SERIES PRECISION MV/V TRANSFER STANDARD LOAD CELL SIMULATOR 

CX SERIES PRECISION mV/V TRANSFER STANDARDModel CX Series Precision mV/V Transfer Standard is the market’s most accurate load cell simulator. This NIST Traceable product is commonly used to calibrate and check instruments in accredited labs.

  • Most accurate load cell simulator
  • Special low thermal EMF construction
  • Each unit is individually calibrated, aged, and recalibrated
  • Strong, rugged design
  • Instrument substitution testing

In the series, models CX-0202, CX-0610, CX-0440, CS-0330, and CX-0220 are used to set up and check the Gold Standard® System Hardware. CX-0440, CX-0330, and CX-0220 are single-step mV/V transfer standards providing precision outputs of ±4, ±3, and ±2 mV/V respectively. CX-0610 is a multi-step unit that allows the user to go from -6 mV/V to +6 mV/V in 1 mV/V steps. Model CX-0404 is specifically designed for instrument substitution testing as per ASTM E74.

EVALUATOR 3 LOAD CELL SIMULATOR 

Evaluator 3 Load Cell SimulatorThe Evaluator 3 variable range simulator is well suited for basic troubleshooting needs, offering nine fixed intervals from -5 mV/V to +4.5 mV/V.

  • ABS plastic case
  • Weighs less than 1 lb (0.45 kg)
  • Fixed rotary switch, -0.5 mV/V to 4.5 mV/V in 9 steps of 0.5mV/V per step
  • Used in testing and troubleshooting mV/V instrumentation

IF500 LOAD CELL SIMULATOR 

The new model IF500 is a 5V or 10V excitation-only load cell simulator with a state-of-the-art microprocessor-based design. It is a cost-effective simulator with advanced instrumentation capabilities. The instrument excitation supply powers the IF500 and requires no batteries.

  • Set “ANY” mV/V value within ±5mV/V
  • State-of-the-art, microprocessor-based design
  • Sleep mode eliminates digital clock noise
  • Powered by instrument excitation supply… No batteries
  • Buffered Ratiometric output
  • 350-ohm bridge configuration
  • Stores up to 10 settings with sequential recall
  • Digital zero trim and storage
  • Low noise, low quiescent current, low-temperature coefficient, high stability amplifiers
  • Compatible with instruments using 5V or 10V excitation, including Interface’s instrument models 9820, 9840, 9860, 9870, 9890, CSC/CSD, DMA/DMA2, DCA, INF1/INF4, ISG, SGA, and VSC
  • Options include: NIST Traceable Calibration Certificate, Screw Terminal Adapters for the BNC Connectors and Cable Adapters

Application Examples for Load Cell Simulators

Manufacturing: Load cell simulators are essential for calibrating and testing force measurement devices used in manufacturing processes, ensuring accurate force control and product consistency. ADDITIONAL RESOURCE: Manufacturing Solutions.

Food Processing: Load cell simulators are critical in calibrating and troubleshooting force measurement devices, ensuring precise portion control, and maintaining food safety standards.  ADDITIONAL RESOURCE: Force Measurement for Efficiency in Food Processing and Packaging

Construction: Load cell simulators are employed for testing and calibrating force measurement devices used in construction applications, such as crane load monitoring and material testing. ADDITIONAL RESOURCE: Construction Solutions

Medical Devices: Load cell simulators are utilized for calibrating and verifying the accuracy of force measurement devices in medical applications, such as patient weighing scales and rehabilitation equipment. ADDITIONAL RESOURCE: Medical and Healthcare

Interface load cell simulators are indispensable tools for scaling force measurement devices, providing a safe, efficient, and cost-effective means to ensure the accuracy and reliability of force measurements across diverse industries. Their ability to calibrate, troubleshoot, and test force measurement devices contributes to product quality, process control, safety, and regulatory compliance, making them essential for maintaining the integrity of force measurement systems.

New Additions to LCM Systems

In June 2023, Interface announced the acquisition of LCM Systems, the maker of specialized load measurement and instrumentation systems. We want to recognize LCM’s newest leaders, Jeff Williams, managing director, and Rob Cooch, production and operations manager, along with key team member Chloé Baile, who is LCM’s new strategic sales engineer.

LCM Systems has seen significant growth across all levels of its business over the past few years. The manufacturer of Interface’s load pins, load shackles, and various custom solutions reports a positive development in terms of exceeding 2023 goals before the year-end. In keeping up with the pace of growth, LCM has invested in key talent to improve production and calibration resources.

Interface CEO Greg Adams notes, “LCM Systems is an outstanding addition to Interface as demonstrated by the growth in 2023, which exceeds our target and is further evidence of the outstanding team, product, and service offerings in high demand. We are extremely confident in the additions of Jeff, Rob, and Chloé to LCM System and their experience in serving as key catalysts to the expansion in business, high-quality measurement solutions, and additional new markets and customers.”

The people below represent key leadership, additions to the team, and expanding roles. Read the full news update here.

Jeff Williams, Managing Director, LCM Systems

Jeff joined Interface in September 2023 and has taken on the role of managing director, where he is responsible for sales, operations, engineering, quality, and supply chain. He has more than 35 years in the electronics and engineering space, and before joining LCM, he served for 10 years as group head of engineering at Flintec. Jeff also spent 24 years in engineering and management roles at Hitachi Home Electronics & Panasonic AVC Design Centre. He offers extensive experience and strategic skills essential to expanding LCM and fulfilling growing customer requests and orders.

Rob Cooch, Production and Operations Manager, LCM Systems

Rob joined LCM in October 2023 as production and operations manager. He is responsible for overseeing the production process and coordinating all activities, day-to-day scheduling of production, and managing the department consisting of eight operators across two areas. Before joining LCM, Rob was a member of a cross-functional team looking at NVA, which significantly reduced build time and manufacturing costs through various lean changes in production. Rob’s role is key in helping LCM fulfill the demands for its products with a highly skilled operations team.

Chloé Baile, Strategic Sales Engineer, LCM Systems

Chloé joined LCM in October 2023 as a strategic sales engineer. Her responsibilities in this role include building effective, strong relationships with key decision-makers of customer accounts and retaining and nurturing business growth. She liaises between customers and LCMs engineering design experts to create optimum solutions. Before joining LCM, her experience was predominantly in the automotive industry. She led engineering business development and was project manager for special Tier 1 Automotive, F1, and Motorsport projects, including Classic Heritage for Aston Martin, Ferrari, Lotus, and Jaguar Land Rover. She is working closely with Interface and LCM customers to grow the business.

Another key appointment at LCM this year is Mark Capodici, who recently joined the LCM Calibration Department full-time as a calibration technician. This critical addition to the team dramatically increases the company’s calibration resources, vital to maintaining LCM’s ability to dispatch products on time and in a timescale that fits customer expectations. Capodici joined LCM Systems three years ago, starting as a supply chain and fulfillment assistant responsible for general store activities, kitting of production materials, and processing and inspection. Capodici sees his role change as a great opportunity to progress within the company and broaden his knowledge and skill set.

“LCM Systems continues to invest in additional personnel and equipment to meet the growing demand, as evidenced in our new members and recent promotions,” said Jeff Williams. “We are committed to providing our customers outstanding service and ensuring orders are fulfilled expeditiously, maintaining our high standards, quality, and accuracy of every product we manufacture.”

ADDITIONAL RESOURCES

Uses Cases for Load Pins

Innovative Interface Load Pin Applications

Load Pin Configuration Submission

Interface Engineered Solutions for Lifting Webinar Recap

Load Pins 101

Load Pins, Tension Links, and Shackles

Load Pin Brochure Pages

 

Force Measurement Tips Related to Data Acquisition Systems

A data acquisition (DAQ) system consists of hardware and software components designed to collect, process, and analyze data from various sources and convert it into digital format for further analysis and storage. Based on the growing requirements to gather more data faster, Interface continues to add to our line of data acquisition systems to use with our load cells, torque transducers, and multi-axis sensors. These systems are designed for comprehensive force and torque measurement data collection and analysis.

Is more data, with easy integration and high accuracy, your objective? Working with our team of application engineers, we can assist you in pairing the best data acquisition system with your specific transducers. Considering the options, our team of experts offers these five essential bits of advice.

Data Acquisition Systems Tips for Test & Measurement

Select the Right Data Acquisition System

Choosing a data acquisition system compatible with your specific force measurement devices and application requirements is crucial. Consider factors such as sensor type, measurement range, accuracy, resolution, sampling rate (considering your over-sampling requirements), and connectivity options. In addition, the size and form factors can be critical to an application.

Proper Sensor Installation and Calibration

Proper sensor installation and calibration are critical for accurate force measurements. Follow the guidelines for sensor installation, including correct mounting, alignment, and wiring. Ensure that the load cell is calibrated according to established procedures and standards and that the calibration is regularly verified to maintain measurement accuracy. Proper sensor installation and calibration help eliminate potential sources of measurement errors.

Signal Conditioning and Filtering

Signal conditioning and filtering techniques are essential for optimizing the quality of the acquired force data. Signal conditioning involves amplification, offsets (zeroing), filtering, and linearization of the sensor output signal. Filtering techniques, such as anti-aliasing filters, IIR, or FIR, can help reduce noise and unwanted signals, ensuring accurate and reliable force measurements.

Data Validation and Analysis

Implement data validation techniques, such as range checking, outlier detection, and data integrity checks, to identify and correct potential data errors or anomalies. Analyze the acquired data using appropriate statistical and data analysis techniques to extract meaningful insights and make informed decisions based on the force measurement data. Be sure to select a force measurement device that is highly accurate and of superior quality.

System Maintenance and Calibration

Regular system maintenance, including sensor calibration and system validation, is crucial for reliable and accurate force measurements. Follow Interface’s recommendations for system maintenance, including sensor cleaning, inspection, and calibration intervals. Regular calibration and validation of the data acquisition system and force measurement devices help ensure the system remains accurate and reliable.

For additional information about Interface data acquisition solutions, watch the Unlocking the Power of DAQ webinar.

Popular Interface Data Acquisition Instruments

BX8 Data Acquisition Series

BX8-AS BlueDAQ Series Data Acquisition System with Industrial Enclosure

BX8-HD15 BlueDAQ Series Data Acquisition System for Discreet Sensors with Lab Enclosure

BX8-HD44 BlueDAQ Series Data Acquisition System for Multi-Axis Sensors with Lab Enclosure

Features & Benefits

  • 8-Channel synchronized sampling + TWO encoder/pulse channels
  • Strain gage, mV/V, ±10VDC, and PT1000 temperature inputs
  • Internal calculation of axis load values for 6-axis sensors
  • Active scaling of analog outputs according to internal calculations
  • ±5V, ±10V, 4-20mA, and 0-20 mA outputs
  • 48K samples/sec/channel, 24-bit internal resolution
  • USB connection to PC, Includes graphing and logging software
  • Excitation sense
  • Strain gage Full, 1/2, and 1/4 bridge, including bridge completion
  • TEDS compatible, ZERO button for 8-channel simultaneous tare, 16 digital I/O
  • Galvanic isolation: Analog input, analog output, digital I/O, USB
  • EtherCAT and CANbus/CANopen options
  • Enclosure Options

BSC4 Digital DAQ Model

BSC4D Multi-Channel Digital PC Interface and Data Acquisition Instrument

Features & Benefits

  • USB outputs
  • Four independent channels
  • For use with model 3AXX series 3-axis load cells
  • It can be used with up to any four standard load cells (with mV/V output)
  • mV/V, +/-5V, +/-10V, PT1000
  • Strain gage quarter/half and full bridges
  • 120, 350 & 1000 Ohm bridge completion
  • Limit frequency 450 Hz
  • Eight digital inputs/outputs

Use Cases for Data Acquisition Systems in Test & Measurement

Robotic Surgery Force Feedback using DAQ System

A biomechanical medical company wants to test its robotic arm’s force, torque, and tactile feedback for invasive surgery. The robotic arm mirrors the surgeon’s movements during surgery, and all haptic force feedback must be measured to ensure safety during invasive surgery. Several of Interface’s force and torque measurement products have been used on this robotic arm, including the ConvexBT Load Button Load Cell, SMTM Micro S-Type Load Cell, and the MRTP Miniature Overload Protected Flange Style Reaction Torque Transducer. Force results are collected when connected to the BX8 8-Channel Data Acquisition and Amplifier and viewed when attached to the laptop.

Material Tensile Testing using Data Acquisition Instrumentation

A customer wants to conduct a tensile force test on different samples and materials until failure. Materials include plastic, steel, or woven fabric. They want to measure tensile strength, yield strength, and yield stress. Interface’s 1200 Standard Precision LowProfile™ Load Cell is installed into the customer’s test frame. The tensile test is conducted, and force results captured by the load cell and extensometer are synced. These results can be displayed on a PC with supplied software.

Planetary Sample Collecting

As space exploration continues to grow and evolve, more robotic systems are created to collect samples of objects and materials on planetary surfaces. Robotic arms with sampling tools must be tested for scooping, drilling, and collecting samples. Interface’s Model 6A40 6-Axis Load Cell can be installed between the flange and the sample collecting tool. When connected to the BX8-HD44 Data Acquisition, the customer can receive force and torque measurements when connected to their control system using BlueDAQ software. Interface’s 6A40-6 Axis Load Cell could measure all forces and torques (Fx, Fʏ, Fz, Mx, Mʏ, Mz.) The BXB-HD44 Data Acquisition could log, display, and graph measurements while sending scaled analog output signals for these axes to the customer’s robot control system.

Learn more about your DAQ system options using Interface’s Data AQ Packs Guide.

Calibration Curve 101

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

Understanding GUM and Measurement Uncertainty

Understanding GUM and adherence to good test and measurement practices are essential to minimize uncertainties and ensure reliable measurement results for every application.

In the context of test and measurement, GUM stands for Guide to the Expression of Uncertainty in Measurement. The GUM is a widely recognized and internationally accepted document published by the Joint Committee for Guides in Metrology (JCGM), which provides guidelines for evaluating and expressing uncertainties in measurement results.

GUM establishes general rules for evaluating and expressing uncertainty in measurement that are intended to be applicable to a broad spectrum of measurements. A critical portion of any measurement process, the GUM outlines a thorough framework for uncertainty estimation. GUM defines terms and concepts related to uncertainty, describes methods for uncertainty calculation, and offers guidance for reporting and the documentation of uncertainties in measurement results.

The GUM provides a systematic approach to assess and quantify uncertainties by source, including equipment constraints, environmental conditions, calibration procedures, and human factors. The standards set by GUM emphasizes the need for considering and quantifying all substantial uncertainty components to ensure reliable and traceable measurement results.

By following the principles and guidelines outlined in the GUM, test and measurement professionals, metrologists, and scientists ensure standardized approach to uncertainty evaluation and reporting, facilitating comparability and consistency of measurement results across different laboratories and industries.

The uncertainty requirement varies for different use cases and industry applications. For example, for aerospace, defense, and medical devices there are strict uncertainty requirements compared to commercial scales or measurement tests that do not need precision accuracy.

When estimating uncertainty in load cell calibration, it is important to refer to the Guide to the Expression of Uncertainty in Measurement (GUM). The GUM provides a comprehensive framework with general rules for evaluating and expressing uncertainty in measurement. It serves as a guide applicable to a wide range of measurements, providing valuable guidance on uncertainty assessment in load cell calibration and other measurement processes.

In test labs that utilize load cells and torque transducers, the principles and guidelines GUM should be consistently applied to accurately evaluate and express uncertainties associated with the measurements obtained from these devices.

The application of GUM in test labs using load cells and torque transducers requires a thorough understanding of the measurement process, relevant standards, and calibration procedures. Read Understanding Uncertainty in Load Cell Calibration for more information.

Different considerations to measure uncertainty

  • Determine what parameter is to be measured and the units of measure.
  • Identify the components of the calibration process and the accompanying sources of error.
  • Write an expression for the uncertainty of each source of error.
  • Determine the probability distribution for each source of error.
  • Calculate a standard uncertainty for each source of error for the range or value of interest.
  • Construct an uncertainty budget that lists all the components and their standard uncertainty calculations
  • Combine the standard uncertainty calculations and apply a coverage factor to obtain the final expanded uncertainty.

GUM is used to identify and characterize uncertainty sources that can affect the measurements obtained from load cells and torque transducers. These sources may include calibration uncertainties, environmental conditions, electrical noise, stability of the test setup, and other relevant factors. Each of these sources should be quantified and considered in the uncertainty analysis.

Quantitative estimates of uncertainty component contributions to the overall uncertainty need to be determined. This can involve conducting experiments, performing calibration procedures, analyzing historical data, or utilizing manufacturer specifications to obtain uncertainty values for each component.

Once sources and estimates are complete, next step is to combine the individual uncertainty components using appropriate mathematical methods prescribed by the GUM. These methods include root-sum-of-squares (RSS), statistical analysis, and other relevant techniques. The aim is to obtain an overall estimate of uncertainty that accounts for the combined effects of all relevant sources.

The GUM provides guidelines on expressing uncertainties in measurement results. It emphasizes the use of confidence intervals, expanded uncertainty, and coverage factors. The uncertainty should be reported alongside the measurement values, indicating the level of confidence associated with the measurement. This allows the users of the measurement data to understand the reliability and accuracy of the obtained results.

For additional information about GUM, errors and setting an uncertainty budget, watch our webinar Accurate Report on Calibration. The video is set to start on the topic of Measurement Uncertainty.

It is essential to consider the specific uncertainty requirement of the application to ensure that the chosen force measurement device is appropriately calibrated for the project. This resource is a helpful recap: Specifying Accuracy Requirements When Selecting Load Cells.

In addition, understanding GUM, reducing uncertainty with regular calibration of testing devices and proper maintenance of the equipment go together with GUM.

ADDITIONAL RESOURCES

Gold Standard® Calibration System

Accurate Report on Calibration

Technical Information

Load Cell Test Protocols and Calibrations

Regular Calibration Service Maintains Load Cell Accuracy

 

Signal Conditioners 101

Signal conditioners are used in instrumentation, control systems, and measurement systems where accurate and reliable signal processing is a requirement. The purpose of a signal conditioner is to ensure that the electrical signal from a sensor is compatible with the input requirements of the subsequent signal processing equipment.

Primary features of signal conditioners include amplification, filtering, isolation, and linearization. It can perform various functions depending on the specific application and the type of signals.

Interface Signal Conditioners are used with a wide range of load cell and force measurement devices. Transducers convert force or weight into an electrical signal. The output signal of a load cell is typically in the form of a small electrical voltage that is proportional to the applied force.

Be sure to reference the Instrumentation Selection Guide to find instrumentation with signal conditioners that will best fit your force measurement application.

Understanding Signal Conditioners Use with Load Cells

Amplification: Load cells produce small electrical signals, which may require amplification to bring them to a usable level. Signal conditioners can include built-in amplifiers that increase the magnitude of the load cell signal. This amplification helps to improve the signal-to-noise ratio and enhances the sensitivity of the system.

Filtering: Load cell signals can be affected by electrical noise or interference, which can degrade the accuracy of measurements. Signal conditioners often incorporate filtering capabilities to remove unwanted noise and interference from the load cell signal. This ensures that the signal is clean and reliable.

Excitation: Load cells require an excitation voltage or current to function properly. Signal conditioners provide a stable and regulated excitation source to power the load cell. This excitation voltage is typically supplied to the load cell through the signal conditioner, ensuring consistent and accurate measurements.

Calibration and Linearization: Load cells may exhibit nonlinear characteristics, meaning that the relationship between the applied force and the output voltage is not perfectly linear. Signal conditioners can include calibration and linearization algorithms to compensate for these nonlinearities. By applying appropriate mathematical adjustments, the signal conditioner can provide a linear output that accurately represents the applied force.

Signal Conversion: Load cell signals are typically analog voltages, but they may need to be converted to digital format for further processing or transmission. Some signal conditioners include analog-to-digital converters (ADCs) that convert the analog load cell signal into digital data, enabling it to be processed by digital systems.

Signal Conditioner Considerations

  • Form factor design: box mount, DIN rail, in-line cable, integral to load cell
  • Output options: ±5/±10VDC, 0.1-5VDC, Current, Frequency, Digital
  • Polarity: Bi-polar or unipolar
  • Bandwidth
  • Onboard filtering
  • Power supply type: cable, built-in, wireless
  • Noise immunity

Interface Top Signal Conditioners

PRODUCT: DMA2 DIN RAIL MOUNT SIGNAL CONDITIONER

  • User selectable analog output +/-10V, +/-5V, 4-20mA
  • 10-28 VDC power
  • Selectable full scale input ranges 5-50mV
  • DIN rail mountable
  • Push button shunt calibration
  • 1000Hz bandwidth

PRODUCT: SGA AC/DC POWERED SIGNAL CONDITIONER

  • User selectable analog output +/-10V, +/-5V, 0-5V, 0-20mA, 4-20mA
  • 110VAC, 220VAC, OR 18-24VDC power
  • Switch selectable filtering 1Hz to 5kHz
  • Single channel powers up to four transducers
  • Selectable full scale input range .06 to 30mV/V
  • Sealed ABS enclosure
  • Optional bridge completion and remote shunt activation module

PRODUCT: ISG ISOLATED DIN RAIL MOUNT SIGNAL CONDITIONER

  • Galvanically isolated power supply
  • High accuracy
  • +/-5VDC or +/-10VDC Analog output (4-20mA optional)
  • 10-30VDC Power
  • Switch selectable filtering 1Hz to 1kHz (up to 10kHz optional)
  • Accepts inputs up to 4.5mV/V
  • DIN rail mountable

CSC and LCSC-OEM Inline Signal ConditionersPRODUCT: CSC and LCSC-OEM INLINE SIGNAL CONDITIONERS

  • IP67 stainless steel enclosure (CSC Only)
  • CE approved (CSC Only)
  • Zero and span adjustments
  • 1 kHz bandwidth

PRODUCT: VSC2 Rugged Compact Vehicle Powered Signal Conditioner

  • High accuracy precision bi-polar differential amplifier
  • ± 5 VDC Output
  • Accepts inputs from ±1.4 to ±-4.2
  • 1000 Hz low pass filter
  • Rugged design and compact size
  • Course, fine zero, and span adjustments
  • Activate R-CAL (Shunt Cal) with internal switch

Signal conditioners ensure that the load cell’s output is optimized for accuracy, stability, and compatibility with the measurement or control system. They help mitigate noise, amplify weak signals, provide excitation, and perform calibration and linearization to ensure precise and reliable measurements of force or weight.

Visit the Interface Instrumentation Selection Guide to see all the products available with signal conditioning functionality.

Watch this Testing Lab Essentials Webinar Part 3 to learn more about the benefits and use cases of Interface Signal Conditioners.

Testing Labs Choose Interface High Accuracy Products

Specialists focused on testing applications work in a variety of testing lab environments. In each lab, technicians rely on the tools to collect and report on data that is used to make products safer, guarantee performance, ensure quality, and to meet the strict industry standards and requirements. Accuracy in testing data is dependent on the precision measurement devices and instrumentation used to capture the results.

We supply lab engineers with high-accuracy sensor technologies used to complete rigid test requirements. Interface is the top provider of test and measurement products used for structural and material testing, static and fatigue testing, torsion effects, tension tests, calibration testing, and environmental testing. Read more in Types of Force Measurement Tests 101.

Our standard high precision load cells, torque transducers, multi-axis sensors, and instrumentation are used on every continent for T&M. Based on our quality and performance, we are the chosen supplier to calibration and testing labs. We see our products used today for continuous improvement programs, advancements in smart manufacturing and new product designs.

If it must be measured, Interface has a solution. Our products are designed for small and large testing facilities, including calibration-grade load cells, load frames and test stands, along with data acquisition systems. The wide variety of our force measurement solutions designed for testing labs means we play a role in every industry that is making a physical product and the test labs that validates the products performance.

Testing Labs and Types of Testing Using Interface Solutions

General Automotive Test Labs:

  • Component and Sub-Component Level Testing
  • Suspension Testing
  • EV Battery Testing

Automotive Driveline Testing:

  • Engine Performance and Durability Tests
  • Motor Efficiency Testing
  • Power Analyzation (Electric)

Aerospace Testing:

  • Full Scale Structural Static Testing
  • Component Fatigue Test
  • High Precision Thrust Testing
  • Simulators
  • Wind Tunnel Testing

Geotechnical and Civil Testing

  • Concrete or Asphalt Core Testing
  • Soils Testing

General Structural and Component Testing

  • General Push and Pull
  • Design Proofing
  • Life Cycle Fatigue Validation

Medical Device Testing:

  • Prototyping
  • PPAP Validation and FDA Certification
  • Device Lifecycle Testing

Consumer Product Testing Labs:

  • Design Validation
  • Material Testing
  • Fatigue and Failure Tests

Interface recently highlighted testing lab applications in our Test Lab Essentials Webinar. Here you can see the lab use cases and products as they are reviewed by our applications experts.

Each of these testing types requires different force testing equipment, and our experts work directly with testing lab professionals to determine the products or systems they need for single and ongoing test requirements.

As testing technologies becomes increasingly complex, off-the-shelf products may not meet the needs of every Interface customer. We lend engineers expertise in test and measurement to support unique and custom requirements to get the right sensor, instrument, and system in place.

Since our first load cells were designed five decades ago, we have built millions upon millions of load cells and torque transducers used in testing labs around the world. Our products are built to withstand the rigor and requirements needed for high quality and reliable data collection in test and measurement. Our test customers depend on us for proving accuracy, consistency, and reliability in performance.

ADDITIONAL RESOURCES

Interface and Testing Lab Applications

Testing Lab Essentials Webinar

Engine Dynamometer App Note

Consumer Product Testing Case Study

Interface Solutions for Safety and Regulation Testing and Monitoring

Metrologists and Calibration Technicians 101

Motor Test Stand

GS-SYS04 Gold Standard® Portable E4 Machine Calibration System

Electric Vehicle Structural Battery Testing

Furniture Fatigue Cycle Testing App Note

Regular Calibration Service Maintains Load Cell Accuracy

 

Shunt Calibration Resistors 101

Shunt calibration is a process of calibrating a measurement instrument using a shunt calibration resistor. The shunt calibration resistor is connected in parallel with the measurement instrument to provide a known resistance value, which is used to calculate the instrument’s accuracy.

In shunt calibration, a known current is passed through the shunt calibration (cal) resistor, which generates a known voltage drop across the resistor. This voltage drop is measured using the measurement instrument being calibrated, and the instrument’s accuracy is calculated based on the known resistance value of the shunt calibration resistor and the measured voltage drop. They create a simulation of load and verify the health of the sensor. Commonly, they are used to scale instruments.

The accuracy of the measurement instrument can be calculated by knowing the shunt resistor’s precision level and applying Ohm’s Law, which states that the current passing through a resistor is proportional to the voltage drop across it and inversely proportional to its resistance value.

Shunt calibration can be used to calibrate force measurement devices, including load cells. Interface provides shunt calibration resistors in our accessories line as “loose” resistors. They are also available with engineered to order requests for designs into cables, connectors and even within the load cell.

Shunt calibration is an important process for ensuring accurate and reliable measurements in various industrial, commercial, and scientific applications. It allows measurement instruments to be calibrated quickly and cost-effectively, and it improves the accuracy and reliability of the measurement data.

What is a shunt calibration resistor?

A shunt calibration resistor is a resistor that is connected in parallel with a measurement instrument to provide a known resistance value. The purpose of the shunt calibration resistor is to calibrate the instrument to accurately measure the current passing through it. Shunt calibration resistors are often used with load cells to improve the accuracy and reliability of their measurements.

How are shunt calibration resistors used with load cells?

Load cells typically generate a small electrical signal in response to applied force or weight. This signal is amplified and processed by a signal conditioning circuit before a data acquisition system or controller uses it. The signal conditioning circuit can utilize an internal shunt calibration resistor on the instrumentation side, or activate a resistor located upstream in the system.

Shunt calibration resistors located either in the sensor, cable, or instrument will be switched into the circuit during the shunt calibration process, shunting and diverting current in the process. This shunting effect unbalances the Wheatstone bridge, simulating loaded output from the sensor. Because the resistance value is known, sensor span output and thus instrument scaling can be accurately verified. This electrical simulated signal negates the need for physical force or torque calibration of the system.

The shunt calibration resistor provides a known resistance value, which is used to verify the health and output of the load cell, ensuring accurate system measurement of the applied force or weight. The resistor diverts a small portion of the load cell’s excitation current. The value of the shunt calibration resistor is carefully selected based on the load cell’s characteristics and the desired measurement accuracy.

Shunt calibration uses the shunt resistor to force a load cell bridge to provide a fake signal output. It allows one to check for sensor health and whether the signal behavior has deviated from an original calibration certification with initial shunt output data.

This forced signal output allows for the attached instrument to be scaled. This could be setting signal conditioner scaling:  When the load cell reaches max calibrated force, is the mV/V input properly scaled for the exact 5V, 10V or 20mA conditioner output? The other setting option is displayed units of measurement on a display: Is the load cell’s calibrated 3.999mV/V output at 100 lbs displaying 100 lbs on the display?

Shunt resistors are sized by resistance value to provide approximately two-thirds or three-quarters full scale output signal. Having this recorded value on the calibration certification the instruments can be scaled as necessary for full scale, and future shunt checks can ensure nothing is changing with the health of the circuit.

Interface Shunt Calibration Resistors – RCAL Resistors

Interface shunt calibration resistors, known as RCAL Resistors, are an accessory product. They are made from the highest components and processes to ensure the specifications for your Interface products perform to meet their published specifications. Available RCAL Models include RS-100-30K, RS-100-40K, RS-100-60K, and RS-100-120K are available.

Interface RCAL Resistors are high precision components and provide an effective, method for checking the calibration of a load cell system in the field or when a means of applying actual forces is unavailable.

  • Designed to work with Interface products.
  • Made with the highest quality components.
  • Created to maintain the specification of the product.
  • Precision wire-wound
  • 5 ppm/°C, 0.01%

U.S. dimensions and capacities are provided for conversion only. Standard product has metric capacities and dimensions. U.S. capacities available upon special request and at an additional cost.

What are the benefits of using shunt calibration resistors?

There are several benefits of using shunt calibration resistors in measurement applications:

  • Calibration: Shunt calibration resistors can be used to scale measurement instruments, ensuring that they provide accurate calibrated unit readings. Shunt calibration can often substitute the need for physical force or torque system calibration
  • Convenience: Shunt calibration can provide a quick and easy system health check either before or immediately after a test. Confirming stable and consistent shunt readings can ensure data integrity in between regular scheduled physical calibration intervals.
  • Cost-effective: Using a shunt calibration resistor is an inexpensive one time investment vs time and cost associated with pre or posttest physical calibrations. This brings the freedom for frequent and quick system calibration checks with minimal equipment down time.
  • Flexibility: Shunt calibration resistors can be used with a wide range of measurement instruments, allowing for greater flexibility in measurement applications. Additionally, many instruments allow shunt resistors to be interchangeable for support of varying sensor outputs.

Overall, shunt calibration resistors are a practical and convenient alternative to physical system calibrations. Shunt calibration resistors can be packaged into all Interface load cells with support across most of the available instrumentation as well. Frequent system health and signal stability checks are vital to ensuring consistent integrity with test data and shunt calibration resistors bring such empowerment for extraordinarily little initial investment.

Contributor: Brian Peters

Additional Resources

Metrologists and Calibration Technicians 101

System Level Calibration Validates Accuracy and Performance

Shunt Calibration for Dummies – Reference Guide

Shunt Calibration 101

Regular Calibration Service Maintains Load Cell Accuracy

Top Five Reasons Why Calibration Matters