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Benefits of Proof Loading Verification

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Proof loading is a critical test that is performed on sensors or load cells to verify their performance and accuracy under extreme conditions. Engineers may need to request proof loading verification to ensure that the sensors or other measuring devices being used in a particular application are accurate, reliable, and safe for use.

Upon request, Interface provides proof loading at the build phase of engineered-to-order load cells, as well as load pins, load shackles and tension links. By simple definition, proof loading is a safe overload rating for a sensor.

Load proofing is a special test that guarantees the sensor performs at maximum capacity before it’s released to the customer. If a manufacturer does proof loading, it will be documented in the sensors specifications that are shipped with the product. It is commonly requested for sensors that are used in lifting applications.

Additionally, quality engineers and testing professionals may request proof loading as part of quality control or compliance requirements. By ensuring that sensors and load cells are tested and validated before use, companies can ensure that they meet regulatory standards and maintain a high level of quality in their products and services.

The Proof Loading Process

By requesting proof loading, sensor users can verify the accuracy and reliability of sensors and load cells and ensure that they are functioning correctly and within their specified limits. Proof loading can also identify any issues or problems with sensors or load cells before they are put into service, allowing for repairs or replacements to be made if necessary.

Proof loading for sensors is a process of subjecting a sensor to a higher-than-normal load or stress to confirm that it can withstand that load or stress without any permanent damage or deviation from its calibration. The purpose of proof loading is to validate the accuracy and reliability of the sensor under extreme conditions, ensuring that it will perform correctly when it is in service.

During proof loading, the sensor is exposed to a controlled overload, typically between 150% to 200% of its maximum rated capacity. The sensor’s response to the load is monitored, and the output is compared to its expected behavior. If the sensor performs within acceptable limits and returns to its pre-loaded state after the load is removed, it is considered to have passed the proof load test.

When should you request proof loading for a load cell?

Proof loading for a load cell should be requested when there is a need to verify its calibration and ensure its accuracy and reliability under extreme conditions. This is particularly important when the load cell is used in safety-critical applications, such as in crane and hoist systems, industrial weighing and process control systems, and structural testing applications.

Proof loading is commonly used for sensors that are used in safety-critical applications, such as load cells used in cranes and hoists, pressure transducers used in oil and gas pipelines, and temperature sensors used in furnace applications. By performing proof loading tests, manufacturers and end-users can have greater confidence in the performance and reliability of their sensors, which can improve overall safety and efficiency.

In general, there are several situations where it is advisable to request proof loading for a load cell:

  • Before critical applications: In safety-critical applications, such as those involving lifting, handling, and transportation of heavy loads, a proof load test should be performed before the load cell is put into service to ensure that it can handle the required load without any issues.
  • After installation: It is recommended to perform a proof load test on the load cell immediately after installation to ensure that it is functioning correctly and within its specified limits.
  • After repair or maintenance: If the load cell has undergone repair or maintenance, a proof load test can be used to verify that it is still performing accurately and within its specifications.
  • After an extended period of non-use: If the load cell has not been used for an extended period, it may be necessary to perform a proof load test to ensure that it is still functioning correctly.

It is important to note that proof loading should only be performed by qualified and trained personnel using the appropriate equipment and procedures. This will ensure that the load cell is not damaged during the testing process and that it continues to perform accurately and reliably after the test is completed.

Proof loading is particularly important in safety-critical applications such as in the construction industry, transportation industry, and other industrial applications where lifting and handling heavy loads are involved. In these applications, the accuracy and reliability of sensors and load cells are crucial, as any inaccuracies or deviations from the expected behavior can result in dangerous and costly accidents.

Overall, proof loading is an essential test that engineers may need to request to ensure the safety and reliability of sensors and load cells in various industrial applications.

ADDITIONAL RESOURCES

IoT Lifting Heavy Objects

Cranes and Lifting

Recap of Use Cases for Load Pins Webinar

Tension Links 101

Aircraft Lifting Equipment App Note

 

Load Cell Sensitivity 101

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

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

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

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

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

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

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

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

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

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

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

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

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

Load Cell Basics Technical Q&A Part One

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

Why Does Interface Use Proprietary Strain Gages?

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

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

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

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

Is Temperature Compensation Achieved Using Dummy Gages?

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

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

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

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

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

Does Variable Altitudes Impact Performance?

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

Can Cables Influence Temperature Errors?

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

Is Creep Due to Material or Strain Gages?

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

Are All Load Cells Intrinsically Safe?

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

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

Contributors:  Keith Skidmore and Brian Peters

Additional Resources

Load Cell Basics Webinar Recap

Interface Load Cell Field Guide