Interface’s technical force measurement webinar Demystifying Specifications details descriptions, terms, values and parameters found in product datasheets for load cells, torque transducers, instrumentation and specialty products. Learn from our experts what specifications need critical review, recommendations based on product categories, and the insider point of view on what is most important in terms of specifications for different use cases and tests.
Load cells are very resilient. Most are constructed with sturdy materials that can withstand long and arduous cycling and multitudes of testing projects. In fact, with proper treatment, regular calibration services and use within specifications, load cells can last many years. Even with such high quality and durability, it is important to perform regular diagnostic checks of a load cell to maintain the health of any force measurement device.
FACT: Interface has load cells that are in use today that we manufactured several decades ago. As the saying goes, Interface load cells are built to last.
A load cell can be damaged or lose accuracy. Load cells can be repaired depending on the extent of damage. Some common issues such as cable damage, electrical faults, or environmental factors can be repaired by replacing parts or recalibrating the load cell. However, more severe damage such as physical damage to the load cell itself may make it beyond repair and require replacement.
What is the most common type of damage to a load cell?
Most often, a load cell is damaged by overloading or exceeding its rated capacity. This can result in physical deformation or strain on the load cell, leading to permanent damage and reduced accuracy.
Other common causes of damage to load cells include exposure to harsh environmental conditions such as extreme temperatures, moisture, or corrosive substances, as well as electrical faults such as voltage spikes or short circuits. Additionally, mechanical stress from improper installation or handling can also cause damage to load cells.
What steps should be taken to evaluate a load cell that might be damaged?
- Visual Inspection: Ensure that the physical installation, correct interconnection of components and the system are all intact. For example, has the load cell been dropped or have any damage to connectors or adapters? Reference the installation and operation manuals available with each product.
- Electrical Testing: Use an Ohmmeter to check the bridge circuitry and zero balance. Evaluate the resistance and output of the load cell. If there is a notable change in resistance or output, it may indicate that the load cell is damaged. This is also a good time to check the troubleshooting guide.
- Test Loads: Apply a range of test loads to the load cell and observe if the readings are consistent and within the expected range.
- Calibration: If the load cell is not functioning correctly, recalibrate it using a weight calibration system or load cell calibrator to see if the readings are within the expected range.
- Professional Evaluation: Request a thorough inspection of the device to determine the load cell can be repaired or needs to be replaced.
It is important to follow safety protocols and to use proper equipment and techniques when evaluating a load cell to avoid causing additional damage.
After a thorough physical inspection along with mechanical and electrical installation checks, it is determined that a load cell is not performing to specifications it is time to contact the manufacturer for Services & Repair to schedule a return of the product for further evaluation and potential load cell repair.
Use Cases for Frequent Calibration Services and Repair Evaluations
- Harsh environmental conditions can cause corrosion and electrical failures
- Loading forces that exceed the load cell rated capacity can cause shifting of the zero-load output of the load cell
- Moment loading of the load cell can cause zero shifts and other undesirable behavior
- High cycle rates or fatigue applications can cause premature failure
Many of these symptoms can be repaired or mitigated if they are identified early during appropriate evaluation and calibration cycles. In addition, load cells are prone to losing accuracy through normal wear and tear and ageing. There are times when loading conditions and use case environments necessitate the need for more frequent evaluation and calibration cycles. The process of calibration can include adjusting the measuring instrument to bring it in alignment with the standard specifications.
It is always recommended that users consult an application engineer or user’s manual to avoid situations where a load cell can be damaged or degrade accuracy too quickly. Interface has deeps expertise in repair and calibration, built and proven over 55 years in the business of making and calibrating load cells.
Interface provides repair evaluation and services on load cells we make and from other manufacturers. Repairs include a complete evaluation of the device prior to repair and calibration upon completion. Our standards for calibration are world-class. Our calibration labs are managed by experts in diagnostics, testing and repair with engineering and metrology grade equipment designed by the leaders in force measurement.
If you’re already a load cell user and have not had your products calibrated in some time, we recommend scheduling your calibration service online here. Load cells can provide years and years of quality data as long as they are properly taken care of. Put your trust In Interface to make that happen.
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.