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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

 

S-Type Load Cells 101

There are many different types of devices used in test and measurement from load cells to torque transducers and tension links to multi-axis sensors. In addition, there are sub-categories in each of these product types that are based on various specifications, capabilities, capacities, and application requirements.

Discussing load cells specifically, there are different models and configurations depending on the use case, the amount of force measurement or weighing requirements for a particular load, dimensions, and even test environment considerations. No matter what our customers need, we have standard and custom load cells up to the task. In our 101 series, we are highlighting the innovative miniature load cell sub-category of Interface S-Type Load Cells.

What Is an S-Type Load Cell and What Is It Used For?

S-type load cells, sometimes called s-beam, gets its nomenclature from the “S” looking model of the load cell. It is shaped this way because it is designed to measure well-controlled tension and compression forces. There are preferred by engineers and testing labs for the precision, size, material, and ability to fit in limited spaces. They are often used for weighing, in test machines as well as product designs for ongoing performance measurement by OEMs.

An s-type load cell will often be used within a system designed to stress test products in a controlled environment for fatigue and product testing to measure the way the product stands up to force over long periods of time. The benefit of Interface S-Type Load Cells is that they are very cost-effective, highly accurate, easy to mount, and offer flexibility because it can be used universally for tension and compression testing. They are also smaller than typical load cells, providing major benefits when there are limitations in space or for smaller test product dimensions.

Interface has a wide range of specialized miniature s-type load cells including sealed, micro-size, fatigue-rated, high-temperature ratings, low height, overload protected and intrinsically safe to meet all types of testing protocols and plans. You can see all the s-type models here.

An s-type load cell is generally used with eyebolts or rod-ends when used in tension and this can cause binding or the associated hardware to unthread. These uniquely designed load cells should not be used when weighing an object that can sway or rotate. Additionally, an s-type load cell is not recommended when the load cell will be used for both tension and compression, where accuracy in compression is critical. In this case we’d recommend a shear type of load cell.

S-Type Load Cell Applications

Prosthetic Load and Fatigue Testing

Prosthetic limbs must be tested for extreme loading that can occur during falls, accidents, and sports movements. Fatigue testing of prosthetic components determines the expected lifespan of the components under normal usage. Interface suggested a static load test apparatus using SSMF Fatigue Rated S-Type Load Cell attached to hydraulic actuators to apply and measure loads. The fatigue testing machine uses SSMF Fatigue Rated S-type Load Cell to apply and measure cyclic loads. During the fatigue test, the actuator repeatedly applies and removes the force to simulate activity such as walking. Tilt tables may also be used to apply forces at various angles to simulate the heel-to-toe movement of walking or running. Using this solution, engineers can determine whether prosthetic materials and designs will withstand the rigors of daily use and occasional high load situations. Read more here.

Furniture Fatigue Cycle Testing

To meet safety protocols in relation to the manufacturing of various furniture products, fatigue testing, shock testing, and proof testing must be rigorously performed before diffusion into the marketplace. Force testing simulations on furniture products are critical in determining the posted max loads to protect manufacturers from liability due to damages that might result from the misuse of those products and overloading. Using an Interface Model SSMF Fatigue Rated S-Type Load Cell along with Interface Model 9890 Strain Gage, Load Cell, & mV/V Indicator provides a solution that measures the force being applied in fatigue cycle testing of a furniture product, in this case testing the rocking mechanism in an office chair. Unlike other similar load cells, the Model SSMF is fatigue rated making it highly suitable for fatigue testing. No fatigue failure of any fatigue-rated Interface load cell, used within its ratings, has ever been reported. The furniture manufacturer was able to obtain accurate data about the rocking mechanism the office chair as it was fatigue cycled into failure. Adjustments were made to the design to improve the safety and life of the furniture, ensuring product quality and protecting the manufacturer from future liability. Read more here.

Interface S-Type Load Cells are highly effective, accurate and flexible products used for a wide variety of applications needing compression and tension force testing. To learn more about Interface’s S-Type Load Cells, you can also visit here or call us today to speak to an application engineer who can help you select the right product for your next project at 480-948-5555.