Force measurement devices like load cells, torque transducers and data acquisition devices are used across industries to design and test hardware. They’re a key factor in the product development process because the force, torque and weight data they collect helps to ensure products are accurately constructed, work as intended, are safe for use, and can withstand the test of time. In highly regulated and complex industries like medical and defense, this data becomes even more important because any miscalculation in the design of a product can put lives at risk.
The first thing to understand is every project requiring a loadcell or torque transducer has different variables affecting accuracy and quality. And for every situation in product development and testing, there is a load cell to fit your precise need. Therefore, the most important step in ensuring accurate and high-quality data is speaking to a force measurement expert about the details of a project.
There are five key factors you need to know related to data accuracy, and three factors related to force measurement device quality. I’ll explain why each factor can contribute to inaccuracies and what to look for when selecting a device based on material selection, build quality, and environmental factors.
Contributing factors to force measurement device quality:
- Repeatability: Many people consider repeatability the most important aspect of buying a force measurement product or system. Anyone can develop an accurate device for the first 10 to 15 measurements, but as contributing factors of environment and stress are inflicted upon the product, it needs to last. This is determined by selecting the right materials for the application based on how the force measurement device will be used and why. Every application is different, and if you understand the application, you can select a force measurement device or work with a manufacturer on a custom device that withstands the various stressors over time without providing diminishing returns.
- Longevity: Like repeatable data accuracy over time, your force measurement device also needs a high-quality and ruggedized build for physical longevity. Constant application of weight, pressure or torque can diminish the build quality and strength of a device if it does not meet the material requirements of the application. This can also lead to higher costs if customers must replace their force measurement products regularly.
- Sensitivity to Off-Axis Loads: A typical force measurement device is designed to measure load in one direction. However, nearly any project using force measurement test processes is going to introduce an off-axis load. If the device is not designed to adjust for this and compensate for moment and side loads, the data output will be skewed. This is another reason you need to be extremely specific when discussing your application. There are several ways to compensate for moment and side loads; however, most of these adjustments are physical and occur in the design and manufacturing process. With a correctly calibrated and designed product, off-axis loads will be eliminated and will not affect data output.
Contributing factors of force measurement device accuracy:
- Creep: This term is used to describe the change in force measurement device output occurring with time while under constant load and with all environmental conditions and other variables also remaining constant. Creep occurs because materials very slowly deform over time when under constant load.
- Side and Moment Load: Most force measurement devices are designed to measure force in one certain direction, which is determined by the way the load cell is mounted (more on this factor below). Inappropriate loading will cause side and moment load, which risks reducing the life of the device and distorting measurement results.
- Temperature: Change in temperature during the measurement process is a significant factor in determining accurate load. The temperature in the air can affect the sensitivity of the force measurement device and lead to inaccuracies if not accounted for. When selecting a device, you need to be clear with the manufacturer about the temperatures your product will be tested in. This helps the manufacturer determine which materials to use in the construction of the force measurement device to best compensate for certain temperatures.
- Humidity: Similar to temperature, humidity also plays a factor in measurement accuracy in certain device designs. The effect humidity has on a force measurement device is a slower process; however, over time it can skew the data. If your product development environment includes high humidity levels, work with your provider to ensure the correct design and materials are selected.
- Mounting Process: This is one of the most important factors for accuracy. A force measurement device mounted incorrectly will significantly decrease accuracy because the mating process determines the sensor’s ability to perform accurate readings. Always make sure to follow the mounting instructions.
In addition to selecting the right device for your specific application, there are several ways to avoid inaccuracies and damage of the device on your end. Below is an explanation of different steps to take to ensure continued accuracy and quality of your force measurement products and systems today and over continued use:
- Utilize a Golden Part: A golden part is the original part you collected data from using your force measurement device the first time. You will want to select the golden part as soon as you receive your device and then whenever you are uncertain about data gathered from it, double-check it on the golden part. If you aren’t receiving accurate readings on the golden part, it means your device needs to be recalibrated or replaced.
- Avoid Misusing the Load Cell: As noted, force measurement devices come in numerous shapes and sizes and there is typically a product for any application. If you are using a device for unintended purposes by overloading it, you will eventually decrease the accuracy or risk breaking it. Misaligned mounting and improper mounting can cause overload and eccentric load which will also decrease performance. It can also wear out the threading, which will also impact accuracy.
- Set a Preventative Maintenance Schedule: Force measurement products should have a long lifetime. I’ve seen devices manufactured more than 50 years ago still in use today. In order to maintain accuracy and quality, you need to set a preventative maintenance schedule to recalibrate your devices or fix damaged devices. It is recommended you calibrate your force measurement products every year. When you first start using a device, you may want to recalibrate more often until you understand changes that occur with the product over time.
- Recalibration: When it is time for recalibration, consult the manufacturer to perform the process or investigate purchasing your own system for faster on-site calibration.
Quality and accuracy are everything in force measurement testing. Manufacturers can’t afford a mistake during testing that leads to longer development times, higher costs and lower-quality products – especially those that can affect the health and safety of a user. By understanding these contributing factors of force measurement accuracy and quality, you can select a device or system that meets your specific needs. NDT