Force Sensors- Accuracy Matters!

As technology becomes more advanced, the margin for error gets slimmer and slimmer. Accurate force is a detail that cannot be overlooked in design. One of the pillars of product accuracy is dependent on the load cells that are used to measure force values.

Load cells come in many shapes and sizes and are used to measure everything from the force of the material inside of an IV bag for medical applications, to the thrust of a rocket engine. If measurements are even a tiny bit off in either of these examples, either patient health is at risk or the enormous investment into a rocket engine is in jeopardy.

In this paper, we discuss the importance of accuracy, the factors of accuracy and the ways engineers can avoid failure. Load cells are used to track factors of force in real-time and over long periods to help with preventative maintenance and to collect data for product development.

Accuracy is the difference between a sturdy, quality product, and a product that becomes a liability to its user. Depending on the application, inaccurate designs can lead to product failure and even death.

The term accuracy throughout this paper describes performance in areas of nonlinearity, hysteresis, and creep, temperature effect on zero and sensitivity, off-axis loading, and repeatability. How does an engineer ensure that the tools they use to design a product are providing them with the most accurate data possible? It all starts with the load cell and how it is designed. For almost every situation in product development and testing, there is a load cell to fit the precise need. Each application has its own distinct measurement requirements. There are many additional factors that contribute to poor accuracy and these are primary considerations to take into account.

Creep: This term used to describe the change in load cell output occurring with time while under constant load.

Side and Eccentric Load: Most load cells are designed to measure force in one 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 distorts measurement results.
Fatigue Specification: The number of fully reversed cycles can affect life and error drift over time.
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Temperature Compensated Strain Gages: Minimized signal loss and accuracy shift due to temperature changes.

Humidity: Similar to temperature, humidity also plays a factor in measurement accuracy in certain load cell designs. The effect humidity has on the load cell is a slower process; however, over time it can skew data.

Mounting Process: This is one of the most important factors for load cell accuracy. A load cell that is mounted off-center will significantly decrease the accuracy of the load cell because the mating process between the product you are measuring, and the load cell determines the sensors ability to provide accurate readings.

How to Avoid Accuracy Failure? There are many ways to ensure you are getting the most accurate data possible out of your load cell. To start, always consult your load cell provider or the load cell manufacturer. They can help you select the right load cell and can teach you how to properly care for the load cell and maintain accuracy. If you are using a load cell for unintended purposes by overloading it, you will eventually decrease the accuracy of the load cell or risk breaking it.

Set a Preventative Maintenance Schedule: Load cells should have a very long lifetime. In order to maintain load cell accuracy, you need to set a preventative maintenance schedule to recalibrate your load cells. It is recommended that you calibrate your load cells every year.
Remember, close only counts in hand grenades and horseshoes!