Modern load cells work using a combination of the Wheatstone bridge equation and the strain gauge. The Wheatstone bridge equation was developed in 1833 by Samuel Hunter Christie, and improved upon and popularized in 1843 by Sir Charles Wheatstone. Wheatstone bridge circuits illustrate the concept of a difference measurement. Today, load cells are usually made up of four strain gauges in a Wheatstone configuration.

The most popular type of force torque sensor is the six-axis sensor. This particular force torque (FT) sensor is capable of measuring forces in every direction. A six-axis FT sensor generally utilizes strain gauge technology; when pressure is applied, the resistance within the gauge increases or decreases proportionally to the force it receives. This is how the sensor measures the movement of its external frames in relation to one another. Six-axis sensors can be found in robotic arms at the “joint.”

The basic principle, it is a measure of the “force” being used (or attempting) to turn an element. This measurement is achieved by the use of strain gauges bonded to the shaft, measuring the strain, induced in the shaft by the applied torque or “force”.

① Repeatability: The maximum difference between load cell output readings for repeated loadings under identical loading and environmental conditions. ② Resolution: The smallest change in mechanical input which produces a change in the output signal. ③ Sensitivity : The ratio of the change in output to the mechanical input.