Load cells are typically built using foil strain gauges that are resistively bonded to a metallic member. When the metallic member becomes stressed by the application of a force, a change in resistance occurs due to the resulting strain. This leads to a change in output voltage.
Strain gauges are resistors that are bonded to a metallic member such as a cantilever beam or diaphragm and are built using standard semiconductor etching techniques. At least four strain gauges are configured in what is referred to as a Wheatstone bridge configuration with four separate resistors connected in a Wheatstone bridge network. An excitation voltage of approximately 10 volts is applied to one set of corners, and the voltage difference is measured between the two remaining corners. When the four resistors are closely matched in value with no applied load, the voltage output is either equal to or close to zero at equilibrium. This is why the Wheatstone bridge network is also referred to as a balanced bridge circuit. After careful amplification of the small millivolt level signals to a higher amplitude, small changes in output can be digitized and measured.
Load cells can provide very accurate readings, but the manufacturing process requires a lot of tedious steps.