A load cell is a transducer that is used to convert a force into a differential electrical signal. While early load cells employed mechanical lever scales (Omega 2005), modern load cells are normally constructed with:

• Hydraulic load cells
• Pneumatic load cells
• Strain gauge load cells

Hydraulic and pneumatic load cells both operate on a mechanical force-balance principle. Hydraulic load cells measure weight as a function of changing pressure of an internal filling fluid, while pneumatic load cells operate by measuring changes in air pressure, causing them to be cleaner and more accurate, but also more costly. Strain gauge load cells, on the contrary, operate on the piezoelectric principle and transduce force to electricity directly.

Today, strain gauge load cells are the most commonly used type four strain gauges in a Wheatstone bridge configuration, but are also available with one or two strain gauges. The electrical signal output is normally in the order of a few millivolts and requires amplification by an instrumentation amplifier before it can be used. The output of the transducer is processed by an algorithm to calculate the force applied to the transducer.

Load cells are highly accurate though often expensive and thus find application in industry. They can be used to give a force reference or to calibrate other types of pressure/force sensors used in musical instruments.

• Omega Engineering Technical Reference, 2005, Introduction to load cells.
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• New Capacitive Load Cell Technology Capacitance Technology