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A load cell is the name typically given to a transducer that is used to convert a force into an electrical signal. This device normally consists of four or more strain gauges in a wheatstone bridge configuration, but some lower performance types are also available with only one or two strain gauges. The load cell is therefore a passive device and 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 signal from a load cell is a ratiometric signal and is usually described in mV per V because any change in the supply voltage (usually termed as excitation) is immediately reflected to the output. Measurement equipment that is specifically designed for load cell applications (or for strain gauge applications such as pressure, force, torque sensors) provides a separate and very stable excitation supply, and peforms two simultaneous measurements of excitation and signal to convert the ratio mV/V into a true measurement result.

 

Multiple load cell outputs are wired in parallel and their outputs are then summed to give the total load result. In the case of floor scales and other applications where the load can be positioned off-center, then it may be necessary to trim the outputs of the individual load cells so that the load result is the same, regardless of load position on the scale. Such devices are known as summing junction boxes or trimming boxes, and can be found in the OTHER PRODUCTS selection on the Mantracourt website.

 

See also :

 

Bending beam load cell

Shear beam load cell

Rocker pin load cell