Load Cell History
Before strain gage-based load cells became the method of choice for
industrial weighing applications, mechanical lever scales were widely
Mechanical scales can weigh everything from pills to railroad cars and
can do so accurately and reliably if they are properly calibrated and
maintained. The method of operation can involve either the use of a
weight balancing mechanism or the detection of the force developed
by mechanical levers. The earliest, pre-strain gage force sensors
included hydraulic and pneumatic designs.
In 1843, English physicist Sir Charles Wheatstone devised a bridge
circuit that could measure electrical resistances. The Wheatstone
bridge circuit is ideal for measuring the resistance changes that
occur in strain gages. Although the first bonded resistance wire strain
gage was developed in the 1940s, it was not until modern electronics
caught up that the new technology became technically and economically
feasible. Since that time, however, strain gages have proliferated both
as mechanical scale components and in stand-alone load cells.
Today, except for certain laboratories where precision mechanical
balances are still used, strain gage load cells dominate the weighing
industry. Pneumatic load cells are sometimes used where intrinsic safety
and hygiene are desired, and hydraulic load cells are considered in
remote locations, as they do not require a power supply. Strain gage
load cells offer accuracies from within 0.03% to 0.25% full scale and
are suitable for almost all industrial applications.
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