What is a Load Sensor?

A load sensor converts tension and compression forces into a corresponding electrical signal. (Getty Images)

A load sensor (more commonly referred to as a “load cell”) is an electronic device that converts tension and compression forces into a corresponding electrical signal. Load sensors are generally used to determine the weight of an object (as in household or industrial scales), but they are also used to quantify tension (such as in pulley cables and ropes). While designs and functions vary among load sensors, they all measure resistance and/or deformation within the sensor to determine the magnitude of tension and compression forces. The manufacturing, medical, grocery and automotive industries all benefit from load sensor technology.

The two simplest load sensor designs are the hydraulic load sensor and the pneumatic load sensor. The hydraulic sensor uses liquid and the pneumatic uses gas. When a tension or compression force is applied, the liquid or gas will expand or contract, generating an electrical signal that is directly proportional to the force applied. These sensors are often attached directly to gauges, and they are examples of pressure sensors.

The most common type of load sensor is the strain gauge load sensor. A strain gauge is comprised of a flexible diaphragm and wire. When this load sensor experiences compression or tension, the electrical resistance within the strain gauge decreases or increases proportionally. Strain gauge load sensors are often arranged in Wheatstone bridge configurations (which are used to calculate an unknown resistance by using three known resistances).

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Diagram of a Wheatstone bridge load cell
Diagram of a Wheatstone bridge load cell. (EE Publishers)

Capacitive load sensors are considered to be the most accurate type of load sensor. They measure capacitance (the ability of the sensor to store electrical charge) to quantify compression forces. Capacitive load sensors consist of two conductive plates that move closer or farther away from one other as the load changes. The capacitance changes as the distance between the plates changes, and the changing capacitance is detected by a measurement circuit.

In addition, there are piezoelectric load sensors (which harness the piezoelectric effect), and beam load sensors (which generate an electrical signal when bent).

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