Load Cell Definition

Load cells are integrated sensors that measure weights and output continuous electrical, pneumatic, or hydraulic analog signals. They are used throughout industry and in a wide range of consumer applications. Load cells perform weighing operations that used to be accomplished with mechanical force or motion-balance devices. The sliding weight scale in the doctor's office is an example of the latter. There are load cells for measuring weights from a few grams of fine sand to those for hundreds of tons. Digital postage, food, and bathroom scales are just a few examples of consumer based load cell applications.

Operating Principle

Most load cells employ motion or force balance strain gages to generate a continuous electrical analog output signal that a user can view on a digital readout device. Strain gages are extremely thin resistive strips of electrically conductive wire or foil that are bonded to specially shaped metal springs or brackets. As weight is applied to the brackets, they deform slightly because of the load. This either elongates and stretches the strain gage, increasing its electrical resistance, or shortens and compresses it, decreasing resistance. This variable resistance is compared to several fixed resistances in a DC powered bridge circuit, and the output amplified and sent as a voltage to the analog input of a digital readout. The readout is application-specific meaning the readout is in the weight units desired such as ounces, pounds, grams or kilograms desired instead of the voltage the meter really sees.

Alternative Outputs

While most load cell systems in homes and industry have proportional electronic outputs, pneumatic load cell systems are often used in industrial areas where explosions or fires could be an issue. In situations where chemical contamination or frequent wash-downs are necessary, sealed hydraulic systems are common.

Modern Automation

Weights and forces measured by today's load cells are used not only for local readouts, but are also consolidated by data acquisition systems for use in plant-wide computer control systems and networks. Precision load cells with extremely fast recovery times are used to check weights of hundreds of packages per minute in many manufacturing operations.

Automated Shipping

Check-weigh systems can automatically weigh each box on a conveyor line to instantaneously calculate shipping or postage charges, and then print out and apply the exact shipping or postage label.

Dieting

Dieters know that good eating habits are a continual tug of war between that large load cell based scale in the bathroom, and the small one for portion control on the kitchen counter.