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A load cell is a device used to measure large pressures and weights. Unlike a typical scale, a load cell actually applies the force to a piezoelectric crystal and measures the voltage across the crystal. The electronic signal produced by this event is so minute that it needs to be amplified before being measured. Non-electric load cells, namely hydraulic and pneumatic load cells, perform similar functions, but by far the most popular design is the electronic strain gauge type load cell.

Before discussing load cell types, it is important to detail how to select the proper load cell, or cells, for a project. First, you should decide whether you need a tension or compression cell. A tension load cell measures the weight pulling on it, and in essence must support that weight. Compression load cells measure the weight pushing on them, and are often placed beneath the object being weighed. In general weights above 20,000 lbs. are too much for tension mounts. Compression assemblies, however, often require lateral restraints to keep them stable. The number of cells used should be determined by the number of supports, because ideally each support should feature a load cell. This is especially necessary if the distribution of the load is not symmetrical between supports. Also, the minimum amount of symmetrical supports is preferred. In some cases, compression and tension load cells are used in tandem.

A strain-gauge load cell essentially converts weight into electronic signals. As weight increases, it deforms a structural component of the load cell. As this component changes shape, the electrical resistance of the gauge changes proportionally. Therefore, the change in resistance equates to a certain weight, and gives a measurement. Accurate to within .25%, these load cells rank as the most widely used, as well as one of the best choices for most applications.

Hydraulic load cells operate without a piezoelectric crystal, functioning on the force-balance principle. When weight is introduced to a hydraulic load cell, it causes a change in the device’s internal fluid pressure. Pressure detecting devices measure this pressure and various tools convert this measurement to weight. Pneumatic load cells also function on the same principle, but tend to have better accuracy. They are typically used on smaller loads when safety is of prime concern.

Applications for load cells include tensile testing of products, control of ingredients in food service products, railcar weighing and scales. Perhaps the most noteworthy use is in truck weighing stations, where load cells are typically employed.