Load Cells for Industrial Scales

A Load Cell is a particular kind of transducer or sensor which converts force into a measurable electrical output. Your typical load cell device consists of four strain gauges in a wheatstone bridge configuration. In an industrial scale this conversion consists of a load being transformed into an analog electrical signal. While there are many different types of load cells, the strain gage load cell is the classical design. In this type of load cell, the conversion is accomplished by the physical deformation of strain gages which are bonded into the load cell beam and wired into a wheatstone bridge configuration.

Compression Load Cells Compression/Tension Load Cells

Compression Load CellsCompression load cells often have an integral button design. They are ideal for mounting where space is restricted and offer excellent long term stability.

Tension Load CellsCompression/tension load cells can be used for applications where the load may go from tension to compression and vice versa. They are ideal for space restricted environments. Threaded ends facilitate easy installation.

   
S-Beam Load Cells Bending Beam Load Cells

S-Beam Load Cells S-Beam load cells get their name from their S shape. S-Beam load cells can provide an output if under tension or compression. Applications include tank level, hoppers and truck scales. They provide superior side load rejection.

Bending Beam Load CellsDetect weight by bending and are used in multiple load cell applications from tank weighing to industrial process control. They feature low profile construction for integration into restricted areas.

   
Platform and Single Point Load Cells Canister Load Cells

Platform and Single Point Load Cells Platform and single point load cells are used to commercial and industrial weighing systems. They provide accurate readings regardless of the position of the load on the platform.

Canister Load CellsCanister load cells are used for single and multi-weighing applications. Many feature an all stainless steel design and are hermetically sealed for washdown and wet areas.

   
Low Profile Load Cells

Low Profile Load CellsCompression and tension/compression load cells. Mounting holes and female threads provide easy installation. Used frequently in weighing research and in-line force monitoring.

   

The History of Load Cells

As a part of the measuring instrument family, the weighing scale is basically a lever. Its classic form is the equal arm balance which consists of a bar with two pans hanging from each end and a fulcrum at the centre of the bar upon which the bar can balance. Used by the ancient Egyptians, these balances were used to measure everything from people to gold. Another classic form is the steelyard invented by the Greeks (Archimedes) and Romans. Unlike the equal arm balance, its fulcrum was placed just off center. An object of unknown weight was hung from the shorter arm, and a known weight, called the poise or counterpoise, was attached to the longer arm in such a way that it could slide back and forth. When the load was in place, the poise's position was adjusted until it balanced the load attached to the shorter arm. The weight of the unknown object was determined by comparing the position of the poise to the markings on the longer arm.

Load Cells for Industrial ScalesAdvancements in scale technology took a huge step forward when Leonardo Da Vinci used positions of calibrated counterweights on a mechanical lever to balance and determine unknown weights. Variation of his designs used multiple levers, each of a different length and balanced with a single standard weight. Before hydraulic and electronic strain gauge load cells replaced mechanical levers for industrial weighing applications, these mechanical lever scales were widely used. They were used to weigh everything from pills to railroad cars and did so accurately and reliably provided they were properly calibrated and maintained. They involved 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, the British physicist 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.

Load CellsHow Load Cells Work

Load cell designs are classified according to the type of output signal generated (pneumatic, hydraulic, electric) or according to the way they detect weight \(compression, tension, or shear) Hydraulic load cells are force -balance devices, measuring weight as a change in pressure of the internal filling fluid. Pneumatic load cells also operate on the force-balance principle. These devices use multiple dampener chambers to provide higher accuracy than can a hydraulic device. Strain-gage load cells convert the load acting on them into electrical signals. The gauges themselves are bonded onto a beam or structural member that deforms when weight is applied.

Kinds of Load Cells

Load cells measure tension, compression, or shear. Compression load cells measure a pushing together force along a single axis. Tension load cells measure a pulling apart force along a single axis. Shear load cells measure the displacement of a structural element to determine force.? Shear cell types for load sensors can be shear beam, bending beam, or single point bending beam. The most common sensor technologies are piezoelectric and strain gauge.

1. Piezoelectric: a piezoelectric material is compressed and generates a charge that is conditioned by a charge amplifier. 2. Strain Gauge: strain-sensitive variable resistors are bonded to parts of the structure that deform when making the measurement. Are typically used as elements in a Wheatstone bridge circuit, which is used to make the measurement.

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