What Is A Load Cell And The History

By Diana Johnson

By definition a load cell is an electronic device (a transducer) that is used to convert a force into an electrical signal. What does this mean? They are a transducer which converts force into a measurable electrical output.

How does this work? The conversion of the force into an electrical current is indirect and happens in two phases. They can consist of one, two or four strain gauges depending on the type of cell, and it is the strain gauge that converts the force into the electrical current. Now not all of them use strain gauges, there are many different types such as hydraulic, pneumatic, fibre optic, button and washer cells to name a few.

What can you do with the electrical output? Well before the electrical current can be used the electrical signal output usually requires amplification by an instrumentation amplifier and then it can be used. They are primarily used as a weighing apparatus. The strain gage-based load cell has become the method of choice for industrial weighing applications.

Which applications use these? To name a few they can be found in electronic crane scales, finding the center of gravity of an object by weight, force measurement, force gauge, onboard weighing, railcar weighing, structural health monitoring, and tension measurement.

Examples of Digital Cells and Their Applications

There is a massive variety of load cells today, all of which are better used in certain applications and circumstance than others for example the new compression cell is used for applications in tough environments. The new beam cell is great for belt scales, platform scales, filling machines, and process equipment. The single point cells are usually found in applications such as multihead weighers, checkweighers, filling machines, belt scales, platform scales, and bench scales. Depending on your requirements and the type of weighing you are conducting will depend on the type of load cell you should use.

A load cell converts force into a measurable output, meaning they allow us to weigh items accurately. Strain gauge based cells are probably the most popular form but there are many different types such as Hydraulic Cells, Pneumatic, and Fiber Optic, and many more. But where did it all begin, how did they come about and who invented the theory behind it all?

It is fact that heavy objects deflect a spring support more than lighter ones. Think of a fisherman and a fishing rod. The fishing pole is securely in place at one end by the grip of the fisherman, and the pole is deflected down in the water by the fish on he other end. If the fish is pulling back the deflection is larger than if the fish is not pulling back at all. We can measure the difference of the deflection to measure the weight of the item as the more the deflection the higher the weight. This is the same idea behind a set of scales. The scale is merely a coiled spring with a scale, the more weight placed on the spring the more it is deflected which will mark off on the scale the weight of the item. A load cell, in its most simplistic form, is a springy element which supports the load, and a deflection measuring element which indicates the amount of deflection caused by the load.

They are used today to weigh industrial applications but this hasn”t always the case. Before mechanical lever scales were used. Mechanical lever scales are accurate if they are calibrated and maintained properly. The principle of the mechanical lever scale is either the use of a weight balancing mechanism or the detection of the force developed by mechanical levers.

In 1843 an English physicist called Sir Charles Wheatstone devised a bridge circuit that could measure electrical resistances. This bridge circuit was used for measuring the resistance changes that occur in strain gages. In the 1940s the first bonded resistance wire strain
gage was developed. Together with the technology developed the strain gages have produced both mechanical scale components and stand-alone load cells.

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If you are looking for load cells take a look at Eilersen Electric′’s website.