What is a load cell? How does a load cell work?

What is a load cell? How does a load cell work?

Design and function of a load cell
Load cells are used to measure weight. They are an integral part of our daily life. “In your car or at the cheese counter in the supermarket – we encounter load cells everywhere,” says HAINA Product Manager Evan. Of course they are usually not immediately recognizable, because they are hidden in the inner workings of instruments.

Load cells generally consist of a spring element on which strain gauges have been placed. The spring element is usually made of steel or aluminum. That means it is very sturdy, but also minimally elastic. As the name “spring element” suggests, the steel is slightly deformed under load, but then returns to its starting position, responding elastically to every load. These extremely small changes can be acquired with strain gauges. Then finally the deformation of the strain gauge is interpreted by analysis electronics to determine the weight.

To understand this last point, let us consider strain gauges in more detail: They are electrical conductors firmly attached to a film in a meandering pattern. When this film is pulled, it – and the conductors – get longer. When it is contracted, it gets shorter. This causes the resistance in the electrical conductors to change. The strain can be determined on this basis, as resistance increases with strain and diminishes with contraction.

The strain gauges are firmly attached to the spring element, and therefore undergo the same movements it does. These strain gauges are arranged in what is called a bridge circuit, or more precisely a Wheatstone bridge circuit (see diagram). This means that four SGs are connected “in a ring” and the measuring grid of the force being measured is aligned accordingly.

If an object is placed on the load cell or suspended from it, the object’s weight can be determined. The intended load for a load cell is always aligned in the direction of the center of the earth, in other words in the direction of gravity. Only that force component of the load should be acquired. That is not the case for force sensors, which are similar in design, and are also frequently specified as “load cells”: They are usually designed to acquire loads that occur in all directions. The direction of the earth’s gravitational force is not relevant to how they are installed.