How does a bending beam load cell work?

Bending beam load cells are the most widely used types of load cells. Read this article to learn more about the benefits and properties of bending beams.

During a measurement, weight acts on the load cell's metal spring element and causes elastic deformation.

This strain (positive or negative) is converted into an electrical signal by a strain gauge (SG) installed on the spring element. The simplest type of load cell is a bending beam with a strain gauge. Often the (mandatory) basic components, i.e. spring element and strain gauge are complemented with additional elements (housing, sealing elements, etc.) protecting the strain gauge elements.

Bending beam load cells

Bending beam load cells are the best fit for many measuring tasks. Here the signal on principle depends on the bending moment. When the load application point in the bending beam's longitudinal direction changes with identical loads, different signals are generated.

For this reason, the single bending beam is rarely used in load cells, because it requires special measures to ensure a constant load application point (lever arm effect).

Multiple bending beams

Multiple bending beams are often used as spring elements for loads up to 5 t. This load cell type mainly uses two (double bending beam) or three (triple beam) bending beams. They are coupled via rigid elements on the clamping and on the load application side. The rigid coupling enforces a purely vertical shift of the load application point and an S-shaped deformation of the two beams.

Fig. 1: Double bending beam principle

This system is significantly less sensitive to load application point shifts than a single bending beam. The S-shaped deformation generates positive and negative strain zones on the surface that are close to each other and considerably facilitate strain gauge installation and wiring. Fig. 2 shows different double bending beam types.

Fig. 2: Double bending beam spring element

Load cells with pressure compensation

When load cells with closed housings are used for the measurement of small loads, atmospheric pressure fluctuations may already be sufficient to cause measurement signal variations with constant loading. To avoid this problem, atmospheric pressure is compensated for through adequate design measures ensuring that the load cell is subjected to the same pressure on all sides.

Fig. 3: FIT ®/4 digital load cell

Bending beam load cells from HBM

HBM's range of load cell types uses various modifications of bending beams. Products include, for example single point load cells like PW15AH or digital load cells like FIT®/4.

Fig. 4: Single point load cells from HBM

There are various load cell designs in addition to bending beams. This includes for example:

  • Load cells with column-shaped spring elements for high loads
  • Hollow cylindrical load cells for very high loads
  • Load cells with spring elements directly from the measuring bracket
  • Ring torsion load cells
  • Shear beam load cells
  • Load cells with diaphragm spring element.
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