How to Select Load Cells

Image Credit: Ametek, DME Company, and Honeywell Sensing and Control

Load cells are force sensors are used in metrology, web control, and weighing applications. They are also used to measure structural stress. Often, load cells incorporate mechanical packaging for incorporation with existing test and monitoring systems. These devices are used to mention tension, compression and/or shear, and can be configured to measure force or load along one or more axes.

Types of Load Cells

The GlobalSpec SpecSearch database enables industrial buyers to source these types of load cells.

• Tension cells are used for measuring a straight-line force "pull apart" along a single axis, and are characterized typically as positive-force devices.
• Compression cells are used to measure a straight-line force "push together" along a single axis, and are characterized typically as negative-force devices.
• Shear cells measure sheer, which is induced by tension or compression along offset axes. Some load cells measure force along only one axis, however. There are three kinds of shear cells: shear beam, bending beam, and single-point bending beam.

Biaxial and triaxial devices also provide load measurements, along two or three (typically orthogonal) axes. 

Load Cell Packages

When selecting products, industrial buyers need to specify a load cell package. There are many different choices, including the following.

• S-beam units are shaped like a squared-off letter S. Variable resistors are bonded to the regions of maximum strain, and change resistance as a load is applied.
• Pancake cells are short, low-profile cylinders. They are capable of measuring very small through very large loads. Donut cells are like pancake cells, buthave athrough-bore or hole.
• Canister cells are instrumented cylinders. Theyhave a considerably higher aspect ratio than pancake cells.
• Bolt load sensorshave one or two threaded ends for attachment to measured systems. These load cellsmeasure force along the long axis of the bolt.
• Link cells are designed for the in-line measurement of tension or compression.
• Tank weighing load cells are designed specifically to support tanks.

Other types of load cell packages include male and female rod ends.

Load Cell Sensor Technologies

In addition to type and package type, load cells are classified by sensor technology.

• Capacitive load cells use the separation between two conductive surfaces to measure the force applied. As the force increases, the separation between the surfaces decreases and the capacitance increases.

Image Credit: Machine Design

• Magnetoelastic load cells detect changes in permeability by measuring changes in their own magnetic field. They are sometimes called pressductor load cells.

Image Credit: ABB Measurement Products

• Piezoelectric load cells use a piezoelectric material that, when compressed, generates a charge that isconditionedby a charge amplifier.
• Strain gages are bonded to the part of the structure that deforms during measurement. They typically require an excitation voltage, and provide output sensitivity proportional to that excitation.

Buyers should also specify the desired sensor output when selecting load cells. 

Resources

Introduction to Load Cells

How to Build Digital Load Cells

Capacitive Load Cells Simply Sensing