Strain gauges are devices that measure the amount of strain an object is subjected to. Usually, these gauges measure the forces at the point of attachment to the object, and they continually monitor them to ensure that they do not fall outside of the specified range.
Manufacturers usually have strain gauges installed in their facilities. However, when they break or come to the end of their useful life, it isn’t always clear which type of gauge to replace them with.
In this post, we take a look at the major types of strain gauge so that you can quickly determine the one you need.
Quarter-Bridge Strain Gauge
The quarter-bridge strain gauge is a device that measures axial or bending strain. In the ideal situation, the strain gauge should only respond to physical strain. However, sometimes, heat can affect the readout, leading to inaccurate readings.
Quarter-bridge strain gauges often come with a second gauge that also responds to the temperature. This part is in close thermal contact with other elements of the device, but it isn’t bonded in the same way. Thus, the strain has virtually no impact on it. However, because temperature changes affect both gauges equally, the ratio of the resistance doesn’t change, and so neither does the voltage across the device, helping to calibrate the reading.
Half-Bridge Strain Gauge
Half-bridge strain gauges attempt to increase the accuracy of strain gauges by including two gauges mounted in a variety of configurations.
In some types of configuration, a half-bridge strain gauge measures axial and bending strain – and in others, it just measures bending strain only.
In the first instance, vendors arrange the resistors perpendicular to each other. That way, they can measure strain in multiple dimensions. When measuring both axial and bending strain, gauges provide a multidimensional readout.
These gauges look similar to quarter-bridge dummy gauges with resistors, but they are not the same. The former has a gauge that does not bond with the strain specimen, while the latter does. In other words, the half-bridge strain gauge in the axial and bending configuration provides measurement in both dimensions. In contrast, the quarter-bridge provides measurement in one direction and uses the second gauge to control for thermal variation.
In the bending-only version of the half-bridge strain gauge, manufacturers stack the two resistors on top of each other, providing strain measurement in one direction only.
Full-Bridge Strain Gauge
A full-bridge strain gauge features four individual strain gauges available in three configurations.
In the first configuration, the gauges are stacked on top of each other and provide a high degree of sensitivity in the bending strain direction only.
The second arrangement measures bending strain only but also accommodates the tensile and compressive Poisson effect.
The third arrangement measures the axial strain. Two of the gauges measure the active tensile strain while the other two measure the Poisson effect.
Choosing the right gauge requires working out which type of strain you need to measure (axial or bending), and the sensitivity that you require. In general, full-bridge gauges are the most sensitive in single directions.