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Measuring mechanical stress with strain gauges

Measuring mechanical stress in assemblies and materials fast and reliably: Strain and compression measurements with strain gauges provide precise results regarding the forces that are applied to components for structure tests, durability measurements as well as product and material testing.

For the optimum dimensioning of components, detailed information on the type of the force, its direction and size is required. To determine forces, strain gauges in the form of Wheatstone bridge circuits are applied on the DUT. Most suitable for this purpose are so-called half and full bridges with two or four strain gauges, respectively. Due to their design, interferences such as the temperature dependence of individual strain gauges can be compensated.

Measuring precisely and reliably with quarter bridge strain gauges thanks to external bridge completion and TEDS

In daily practice, full and half bridges can often not be applied due to time and financial reasons. Moreover, their application can be difficult due to lack of space. This applies in particular for measurement setups with great numbers of strain gauges, e.g. in cranes and heavy construction machinery. In many cases, hundreds of quarter bridges are applied as stress sensors, each one consisting of only one strain gauge and and often located far apart from each other. An adverse effect from a measurement point of view is, however, that quarter bridges are more susceptible to interferences as they only provide a rather low useful signal. In addition, the measured value depends on the temperature at the point of measurement. This means, in turn, that precise measurements require temperature compensation.

With its STGMM measurement modules, CSM offers very precise and extremely robust CAN- and EtherCAT®-based measurement devices which are very well suited for all kinds of strain gauge measurements. The modules can be mounted close to the points of application of the strain gauges which minimizes interferences and reduces cabling costs. Details on the points of application and the measurement module configuration are stored in the TEDS element that is integrated in the measurement cable.

The matching completion resistor, required for the quarter bridge is integrated in the measurement cable, close to the point of application. This reduces interferences caused by cable resistances and temperature differences between the point of application and the measurement module. Optionally, an additional temperature sensor can be connected to the STGMM measurement module to compensate the temperature dependence of quarter-bridge strain gauges.

 

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