Temperature compensation for optical strain gages

For its type K-OL and K-OR optical strain gages, HBM now provides the K-OTC sensor, which can be used to compensate the temperature response of optical SGs.

Experimental stress analysis is a typical application for optical strain gages (SG) based on so-called fiber Bragg gratings, such as the K-OL and K-OR types from HBM.

As the strains are measured by light, optical strain gages dispense with electrical signals, allowing them to be used under difficult conditions such as under high voltage, when there is powerful magnetic interference or in potentially explosive atmospheres.

The measurement signal in optical strain gages is temperature-dependent firstly as a result of the temperature sensitivity of the fiber Bragg grating and secondly thanks to the thermal dilatation of the measurement object itself.

Depending on the material involved, this can be as much as 30 µm/m/K. But in stress analyses, the user is normally only interested in mechanical strain.

So particularly when the strains are relatively small and the differences in temperature are high, it is essential to compensate the temperature sensitivity of the optical strain gage.

HBM now provides an elegant way to do this, with the K-OTC temperature compensation sensor. The K-OTC is also based on an optical strain gage, applied to an aluminum sensor body. This is attached to the measurement object so that although temperature compensation does take place, no mechanical strain is transferred.

Thus the K-OTC is only measuring the thermal dilatation of the aluminum and the temperature-dependent signal change of the fiber Bragg grating. This allows the signal of the actual optical strain gage to be compensated by computation.

This is particularly easy for the user, as the signal of the K-OTC is simply read into the catman®AP software together with the signals of the optical strain gages, and compensation occurs automatically.

HBM offers users of strain gages all the components they need from one source. As well as optical strain gages of the K-OL and K-OR type and the new K-OTC temperature compensation sensor, this includes interrogators and the data acquisition software catman®AP, which has a special EasyOptics module for optical SGs.

For more information, go to www.hbm.com/en/menu/products/measurement-electronics-software/opto-electrical-interrogators/single/categorie/opto-electrical-interrogators/product/k-otc/backPID/opto-electrical-interrogators/