Optical strain gauge offers many benefits

HBM's measurement technology enables the best of both worlds — the simultaneous acquisition of data using both electrical and optical strain gauges. The EasyOptics module in HBM's catmanAP software enables users to jointly acquire and analyze data from different types of sensors.

HBM patented optical strain gauges, available from Durham Instruments, utilize proven technology, and are easy to work with. The optical strain gauge K-OL is made from fibres of glass with a very small core diameter of no more than five micrometres. In comparison, the diameter of human hair ranges from 60 to 80 micrometres. The fibre core is surrounded by a cladding layer from purest glass with a diameter of 125 micrometres.

The optical effect that is used for strain measurement is because of the distance of the reflection points and, therefore, the wavelength of the reflected light being changed by the induced strain.

Like all sensors based on Bragg gratings, K-OL has the following advantages:

• Insensitive to electromagnetic fields;
• Can potentially be used in highly explosive atmospheres;
• Suffers no mechanical failure of sensor material (glass) under high vibration loads;
• Reduced numbers of connection lines and hence less impact on test objectives;
• Low interconnection needs as numerous sensors with different Bragg wavelengths can be included in one fibre; and 
• 10 million load cycles at ±3.000 µm/m alternating strain.

Previously, installation of a glass fibre with Bragg grating on a test object was implemented with adhesive glue applied to either side of the Bragg grating. The glass fibre must therefore be pre-strained to measure negative strains (compressions) as well. This means that the measurement range in the negative strain direction is limited, as it exactly corresponds to the direction and value of the pre-strain. Because the Bragg gratings are located inside the fibre, pre-straining and installing the gauges can cause unwanted damage to the fibre. This is where the advantages of the optical strain gauge K-OL come in, because the glass fibres with the Bragg gratings are symmetrically embedded in the composite material. Thanks to this patented design, both positive and negative strains can be induced in the Bragg grating.

There is no difference in the handling of optical or traditional (electrical) types of strain gauges. You don't have to learn new skills. Bonding, covering, connecting, etc., are all identical. The patented design protects the fibre and makes configuring your test setup quick and convenient. 

To learn more about the optical strain gauge K-OL, contact Durham Instruments. 

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