Fibre Bragg Sensors Compared with Electrical Strain Gauges for Use in Force Measurement - Prospects and Potentials

− This article deals with the technical properties of fiber Bragg gratings with regard to their use as the strain-sensitive element in force transducers. Electrical strain gages are widely used in modern, precise force transducers. The electrical strain gage provides both outstanding technical properties and cost-effectiveness. Besides the electrical strain gage, the measurement principle of fiber Bragg-based sensors has recently become established. First applications in experimental mechanics have shown that this technology offers a lot of potential. Optical strain gauges are available on the marked since one year and are proofed in many applications. These sensors are mainly based on so-called fiber Bragg gratings. Such a Bragg grating uses a great many reflection points at regular spacing. At each of these points, part of the radiated light is reflected. The reflected light interferes (constructive interference) and generates a reflection peak. This peak shows a characteristic wavelength which is dependent on the spacing of the reflection points. The following sketch shows a Bragg grating in a fibre and its influence on the spectrum of the transmitted and reflected light. Fig. 1. Principle of a fibre Bragg Grating. Diagram a shows the spectrum of the light which is send into the fibre. The light at the Bragg wavelength is reflected (b). Diagram c shows the spectrum of a Bragg grating in transmission. This article presents the properties relevant to use in the manufacture of transducers such as: Creep Temperature behaviour Drift Electromagnetic compatibility and others and compares them with the properties of electrical strain gages.