An optical strain gauge is developed and characterised for an active pantograph for high-speed electrical trains applications. The pantograph is subjected to a continuous impact forces when it makes contact with the 25 kV overhead AC line. The carbon based pantograph head is susceptible to crack damage due to these impacts An optical strain gauge based on the photo-elastic effect has been developed to monitor on line the contact force applied to the pantograph. The sensing system exploits the concept of chromatic modulation that can be produced by spectral changes induced by a controlled birefringence. Moreover the chromatic sensing technique is independent of the light intensity and provides total electrical isolation. The developed optical strain gauge was assessed to evaluate its performance and to find the range of operation. Static, hysterisis, repeatability and dynamic tests were carried out and the results compared to the theory when applicable. In the static test, it was found that the force against dominant wavelength was linear in the range of 0 to 80 N and became progressively non-linear for forces above 80 N, this is in a good agreement with the theory. These tests were carried out several times over a long period of time, and the results showed a good repeatability, although an acceptable degree of hysterisis was noted. Finally the resistance of the optical strain gauge was tested against dynamically varying loads and found that it exhibited a good resistance. These tests proved the suitability of this proposed optical strain gauge for the development of an active pantograph for high-speed electrical trains applications
