Displacement monitor with FBG deforming ring and its application in high speed railway

A displacement monitor with deforming ring is developed to ensure the FBG suspended and to avoid it to be chirped by covering glue. The mechanical analysis provides ring size to ensure suitable BFG wavelength shift extent within detected range. Two pieces of FBG are crosswise fixed on the ring and pre-drawn properly. Rail creep force of high speed railway makes one tense, the other compress. To add these two wavelength shifts, the sensitivity is doubled, and environmental temperature interference is eliminated. Its general error is ±0.25% FS; repeatability is 0.2% FS; resolution is 0.1mm; the temperature error, from -20 to 60Cº, is ±0.45mm in 50mm range.