Patent ID: 8320719
Filing Date: 2012-11-27
Classification: G01R

Abstract:
1. A method for manufacturing a fiber optic current sensor, wherein the fiber optic current sensor comprises: a sensing fiber to be exposed to a magnetic field of a current I to be measured, wherein said sensing fiber has a Verdet constant V and a birefringent linear phase retardation δ, at least one fiber optical retarder coupled to said fiber for converting light between linear and elliptical polarization, wherein a slow axis of said retarder is at an angle 45°−β in respect to a slow axis of said sensing fiber, and wherein a differential retardation ρ induced by said retarder is dependent on temperature where and a control unit generating a sensor signal σ dependent on a current-induced phase shift Δφ, in particular proportional to said phase shift Δφ, which phase shift can be written as with φ F =V·N·I, and wherein N is a number of loops of said sensing fiber and S is a scale factor, said method comprising: exposing said sensing fiber to a magnetic field; in an initial step, measuring a dependence A of said sensor signal a on a temperature T of said retarder; defining a target dependence; of the sensor signal a on the temperature T of said retarder; determining, from A, B, Q, δ and β, a ratio r with between an initial sensor signal σ ini before a thermal treatment of said retarder and a target sensor signal σ fin after a thermal treatment of said retarder; and subjecting said retarder to said thermal treatment and measuring said sensor signal σ until said sensor signal σ has substantially changed by said ratio r.