Current measuring method and device

Abstract

A method of determining the magnitude of an exceptionally large current which comprises measuring the angle of rotation of polarized light in a magnetic field created by the current with a glass fiber sensor composed of a fluoride glass having a low Verdet constant and a photoelastic coefficient not over about 0.25 (nm/cm)/(kg/cm 2 ).

We claim:  
     
         1 . A method of reducing the photoelastic coefficient of a fluoride glass that has a low Verdet constant at a wavelength suitable for measurement, and that contains zirconium fluoride as a primary component of its composition, the method comprising the step of incorporating a small amount of lead fluoride in the glass composition.  
     
     
         2 . The method of    claim 1    which comprises incorporating an amount of lead fluoride in the fluoride glass composition that is not over about 3.0 mole %.  
     
     
         3 . The method of    claim 1    which comprises incorporating the lead fluoride in a fluoride glass composition which is predominantly zirconium fluoride and contains smaller amounts of barium, lanthanum, aluminum, and sodium fluorides.  
     
     
         4 . The method of    claim 3    which comprises incorporating the lead fluoride in a glass composition consisting essentially of, in mole %: 53% ZrF 4 , 20% BaF 2 , 4% LaF 3 , 3% AIF 3  and 20% NaF.  
     
     
         5 . The method of    claim 1    which comprises reducing the photoelastic coefficient to a value less than about 0.20 (nm/cm)/(kg/cm 2 ).  
     
     
         6 . A method of determining the magnitude of an exceptionally large current of up to about 200 kA which comprises, 
 providing a glass fiber, current sensor, the core glass of which has a composition composed predominantly of zirconium fluoride and containing up to about 3 mole % lead fluoride, having a low Verdet constant at the wavelength used for measurement, and capable of causing an angular rotation of polarized light less than 0.45° per kA, per pass at that wavelength,    passing a current through a conductor to create a magnetic field surrounding the conductor,    positioning the current sensor within the magnetic field thus created,    propagating polarized light into the glass fiber, current sensor,    measuring the angle of rotation of the polarized light in the glass fiber sensor, and    determining the magnitude of the current from the angle of rotation of the polarized light.    
     
     
         7 . The method of    claim 6    which comprises forming the glass current sensor as a coil through which the conductor extends.  
     
     
         8 . The method of    claim 6    which comprises providing a glass fiber sensor that has a photoelastic coefficient not over 0.25 (nm/cm)/(kg/cm 2 ).  
     
     
         9 . A glass fiber sensor for measuring an exceptionally large current in a magnetic field, the core glass having a fluoride glass composition containing ZrF 4  as a primary component and not over 3 mole percent PbF 2  whereby the photoelastic coefficient of the glass is reduced to a value not over 0.25 (nm/cm)/(kg/cm 2 ).  
     
     
         10 . A glass fiber sensor in accordance with    claim 9    wherein the core glass consists essentially of, as calculated in mol %:  
                                           52-56%   ZrF 4           14-24%   BaF 2           3-6%   LaF 3           3-6%   AlF 3           14-22%   NaF         up to about 3%   PbF 2