Method for non-intrusive measurement of low water content in oil

Abstract

The present invention relates to a method and apparatus for determining trace amounts of water in oil, including the steps of obtaining a blended sample of a low water content fluid including an amount of water and an amount of oil, transferring a portion of the blended sample to a cuvette to create a measurement sample, covering a viewing surface of the cuvette with an opaque sheet with a slit, providing a barrier with a fixed opening between a laser source and a laser-receptive surface of the cuvette, transmitting a pulsed laser beam from the laser source into the cuvette; inducing fluorescence in the measurement sample, focusing the fluorescence through a collecting lens and transmitting the fluorescence to a spectrometer, and measuring the fluorescence with the spectrometer by dispersing the fluorescence with a spectrograph and intensifying the fluorescence with an intensified charge coupled device.

What is claimed is: 
     
         1 . An apparatus for determining trace amounts of water in oil, the apparatus comprising:
 a cuvette with a laser-receptive surface and with a viewing surface, the cuvette configured to hold a blended sample of a low water content fluid, wherein the low water content fluid comprises an amount of water and an amount of oil, and wherein the amount of water in the blended sample is distributed as water droplets, the water droplets having an average diameter;   an opaque sheet with a slit, the opaque sheet configured to block transmission of fluorescence through a portion of the viewing surface of the cuvette, the slit configured to allow fluorescence to pass through a portion of the viewing surface from the cuvette, wherein the opaque sheet is applied to the viewing surface of the cuvette such that the position of the slit is fixed for all measurements, wherein the slit is 0.5 mm wide;   a laser source, the laser source configured to direct a pulsed laser beam through a laser-receptive surface of the cuvette, the pulsed laser beam configured to induce fluorescence in a fluorescence spectrum of the blended sample;   a collecting lens, the collecting lens configured to collect and focus the fluorescence to a spectrometer, the spectrometer configured to measure the fluorescence that passes through the slit; and   the spectrometer, comprising:
 a spectrograph configured to disperse the fluorescence; and 
 an intensified charge coupled device configured to intensify the fluorescence. 
   
     
     
         2 . The apparatus of  claim 1 , further comprising a barrier defining a fixed opening, the fixed opening located between the cuvette and the laser source, wherein the fixed opening is configured to reduce a diameter of the pulsed laser beam. 
     
     
         3 . The apparatus of claim Error! Reference source not found., wherein the average diameter of the water droplets is in a range between 30 μm and 70 μm. 
     
     
         4 . The apparatus of claim Error! Reference source not found., wherein the pulsed laser beam has a wavelength of 266 nm. 
     
     
         5 . The apparatus of claim  12 , wherein the fluorescence spectrum is in a range between 280 nm and 450 nm. 
     
     
         6 . The apparatus of claim Error! Reference source not found., wherein the spectrograph is located between the collecting lens and the intensified charge coupled device, and wherein the intensified charge coupled device is synchronized with the pulsed laser beam. 
     
     
         7 . The apparatus of claim Error! Reference source not found., wherein the pulsed laser beam pulses for a temporal span of 6 ns/pulse at an energy of 20 mJ/pulse. 
     
     
         8 . The apparatus of claim Error! Reference source not found., wherein the slit is 4 mm from an edge of the cuvette joining the laser receptive surface and the viewing surface. 
     
     
         9 . The apparatus of claim  12 , wherein the fluorescence spectrum of the measurement sample as measured by the spectrometer is in a range between 355 nm and 375 nm.