Patent ID: 7961327

Claim:
A method to sense pH of a fluid, said method comprising the steps of: supplying an optical source through an input fiber; passing said optical source at a range of predetermined input angles to a sensor head having a transparent window in contact with a fluid, wherein said window has a high refractive index, and wherein a side of said window in contact with said fluid is coated with a thin protein layer to prevent fouling of said window due to accumulation of fat, oil and/or grease within said fluid on said window; forming a reflective boundary between said fluid and said side of said window in contact with said fluid, collecting optical power reflected from said reflective boundary between said window and said fluid by a plurality of output fibers in said sensor head, wherein said output fibers are positioned with respect to said input fiber so as to collect optical power reflected from said reflective boundary at predetermined output angles; and detecting a fouling of said sensor head based on reflected optical power collected by said output fibers; if no fouling of said sensor head is detected, converting said reflected optical power collected by said output fibers to pH of said fluid.