An on-line precision solution refractive index monitor.

The chemical composition of a binary solution can be characterized by the refractive index of the solution. An on-line monitor suitable for process control applications has been developed. A dual wavelength technique giving intrinsic stability has been used as the basis of the design. The probe contacting the solution is a glass prism. Fiber optic bundles are used to reflect light from the prism-solution interface and to divide the reflected beam into two wavelengths by using interference filters. For a given application, the composition of the glass prism, the angle of incidence, and the wavelengths of light are theoretically optimized to give a signal which varies approximately linearly with solution composition.