Digital silver ion concentration controller for the precipitation of silver halide emulsions

Claim 1

Apparatus for controlling the concentration of silver ions during the precipitation of a silver halide in a precipitation vessel comprising: a first means for controllably introducing a silver salt into said precipitation vessel; a second means for controllably introducing a halide salt into said precipitation vessel; an ion sensor positioned in said precipitation vessel for generating a voltage representative of the amount of silver ion in solution therein; a temperature sensor positioned in said precipitation vessel for generating a voltage representative of the temperature of the silver ion solution therein; means for converting the ion sensor voltage and the temperature sensor voltage to digital values; computer means for receiving the digital values of the ion sensor and the temperature sensor for converting the digital value of the ion sensor to a digitized concentration value by computing the equation: wherein: R is a gas constant T is the absolute temperature of the solution in degrees Kelvin F is the Faraday constant and by transforming the digitized concentration value to an equivalent constant coefficient differential equation: dY/dt+aY=bD+bU where: Y=[Ag+] 1/n and where: n=2 D is the disturbance of the system U is the control effort b is a constant, and a is a constant; means for comparing the transformed digitized concentrated value against a digitized set point value to provide a difference signal; and means for controlling said first and said second means as a function of said difference signal so as to drive said difference signal towards a zero value.