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

• US 4,933,870 A
• Filed: 07/14/1988
• Issued: 06/12/1990
• Est. Priority Date: 07/14/1988
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Chang, Yun C.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): Ramirez, Ellis B.
• Application Number:
  US07/218,772
• Time in Patent Office: 698 Days
• Field of Search: 364/497, 364/500, 364/857, 364/861, 204/1 T, 204/1 R, 204/400, 204/405, 204/406, 422/68, 422/82, 430/400, 430/30, 324/446, 324/432
• US Class Current: 700/268
• CPC Class Codes: G05D 21/02 characterised by the use of electric means

Abstract

Apparatus for controlling the concentration of silver ions during the precipitating of a silver halide emulsion in a precipitation vessel. The introduction of a silver salt and a halide salt is controlled in accordance with a preselected program, which in turn is responsive to the silver ion concentration measured in the vessel by a silver ion sensor. Linerization of the output signal from the sensor is accomplished by converting the sensor'"'"'s output voltage into a concentration voltage through the use of a Nernst equation and by transforming the concentration voltage into a variable value denoted Y representing a constant coefficient differential equation that is linear. The linear equation is then used to control the addition of the silver salt and the halide salt to the precipitation vessel.

Claims

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;

space="preserve" listing-type="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.

2. Method for controlling the concentration of silver ions during the precipitation of a silver halide in a precipitation vessel comprising the steps of:

(a) measuring the amount of silver ion in the precipitation vessel with an ion sensor to provide a measured value;

(b) converting the measured value to a concentration value;

(c) transforming the concentration value to an equivalent constant coefficient differential equation; and

(d) controlling the amount of silver ions added to the precipitation vessel as a function of the constant coefficient differential equation.

3. The method according to claim 2 and further comprising the step of:

determining the temperature of the solution in the precipitation vessel; and

in step (b) converting the measured value to a concentration value following the equation;

wherein;

R is a gas constant

T is the absolute temperature of the solution

in degrees Kelvin

F is the Faraday constant.

4. The method according to claim 2 wherein step (c) transforms the concentration value V_Ag by employing:

space="preserve" listing-type="equation">Y=[Ag+].sup.1/n

wherein n is given a value of 2.