Method of producing a silver halide photographic emulsion, apparatus for the same, method of measuring a silver or halogen ion concentration and an apparatus for the same

A method of producing a silver halide photographic emulsion in which a silver ion concentration in precipitation of a silver halide emulsion in a precipitation bath is controlled by a flow rate controller, wherein a precipitation bath in which stirring is conducted rapidly and uniformly and crystal formation and crystal growth are uniformly performed is used, said method comprising the steps of:

• starting delivery of a silver nitrate solution and a halogen salt solution while holding the flow rates of the silver nitrate solution and halogen salt solution constant so as to maintain a constant-ratio flow rate of the silver nitrate and halogen salt solutions independently of flow rate measurements and calculations performed by the flow rate controller;
• designating in the flow rate controller a target E.sub.Ag value which corresponds to a pAg value for the desired silver ion concentration;
• when an E.sub.Ag value of the precipitation bath measured by the flow rate controller reaches a range about the target E.sub.Ag value, starting a control of the flow rate of the halogen salt solution to provide controlled variable flow rate by using the flow rate controller which has an operation period equal to or shorter than 1 sec. and has a proportional, integral and differential (PID) action controller using a tuning parameter preset to a minimum response level;
• and
• deriving an optimum control tuning parameter, which corresponds to the preset target E.sub.Ag value and a solubility rate of silver/halogen ions to be added, using a theoretical model, and replacing the minimum response level with the optimum control tuning parameter.