Model based on Bernoullis equation and coefficient of discharge as a function of the Reynolds number was applied at different levels in different fluid system in Industrial operation of orifice plate. The model was based on the principle of constant area, variable pressure drop. The experimental results obtained from the research work were used in monitoring and predicting the usefulness of pneumatic proportional integral (reset) control on flow characteristics of different fluid flowing through an orifice plate. Mathematical models were developed for both compressible and non compressible fluid in terms of flow rate as well related to the pneumatic proportional integral (Reset) control. The proportional and integral gain is one of the functional parameters that control and determine the effectiveness of the industrial operation of the system by reducing the error value for laminar and turbulent flow experienced by the orifice plate.