System and method for variable gain proportional-integral (pi) controller

Abstract

A method for generating a valve drive signal using a variable gain PI controller in a mass flow controller. The integral function includes an integral gain factor which functions as the variable gain in the PI controller. For set-point signals less than a normalized predetermined percentage of the maximum set-point, the gain factor is equal to formula (I), where a is a first gain constant and B is a second gain constant. Otherwise, the integral gain factor is formula (II), where A is the first gain constant, B is the second gain constant, and x is the normalized set-point signal.

Description

technical field [0001] The present invention relates generally to proportional-integral (PI) control systems and methods, and more particularly to proportional-integral control methods in mass flow controllers. Background technique [0002] Many manufacturing processes require tightly controlled rate of introduction of process gases into the process chamber. These types of processes can use a mass flow controller (MFC) to control the flow rate of the gas. A mass flow controller is a closed loop device that sets, measures and controls the mass flow of process gas into the process chamber. Semiconductor applications have been and continue to be the driving force behind mass flow controller technology product development. However, mass flow control is useful in other industries, such as the pharmaceutical and food industries. [0003] Thermal mass flow controllers consist of a front half containing a flow sensor and a rear half containing a control valve. Flow sensors often...

AI Technical Summary

Problems solved by technology

[0008] A persistent problem with typical mass flow controllers is that solenoid valve action is not a linear function of the valve actuation signal (control signal)

The nonlinear characteristics associated with solenoid valves are difficult to control and cannot be fully compensated for

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