System and method for digital mass flow controller

Abstract

A method for controlling the gas flow within a digital mass flow controller. The method calculates a digitally enhanced flow rate signal that more accurately represents an actual flow rate through the digital mass flow controller. The digitally enhanced flow rate is calculated using a sensed flow rate signal output from a flow sensor, a scaled first derivative of the sensed flow rate signal, and a scaled, filtered second derivative of the sensed flow rate signal. A set-point signal is compared to the digitally enhanced flow rate signal to generate a digital error signal. The digital error signal is provided to a digitally realized PI (proportional integral) controller. The PI controller generates a digital control signal which is used to control a valve in the digital mass flow controller.

Description

technical field [0001] The present invention generally relates to a method and system for controlling gas flow in a mass flow controller, and more particularly to a method and system for generating a digital signal with fast response to set point step input in a digital mass flow controller. Background technique [0002] A mass flow controller (MFC) is a closed loop device used to set, measure and control the mass flow of a process gas. Semiconductor applications have been and continue to be the driving force behind the development of mass flow controller technology. Furthermore, mass flow control is also useful in other industries such as the pharmaceutical industry and the food industry. [0003] The thermal mass flow controller consists of the first half including the flow detector and the second half including the control valve. Flow detectors typically consist of two resistance temperature detectors wrapped around a capillary. As the gas flows through the detector, h...

AI Technical Summary

Problems solved by technology

The first disadvantage is that flow detectors are generally not linear

Therefore, there is a certain amount of inherent error in the flow detector signal input to the control system

[0013] The second disadvantage is that the differentiator is generally an analog device

[0014] The final first order differential feedback control system does not recognize that the flow of gas through the flow controller is indeed not a true first order exponential

Therefore, such systems have some inherent error

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