System and method for a digital mass flow controller
AssigneeMykrolis Corporation
InventorEmmanuel Vyers
Life of this patent
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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.
Claims47
A method for controlling a gas flow within a digital mass flow controller having a valve that governs the flow rate of gas in said digital mass flow controller and a flow sensor that measures an actual gas flow rate through said digital mass flow controller and outputs a sensed flow rate signal, said method comprising:
- generating a digitally enhanced flow rate signal representing a final steady-state flow rate in said digital mass flow controller based on a summation of a weighted first derivative of said sensed flow rate signal, a filtered weighted second derivative of said sensed flow rate signal, and said sensed flow rate signal;
- comparing a set-point signal with said digitally enhanced flow rate signal to generate a digital feedback error signal;
- and
- generating a digital control signal that controls said valve in said digital mass flow controller by inputting said digital feedback error signal into a proportional integral (PI) controller and outputting from said PI controller said digital control signal.
A method for generating a digitally enhanced flow rate signal that represents a final steady-state flow rate from a sensed flow rate signal provided by a flow sensor in a digital mass flow controller, said method comprising:
- calculating a first derivative of said sensed flow rate signal;
- calculating a second derivative of sensed flow rate signal;
- weighting said first derivative with a first weight to generate a weighted first derivative signal;
- weighting said second derivative with a second weight to generate a weighted second derivative;
- implementing a digital lowpass filter operation on said weighted second derivative to generate a filtered weighted second derivative;
- and
- summing said sensed flow rate signal with said weighted first derivative signal and said filtered weighted second derivative signal to generate said digitally enhanced flow rate signal.
A digital mass flow controller for controlling the flow of gas in a process, said digital mass flow controller comprising:
- a flow sensor that measures an actual gas flow rate through said digital mass flow controller and outputs a sensed flow rate signal;
- a digital microcontroller which generates a digital control signal using said sensed flow rate signal, a first derivative of said sensed flow rate signal, a filtered second derivative of said sensed flow rate signal, and a set-point signal;
- and
- a valve in said digital mass flow controller which is controlled by said digital control signal
- wherein said microcontroller is executable to calculate said first derivative of said sensed flow rate signal,
- calculate a second derivative of said sensed flow rate signal,
- weight said first derivative with a first weight to generate a weighted first derivative,
- weight said second derivative with a second weight to generate a weighted second derivative,
- implement a digital lowpass filter operation on said weighted second derivative to generate a filtered weighted second derivative, and
- sum said sensed flow rate signal with said weighted first derivative signal and said weighted second derivative signal to generate a digitally enhanced flow rate signal.
A system for generating a digitally enhanced flow rate signal from a sensed flow rate signal provided by a flow sensor in a mass flow controller, said system having a computer program stored on a digital signal processor controller, said digital signal processor controller executable to:
- calculate a first derivative of said sensed flow rate signal;
- calculate a second derivative of sensed flow rate signal;
- weight said first derivative with a first weight to generate a weighted first derivative signal;
- weight said second derivative with a second weight to generate a weighted second derivative;
- implement a digital lowpass filter operation on said weighted second derivative to generate a filtered weighted second derivative;
- and
- sum said sensed flow rate signal with said weighted first derivative signal and said filtered weighted second derivative signal to generate said digitally enhanced flow rate signal.
Dependencies are inferred from the claim text.