APPARATUS AND METHOD FOR PRESSURE FLUCTUATION INSENSITIVE MASS FLOW CONTROL
First Claim
1. A system comprising a plurality of flow paths, each between a gas inlet and an outlet, the system further comprising:
- a mass flow controller for each of the flow paths, each mass flow controller including a mass flow sensor for sensing the mass flow along the respective flow path and a control valve, responsive to a control signal, for controlling the mass flow through the corresponding outlet;
a pressure sensor for each of the flow paths for measuring fluctuations in pressure of gas along the respective flow path; and
at least one process controller for generating each control signal as a function of the sensed mass flow and measured fluctuations in pressure of gas so as to provide a substantially constant flow of gas at each of the outlets irrespective of fluctuations in pressure of gas at the respective inlet.
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Abstract
A mass flow controller includes a thermal mass flow sensor in combination with a pressure sensor to provide a mass flow controller that is relatively insensitive to fluctuations in input pressure. The pressure sensor and thermal sensor respectively provide signals to an electronic controller indicating the measured inlet flow rate and the pressure within the dead volume. The electronic controller employs the measured pressure to compensate the measured inlet flow rate and to thereby produce a compensated measure of the outlet flow rate, which may be used to operate a mass flow controller control valve.
59 Citations
21 Claims
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1. A system comprising a plurality of flow paths, each between a gas inlet and an outlet, the system further comprising:
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a mass flow controller for each of the flow paths, each mass flow controller including a mass flow sensor for sensing the mass flow along the respective flow path and a control valve, responsive to a control signal, for controlling the mass flow through the corresponding outlet;
a pressure sensor for each of the flow paths for measuring fluctuations in pressure of gas along the respective flow path; and
at least one process controller for generating each control signal as a function of the sensed mass flow and measured fluctuations in pressure of gas so as to provide a substantially constant flow of gas at each of the outlets irrespective of fluctuations in pressure of gas at the respective inlet. - View Dependent Claims (2, 3)
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4. A system, defining a plurality of flow paths, each between a gas inlet and an outlet, the system comprising:
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a mass flow controller for each of the flow paths, each mass flow controller including a mass flow sensor for sensing the mass flow rate along the respective flow path and a control valve, responsive to a control signal, for controlling the mass flow through the corresponding outlet;
a pressure sensor for each flow path for measuring fluctuations in pressure of gas along the corresponding flow path; and
at least one process controller for generating each control signal as a function of the sensed mass flow rate at the respective inlet and the measured fluctuations in pressure of gas so as to compensate the flow rate measured by the sensor at the corresponding inlet to more closely approximate the flow rate at the outlet. - View Dependent Claims (5, 6)
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7. A control system for controlling the flow of gas in each of a plurality of flow paths, the control system comprising:
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a mass flow controller for each of the flow paths constructed and arranged so as to receive fluid flowing from a inlet supply line, each mass flow controller including a thermal mass flow sensor and an outlet valve;
a pressure sensor for each of the flow paths; and
at least one process controller including at least one pressure sensor interface for coupling the controller to a respective pressure sensor, wherein the controller employs data obtained at the pressure sensor interface to compensate for fluctuations induced in the thermal mass flow sensor by pressure transients in the inlet supply line. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A control system for controlling the flow through each of a plurality of flow paths, the system comprising:
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a mass flow controller for each of the flow paths including (A) an inlet for receiving fluid from an inlet supply line, (B) a thermal mass flow sensor constructed and arranged so as to sense mass flow of fluid at the inlet, and (C) an outlet valve; and
a pressure sensor for each flow path constructed and arranged so as to sense the pressure of the fluid; and
at least one system controller including (i) a pressure sensor interface arranged so as to couple the system controller to a corresponding pressure sensor, and (ii) a mass flow interface arranged so as to couple the system controller to a corresponding thermal mass flow sensor;
wherein the system controller employs readings from the pressure sensor interface to compensate flow measurements obtained at the mass flow interface from the thermal mass flow sensor as the mass flow sensor senses mass flow of fluid at the corresponding inlet of the mass flow controller. - View Dependent Claims (14, 15, 16, 17, 18)
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19. An electronic controller designed and arranged for controlling the mass flow Qi of a gas through a plurality of mass flow controllers each of the type including an inlet, an inlet flow sensor and bypass system, a control valve and an outlet, wherein a dead space is defined between each inlet flow sensor and bypass system and the control valve, and each inlet flow sensor and bypass system define an effective flow path inner diameter, the mass flow being controlled by the electronic controller in accordance with the following relationship:
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and Qi=(1+α
)Qc wherein;
dc=inside diameter of the capillary tube (m);
Lc=length of the capillary tube (m);
μ
=the gas viscosity (Poise);
Pi=the pressure at the inlet of the mass flow controller (Pa);
PR=the pressure at the outlet of the mass flow controller (Pa);
P=the pressure in the dead volume of the mass flow controller (Pa); and
α
=the bypass ratio (dimensionless) defined as the ratio of flow through the bypass divided by the flow through the capillary tube.
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20. An electronic controller for use with a plurality of mass flow controllers each of the type having an inlet, an outlet, a wall and a dead volume, the electronic controller being designed and arranged so as to control the mass flow Qo of a fluid at the outlet of each mass flow controller in response to dead volume pressure transients
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P ⅆ t of the fluid within the dead volume of the mass flow controller in accordance with the following relationship;
wherein;
PR=pressure at standard temperature and pressure (760 Torr);
TR=temperature at standard temperature and pressure (273°
K);
TW=wall temperature (temperature of the wall of the mass flow controller in °
K);
V=volume of the dead volume (cm3);
Qi=inlet flow to the mass flow controller (sccm); and
Q0=outlet flow from the mass flow controller (sccm).
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21. An electronic controller for use with a plurality of mass flow controllers each of the type having an inlet, an outlet and a dead volume, the electronic controller being designed and arranged so as to compensate the mass flow rate Qo at the outlet of a mass flow controller in response to dead volume pressure transients
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P ⅆ t of a fluid within the dead volume of the mass flow controller in accordance with the following relationship;
Qo=Qi−
C1(V/T)(dP/dt)wherein;
Qo=the compensated sensed inlet flow rate (sccm);
Qi=the sensed inlet flow rate (sccm);
C1=a normalizing constant relating the temperature (°
K) and pressure (torr) of the fluid to standard temperature (°
K) and pressure (torr);
V=the dead volume (cm3), T=the temperature (°
K) of the fluid within the dead volume, anddP/dt=time rate of change of pressure within the dead volume (torr/min).
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Specification