Wide range gas flow system with real time flow measurement and correction

• US 6,216,726 B1
• Filed: 08/17/2000
• Issued: 04/17/2001
• Est. Priority Date: 05/26/1999
• Status: Expired due to Term

• Current Assignee: Pivotal Systems Corporation
• Original Assignee: Cyber Instruments Technology LLC
• Inventors: Brown, Timothy R., Judd, Daniel R.
• Primary Examiner(s): Michalsky, Gerald A.
• Application Number:
  US09/641,882
• Time in Patent Office: 243 Days
• Field of Search: 137/486, 137/487.5
• US Class Current: 137/486
• CPC Class Codes: G01F 1/50 Correcting or compensating means
• CPC Class Codes: G01F 1/88 with differential-pressure measurement to determine the volume flow
• CPC Class Codes: G01F 15/046 involving digital counting
• CPC Class Codes: G05D 7/0658 the plurality of throttling means being arranged for the control of a single flow from a plurality of converging flows G05D7/0652 takes precedence; ratio control G05D11/13
• CPC Class Codes: Y10T 137/0396 Involving pressure control
• CPC Class Codes: Y10T 137/7759 Responsive to change in rate of fluid flow
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve

Abstract

A gas delivery system accurately measures and optionally regulates mass flow rate in real time. A fluid conduit connects an inlet valve, calibration volume, flow restrictor, and outlet valve in series. Pressure and temperature sensors are coupled to the calibration volume. One or more pressure sensors may be attached across the flow restrictor. Alternatively, an absolute pressure sensor may be attached upstream of the flow restrictor. One embodiment of differential pressure sensors comprises a floating reference differential pressure sensor, including a first transducer attached to the fluid conduit upstream of the flow restrictor and a second transducer attached to the conduit downstream of the flow restrictor. In this embodiment, each transducer receives a reference pressure from a reference source, and optionally, after the calibration volume is charged, the floating reference differential pressure transducers are calibrated. When gas flow is initiated, differential and/or absolute pressure measurements are repeatedly taken, and a measured mass flow rate calculated thereon. Gas flow is adjusted until the measured mass flow rate reaches a target mass flow. Using the temperature/pressure sensors at the calibration volume, repeated calculations of actual flow rate are made to uncover any discrepancy between actual and measured mass flow rates. Whenever a discrepancy is found, the manner of calculating measured mass flow is conditioned to account for the discrepancy; thus, the measured mass flow rate more accurately represents the actual mass flow rate thereby providing an actual mass flow rate more accurately achieving the target mass flow rate.

Claims

1. A gas delivery system, comprising:

a first conduit having an upstream end and a downstream end;

a calibration volume positioned in series with the first conduit;

a first pressure sensor coupled to at least one of the calibration volume and the first conduit in a suitable location to measure pressure of gas in the calibration volume;

a flow restrictor positioned in series with the first conduit downstream of the calibration volume;

a reference conduit separate from the first conduit; and

a floating reference differential pressure sensor including a first transducer attached to the first conduit upstream of the flow restrictor and a second transducer attached to the first conduit downstream of the flow restrictor, each transducer measuring pressure relative to pressure in the reference conduit.

2. The system of claim 1, each transducer comprising a housing containing a diaphragm with sensing equipment to provide a pressure output in accordance with position of the diaphragm.

3. The system of claim 2, each transducer comprising a capacitance manometer.

4. The system of claim 2, the system including:

one or more additional conduits, each additional conduit including a respective calibration volume, absolute pressure sensor, temperature sensor, flow restrictor and differential pressure sensor; and

an output valve selectively coupling one of the conduits to a process chamber.

5. The system of claim 2, further comprising:

one or more additional conduits, each with a respective flow restrictor and differential pressure sensor; and

a multi-port valve with each conduit being coupled to a different port to connect a selected one of the conduits at a time to the calibration volume.

6. The system of claim 2, further comprising:

one or more gas inlets; and

a multi-port valve coupled to each gas inlet and the calibration volume to select between different process gasses entering the calibration volume.

7. The system of claim 2, further comprising multiple valves positioned in series with the first conduit to direct and regulate gas flow through the first conduit, each of the valves comprising one of the following:

a variable adjustment flow control valve, or a multi-way valve.

8. The system of claim 2, further including a temperature sensor coupled to at least one of the calibration volume and the first conduit in a suitable location to measure temperature of gas in the calibration volume.

9. A gas delivery mass flow control system, comprising:

a conduit having an upstream end and a downstream end;

a calibration volume positioned in series with the conduit;

means for measuring pressure of gas in the calibration volume;

means for restricting gas flow in the conduit downstream of the calibration volume;

a reference conduit and means for selectively adjusting pressure in the reference conduit; and

means for differentially measuring pressure across the means for restricting gas flow, said measurement of pressure being relative to pressure in the reference conduit.