Real Time Gas Flow Measurement System
Keywords: Sensors, Measurement, Distance measurement
Real Time Gas Flow Measurement System
Applicant: Cyber Instrument Technologies LLC, USAPatent number:US6,216,726Publication date: 17 April 2001Title: Wide Range Gas Flow System with Real Time Flow Measurement and Correction
A gas delivery system which accurately measures and optionally regulates mass flow rate in real time is described. The invention concerns an improved gas flow system that accurately measures gas flow during the delivery of gas to a processing chamber. Added operations may be performed to regulate gas flow in accordance with these measurements.
The system comprises a fluid conduit which connects an inlet valve,calibration volume, flow restrictor, and outlet valve in series. Pressure and temperature sensors are coupled to the calibration volume and one or more pressure sensors may be attached across the flow restrictor. Mass flow sensors are also located downstream of the calibration volume.
In one example, the downstream mass flow sensors include a floating reference differential pressure sensor that includes two pressure transducers. A first transducer is attached to the conduit upstream of the flow restrictor, and a second transducer is 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 can be calculated. The gas flow can then be adjusted until the measured mass flow rate reaches a target mass flow. Using the temperature and 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. The manner of calculating measured mass flow can be conditioned to account for any discrepancy and therefore provides an actual mass flow rate that is more accurate than would otherwise be achieved.
