Detector of low levels of gas pressure and flow

• US 20080053196A1
• Filed: 08/31/2007
• Published: 03/06/2008
• Est. Priority Date: 09/01/2006
• Status: Active Grant

• Current Assignee: Clean Alert Innovations LLC (Jeffrey M. Gross)
• Original Assignee: Jacob Fraden
• Inventors: Fraden, Jacob
• Granted Patent: US 7,490,512 B2
• Time in Patent Office: Days
• US Class Current: 73/31.04
• CPC Class Codes: G01F 1/46 Pitot tubes
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/699 by control of a separate heating or cooling element
• CPC Class Codes: G01L 11/002 by thermal means, e.g. hypsometer

Abstract

A detector for monitoring the low levels of differential pressures and the rate of mass flow rate of gas (air, e.g.) in a duct. The sensor'"'"'s temperature is maintained at a constant gradient above temperature of the flowing gas, typically 4-7° C. higher. The detector consists of two thermally decoupled sensors—one is the air temperature sensor and the other is a temperature sensor coupled to a heater. The sensors are connected to an electronic servo circuit that controls electric power supplied to the heater. The sensors are positioned outside of the air duct and coupled to the duct via a relatively thin sensing tube protruding inside the duct. The end of the tube has an opening facing downstream of the gas flow, thus being exposed to a static gas pressure. The detector can be employed in fuel burners of the HVAC systems, internal combustion engines, medical equipment to control flow of anesthetic gases, in the security systems to monitor minute changes in air pressure resulted from opening and closing of doors and windows in a protected facility.

Claims

1. A pressure sensor for measuring static and dynamic pressures in a flow of gas, comprising

a sensing tube having proximal end and a distal end, wherein an opening is formed in the proximal end and positioned in the flow of gas, while the distal end is positioned outside of the flow of gas;

an air flow sensor positioned inside the sensing tube;

a signal processing circuit attached to said air flow sensor.

2. A pressure sensor of claim 1 where said air flow sensor is a thermo-anemometer.

3. A pressure sensor of claim 2 where said thermo-anemometer sensor comprises a heater and two thermocouple junctions, wherein the first junction is thermally coupled to the heater and the second junction is thermal insulated from the heater, while both junctions are being exposed to flow of gas.

4. A pressure sensor of claim 1 where said distal end of the sensing tube has an opening exposed to a reference gas pressure.

5. A gas flow sensor comprising a first heater and a heated temperature sensor to monitor temperature of the first heater being above the gas temperature and a reference temperature sensor for measuring temperature of gas, comprising

a second heater being positioned between the heated temperature sensor and the reference temperature sensor.

a feedback circuit for providing electric power to first heater in proportion to temperature difference between the heated temperature sensor and reference temperature sensor.

6. Method of monitoring of gas flow in a duct by a gas flow sensor and a sensing tube, having a proximal end and a distal end, including the steps of

forming openings in the distal end and proximal end of said sensing tube;

inserting a proximal end of a sensing tube into the duct;

positioning a flow sensor inside the sensing tube;

exposing a distal end of a sensing tube to a reference pressure;

monitoring the output signal of said flow sensor;

relating the output signal to the gas flow in the duct.