Fluid property and flow sensing via a common frequency generator and FFT

• US 6,169,965 B1
• Filed: 12/31/1997
• Issued: 01/02/2001
• Est. Priority Date: 12/31/1997
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Bonne, Ulrich, Kubisiak, David
• Primary Examiner(s): SHAH, KAMINI S
• Application Number:
  US09/001,453
• Time in Patent Office: 1,098 Days
• Field of Search: 702/136, 702/127, 702/137, 702/50, 374/43, 374/40, 374/44, 374/137, 732/041.8, 73/617.6, 73/544.2, 431/121, 431/2, 431/9
• US Class Current: 702/136
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/698 Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
• CPC Class Codes: G01F 1/7084 using thermal detecting arrangements
• CPC Class Codes: G01F 1/712 using auto-correlation or cross-correlation detection means
• CPC Class Codes: G01F 5/00 Measuring a proportion of the volume flow
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18
• CPC Class Codes: G01N 27/18 caused by changes in the thermal conductivity of a surrounding material to be tested G01N27/20 takes precedence
• CPC Class Codes: G01N 27/185 using a catharometer

Abstract

A method and apparatus for using a common frequency generator for measuring selected properties of a fluid of interest via one or more heater and/or sensor elements. The common frequency generator may sequentially and/or simultaneously provide input signals to selected heater and/or sensor elements. Application of more than one frequency component by the common frequency generator enables the determination of one or more time and/or phase lags more efficiently, especially when using an FFT analysis technique. From the time and/or phase lags, the selected fluid properties including fluid flow speed can be determined.

Claims

1. Apparatus for determining a selected property of a fluid of interest, comprising:

heater means in thermal communication with the fluid of interest, said heater means having a resistance that changes with temperature;

energizing means connected to said heater means for energizing said heater means, said energizing means providing a periodic time-varying input signal to said heater means to induce a transient elevated temperature condition in said heater means;

output means for providing an output signal that is related to the resistance of said heater means;

FFT means for determining a phase lag between the input signal and the output signal during the transient elevated temperature condition using an FFT analysis; and

determining means for determining the selected property of the fluid of interest using the phase lag.

2. Apparatus according to claim 1 wherein the FFT analysis includes a cross-correlation analysis for cross-correlating the input signal and the output signal during the transient elevated temperature condition to determine the phase lag therebetween.

3. Apparatus according to claim 1 wherein said periodic time-varying input signal comprises two or more frequency components, and said FFT means determines a phase lag for each of the two or more frequency components.

4. Apparatus according to claim 1 wherein said selected property is selected from the group consisting of temperature, pressure and thermal conductivity.

5. A method for determining a selected property of a fluid of interest using a heater element, wherein the heater element has a resistance that changes with temperature and is in thermal communication with the fluid of interest, the method comprising the steps of:

providing a time-varying input signal to the heater element, the input signal causing a temperature change, and a corresponding resistance change, in the heater element;

sensing the resistance change of the heater element;

determining a phase lag between the input signal and the sensed resistance change of the heater element using an FFT analysis; and

determining the selected property of the fluid of interest using the phase lag.

6. A method according to claim 5 wherein said periodic time-varying input signal comprises two or more frequency components, and a phase lag is determined for each of the two or more frequency components.

7. A method according to claim 5 wherein said selected property is selected from the group consisting of temperature, pressure and thermal conductivity.