Thermal flowmeter with fluid descriminant function

• US 6,681,624 B2
• Filed: 10/15/2002
• Issued: 01/27/2004
• Est. Priority Date: 12/15/1999
• Status: Expired due to Fees

• Current Assignee: Mitsui Mining and Smelting Company Limited
• Original Assignee: Mitsui Mining and Smelting Company Limited
• Inventors: Yamagishi, Kiyoshi, Furuki, Shinya
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): Thompson, Jewel V.
• Application Number:
  US10/149,867
• Publication Number:
  US 20030056585A1
• Time in Patent Office: 469 Days
• Field of Search: 732/04, 732/041.3, 732/041.7, 732/042.3
• US Class Current: 73/204.13
• CPC Class Codes: G01F 1/696 Circuits therefor, e.g. constant-current flow meters
• CPC Class Codes: G01F 1/6986 with pulsed heating, e.g. dynamic methods
• CPC Class Codes: G01F 1/699 by control of a separate heating or cooling element
• CPC Class Codes: G01N 27/18 caused by changes in the thermal conductivity of a surrounding material to be tested G01N27/20 takes precedence

Abstract

A thermal flowmeter is provided with a flow rate detecting unit (4) containing a heating element, a flow rate detecting temperature sensing element and a flow rate detecting electroconductive fin plate (44) extending into a fluid flow passage (3), which are disposed so as to enable heat transfer therebetween, the flow rate detecting temperature sensing element varying in electrical characteristic value in accordance with the flow of the fluid in the fluid flow passage (3); and, a fluid temperature detecting unit (6) containing a fluid temperature detecting temperature sensing element and a fluid temperature detecting electroconductive fin plate (44′) extending into the fluid flow passage (3), which are disposed so as to enable heat transfer therebetween, the fluid temperature detecting temperature sensing element varying in electrical characteristic value in accordance with the temperature of the fluid. The flow rate of the fluid is detected on the basis of the electrical characteristic values of the flow rate detecting and fluid temperature detecting temperature sensing elements, and a fluid discrimination is effected by determining a conductivity between the flow rate detecting and fluid temperature detecting fin plates (44, 44′). According to this thermal flowmeter, with simple constitution, discrimination of whether the fluid is the required one or not is effected so that passage of erroneous fluid can be avoided.

Claims

1. A thermal flowmeter, comprising:

a flow rate detecting unit comprising a heating element, a flow rate detecting temperature sensing element and a flow rate detecting electroconductive heat transfer member extending into a fluid flow passage, which are disposed so as to enable heat transfer therebetween, said flow rate detecting temperature sensing element varying in electrical characteristic value in accordance with the flow of the fluid in the fluid flow passage through heat exchange with the fluid in the fluid flow passage which is carried out through the flow rate detecting electroconductive heat transfer member; and

a fluid temperature detecting unit comprising a fluid temperature detecting temperature sensing element and a fluid temperature detecting electroconductive heat transfer member extending into said fluid flow passage, which are disposed so as to enable heat transfer therebetween, said fluid temperature detecting temperature sensing element varying in electrical characteristic value in accordance with the temperature of the fluid through the heat exchange with the fluid in the fluid flow passage,

wherein the flow rate of the fluid is detected on the basis of the electrical characteristic value of the flow rate detecting temperature sensing element and the electrical characteristic value of the fluid temperature detecting temperature sensing element, and wherein said thermal flowmeter is adapted to determine a conductivity of the fluid between the flow rate detecting electroconductive heat transfer member and the fluid temperature detecting electroconductive heat transfer member to thereby effect a fluid discrimination.

2. The thermal flowmeter as claimed in claim 1, wherein the fluid discrimination is effected by judging the fluid as a required one in case that when a detected value of current flowing between the flow rate detecting electroconductive heat transfer member and the fluid temperature detecting electroconductive heat transfer member therethrough falls within a predetermined range for the required fluid, while judging the fluid as not the required one in case that the detected value of current falls without the predetermined range for the required fluid.

3. The thermal flowmeter as claimed in claim 1, wherein the flow rate of the fluid is detected on the basis of an output of a detection circuit containing said flow rate detecting temperature sensing element and said fluid temperature detecting temperature sensing element and a calibration curve.

4. The thermal flowmeter as claimed in claim 1, wherein a portion of said flow rate detecting electroconductive heat transfer member comprises a first electrode terminal for a circuit for determining the conductivity, and a portion of said fluid temperature detecting electroconductive heat transfer member comprises a second electrode terminal for said circuit for determining the conductivity.

5. The thermal flowmeter as claimed in claim 4, wherein said flow rate detecting unit further comprises a first housing comprising said heating element and said flow rate detecting temperature sensing element, wherein said first electrode terminal extends from said first housing;

and

wherein said fluid temperature detecting unit comprises a second housing comprising said fluid temperature detecting temperature sensing element, wherein said second electrode terminal extends from said second housing.

6. The thermal flowmeter as claimed in claim 1, further comprising a circuit for determining the conductivity comprising a power circuit for applying a voltage between said flow rate detecting electroconductive heat transfer member and said fluid temperature detecting electroconductive heat transfer member, and a detector for detecting a resistance value of the fluid between said flow rate detecting electroconductive heat transfer member and said fluid temperature detecting electroconductive heat transfer member.

7. The thermal flowmeter as claim in claim 6, wherein said detector comprises a resistor having ends through which the voltage is applied between said flow rate detecting electroconductive heat transfer member and said fluid temperature detecting electroconductive heat transfers member, and a voltmeter for detecting a voltage value between the ends of said resistor.