Thermal flowmeter with fluid descriminant function

• US 20030056585A1
• Filed: 10/15/2002
• Published: 03/27/2003
• Est. Priority Date: 12/15/1999
• Status: Active Grant

• Current Assignee: Mitsui Mining and Smelting Company Limited
• Original Assignee: Mitsui Mining and Smelting Company Limited
• Inventors: Furuki, Shinya, Yamagishi, Kiyoshi
• Granted Patent: US 6,681,624 B2
• Time in Patent Office: Days
• US Class Current: 73/204.19
• 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 containing 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 the 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 containing 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 a fluid discrimination is effected by determining a conductivity between the flow rate detecting electroconductive heat transfer member and the fluid temperature detecting electroconductive heat transfer member.

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 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 constitutes an electrode terminal of the flow rate detecting unit, and a portion of said fluid temperature detecting electroconductive heat transfer member constitutes an electrode terminal of the fluid temperature detecting unit.