Thermal flowmeter with fluid descriminant function

#The present invention relates to a fluid flow rate detecting technique, and particularly to a thermal flowmeter having a fluid discriminate function.

#Various types have been known for a flowmeter [flow rate sensor] (or current meter [flow velocity sensor]) for measuring or detecting the flow rate (or flow velocity) of various kinds of fluid, particularly liquid. Of these types of flowmeters, a so-called thermal type (particularly, indirectly heated type) flowmeter has been used because the price thereof is lower.

#One of indirectly heated type flowmeters is designed and used so that a sensor chip comprising a thin-film heating element and a thin-film temperature sensing element which are laminated on a substrate through an insulating layer by using the thin film technique is disposed so as to enable the heat transfer between the sensor chip and fluid flowing in a pipe. The electrical characteristic of the temperature sensing element, for example, the value of the electrical resistance is varied by supplying current to the heating element to heat the temperature sensing element. The variation of the electrical resistance value (based on increase of the temperature of the temperature sensing element) is varied in accordance with the flow rate (flow velocity) of the fluid flowing in the pipe. This is because a part of the heating value of the heating element is transferred into the fluid, the heating value thus diffused into the fluid is varied in accordance with the flow rate (flow velocity), and the heating value supplied to the temperature sensing element is varied in accordance with the variation of the heating value diffused into the fluid, so that the electrical resistance value of the temperature sensing element is varied. The variation of the electrical resistance value of the temperature sensing element is also varied in accordance with the temperature of the fluid. Therefore, a temperature sensing element for temperature compensation is installed in an electrical circuit for measuring or detecting the variation of the electrical resistance value of the temperature sensing element to reduce the variation of the flow rate measurement value due to the temperature of the fluid as much as possible.

#FIG. 1 is a schematic, partial cross-sectional view showing an embodiment of a flowmeter according to the present invention;

#FIG. 2 is a cross-sectional view of a flow rate detecting unit;

#FIG. 3 is a cross-sectional view of a flow rate detecting unit;

#Preferred embodiments according to the present invention will be described hereunder with reference to the accompanying drawings.

#FIG. 1 is a schematic, partial cross-sectional view showing an embodiment of a flowmeter according to the present invention. As shown in FIG. 1, a fluid flow passage 3 is formed in a casing member 2. The casing member 2 is made of synthetic resin such as epoxy resin or polyphenylene sulfide resin or of metal. In case of metal casing member, it is preferable to form an insulating film on the inner surface thereof which determines the fluid flow passage 3. A flow rate detecting unit 4 and a fluid temperature detecting unit 6 are attached to the casing member 2 so as to confront the fluid flow passage 3.

#Fluid flows in the direction of arrow in the fluid flow passage 3. That is, the casing member 2 has a fluid flow-in port (not shown) formed at a left-side end in FIG. 1 so as to communicate to the fluid flow passage 3, and a fluid source side pipe line is connected to the fluid flow in port. The casing member 2 also has a fluid flow-out port (not shown) formed at a right-side end in FIG. 1 so as to communicate to the fluid flow passage 3, and a fluid demand side pipe line is connected to the fluid flow-out port.