JPS63293419A - Flow sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor which has excellent interchangeability and can be reduced in size and mass-produced by integrating a heating element and a fluid temp. detecting element for detecting the temp. of fluid on the same thermal insulting substrate. CONSTITUTION:A thin metallic film having a large coefft. of resistance temp. such as platinum is deposited by a vacuum deposition method, etc., on, for example, a glass substrate as the thermal insulating substrate and is then patterned by an etching technique to form bonding pads 2, the heating element 3 and the fluid temp. detecting element 4. The glass substrate 1 with the heating element 3 and the fluid temp. detecting element 4 as one set is cut to obtain individual sensor element. The resulted sensor element has the structure in which the heating element 3 and the fluid temp. detecting element 4 are disposed at both ends of the glass substrate 1. The size thereof is very small as about several millimeters and the mass production of the sensor elements having uniform characteristics is possible if a so-called batch treatment to array many pieces of the elements on a sheet of the substrate and to manufacture many elements simultaneously is adopted.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a thermal flow sensor in which a heating element and a fluid temperature sensing element are integrated on the same thermally insulating substrate.

<Background of the Invention> As a conventionally used thermal flow sensor, a side pipe for a bypass flow path is provided in the main pipe for the flow path, a heater is connected to this Kushiro pipe, and the fluid is heated when the side pipe is fully heated. There is a flow meter that uses a method of detecting the flow line from the temperature distribution force S generated in the flow direction of the side pipe due to the flow. This flowmeter has good accuracy and is widely used as a flow rate controller for semiconductor gases, but its structure makes it unsuitable for miniaturization and mass production, and its high cost limits its uses.

Another thermal flow sensor is a method in which a heating element and a fluid temperature detection element are provided in the fluid, the heating element is heated, and the flow velocity is measured by utilizing changes in the amount of heat transferred from the heating element to the surrounding fluid. There is also a 70-sensor using In this method, the temperature of the fluid is detected by a fluid temperature sensing element, and by keeping the temperature difference between the fluid and the heating element constant, the influence of the fluid temperature can be compensated for. You can get a response. Further, by setting the temperature difference to be large, it is also possible to increase the output of the flow sensor. A conventional flow sensor using this method is a flow sensor configured using a heat generation transistor and a fluid temperature detection transistor formed on a silicon chip. This 70-sensor uses silicon process technology, so it is excellent in mass production, but on the other hand, it has drawbacks such as large variations in temperature characteristics between elements and the inability to set the heat generation temperature high. . Furthermore, some of the above methods use resistance wires made of platinum, tungsten, etc. for the heating element and fluid temperature sensing element, but the resistance value is small and the variation between elements is large, making it difficult to control the heating temperature and the accuracy of temperature measurement. It has all the disadvantages such as not only poor performance but also difficulty in processing due to the use of thin wire and lack of mass productivity.

Thermal film type 70 sensor, which uses a thin heating element and fluid temperature sensing element on an insulated substrate instead of a resistance wire, can be miniaturized and can be fabricated by arranging many elements on a single substrate. It has many advantages such as excellent mass production and small variation. However, in order to measure the flow rate,
The fluid temperature must be detected by the fluid temperature sensing element, and in order to accurately detect the temperature, the fluid temperature sensing element must be thermally insulated from the heating element.

Therefore, conventional thermal flow sensors are constrained by having to have a structure in which both the heating element and the fluid temperature detection element are supported separately, and have drawbacks such as large dimensions and poor mass production. . In order to integrate both the heating element and the fluid temperature sensing element, a material with low thermal conductivity must be used to prevent the heat of the heating element from being transmitted to the fluid temperature sensing element.

<Object of the Invention> Figure 3 shows the results of determining the temperatures at all points separated by [, a-] from the heating element. However, the temperature of the heating element is 40
℃, the temperature of the fluid is 25 ℃, and the thermal conductivity of the substrate is 2.0.40.150 W/mK, respectively. From this result, it can be seen that if the thermal conductivity k of the substrate is 2.0 W/m K or less, the distance over which the substrate is not affected by the heat transmitted from the force of the heating body becomes small.

The present invention utilizes a thermally insulating substrate with low thermal conductivity to thermally insulate the heating element and the fluid temperature sensing element, and at the same time, by integrating and arranging both in the same element, compatibility is achieved. The overall purpose of this invention is to provide a flow sensor that is superior in size, can be miniaturized, and can be mass-produced.

<Example> Hereinafter, the present invention will be explained in detail according to examples.

FIG. 1 is a schematic plan view of a flow sensor showing one embodiment of the present invention. As a thermally insulating substrate, for example, a thin metal film having a large resistance temperature coefficient such as platinum is deposited on a glass substrate 1 using a vacuum evaporation method.
After depositing by a sputtering method or a plasma CVD method, it is patterned by an etching technique to form a bonding pad 2, a heating element 3, and a fluid temperature sensing element 4. The fluid temperature sensing element 1- is arranged in a thermally insulated state and separated from the heating element 3 by a necessary distance so that the temperature of the fluid can be accurately detected. Next, heating element 3
The glass substrate 1 is cut into a set of the and fluid temperature sensing elements 4 to form individual sensor elements.

The resulting mental sensor element has a structure in which a heating element 3 and a fluid temperature sensing element 4 are arranged at both ends of a glass substrate 10. Furthermore, the size of the sensor elements is minute, on the order of several millimeters, and sensor elements with uniform characteristics can be mass-produced by performing so-called batch processing, in which a large number of sensor elements are simultaneously fabricated on one substrate. In addition to glass, the material of the substrate 1 may be a material having a thermal conductivity of 2 W/mK or less, such as ceramic,
Highly insulating organic material 1 Quartz, mica, etc. may be used. Further, as the material of the metal thin film, other than platinum, a metal material having a large resistance temperature coefficient, such as nickel or a nickel alloy, may be used. Transistor instead of metal 1 [,
It is also possible to use a diode, a thermistor, a semiconductor, or the like.

The heating element 3 and fluid temperature sensing element 4 manufactured in this way
Fig. 2 shows a schematic diagram of the main parts of a flow sensor using a flow sensor. A pair of fluid temperature sensing elements 4 and a heating element 3 manufactured by the above manufacturing method are installed in the flow path 7 through which the fluid passes. The fluid temperature sensing element 4 and the heating element 3 are each connected to another electrical resistance element 5.6, forming a bridge. The intermediate connection point of the electrical resistance element 5.6 is grounded. These bridges differentially amplify the voltage difference between the bridge resistances with an amplifier 8, and connect the fluid temperature sensing element 4 and the heating element 3.
The transistors 9 and 9 are connected to a feed punch circuit that drives the transistors 9 by controlling the base potential of the switching transistors 9 whose emitter terminals are commonly connected. Note that lO is an input terminal connecting the collector terminal of the transistor 9 and the current source.

The driving principle of the flow sensor will be explained below.

The transistor 9 is turned on and the current supplied from the input terminal IO is applied to the heating element 3 to generate heat. When the velocity of the fluid is high, a large amount of heat is taken away from the heating element 3 by the fluid. Conversely, when the flow rate is slow, the amount of heat removed from the heating element 3 is also small.

Therefore, by determining the temperature of the fluid with the fluid temperature detection element 4 and controlling the current value flowing through the heating element 3 via the feedback circuit so as to keep this temperature difference constant, the temperature of the fluid is adjusted in response to changes in the current value. The flow velocity (flow rate) is determined. Since the heat generated by the heating element 3 does not affect the temperature measurement of the fluid by the fluid temperature detection element 4, the temperature measurement operation of the fluid temperature detection element 4 becomes very accurate.

<Effects of the Invention> As detailed above, the thermal flow sensor of the present invention has the following practical advantages.

(1) Since a substrate with low thermal conductivity is used, the thermal insulation effect is excellent and measurement accuracy is improved.

(2) The heating element and the fluid temperature sensing element can be integrated and arranged in the same element, achieving miniaturization.

(3) Lower power consumption is possible.

(4) Since it is manufactured by patch processing, it has excellent mass productivity and compatibility.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of a flow sensor showing one embodiment of the present invention. FIG. 2 is a schematic configuration diagram of main parts for explaining the operation of the flow sensor shown in FIG. 1. FIG. FIG. 3 is an explanatory diagram showing the temperature distribution of materials having different thermal conductivities. DESCRIPTION OF SYMBOLS 1... Heat insulating board, 2... Pumping tube, 3... Heating element, 4... Fluid temperature detection element, 5.6
... fixed resistance, 7 ... flow path, 8 ... operational amplifier,
9...Transistor, 10...Input terminal. Agent Patent attorney Takeshi Sugiyama (and 1 other person) Figure 1

Claims (1)

[Claims] 1. In a flow sensor that determines the flow velocity based on the amount of heat removed by the fluid from the heating element, a fluid temperature detection element that detects the temperature of the heating element and the fluid is integrated on the same thermally insulating substrate. A flow sensor featuring: 2. The flow sensor according to claim 1, wherein the thermally insulating substrate is made of a material having a thermal conductivity of 2 W/m·K or less. 3. The flow sensor according to claim 2, wherein glass, quartz, or mica is used as the material of the thermally insulating substrate. 4. The flow sensor according to claim 1, wherein an electric resistor is used as the heating element. 5. The flow sensor according to claim 1, wherein an electric resistor is used as the fluid temperature sensing element. 6. The flow sensor according to claim 4, wherein platinum, nickel, or a nickel alloy is used as the heating element. 7. The flow sensor according to claim 5, wherein platinum, nickel, or a nickel alloy is used as the fluid temperature sensing element.