JPH03255918A - Thermally sensitive type gas flow rate detecting device - Google Patents

Abstract

PURPOSE:To obtain the detector which responds fast has high accuracy and long life and is small in size by forming thermally sensitive resistors for flow rate detection and temperature compensation on an undergraved layer which is formed on a glass substrate and has a lower softening point when the glass substrate. CONSTITUTION:The thermally sensitive resistor 3 for flow rate detection is powered on by a DC power source to generate heat, but it is arranged in a flow of gas to be measured, so the quantity of heat radiation varies with the flow rate of the gas and the resistance varies with temperature. The resistance value variation corresponding to the gas flow rate is temperature-compensated by a bridge circuit and led out as the output of an operational amplifier. The resistor 3 and a thermally sensitive resistor 6 for temperature compensation are adhered strongly to the glass substrate 1 across the undergraved layer 2 which has the lower softening point. The resistors 3 and 6 are put in the flow of the gas to be measured without reference to whether they are on the same substrate 1 or on different substrates, and in the former case a hole 7 is formed in the substrate 1 for thermal insulation to make the thermal mutual interference between the resistors 3 and 6 small. Therefore, the temperature compensation is accurately performed and the measurement accuracy is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermal air flow rate detector that detects the flow rate of suction air in vacuum cleaners, automobile engines, air conditioners, etc. by utilizing the thermal effect of a detection element. .

BACKGROUND OF THE INVENTION Conventionally, in most air flow measurement methods of this type, the air flow rate was indirectly detected by a pressure sensor based on changes in air pressure.

In conventional configurations that utilize such pressure sensors, changes in air pressure do not correspond exactly to changes in air flow rate, so it has been impossible to accurately detect air flow rate.

For example, it was not possible to accurately detect the air flow rate in response to fluctuations in temperature, atmospheric pressure, etc. Moreover, the miniaturization of pressure sensors has reached its limit due to its structure, and it has become unable to respond to the recent miniaturization and weight reduction of devices.

Furthermore, it has been difficult to maintain correct pressure detection characteristics over a long period of time due to dust adhesion to the pressure sensor.

Recently, thermal gas flow rate detectors have been developed that measure the gas flow rate by placing a heat-sensitive resistor thin film in the airflow while electrically heating it, and detecting the amount of change in the cooling rate that changes depending on the gas flow rate. It is starting to be used. This generally has a structure in which a thin platinum film is formed on an alumina substrate.

Problems to be Solved by the Invention However, in order to detect a slight change in the flow rate of a gas having a small heat capacity with good responsiveness, the heat capacity of the alumina substrate must also be extremely small.

When the thickness of the alumina substrate is reduced in order to reduce its heat capacity, alumina is limited to a purity of 99.5% or higher in order to maintain its mechanical strength. Such substrates are expensive, and high purity alumina of 99.5% or more has poor adhesion to metal resistive films.

The present invention solves the above problems, and aims to provide a small thermal gas flow rate detector that responds at high speed, has high accuracy, and has a long life.

Means for Solving the Problems In order to achieve the above object, the present invention forms an underglaze layer with a softening point lower than that of the glass substrate on a thin glass substrate with a small heat capacity, and then forms an underglaze layer with a large temperature coefficient of resistance. A thin film of a heat-sensitive resistor made of a material that has good adhesion to the glaze layer is formed on the underglaze layer.

When a heat-sensitive resistor for flow rate detection and a heat-sensitive resistor for temperature compensation are arranged on the same glass substrate, a hole is formed in the glass substrate between the two heat-sensitive resistors.

Function The present invention can improve thermal responsiveness because the heat capacity of the glass substrate is small due to the above-described configuration. In addition, the underglaze layer on the glass substrate has a lower softening point than the glass substrate, so by heat-treating it below the softening point of the glass substrate, only the underglaze layer will soften, making it possible to firmly bond the glass substrate and the heat-sensitive resistor. I can do it.

Furthermore, by providing a hole in the glass substrate in the middle of the heat-sensitive resistor for flow rate detection and the heat-sensitive resistor for temperature compensation, good thermal insulation can be maintained between the two, and the adverse effects of mutual thermal interference between the two can be maintained. can be prevented.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3.

As shown in FIGS. 1 and 2, a glass substrate 1 (alkali-free glass 70 manufactured by Corning Co., Ltd.
59) After printing silicic acid underglaze glass with a softening point of 590°C on top and baking it at 640°C to form underglaze layer 2, platinum conductive paste is printed in a predetermined pattern and baking at 580°C. Then, a platinum thin film with a thickness of 0.4 μm is formed, and laser trimming is performed to obtain a predetermined resistance value to obtain a heat-sensitive resistor 3 for flow rate detection.

Furthermore, a conductive paste containing silver as the main component was printed, and 55
It is fired at 0° C. to form the extraction electrode 4. Thereafter, a lead borosilicate-based overcoat glass layer 5 is applied as a protective layer. The heat-sensitive resistor 3 for flow rate detection thus formed is at 0°C.
It has a resistance value of 20Ω and a resistance temperature coefficient of 3500 ppm/. Generally, a platinum thin film does not adhere to the glass substrate 1, but by softening and solidifying the underglaze layer 2 according to the present invention, it can be firmly adhered to the glass substrate 1.

6 is a heat-sensitive resistor for temperature compensation, which is formed by the same manufacturing method as the heat-sensitive resistor 3 for flow rate detection, and has a temperature coefficient of resistance of 3.
At 500 ppm/, the resistance value at 0°C is 1000Ω. In this embodiment, the glass substrate 1 is further provided with holes 7 for thermal insulation. Through this hole 7, a heat-sensitive resistor 3 for detecting the flow rate is inserted.
and the heat-sensitive resistor 6 for temperature compensation are thermally insulated,
Decrease in flow rate detection accuracy due to mutual thermal interference between the two is significantly reduced. The larger the hole diameter, the greater the thermal insulation effect, but in consideration of the mechanical strength of the substrate, 3×6 long holes were made in this example.

Lead wires are connected to the heat-sensitive resistor 3 for flow rate detection and the heat-sensitive resistor 6 for temperature compensation through the extraction electrode 4, and these constitute a bridge circuit with a resistor 8 and a resistor 9 as shown in FIG. Connect to DC power supply.

The output end of this bridge circuit is connected to an inverting input terminal and a non-inverting input terminal of an operational amplifier 10 constituting a differential amplifier circuit via resistors 11 and 12, respectively.

To explain the operation in the above configuration, the heat-sensitive resistor 3 for flow rate detection is energized by a DC power supply and generates heat, but since it is placed in the gas flow to be measured, the amount of heat released changes in accordance with the flow rate of the gas. , the temperature changes and the resistance value changes accordingly. The resistance value change corresponding to this gas flow rate is the third
Temperature compensation is performed by the bridge circuit shown in the figure, and the output is taken out as the output of the operational amplifier.

Heat sensitive resistor 3 for flow rate detection and heat sensitive resistor 6 for temperature compensation
is firmly adhered to the glass substrate 1 via an underglaze layer 2 having a low softening point. The heat-sensitive resistor 3 for flow rate detection and the heat-sensitive resistor 6 for temperature compensation are both in the gas flow to be measured, whether they are on the same glass substrate 1 or on separate glass substrates, and the former In the case of , holes 7 are provided on the glass substrate 1 for thermal insulation, and the mutual thermal interference between the thermal resistors on both paths is extremely small, so accurate temperature compensation is achieved and the gas flow rate is The measurement accuracy of the detector is high.

In this embodiment, platinum was used as the material for the heat-sensitive resistor 3 for flow rate detection and the heat-sensitive resistor 6 for temperature compensation, but in addition to platinum, gold, silver,
Palladium, tungsten, copper, aluminum, molybdenum.

Single substances such as chromium, ruthenium oxide, and rhodium oxide, or alloy compositions containing these as main components can also be used. All of these substances had a large temperature coefficient of resistance and exhibited good adhesion to the underglaze layer 2 of this example.

Furthermore, commercially available materials other than those used in this example can be used for the glass substrate material, underglaze layer material, electrode material, and overcoat glass layer material.

Further, in this embodiment, a glass substrate of 0.2 Na++ is used, but in order to improve detection sensitivity, it may be made thinner. If mechanical strength is required, it is also possible to increase the thickness without reducing responsiveness.

Effects of the Invention As is clear from the above embodiments, according to the present invention, thermal mutual interference between the heat-sensitive resistor for flow rate detection and the heat-sensitive resistor for temperature compensation is significantly reduced, and each The heat-sensitive resistor is firmly bonded to an inexpensive substrate material such as glass with an underglaze layer, making it a heat-sensitive gas with high precision, high speed, high reliability, and long life within the practical operating temperature and pressure range. A flow sensor can be provided.

[Brief explanation of drawings]

Fig. 1 is a plan view of the main parts of a thermal gas flow rate detector according to an embodiment of the present invention, Fig. 2 is a cross-sectional view taken along the line A-A' in Fig. 1, and Fig. 3 is a thermal gas flow rate detector as well. FIG. 3 is a flow rate circuit diagram of the device. DESCRIPTION OF SYMBOLS 1... Glass substrate, 2... Underglaze layer, 3... Heat sensitive resistor for flow rate detection, 6
...Heat-sensitive resistor for temperature compensation, 7...
Hole.

Claims (3)

[Claims] (1) Thermal gas flow rate detection method that measures the gas flow rate by placing an electrically heated heat-sensitive resistor thin film in the gas and detecting the amount of change in the cooling rate that changes depending on the gas flow rate. A heat-sensitive gas flow rate detector in which a heat-sensitive resistor for flow rate detection and a heat-sensitive resistor for temperature compensation are formed on an underglaze layer formed on a glass substrate and having a softening point lower than that of the glass substrate. (2) A heat-sensitive resistor for flow rate detection and a heat-sensitive resistor for temperature compensation are formed on the same glass substrate, and a hole is formed on the glass substrate between the two heat-sensitive resistors. Thermal gas flow detector. (3) The heat-sensitive resistor is platinum, gold, silver, palladium, tungsten, copper, nickel, aluminum, molybdenum,
3. The thermal gas flow rate detector according to claim 1, which is made of a single substance such as chromium, ruthenium oxide, or rhodium oxide or an alloy composition containing these as main components.