JPH1048018A - Flow rate sensor and flow rate detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the mechanical strength while making a device compact, by separately installing a sensitive resistor film having the temperature characteristics of resistance which is rectilinearly varied, and a resistor film of a flat temperature characteristics, on a single ceramic substrate. SOLUTION: A temperature sensitive resistor film 3 composed of platinum, nickel or the like, and a resistor film 4 of a resistor composed of nickel chrome, cupper nickel or the like, are separately formed on a ceramic single substrate 2. The resistor film 3 has the temperature characteristics of resistance which is rectilinearly varied on the basis of the temperature coefficient of resistance of 2500-5000ppm/ deg.C, and the temperature coefficient of resistance of the resistor film 4 has the temperature characteristics of resistance substantially flat within ±100ppm/ deg.C of allowable extent. The external electrode films 5 are connected with both edge parts of the both resistor films 3, 4 respectively, to form the chip shape, and to make it compact. Further for the benefit of this thin film structure on the substrate 2, the film formation can be performed by baking, the separation of the resistor films 3, 4 from the substrate 2 can be prevented, and the constant mechanical strength can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate sensor for detecting a flow rate of a fluid and a flow rate detection device using the same.
In particular, the present invention relates to a thermal type flow sensor and a flow detection device used for the purpose of air flow detection and filter clogging detection.

[0002]

2. Description of the Related Art As an example of a conventional thermal flow sensor,
2. Description of the Related Art A wind speed sensor for measuring an air flow in an electronically controlled fuel injection device of an automobile is known. In this method, a heated resistor is exposed to an air current, and the wind speed is detected from the magnitude of the heat radiation effect. Such a wind speed sensor includes a heating resistor, a temperature compensating resistor, and a signal processing circuit for processing a signal from these resistors. Heating of the heating resistor is controlled so as to be higher than the temperature of the fluid. When the wind speed increases (or decreases), heat radiation increases (or decreases), and the temperature and the resistance value decrease (or increase). The temperature compensating resistor is provided on the windward side of the heat generating resistor, and is used for detecting the temperature of the fluid itself and compensating for the influence of a change in the fluid temperature. In order to accurately detect the wind speed in the wind speed sensor having the above-described configuration, the two resistors need to be brought close to each other to some extent, and the resistance between the two resistors must be set so that the heat of the heating resistor is not conducted to the temperature compensation resistor. It is necessary to surely perform the thermal separation. Therefore, as a conventional flow sensor, for example, a structure has been proposed in which a heating resistor and a temperature-sensitive resistor are provided on a substrate such as alumina, and thermal separation between the two resistors is achieved by slits or window-shaped openings. ing. Further, a configuration in which a resin having relatively good thermal insulation properties is used as a substrate material is also known. Further, a configuration is known in which a heating resistor and a temperature compensating resistor are formed on an extremely thin bridge by a fine processing technique such as a micromachining method using a Si process.

[0003]

However, the above-mentioned conventional flow sensor has the following problems. Even if a slit or window-shaped opening is provided in the substrate, sufficient thermal separation cannot be performed because the thermal conductivity of the substrate such as alumina is large. Therefore, there is a limit to downsizing, and high accuracy and responsiveness cannot be obtained. When a resin substrate is used, the resistor cannot be formed directly on the substrate because the heat resistance of the resin is low. Therefore, a step of attaching the resistor to the substrate is required separately from the manufacturing process of the substrate, and an integrated construction method with the substrate cannot be performed. Due to the separate attachment step, there is a limit to miniaturization of the flow sensor. In addition, there is a problem that the resistor is separated from the substrate due to a difference in thermal conductivity between the substrate and the resistor. The micromachining method is suitable for reducing the size of the flow sensor, but requires a large-scale production facility, which leads to an increase in cost. In addition, there is a problem that the mechanical strength is weak due to the fine structure. As described above, with the conventional flow rate sensor, it has not been possible to reduce the size and improve the performance without increasing the cost and to obtain a configuration having sufficient mechanical strength.

[0004] In view of the above-mentioned conventional problems, the present invention aims at miniaturization and high performance without increasing the cost.
It is an object of the present invention to provide a flow sensor and a flow detection device having a configuration having sufficient mechanical strength.

[0005]

A flow sensor according to the present invention comprises:
On a single ceramic substrate, a temperature-sensitive resistor film having a resistance-temperature characteristic that changes linearly based on a predetermined resistance temperature coefficient and a resistor film having a substantially flat resistance-temperature characteristic are separated from each other. It is provided. In the flow sensor configured as described above, when a constant voltage or a constant current is supplied, the resistor film gives a substantially constant heating value to the temperature-sensitive resistor film regardless of the ambient temperature. The membrane radiates heat according to the flow rate of the fluid, and changes its resistance linearly with respect to the ambient temperature. The flow sensor comprises only a temperature-sensitive resistor film and a resistor film which do not need to be thermally separated from each other, and does not include a compensation resistor. Therefore, it becomes possible to make the flow sensor a small one-chip configuration. For example,
A structure suitable for obtaining one chip by dividing a temperature-sensitive resistor film and a resistor film formed on a ceramic substrate by screen printing or the like is obtained. Further, such a thin film configuration on the ceramic substrate can be deposited by firing.

In the above flow rate sensor, the temperature coefficient of resistance of the temperature-sensitive resistor film is 2500 to 5000 ppm / ° C., and the resistance film has a temperature coefficient of resistance within a tolerance of ± 100 ppm / ° C. Is also good. In a flow sensor configured to have such specific numerical values, the resistance temperature characteristic of the temperature-sensitive resistor film is represented by a straight line having a substantially constant slope irrespective of the flow rate of the fluid to be measured. The ratio of the change in the resistance value of the temperature-sensitive resistor film to the change in the temperature is constant even if the flow rate changes.

The above-mentioned flow sensor can be formed in a chip type in which three or four external electrodes are connected to the temperature-sensitive resistor film and the resistor film. Such a chip type flow sensor is extremely small and can be manufactured at low cost.

Similarly, according to the application, three or four external terminals are connected to the temperature-sensitive resistor film and the resistor film to form a SIP.
Mold or DIP mold.

Further, the flow rate detecting device according to the present invention is characterized in that a temperature-sensitive resistor film having a resistance-temperature characteristic which changes linearly based on a predetermined temperature coefficient of resistance is formed on a single ceramic substrate, and a substantially flat temperature-sensitive resistor film is formed. A flow rate sensor provided with a resistor film having resistance temperature characteristics separated from each other, a first resistor connected in series with the temperature sensitive resistor film, and the same temperature coefficient of resistance as the temperature sensitive resistor film. A temperature-sensitive resistor, a second resistor connected in series with the temperature-sensitive resistor, a series-connected body of the temperature-sensitive resistor film and the first resistor, and a temperature-sensitive resistor and a second resistor. A constant voltage source for supplying a constant voltage to a series connection of the resistor and the resistor, a voltage at a connection point between the temperature-sensitive resistor film and the first resistor, and a temperature-sensitive resistor and a second resistor. And a differential amplifying circuit for outputting a voltage obtained by differentially amplifying the voltages at the connection point. The flow rate detecting device thus configured has a differential amplifier circuit and a differential input between the temperature-sensitive resistor film and the temperature-sensitive resistor. , And only the voltage signal corresponding to the temperature change corresponding to the flow rate is amplified and output.

Further, the flow rate detecting device according to the present invention is characterized in that a temperature-sensitive resistor film having a resistance-temperature characteristic that changes linearly based on a predetermined temperature coefficient of resistance is formed on a single ceramic substrate, and a substantially flat surface is formed. A flow sensor having a resistor film having resistance temperature characteristics separated from each other, a constant current source connected in series to the temperature-sensitive resistor film, and an amplifier for amplifying a voltage generated at both ends of the temperature-sensitive resistor film And a temperature-sensitive resistor having the same temperature coefficient of resistance as the temperature-sensitive resistor film, and refers to predetermined internal data according to the resistance value of the temperature-sensitive resistor, and outputs the output of the amplifier based on the referenced internal data. And a signal processing circuit for correcting The flow rate detecting device thus configured has a signal processing circuit in addition to the features of the flow rate sensor described above.
By correcting the output of the temperature-sensitive resistor film based on the data referred to according to the input from the temperature-sensitive resistor, the influence of the change in the ambient temperature is removed, and only the signal corresponding to the temperature change corresponding to the flow rate is extracted.

[0011]

FIG. 1 is a perspective view showing a flow sensor 1 according to an embodiment of the present invention. In the figure, on a substrate 2 made of ceramic, a temperature-sensitive resistor film 3 made of a metal such as platinum, nickel, ruthenium, iron, or copper or an alloy thereof and a resistance film made of nickel chromium, copper nickel, a metal oxide film or the like are provided. A resistor film 4 made of a body is formed separately from each other. The temperature-sensitive resistor film 3 is 2500 to 5000 ppm /
The resistance film 4 has a temperature coefficient of resistance that varies linearly based on the temperature coefficient of resistance, and the resistor film 4 has a temperature coefficient of resistance within a tolerance of ± 100 ppm / ° C. Since the resistance temperature coefficient of the resistor film 4 is much smaller than the resistance temperature coefficient of the temperature-sensitive resistor film 3, the resistance film 4 has a flat resistance temperature equivalent to substantially no resistance temperature coefficient. It can be said that it is a characteristic. External electrode films 5 are formed on both ends of the temperature-sensitive resistor film 3 and the resistor film 4, respectively. On the temperature-sensitive resistor film 3 and the resistor film 4, a protective film (not shown) for covering them is provided. Taking specific numerical values as an example, the thickness of each of the temperature-sensitive resistor film 3 and the resistor film 4 is 0.1 to 50 μm. The thickness of the substrate 2 is 0.3, 0.635 or 0.8.
mm.

Next, a manufacturing procedure of the flow sensor 1 shown in FIG. 1 will be described. First, in FIG. 2A, a ruthenium thick film paste is patterned on a substrate 2 (usually 2 inches × 2 inches) as a temperature-sensitive resistor film 3 at a predetermined position, and screen printing is performed. Next, as shown in (b), a thick ruthenium oxide paste is patterned as a resistor film 4 at a predetermined position, and screen printing is performed. After that, a film of each paste is formed and functional characteristics are obtained by primary baking. Next, as shown in FIG.
Screen printing of an electrode paste such as Ag / Pd, and secondary baking. Further, printing of a protective film paste using glass or the like and tertiary baking are performed. Thereafter, as shown in FIG. 3B, the substrate 2 is divided into one chip size by dicing along the dicing line D, and a number of basic constituent elements of the flow sensor 1 as shown in FIG. 1 are obtained. When the external electrode 6 is attached to this, the chip type flow sensor 1 shown in FIG. 4A is completed. When an external terminal 7 is provided instead of the external electrode 6, a DIP (Dual Inline Package) shown in FIGS. 4B and 4C, respectively.
And a SIP (Single Inline Package) type flow sensor 1. Thus, flow sensors of various shapes can be provided according to the application. Note that the flow rate sensor 1 of any type shown in FIG.
However, if one end of each of the temperature-sensitive resistor film 3 and the resistor film 4 is connected to each other, the number of the external electrodes 6 or the external terminals 7 can be reduced to three.

The flow sensor 1 manufactured as described above is disposed in a fluid flow path, and a constant voltage is applied to the resistor film 4 or a constant current is caused to flow to generate constant heat. As described above, since the resistance temperature characteristic of the resistor film 4 is flat, the amount of heat generated by the resistor film 4 is constant regardless of the ambient temperature. The temperature of the temperature-sensitive resistor film 3 rises due to the heat generated by the resistor film 4,
Higher than the fluid temperature. When the flow rate sensor 1 is exposed to a fluid (for example, air) in this state, the resistance of the temperature-sensitive resistor film 3 changes due to heat radiation corresponding to the flow rate (wind speed).

FIG. 5 is a graph showing the change in the resistance value R (kΩ) of the temperature-sensitive resistor film 3 with respect to the wind speed (m / sec) of the fluid, using the ambient temperature as a parameter. The resistance value at a constant wind speed increases as the ambient temperature increases. At each constant ambient temperature, the resistance value R gradually decreases as the wind speed increases. Next, FIG. 6 is a graph showing a change in the resistance value R (kΩ) with respect to the ambient temperature using the wind speed as a parameter. As is clear from this graph, the change characteristic of the resistance value R depending on the ambient temperature shows extremely excellent linearity, and there is no variation in the slope coefficient of the straight line due to the wind speed. That is,
The slope coefficient of the straight line is constant regardless of the wind speed. This is based on the use of the temperature-sensitive resistor film 3 having linear characteristics and the resistor film 4 having flat characteristics. Therefore, even when the flow sensor is used in an environment where the ambient temperature condition is not constant, high accuracy can be obtained by performing temperature compensation by a simple primary conversion on the output of the flow sensor.

FIG. 7 is a circuit diagram showing an example of the temperature compensation circuit. The temperature compensation circuit 10 includes a constant voltage source 11, an operational amplifier 15, resistors 12, 13, 16 to 19, 21, 22, a capacitor 20, and a temperature-sensitive resistor 14. The temperature-sensitive resistor 14 has the same temperature coefficient of resistance as the temperature-sensitive resistor film 3. The constant voltage supplied from the constant voltage source 11 is divided by the resistor 12 and the temperature-sensitive resistor film 3 of the flow sensor 1, and a voltage corresponding to the resistance value of the temperature-sensitive resistor film 3 is supplied to the inverting input terminal side of the operational amplifier 15. Is input to Similarly, the constant voltage supplied from the constant voltage source 11 is divided by the resistor 13 and the temperature sensitive resistor 14, and a voltage corresponding to the resistance value of the temperature sensitive resistor 14 is input to the non-inverting input terminal side of the operational amplifier 15. Is done. The operational amplifier 15 performs differential amplification based on two inputs. The resistance values of the resistors 12 and 13 are set so that the differential input of the operational amplifier 15 becomes 0 when the flow rate is 0.
Here, since the temperature-sensitive resistor 14 has the same temperature coefficient of resistance as the temperature-sensitive resistor film 3, a change in the resistance value due to a change in the ambient temperature changes between the temperature-sensitive resistor 14 and the temperature-sensitive resistor film 3. There is no. Therefore, what corresponds to the differential input voltage to the operational amplifier 15 is a voltage change caused by the temperature-sensitive resistor film 3 radiating heat in accordance with the flow rate of the fluid and the resistance value fluctuating. In this way, by amplifying the differential input between the temperature-sensitive resistor film 3 and the temperature-sensitive resistor 14, the influence of the fluctuation of the ambient temperature is canceled, and only the flow signal is amplified and output as the voltage signal (flow signal) Vout. can do. Since a negative change in which the resistance value decreases with an increase in the flow rate is changed to a positive change in which the voltage increases, the handling of the detection signal is also convenient.

FIG. 8 is a circuit diagram showing another example of the temperature compensation circuit. The temperature compensation circuit 30 includes a constant current source 31, an amplifier 3
2. It is composed of a signal processing circuit 33 and a temperature sensitive resistor 34. A constant current is passed from the constant current source 31 to the temperature-sensitive resistor film 3 of the flow sensor 1, and a change in the resistance value is extracted as a change in the voltage. This voltage is amplified to a desired voltage level by the amplifier 32 and input to the signal processing circuit 33. The signal processing circuit 33 takes in the signal from the temperature-sensitive resistor 34,
Compensation (data correction) for the signal, that is, a signal representing the ambient temperature, is performed with reference to a built-in ROM table. In this manner, the signal processing circuit 33 outputs a signal obtained by performing temperature compensation on the flow signal as an analog voltage signal Vout or a digital signal. The temperature-sensitive resistor 34 has the same temperature coefficient of resistance as the temperature-sensitive resistor film 3, similarly to the temperature-sensitive resistor 14 in the circuit example of FIG. Thus, FIG.
As in the case of the above circuit example, it is possible to output a flow rate signal in which the influence of the fluctuation of the ambient temperature is compensated (corrected).

In the above embodiment, the resistor film 4 and the temperature-sensitive resistor film 3 of the flow sensor are formed by the screen printing method. However, the same resistor film may be formed by a thin film technique such as selective plating and a stamper. Can be. The formation of the temperature-sensitive resistor film 3 and the resistor film 4 may be performed not only on one side of the substrate 2 but also on both sides. Further, trimming by laser or the like before forming the protective film for adjusting the resistance value contributes to the improvement of the accuracy of the flow sensor.

[0018]

The present invention configured as described above has the following effects.

A flow sensor according to the present invention comprises a temperature-sensitive resistor film having a resistance-temperature characteristic which varies linearly based on a predetermined resistance-temperature coefficient, and a substantially flat resistance-temperature characteristic on a single ceramic substrate. Is provided separately from the resistor film, so that when a constant voltage or a constant current is supplied, the resistor film gives a substantially constant calorific value to the temperature-sensitive resistor film regardless of the ambient temperature, The temperature-sensitive resistor film radiates heat according to the flow rate of the fluid, and changes its resistance value linearly with respect to the ambient temperature. The flow sensor comprises only a temperature-sensitive resistor film and a resistor film which do not need to be thermally separated from each other, and does not include a compensation resistor. Therefore, a very small and inexpensive flow sensor can be provided by a predetermined manufacturing method. Further, according to such a thin-film configuration on the ceramic substrate, the film can be deposited by firing, so that the temperature-sensitive resistor film and the resistor film do not peel off from the substrate and have a certain mechanical strength.

The temperature coefficient of resistance of the temperature-sensitive resistor film is 25.
If the resistance film is configured to have a temperature coefficient of resistance within a tolerance of ± 100 ppm / ° C., the temperature-sensitive resistance film is constant regardless of the ambient temperature. A linear resistance-temperature characteristic having the following gradient can be obtained, so that temperature compensation for eliminating the influence of a change in ambient temperature can be performed by a simple primary conversion. Therefore, post-processing for removing the influence of the change in the ambient temperature is simple, and a highly accurate flow rate detection device can be constructed.

The temperature-sensitive resistor film and the resistor film may have
When the flow sensor is formed in a chip type by connecting one or four external electrodes, an extremely small and inexpensive flow sensor can be provided.

The temperature-sensitive resistor film and the resistor film may have three
When one or four external terminals are connected to form a flow sensor of SIP type or DIP type, it is possible to provide an extremely small and inexpensive flow sensor optimal for the application.

On the other hand, the flow rate detecting device of the present invention uses a differential amplifier to differentially output the output of the temperature-sensitive resistor film of the flow rate sensor configured as described above and the output of the temperature-sensitive resistor provided outside. Since the amplifier is configured to amplify, in addition to the effect of the above-described configuration of the flow sensor itself, the differential amplification circuit takes a differential input between the temperature-sensitive resistor film and the temperature-sensitive resistor to reduce the change in ambient temperature. By canceling out the influence, it is possible to amplify and output only the voltage signal corresponding to the temperature change corresponding to the flow rate. Therefore, the flow rate can be detected with high accuracy regardless of the ambient temperature.

Further, another flow rate detection device of the present invention provides a flow rate sensor having the above-described configuration, in which a constant current is applied to the temperature-sensitive resistor film to convert a change in resistance value into a voltage and amplify the output. Since a signal processing circuit for correcting based on the built-in data referred to in accordance with the resistance value of the temperature-sensitive resistor having the same temperature coefficient of resistance as the temperature-sensitive resistor film is provided, the effect of the above-described configuration of the flow rate sensor itself is provided. In addition, the signal processing circuit corrects the output of the temperature-sensitive resistor film based on the data referred to in accordance with the input from the temperature-sensitive resistor, thereby removing the influence of the change in the ambient temperature, and removing the temperature corresponding to the flow rate. The change signal can be extracted. Therefore, the flow rate can be detected with high accuracy regardless of the ambient temperature.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a flow sensor according to an embodiment of the present invention.

FIG. 2 is a view showing a first half of a manufacturing process of the flow sensor shown in FIG. 1;

FIG. 3 is a view showing the latter half of the manufacturing process of the flow sensor shown in FIG. 1;

FIG. 4 is a perspective view showing an appearance of a flow sensor, and FIG.
Is chip type, (b) is DIP type, (c) is SI
Indicates P type.

FIG. 5 is a graph showing output characteristics of the flow sensor according to the present invention.

FIG. 6 is a graph showing temperature characteristics of the flow sensor according to the present invention.

FIG. 7 is a circuit diagram illustrating an example of a temperature compensation circuit of the flow rate detection device according to the present invention.

FIG. 8 is a circuit diagram showing another example of the temperature compensation circuit of the flow detection device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flow rate sensor 2 Substrate 3 Temperature sensitive resistor film 4 Resistive film 5 External electrode film 10 Temperature compensation circuit 11 Constant voltage source 12, 13 Resistance 14 Temperature sensitive resistor 15 Operational amplifier 16, 17, 18, 19 Resistor 20 Capacitor 21, 22 resistor 30 temperature compensation circuit 31 constant current source 32 amplifier 33 signal processing circuit 34 temperature sensitive resistor

Claims (6)

[Claims] 1. A temperature-sensitive resistor film having a resistance-temperature characteristic that changes linearly based on a predetermined temperature coefficient of resistance, and a resistance film having a substantially flat resistance-temperature characteristic on a single ceramic substrate. And a flow sensor provided separately from each other. 2. The resistance temperature coefficient of the temperature-sensitive resistor film is 25.
00 to 5000 ppm / ° C., and the resistance film is ± 1
2. The flow sensor according to claim 1, having a temperature coefficient of resistance within a tolerance of 00 ppm / .degree. 3. The flow rate sensor according to claim 1, wherein the flow rate sensor is formed in a chip shape with the temperature-sensitive resistor film and three or four external electrodes connected to the resistor film. 4. The temperature-sensitive resistor film and three or four external terminals connected to the resistor film are formed into one of a SIP type and a DIP type. The flow sensor according to claim 1, wherein 5. A temperature-sensitive resistor film having a resistance-temperature characteristic that changes linearly based on a predetermined temperature coefficient of resistance, and a resistor film having a substantially flat resistance-temperature characteristic on a single ceramic substrate. And a flow sensor provided separately from each other, a first resistor connected in series with the temperature-sensitive resistor film, and a temperature-sensitive resistor having the same temperature coefficient of resistance as the temperature-sensitive resistor film. A second resistor connected in series with the temperature-sensitive resistor, a series-connected body of the temperature-sensitive resistor film and the first resistor,
And a constant voltage source for supplying a constant voltage to a series connection of the temperature-sensitive resistor and the second resistor; a voltage at a connection point between the temperature-sensitive resistor film and the first resistor; And a differential amplifier circuit for outputting a voltage obtained by differentially amplifying a voltage at a connection point between the temperature-sensitive resistor and the second resistor. 6. A temperature-sensitive resistor film having a resistance-temperature characteristic that changes linearly based on a predetermined resistance-temperature coefficient on a single ceramic substrate, and a resistance film having a substantially flat resistance-temperature characteristic. And a constant current source connected in series to the temperature-sensitive resistor film; an amplifier for amplifying a voltage generated at both ends of the temperature-sensitive resistor film; and the temperature-sensitive resistor. A temperature-sensitive resistor having the same temperature coefficient of resistance as the body membrane; a signal for referring to predetermined internal data according to the resistance value of the temperature-sensitive resistor and correcting the output of the amplifier based on the referred internal data. A flow detection device comprising a processing circuit.