JP2005283536A - Air velocity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air velocity sensor having low power consumption, excellent heat efficiency, and excellent sensitivity and responsiveness to air velocity. <P>SOLUTION: An air velocity-detecting negative characteristic thermistor 9 and a temperature-compensating negative characteristic thermistor 10 are provided in sides different from each other to form a bridge circuit 20, and the air velocity-detecting negative characteristic thermistor 9 and a heating negative characteristic thermistor 17 are thermally connected. The air velocity-detecting negative characteristic thermistor 9 and the heating negative characteristic thermistor 17 are configured by an integrated composite type negative characteristic thermistor element 2 with a chip-like component body. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wind speed sensor, and more particularly to a wind speed sensor using a negative characteristic thermistor.

  An interesting wind speed sensor for this invention is a thermal flow meter described in Japanese Patent Laid-Open No. 6-82286 (Patent Document 1). This thermal flow meter has the following configuration.

  The temperature sensing resistor for detection and the temperature sensing resistor for temperature compensation are provided on separate sides to form a bridge circuit. A heating resistor is thermally and integrally coupled to the temperature sensing resistor. A differential output between the bridge side output voltage of the temperature sensing resistor for detection and the bridge side output voltage of the temperature compensation temperature sensing resistor is applied to the heating resistor.

  In a thermal flow meter with such a configuration, heat is generated from the temperature sensing resistor for detection according to the flow rate due to the fluid flow, the temperature of the temperature sensing resistor for detection decreases, the resistance value changes, and The bridge side output voltage on the temperature resistor side changes. Then, a differential output between the bridge side output voltage on the temperature sensing resistor side for detection and the bridge side output voltage on the temperature compensation temperature sensor side is detected as a flow rate. This differential output is also applied to the heating resistor. Due to the heat generated by the heating resistor, the detection temperature-sensitive resistor is heated by the temperature drop due to the heat radiation. Control is performed so that the temperature difference from the temperature-compensating temperature-sensitive resistor is constant.

  According to such a thermal flow meter, in the detection temperature resistor installation portion, a simple structure in which the detection temperature resistor and the heating resistor are integrally formed thermally can be taken. Therefore, the thermal efficiency is good, and therefore the sensitivity is good, and the size can be reduced. Further, in the drive circuit, since the differential output from the bridge circuit is applied to the heating resistor, there is a circuit configuration for making the temperature difference between the temperature compensation temperature sensing resistor and the detection temperature sensing resistor constant. It becomes extremely simple and this also contributes to miniaturization.

In a preferred embodiment described in Patent Document 1, the temperature sensing resistor for detection and the temperature sensing resistor for temperature compensation are composed of negative characteristic thermistors having the same resistance temperature coefficient, while the heating resistor is It does not have a specific resistance temperature coefficient, but is simply composed of a resistor having a small resistance value. In a preferred embodiment, the detection temperature-sensitive resistor and the heating resistor are thermally coupled to each other on a common substrate having high thermal conductivity.
Japanese Patent Laid-Open No. 6-82286

  However, in the thermal flow meter described in Patent Document 1, since the temperature sensing resistor for detection and the resistor for heating are thermally coupled via the substrate, the temperature sensing resistor for detection is used for heating. When heating with a resistor, the power required for heating becomes relatively large. Further, when the heated temperature sensing resistor for detection dissipates heat by the flow of fluid, for example, wind, heat conduction to the substrate occurs, so that the response speed to the wind speed becomes slow.

  In Patent Document 1, in addition to the thermal coupling structure of the detection temperature-sensitive resistor and the heating resistor via the substrate, there is also a structure in which the detection temperature-sensitive resistor is directly fixed on the heating resistor. It is disclosed. However, even if such a structure is adopted, since the heating resistor and the detection temperature-sensitive resistor are separate and independent components, further improvement in the efficiency of the thermal coupling between each other is required. Not only can there be room for improvement, but the thermal coupling conditions differ depending on the contact state between each other or the material and thickness of the heat transfer medium such as an adhesive that exists between them. The bonding state is unstable and the characteristics tend to vary from product to product.

  Therefore, an object of the present invention is to provide a wind speed sensor that can solve the above-described problems.

  In the wind speed sensor according to the present invention, a negative characteristic thermistor for detecting wind speed and a negative characteristic thermistor for temperature compensation are provided on separate sides to form a bridge circuit, and the negative characteristic thermistor for heating includes a negative characteristic thermistor for heating. The negative characteristic thermistor for detecting wind speed and the negative characteristic thermistor for heating are composed of a composite negative characteristic thermistor element integrated with a common chip-shaped component body. It is a feature.

  According to the present invention, since the negative characteristic thermistor for detecting wind speed and the negative characteristic thermistor for heating are constituted by the composite negative characteristic thermistor element having a common chip-shaped component body, the heat generated in the negative characteristic thermistor for heating is Directly transmitted to negative characteristic thermistor for wind speed detection. Therefore, thermal coupling having high heat transfer efficiency can be realized between the negative characteristic thermistor for detecting the wind speed and the negative characteristic thermistor for heating, and the power required to heat the negative characteristic thermistor for detecting the wind speed can be reduced. As a result, the power consumption of the wind speed sensor can be reduced. In addition, since the wind speed sensor according to the present invention can be driven at a low voltage, it is possible to suppress heat generation in an amplifying means such as a power transistor for obtaining power for generating heat in the heating negative characteristic thermistor.

  Also, since the substrate is not substantially involved in the thermal coupling between the negative temperature thermistor for detecting the wind speed and the negative temperature thermistor for heating, the sensitivity to the wind speed decreases due to heat conduction to the substrate, and the wind speed It can suppress that the responsiveness with respect to falls.

  Moreover, since the thermal coupling state of the negative characteristic thermistor for detecting the wind speed and the negative characteristic thermistor for heating can be stabilized, variation in characteristics between the wind speed sensors as products can be suppressed.

  FIG. 1 is a circuit diagram showing electrical elements included in a wind speed sensor 1 according to an embodiment of the present invention. FIG. 2 is a plan view schematically showing a mechanical configuration of the wind speed sensor 1 shown in FIG. FIG. 3 is an enlarged perspective view showing the appearance of the composite negative characteristic thermistor element 2 provided in the wind speed sensor 1 shown in FIG. 4 is a cross-sectional view showing an internal structure of the composite negative characteristic thermistor element 2 shown in FIG.

  First, the wind speed sensor 1 has a mechanical configuration as shown in FIG. That is, for example, a substrate 3 made of a material having a thickness of 1.0 mm and a relatively low thermal conductivity such as a glass epoxy material is provided, and various circuits are formed on the substrate 3 so as to constitute the circuit shown in FIG. The electrical elements are implemented. The substrate 3 is also provided with terminals for connection to the outside, more specifically, a power supply terminal 4, an output extraction terminal 5, and a ground terminal 6.

  In order to make it easier to understand the correspondence between the electrical configuration shown in FIG. 1 and the mechanical configuration shown in FIG. 2, reference numerals common to corresponding elements in FIGS. Is attached.

  The wind speed sensor 1 is driven by a DC power source 7 shown in FIG. This DC power supply 7 is supplied to, for example, the collector of an NPN type power transistor 8 through the power supply terminal 4 shown in FIG.

  The wind speed sensor 1 also includes a wind speed detecting negative characteristic thermistor 9, a temperature compensating negative characteristic thermistor 10, and a differential amplifier 11.

  Further, as shown in FIG. 1, a bridge circuit 12 is formed in the wind speed sensor 1. In the bridge circuit 12, the wind speed detecting negative characteristic thermistor 9 and the temperature compensating negative characteristic thermistor 10 described above are provided on separate sides.

  A fixed resistor 13 is connected between the one end of the wind speed detecting negative characteristic thermistor 9 and the emitter of the transistor 8 on the side of the bridge circuit 12 where the wind speed detecting negative characteristic thermistor 9 is provided. The other end of the negative characteristic thermistor 9 is grounded via the ground terminal 6.

  A fixed resistor 14 is connected between the one end of the temperature compensation negative characteristic thermistor 10 and the emitter of the transistor 8 on the side of the bridge circuit 12 where the temperature compensation negative characteristic thermistor 10 is provided. The other end of the temperature compensation negative characteristic thermistor 10 is grounded via the ground terminal 6.

  The output voltage at the connection point 15 between the negative characteristic thermistor 9 for detecting wind speed and the fixed resistor 13 on the side of the negative characteristic thermistor 9 for detecting wind speed of the bridge circuit 12 is the non-inverting input of the differential amplifier 11. Given to the terminal. On the other hand, the output voltage at the connection point 16 between the temperature compensation negative characteristic thermistor 10 and the fixed resistor 14 on the side of the bridge circuit 12 on the temperature compensation negative characteristic thermistor 10 side is the inversion of the differential amplifier 11. It is given to the input terminal. The differential output voltage of the differential amplifier 11 is applied to the base of the transistor 8.

  The wind speed sensor 1 includes a heating negative characteristic thermistor 17 that is thermally coupled to the wind speed detecting negative characteristic thermistor 9. A fixed resistor 18 for current limiting is connected to one end of the heating negative characteristic thermistor 17, and the heating negative characteristic thermistor 17 is connected to the emitter of the transistor 8 through the fixed resistor 18 and the bridge circuit 12. Is done. The other end of the heating negative characteristic thermistor 17 is grounded via the ground terminal 6.

  As described above, the negative characteristic thermistor 9 for detecting the wind speed and the negative characteristic thermistor 17 for heating that are thermally coupled to each other are the combined negative characteristic thermistor element 2 in which these are integrated with a common chip-shaped component body 19. Consists of.

  Referring mainly to FIGS. 3 and 4, the chip-shaped component body 19 has a structure in which a plurality of ceramic layers 20 having thermistor characteristics having a negative resistance temperature coefficient are laminated. As shown in FIG. 4, the right half of the component main body 19 provides a negative characteristic thermistor 9 for detecting wind speed, and the left half provides a negative characteristic thermistor 17 for heating.

  For example, a pair of internal electrodes 21 and 22 facing each other at the edge are formed along a specific interface between the ceramic layers 20 at a portion of the component main body 19 where the wind speed detecting negative characteristic thermistor 9 is provided. On the other hand, in the portion of the component main body 19 that provides the heating negative characteristic thermistor 17, a plurality of sets of internal electrodes 23 and 24 facing each other through the ceramic layer 20 are formed along specific interfaces between the ceramic layers 20. Has been.

  A through-hole conductor 25 is provided at a boundary portion between the portion that should become the negative characteristic thermistor 9 for detecting wind speed and the portion that should become the negative characteristic thermistor for heating in the component main body 19. The internal electrodes 22 and 24 described above are electrically connected to the through-hole conductor 25. Further, an external electrode 26 is formed on the outer surface of the component main body 19 at the center in the longitudinal direction, and the above-described through-hole conductor 25 is electrically connected to the external electrode 26.

  External electrodes 27 and 28 are formed on the outer surface of the component main body 19 and at the respective ends in the longitudinal direction. The aforementioned internal electrode 21 is electrically connected to the external electrode 27, and the aforementioned internal electrode 23 is electrically connected to the external electrode 28.

  In such a composite negative characteristic thermistor element 2, the external electrode 26 is electrically connected to the ground terminal 6 shown in FIG. The external electrode 27 is electrically connected to the non-inverting input terminal of the differential amplifier 11 and the fixed resistor 13. The external terminal 28 is electrically connected to the current limiting fixed resistor 18.

  The composite negative characteristic thermistor element 2 shown in FIGS. 3 and 4 can be manufactured as follows, for example.

  Using an oxide such as Mn, Ni, or Cu, a raw material powder that becomes a negative characteristic thermistor material having a specific resistance of 100 Ω · cm and a B constant of 3200 K, for example, is prepared. Next, a slurry is obtained by mixing this raw material powder with a binder or the like. Next, by applying a doctor blade method or the like, the slurry is formed into a sheet shape, for example, a green sheet having a thickness of 60 μm is obtained, and this is cut into a predetermined dimension.

  The internal electrodes 21 to 24 are formed on a specific one of the plurality of green sheets obtained in this manner by, for example, printing a conductive paste containing an Ag—Pd alloy as a conductive component. Next, a plurality of green sheets are laminated so that the arrangement state of the internal electrodes 21 to 24 as shown in FIG. 4 is obtained, and then thermocompression bonded in the laminating direction to obtain a raw laminated body. Next, in order to provide the through-hole conductor 25 in the raw laminate, a through-hole is formed, and a conductive paste containing, for example, an Ag—Pd alloy as a conductive component is injected therein.

  Next, after cutting the raw laminate as necessary, for example, it is fired at a temperature of about 1200 ° C. for 2 hours to obtain a sintered laminate, that is, a chip-shaped component body 19.

  Next, in order to form the external electrodes 26 to 28 on the outer surface of the chip-shaped component body 19, for example, a conductive paste containing Ag as a conductive component is applied and baked at a temperature of about 700 ° C. to form an Ag thick film. After the formation, Ni plating and Sn plating are sequentially performed.

  The composite negative characteristic thermistor element 2 can be obtained as described above.

  The temperature compensation negative characteristic thermistor 10 is also composed of a negative characteristic thermistor element having a chip-shaped component body as shown in FIG. 2, although the internal structure thereof is different from the composite negative characteristic thermistor element 2.

  Also, as shown in FIG. 2, each of the fixed resistors 13, 14 and 18 is provided by a chip resistor. These fixed resistors 13, 14 and 18 may be provided by a thick film resistor or a thin film resistor formed directly on the substrate 3.

  In the wind speed sensor 1 described above, in one embodiment, the negative characteristic thermistor 9 for detecting wind speed has a resistance value of 2.2 kΩ at 25 ° C., and the negative characteristic thermistor 10 for temperature compensation has a resistance value at 25 ° C. Is 1.5 kΩ, and the heating negative characteristic thermistor 17 has a resistance value of 10Ω at 25 ° C. The fixed resistor 13 has a resistance value of 2.2 kΩ, the fixed resistor 14 has a resistance value of 1.5 kΩ, and the fixed resistor 18 has a resistance value of 10Ω. Generally speaking, the resistance value of the negative characteristic thermistor 9 for detecting wind speed, the negative characteristic thermistor 10 for temperature compensation, and the fixed resistors 13 and 14 is set to several kΩ, and the resistance value of the negative characteristic thermistor 17 for heating is several. The resistance value of the current limiting fixed resistor 18 is several Ω.

  The operation of the wind speed sensor 1 will be described with reference to FIG. 1. When the DC power supply 7 is supplied, a current flows from the transistor 8 to the fixed resistor 18 and the heating negative characteristic thermistor 17. At this time, almost no current flows through the fixed resistors 13 and 14, the wind speed detecting negative characteristic thermistor 9 and the temperature compensating negative characteristic thermistor 10 having a high resistance value of several kΩ.

  In the above-described state, the heating negative characteristic thermistor 17 self-heats when energized, and this heat generation heats the wind speed detecting negative characteristic thermistor 9, and the resistance value of the wind speed detecting negative characteristic thermistor 9 decreases. Under such circumstances, the bridge of the differential amplifier 11 is in a balanced state. That is, the difference between the output voltage applied from the bridge circuit 12 to the non-inverting input terminal of the differential amplifier 11 and the output terminal applied to the inverting input terminal is minimized.

  On the other hand, when the wind hits the negative characteristic thermistor 9 for detecting wind speed as described above, the negative characteristic thermistor 9 for detecting wind speed is cooled by the heat dissipation effect, and the resistance value of the negative characteristic thermistor 9 for detecting wind speed is increased. To do. As a result, the output voltage from the bridge circuit 12 applied to the non-inverting input terminal of the differential amplifier 11 increases, and thus the differential output voltage from the differential amplifier 11 increases.

  The differential output voltage is extracted as a wind speed detection signal.

  The differential output voltage is amplified by the transistor 8 and applied to the heating negative characteristic thermistor 17. As a result, the heating negative characteristic thermistor 17 generates heat, the wind speed detecting negative characteristic thermistor 9 thermally coupled thereto is heated, and the resistance value of the wind speed detecting negative characteristic thermistor 9 decreases. As a result, the output voltage from the bridge circuit 12 applied to the non-inverting input terminal of the differential amplifier 11 decreases, and the difference between the voltage applied to the non-inverting input terminal and the voltage applied to the inverting input terminal is minimized again. Become.

  At this time, the wind speed can also be detected by detecting the current flowing from the transistor 8 to the fixed resistor 18.

  Next, the effect obtained by the present invention, in particular, the effect obtained by using the composite negative characteristic thermistor element 2 in which the wind speed detecting negative characteristic thermistor 9 and the heating negative characteristic thermistor 17 are integrated will be more specifically described. Explained.

  First, when a composite negative characteristic thermistor element (Example) according to the present invention having a planar dimension of 1.6 mm × 0.8 mm was produced, it had a heat dissipation constant of about 1.0 mW / ° C. in a windless state. was gotten.

  On the other hand, on the alumina substrate having a structure as described in Patent Document 1 and having a planar dimension of 3 mm × 3 mm and a thickness of 0.63 mm, the planar dimension is 1.6 mm × 0.8 mm. As a result, a device having a heat dissipation constant of about 6.0 mW / ° C. was obtained in a no-wind state.

  Comparing these examples and the comparative example, in order to make the temperature difference between the negative characteristic thermistor for detecting wind speed and the negative characteristic thermistor for temperature compensation 10 ° C. in the absence of wind, the negative characteristic thermistor for detecting wind speed is 10 ° C. It is necessary to raise the temperature. The power required for this temperature increase is 1.0 mW / ° C. × 10 ° C. = 10 mW in the example, while 6.0 mW / ° C. × 10 ° C. = 60 mW in the comparative example. Compared with the comparative example, power saving of about 50 mW is possible.

  In addition, when the wind speed is 10 m / sec, the heat dissipation constant is about twice, so the power consumption is 1.0 mW / ° C. × 2 × 10 ° C. = 20 mW in the example, while in the comparative example, 6.0 mW / ° C. × 2 × 10 ° C. = 120 mW, and according to the embodiment, power saving of about 100 mW can be achieved as compared with the comparative example.

  Further, when comparing the response speed, in the above-described example, the 63% response time is about 10 seconds, and in the comparative example, it is about 20 seconds. According to the example, the response time is about half that of the comparative example. can do. Therefore, according to the embodiment, the response time as the wind speed sensor can be reduced to about half that of the comparative example.

The electric element with which the wind speed sensor 1 by one Embodiment of this invention is equipped is shown with the circuit diagram. It is a top view which shows roughly the mechanical structure of the wind speed sensor 1 shown in FIG. FIG. 3 is an enlarged perspective view showing an appearance of a composite negative characteristic thermistor element 2 provided in the wind speed sensor 1 shown in FIG. 2. FIG. 4 is a cross-sectional view showing an internal structure of the composite negative characteristic thermistor element 2 shown in FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wind speed sensor 2 Composite type negative characteristic thermistor element 9 Negative characteristic thermistor for wind speed detection 10 Negative characteristic thermistor for temperature compensation 11 Differential amplifier 12 Bridge circuit 17 Negative characteristic thermistor for heating 19 Chip-shaped component main body 20 Ceramic layers 21-24 Internal electrodes 25 Through-hole conductor 26-28 External electrode

Claims (1)

  A negative characteristic thermistor for detecting wind speed and a negative characteristic thermistor for temperature compensation are provided on separate sides to form a bridge circuit, and the negative characteristic thermistor for heating is thermally coupled to the negative characteristic thermistor for detecting wind speed. The wind speed detecting negative characteristic thermistor and the heating negative characteristic thermistor are constituted by a composite negative characteristic thermistor element in which they are integrated with a common chip-like component body.

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