JPH0697233B2 - Flow velocity sensor and flow velocity measuring device using the same - Google Patents

Description

The present invention relates to an omnidirectional flow velocity sensor characterized by the structure of a flow velocity sensor and a flow velocity measuring device using the flow velocity sensor.

[Prior art]

FIG. 6 shows an example of a conventional nondirectional spherical flow velocity sensor 1. As shown in this figure, the conventional flow velocity sensor 1
Is provided with an aluminum sphere 2, a glass tube 3 fixed inside the sphere 2, and an ultrafine platinum resistor 4 which is held by the glass tube 3 and located at the center of the sphere 2. The platinum resistor 4 has a positive temperature characteristic and is often used as a temperature sensor in terms of heat resistance and stability. Coated lead wires 5a and 5b are connected to both ends of the platinum resistor 4, and are fixed by an adhesive 6 on the surface of the sphere 2.

When the flow velocity sensor 1 using such a platinum resistor 4 constitutes a constant temperature type velocity meter, for example, a bridge circuit is formed by the platinum resistor 4 and a fixed resistor. The bridge is kept in balance by connecting a feedback amplifier that supplies a potential difference between a pair of terminals of the bridge circuit as a feedback current. Then, when the fluid flows around the flow velocity sensor 1 and the temperature of the platinum resistor 4 changes via the sphere 2, a current that compensates for the temperature change flows in the bridge circuit and the bridge top voltage changes, so that the feedback amplifier. And the flow velocity of the fluid can be measured based on the output.

As another flow velocity sensor, a flow velocity sensor using a thermistor having positive and temperature characteristics has been proposed (Japanese Patent Publication No. Sho 49-
No. 3870).

[Problems to be solved by the invention]

In such a conventional flow velocity sensor and the flow velocity measuring device using the flow velocity sensor, the platinum resistor 4, which is the temperature sensor, is covered with the sphere 2 to make it non-directional. Therefore, the heat capacity of the sphere 2 cannot be ignored, and it takes time for the temperature change on the surface of the sphere 2 to propagate to the platinum resistor 4, which causes a problem that the response speed is slow.

When detecting the flow velocity of the fluid from a certain direction on the surface of the sphere, temperature distribution may occur on the surface of the sphere, and the resistance value of the platinum resistor does not change according to the wind speed, and the accurate flow velocity of the fluid is There was a problem that measurement could not be performed.

Further, according to the flow velocity sensor using the positive temperature coefficient thermistor, since the thermistor is a bead type, it has a large resistance value, and there is a drawback that a large amount of electric power is required to raise its temperature. Further, when it is held in a sphere like the platinum resistor, there is a drawback that the temperature distribution is not uniform.

The present invention has been made in view of the problems of such a conventional flow velocity sensor and a flow velocity measuring device using the flow velocity sensor, and has a high response speed of flow velocity measurement, and measures the flow velocity with high accuracy without directivity. Making it possible is a technical issue.

[Means for solving problems]

A first invention of the present application is a spherical flow velocity sensor for measuring a flow velocity of a fluid, and as shown in FIG. 1, a spherical electric insulator and a first thin film electrode formed on the surface of the electric insulator. When,
The present invention is characterized by including a thin film thermistor uniformly formed on the surface of the first thin film electrode and having a positive temperature characteristic, and a second thin film electrode formed on the surface of the thermistor. A second invention of the present application is a flow velocity measuring device using the flow velocity sensor, comprising a spherical electric insulator and a first thin film electrode formed on the surface of the electric insulator as shown in FIG. , Uniformly formed on the surface of the first thin film electrode,
A bridge circuit having a thin film thermistor having a positive temperature characteristic and a flow velocity sensor having a second thin film electrode formed outside the thermistor on one side, and a pair of terminals of the bridge circuit connected to an input end. A feedback amplifier that keeps the bridge in balance by supplying a feedback current to the bridge circuit, and detects the flow velocity of the fluid passing through the flow velocity sensor based on the output of the feedback amplifier. .

[Action]

The flow velocity sensor according to the first invention of the present application having such a feature is formed in a spherical shape, and the thermistor having a positive temperature characteristic is thinly surrounded by the first and second thin film electrodes. Therefore, since the contact area with the fluid is large and the fluid comes into contact with the thin film electrode, the temperature distribution does not occur on the surface, and the flow velocity can be detected with high sensitivity.

Further, according to the second invention of the present application, the spherical velocity sensor configured as described above is provided on one side of the bridge circuit to make the bridge parallel. Therefore, the flow velocity can be detected by the output of the feedback amplifier which keeps the thermistor at a constant temperature.

[Explanation of Examples]

(Description of Embodiments of First Invention) FIG. 1 is a sectional view showing an embodiment of a spherical wind speed sensor according to the first invention of the present application. In this figure, the wind speed sensor 10
Has a spherical electrical insulator 11 which holds the wind speed sensor itself. The first thin film electrode 12 is provided on the entire surface of the electrical insulator 11.
Are uniformly formed, and a thin film having a positive temperature coefficient and PTC (Positive Temperature Coeffici
ent) Thermistor 13 is formed. The electrical insulator 11 is preferably selected so as to have a body expansion coefficient substantially the same as that of the PTC thermistor 13 so that the PTC thermistor 13 is not destroyed by the expansion, and for example, a ceramic material is used. A second thin film electrode 14 is further formed on the surface of the PTC thermistor 13. Then, the wind speed sensor 10 is configured by connecting the electrode lead wires 15a and 15b to the first and second thin film electrodes 12 and 14, respectively. Here, the resistance value R of the PTC thermistor 13
The following relationship is established between 1 and the temperature Tw of the PTC thermistor 13.

t: Thickness of PTC thermistor 13 (mm) r: Radius of PTC thermistor 13 (mm) α: Constant Tw: Temperature of PTC thermistor 13 (° C) Tc: Curie temperature of PTC thermistor 13 (° C) A: Constant For example 0.09235 As described above, the resistance value R1 of the PTC thermistor 13 changes depending on its temperature Tw. FIG. 2 shows an example thereof, and the resistance value exponentially increases above the Curie temperature Tc (about 82 ° C. in this case). When the temperature Tw of the PTC thermistor 13 is thus determined, its resistance value R1 is determined based on the equation (1). Here, when a current is passed through the PTC thermistor 13, its resistance value R1 and the current I flowing through the PTC thermistor 13
Between (A) and the wind speed u (m / sec), the following formula established by Kramer is established.

I ² × R1 = (Bun + C) × (Tw−Ta) (2) Ta is the ambient temperature, for example 28 ° C, and the constants B and C are the heat radiation coefficients, which are determined by the size and shape of the PTC thermistor 13. A constant, n is a constant (usually 1/2).

Therefore, for example, as shown in FIG. 3, a constant voltage V is applied to the PTC thermistor 13 of the anemometer 10 by the constant voltage source 16 and the current flowing therethrough is detected by the ammeter 17 to obtain the PT.
The wind speed value can be measured from the resistance change of the C thermistor 13.

That is, the resistance value of the PTC thermistor 13 when the wind speed value u is 0 is R
If the temperature is ₁₀ and its temperature is Tw ₀ , the following formula is established with the current flowing at that time as I ₀ .

I ₀ ² R1 ₀ = C (Tw−Ta) (3) If R1 · I = V and R1 ₀ · I ₀ = V ₀ , then equation (2),
From (3) However, ΔT = Tw−Tw ₀ , V = V ₀ Now, the difference Tw ₀ −Ta between the temperature of PTC thermistor 13 and room temperature is 100
Each value is shown in the following table, for example, assuming that the temperature is 0.1, the count A is 0.1, the B / C is 0.2, and the n is 1/2.

As is known from this table, if the wind speed value u is low, ΔT is a relatively small value, so it is a constant temperature, and ΔT << Tw
If ₀ −Ta, the following equation holds.

I≈Io (1 + B / C · un) In this way, the wind speed value u can be obtained from the current value I. As described above, the PTC thermistor 13 is covered by the metal thin film electrode 14 in the constant voltage method, but the resistance value is sensitively changed depending on the wind speed because it is easily affected by the external environment. Therefore, it is possible to measure the wind speed with high sensitivity with an extremely easy circuit configuration.

(Structure of Embodiment of Second Invention) FIG. 4 is a circuit diagram showing an embodiment of a wind speed measuring apparatus according to the second invention of the present application. In this figure, the wind velocity measuring device is a bridge circuit in which the PTC thermistor 13 of the wind velocity sensor 10 and the fixed resistors R2, R3 and R4 according to the embodiment of the first invention described above are combined.
Has 20. In the bridge circuit 20, the middle point of the resistor R2 and the thermistor 13 is a, the middle point of the resistors R3 and R4 is b, and the middle point is
a and b are connected to the inverting input terminal and the non-inverting input terminal of the operational amplifier 21, respectively. The operational amplifier 21 amplifies the potential difference between them, and outputs its output to the bridge circuit 20 resistors R2 and R2.
A feedback loop is formed by applying it to the connection point c of 3. The output of the operational amplifier 21 is also given to the voltmeter 22. In this embodiment, the fixed resistance R2 is 20Ω, R3 is 300Ω, and R4 is 151Ω.
It is set to 5Ω.

(Operation) Next, an operation of the wind speed measuring device according to the present embodiment will be described. The wind velocity measuring device of the present invention is a constant temperature type wind velocity measuring device that controls the temperature 13 of the PTC thermistor so as to always keep the temperature constant, and measures the wind velocity based on the manipulated variable. In the windless state, the PTC thermistor 13 is kept at a constant temperature determined by the equation (2). That is, since the feedback current is supplied by the operational amplifier 21 so that the voltages at the midpoints a and b of the bridge circuit 20 become equal, the system is established in the steady state.

R1 · R3 = R2 · R4 (5) When the resistance value R1 of the PTC thermistor 13 and the current I ₁ flowing through it are determined in this way, the temperature Tw of the PTC thermistor 13 is determined according to the equation (1). This temperature Tw is sufficiently higher than room temperature,
For example, it is set to 90 ° C.

When the wind speed sensor 10 is placed in the non-measurement area and the wind hits the wind speed sensor 10, the surface of the wind speed sensor 10 is cooled and the temperature Tw of the PTC thermistor 13 decreases. ). At this time, a potential difference occurs between the middle points a and b of the bridge circuit 20, so that the feedback amplifier 2
The current I ₁ flowing in the feedback loop of ₁ increases and the bridge circuit 20 reaches a new balance. As described above, since the wind speed u and the bridge top voltage E at the connection point c have a one-to-one correspondence, the wind speed u can be obtained based on the voltage value of the voltmeter 22. FIG. 5 is a graph showing an example of the relationship between the bridge top voltage E (v) and the wind speed u (m / sec) obtained by the wind speed measuring device.

As described above, the wind velocity measuring device according to the present embodiment has a high responsiveness and a large resolution at a low wind velocity as shown in FIG. 5, so it is effective to use it as an anemometer at a low wind velocity.

Although the above-described embodiments have described the flow velocity sensor and the flow velocity measuring device for measuring the flow velocity of gas, it goes without saying that the flow velocity sensor and the flow velocity measuring device of the present application can be applied to the flow velocity measurement of liquid. .

〔The invention's effect〕

Thus, according to the first invention of the present application, the thermistor having a positive temperature coefficient is provided on the surface of the sphere through the metal thin film. Therefore, the thermistor is easily influenced by the fluid, and when the thermistor is kept at a high temperature, the resistance of the thermistor changes in a short time due to the change of the flow velocity. Therefore, it is possible to obtain a flow velocity sensor having a high response speed.

Further, in the flow velocity measuring device according to the second invention of the present application, since the temperature of the flow velocity sensor connected to one side of the bridge circuit is kept constant by using the bridge circuit and the feedback amplifier, the flow velocity sensor has the influence of the flow velocity. The resistance value changes sensitively when received. Therefore, the change in the flow velocity can be detected with high sensitivity based on the feedback current. Further, the temperature distribution does not occur in the thermistor, and there is no fear of causing a measurement error due to the temperature distribution. Therefore, a highly sensitive non-directional flow velocity sensor and flow velocity measuring device can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of a wind speed sensor according to an embodiment of the first invention of the present application, FIG. 2 is a graph showing a temperature characteristic of a PTC thermistor, and FIG. 3 is a view showing a usage state of the wind speed sensor of this embodiment, FIG. 4 is a circuit diagram showing a wind speed measuring device according to an embodiment of the second invention of the present application using the wind speed sensor, and FIG. 5 is a graph showing the relationship between the bridge top voltage and the wind speed of the wind speed measuring device of this embodiment. , FIG. 6 is a sectional view showing an example of a conventional flow velocity sensor. 10 …… wind speed sensor, 11 …… electrical insulator, 12 …… first thin film electrode, 13 …… PTC thermistor, 14 …… second thin film electrode, 16 …… constant voltage source, 17 …… ammeter, 22 …… Voltmeter, 20
...... Bridge circuit, 21 …… Feedback amplifier

Claims (3)

[Claims] 1. A spherical flow velocity sensor for measuring the flow velocity of a fluid, comprising a spherical electrical insulator, a first thin film electrode formed on the surface of the electrical insulator, and a first thin film electrode. A thin film thermistor uniformly formed on the surface and having a positive temperature characteristic; and a second thin film electrode formed on the surface of the thermistor,
A flow velocity sensor comprising: 2. The flow velocity sensor according to claim 1, wherein the electrical insulator is a ceramic having a body expansion coefficient substantially the same as that of the thermistor. 3. A spherical electric insulator, a first thin film electrode formed on the surface of the electric insulator, and a thin film thermistor uniformly formed on the surface of the first thin film electrode and having a positive temperature characteristic. , And a bridge circuit having on one side a flow velocity sensor provided with a second thin film electrode formed outside the thermistor, and a pair of terminals of the bridge circuit is connected to an input end, and a feedback current is supplied to the bridge circuit. A feedback amplifier that keeps the bridge in a balanced state by supplying the bridge, and detects the flow velocity of the fluid passing through the flow velocity sensor based on the output of the feedback amplifier.