JPH11118567A - Flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high sensitivity flow sensor in which occurrence of detection error due to temperature environment is prevented. SOLUTION: Series circuits are formed by resistors R11, R12, R13 and R14 composed, respectively, of four temperature sensor wires and exhibit reverse phase resistance variation due to temperature distribution created by movement of fluid. More specifically, a first temperature sensor wire 18 (R11) arranged on the right side of a heater wire is connected in series with a fourth temperature sensor wire 28 (R14) arranged on the left side of the heater wire and applied with a constant voltage V0. Similarly, a second temperature sensor wire 30 (R12) arranged on the right side of the heater wire is connected in series with a third temperature sensor wire 20 (R13) arranged on the left side of the heater wire and applied with a constant voltage V0. Differential voltage between the voltages V1, V2 at the joints of both series circuits is amplified by a differential amplifier 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor utilizing the principle of a Thomas gas meter, and more particularly, to a flow sensor which has improved detection sensitivity and prevents a decrease in detection sensitivity due to a temperature change.

[0002]

2. Description of the Related Art A thermal type flow sensor using a heater wire is used to measure the flow rate and flow rate of a fluid such as gas or liquid. Such a flow sensor is, for example, a tube-type flow sensor in which a heater wire and temperature sensor wires on both sides thereof are provided outside a thin tube, or a micro-flow sensor in which a heater wire and temperature sensor wires on both sides thereof are provided on a diaphragm on the surface of a semiconductor substrate. Flow sensors and the like are known.

Such a flow sensor is based on the principle of a Thomas gas meter. The principle is that the temperature distribution due to the heat generated from the heater wire changes according to the flow velocity, and the temperature distribution having the changed temperature distribution is provided on both sides. It is to detect by a sensor line.

FIG. 1 is a plan view of a conventional micro flow sensor. In this example, a through hole 12 is formed in the semiconductor substrate 10 from the back side, and a diaphragm film 14 that closes the through hole 12 is formed on the front side. The heater wire 16 is provided on the diaphragm film 14 and the temperature sensor wires 1 are provided on both sides thereof.
8, 20 are provided. The temperature sensor wires 18 and 20 are formed of U-shaped resistance wires formed between the electrodes at both ends. Further, the heater wire 16 is constituted by a pair of U-shaped resistance wires formed between the electrodes at both ends.

In the drawing, when the fluid moves in the direction of arrow 22, the movement of the fluid causes the temperature distribution generated by the heater wire 16 to be higher at the temperature sensor line 18 and lower at the temperature sensor line 20. The distribution is called temperature. A difference is generated between the resistance values of the two temperature sensor lines 18 and 20 due to the temperature difference. The flow rate and flow velocity of the fluid are detected according to the difference between the resistance values.

FIG. 2 is a diagram showing a detection circuit of the above flow sensor. A temperature sensor line 18 (R1) is connected in series with an external resistor r1, and a temperature sensor line 20 (R2) is connected in series with an external resistor r2. Applied. Then, the difference between the voltages V1 and V2 at both connection points is detected by the differential amplifier 26. As described above, when the temperature on the temperature sensor line 18 side increases and the temperature on the temperature sensor line 20 side decreases, the resistance R1 increases and the resistance R2 decreases. As a result, the voltage V1 decreases and the voltage V2 increases. This voltage difference is
It is detected by the differential amplifier 26.

The above detection circuit forms a Wheatstone bridge circuit. This Wheatstone bridge circuit has four resistors R1, R2, r1, when the flow velocity is zero.
It is known that by setting all r2 equal, the variation of the difference between the voltages V1 and V2 due to the variation of the resistance value can be maximized.

[0008]

In the case of the detection circuit shown in FIG. 2, the resistance R1,
Only R2 changes. External resistors r1, r
Since 2 is a constant resistance, the degree of change of the voltages V1 and V2 does not become too large. This means that the sensitivity of the flow sensor is low especially in a region where the flow velocity is low.

When the flow velocity is zero, four resistors R1,
Even if R2, r1, and r2 are set to be equal to each other and the rate of change of the voltage difference with respect to the change in the resistance value is set to the maximum, the temperature at which the sensors provided with the temperature sensor lines 18 and 20 are placed and the detection If the temperature at which the resistors r1 and r2 of the circuit are placed is different, the resistors R1 and R2 and the resistors r1 and
The resistance value differs from r2, and the rate of change of the voltage difference with respect to the change in the resistance value also changes. The change in the rate of change of the voltage difference is
This means that the detected flow rate or flow rate has an error depending on the temperature at which the resistor is placed.

Accordingly, an object of the present invention is to provide a high-sensitivity flow sensor.

Still another object of the present invention is to provide a flow sensor which eliminates an error in a detection value generated depending on temperature.

[0012]

In order to achieve the above object, according to the present invention, four resistors of a Wheatstone bridge circuit of a detection circuit are constituted by four temperature sensor wires provided on both sides of a heater wire. I do. Then, a series circuit of a temperature sensor wire provided on one side of the heater wire and a temperature sensor wire provided on the other side, and a temperature sensor wire provided on the other side of the heater wire and a temperature sensor wire provided on one side are provided. A constant voltage is applied to the series circuit and a voltage difference between the connection points of the two series circuits is detected.

With this configuration, first, a change in the voltage at the connection point is amplified by a decrease and an increase in the resistance value of the temperature sensor line caused by the temperature distribution. Moreover, since the direction of the change is opposite at both connection points, the voltage difference between the connection points is also amplified. Therefore, it is possible to provide a high-sensitivity flow sensor capable of detecting a slight change in the flow rate or the flow velocity.

Further, by forming the four temperature sensor wires from the same material and placing them in the same temperature environment, the four resistances of the detection circuit can be maintained at the same state when the flow velocity is zero. Therefore, a constant detection sensitivity can be maintained without depending on the temperature of the environment where the sensor is placed, and a detection error can be eliminated.

In order to achieve the above object, according to the present invention, a temperature sensor wire is provided on both sides of a heater wire, and the flow rate or the flow rate is changed according to the resistance value of the temperature sensor wire which changes according to the flow rate or the flow rate of the fluid. In the flow sensor to detect,
A first temperature sensor line provided on one side of the heater wire, and a third and fourth temperature sensor line provided on the other side of the heater wire; A first series circuit of a sensor line and a fourth temperature sensor line;
A predetermined constant voltage is applied to the first temperature sensor line and the second series circuit of the third temperature sensor line, and a first potential at a connection point between the first and fourth temperature sensor lines and the second and The flow rate or the flow velocity is detected according to a potential difference from a second potential at a connection point of the third temperature sensor line.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention is not limited to the embodiment.

FIG. 3 is a plan view of the micro flow sensor according to the embodiment. FIG. 4 is a diagram of the detection circuit. As shown in FIG. 3, in the present embodiment, the first and second temperature sensor wires 18 are connected to one side of the heater wire 16.
(R11) and 30 (R12) are provided in parallel,
The third and fourth temperature sensor wires 2 are connected to the other side of the heater wire 16.
0 (R13) and 28 (R14) are provided in parallel.

In the example shown in FIG. 3, the heater wire 16 formed of, for example, a platinum layer is formed in a W shape. Further, the four temperature sensor wires 18, 30, 20, 28 on both sides thereof are also formed of, for example, a platinum layer. These lines are connected to the semiconductor substrate 1
0 is formed on the diaphragm film that closes the surface of the through-hole 12 formed from the back side of the “0”.

As shown in the detection circuit of FIG.
Resistors R11, R12,
As for R13 and R14, a series circuit is formed by resistors in which changes in resistance value due to a change in temperature distribution generated by movement of the fluid are in opposite phases. That is, the heater wire 16
Temperature sensor line 18 (R11) arranged on the right side of
And the fourth temperature sensor line 28 (R14) disposed on the left side of the heater line 16 are connected in series, and a constant voltage V0 is applied. Similarly, a second temperature sensor line 30 (R12) disposed on the right side of the heater line 16 and a third temperature sensor line 20 (R13) disposed on the left side of the heater line 16 are connected in series, A constant voltage V0 is applied. Then, the difference voltage between the voltages V1 and V2 at the connection point of the two series circuits is amplified by the differential amplifier 26.

Assume now that the fluid has moved in the direction of arrow 22 in FIG. As a result, the temperature distribution generated by the heater wire 16 changes, so that the temperature downstream (right side) of the heater wire 16 becomes higher and the temperature upstream (left side) becomes lower. As a result, the first and second temperature sensor wires 18 (R1
1), the resistance of 30 (R12) increases, and the resistance of the third and fourth temperature sensor lines 20 (R13), 28 (R14) decreases.

As is apparent from the detection circuit shown in FIG.
In the DC circuit composed of the resistor 11 and the resistor R14, the voltage V1 drops significantly due to the rise of the resistor R11 and the decrease of the resistor R14. Similarly, in the DC circuit composed of the resistors R12 and R13, the rise of the resistor R12 and the decrease of the resistor R13 cause
Voltage V2 rises significantly. As a result, the difference ΔV
= V2-V1 also changes greatly. That is, in both DC circuits,
The change in the voltages V1 and V2 at the connection point is amplified by the change in the upper and lower resistances. Compared to the case where only the upper resistors R1 and R2 shown in FIG. 2 change, a slight change in the flow rate or the flow velocity can be detected as a large voltage difference ΔV. Therefore, a flow sensor with high sensitivity can be realized.

FIG. 5 is a graph showing the relationship between the flow rate and the voltage difference in the conventional example and the present invention. The broken line shows the characteristics of the conventional example, and the solid line shows the characteristics of the present invention. Generally, in a region where the flow velocity is low, the voltage difference ΔV increases in proportion to the increase in the flow velocity. However, when the flow rate exceeds a certain flow rate, the temperature difference between the two sides of the heater wire decreases, and the temperature eventually becomes almost the same. Therefore, the voltage difference ΔV decreases.

As described above, in the flow sensor of the present invention, since the four resistance values of the detection circuit are amplified and change in a certain direction, the detection sensitivity is about twice that of the conventional example.
That is, the amount of change in the voltage difference ΔV with respect to a constant change in the flow velocity becomes about twice.

Further, in the present embodiment, the detection circuit 4
Sensor wires 18, 28, 20, 3 forming two resistors
0 are all provided on the same semiconductor substrate and are made of the same material. Accordingly, the resistance values of the four temperature sensor lines at the time of the zero flow velocity are initially set to be equal. Even if the environmental temperature changes, the resistance values of the four temperature sensor lines change equally. Therefore, the state of the same resistance value is maintained. Further, in the state where the flow velocity is zero, since the resistors R11 and R14 and the resistors R12 and R13 of the series circuit are respectively provided at positions symmetrical with respect to the heater wire 16, the voltage difference ΔV = V1−V2 is exactly zero. Therefore, high sensitivity can be realized.

Referring to one of the series circuits of the detection circuit shown in FIG. 4, the voltage V1 at the connection point is obtained by the following equation: V1 = V0 * R14 / (R11 + R14). Therefore, if R14 is a large value with respect to R11, the change in R14 does not significantly affect the change in V1, and the change in R11 does not significantly affect the change in R11 because R14 is a large value. . On the other hand, R1
When the value of R11 is larger than 4, the change of R11 mainly affects the change, and the change of R14 has a small effect. Therefore, the closer the state of R11 = R14 is, the more the resistances R11, R
It can be seen that the change in V.14 greatly affects the change in V0. That is, in the Wheatstone bridge circuit,
The case where the four resistance values are equal has the highest sensitivity with respect to the change in the difference voltage.

As shown in the graph of FIG. 5, in the conventional detection circuit, resistors R1 and R
2 and the external resistors r1 and r2 are different in environmental temperature, and the rate of change of the resistance value with respect to temperature change is also different. Therefore, as shown by the broken line in FIG. 5, the characteristic curve shifts depending on the environmental temperature. As a result, different voltage differences ΔV are detected for the same flow velocity, which involves a detection error.

On the other hand, in the present embodiment, since the four resistors R11 to R14 always maintain the same relationship at zero flow velocity, they always have the characteristic curve (solid line) with the highest sensitivity. As a result, a detection error depending on the environmental temperature can be eliminated.

FIG. 6 is a partially enlarged plan view of a micro flow sensor according to another embodiment. In this example, a pair of temperature sensor wires 18 and 30 on both sides of the heater wire 16 are provided.
And 20, 28 are arranged in a Z-shape in parallel so that they are located in the same temperature environment as much as possible. That is, the temperature sensor line 18 includes a line 18 a closest to the heater line 16, a line 18 b slightly distant from the heater line 16,
8c. On the other hand, the temperature sensor wires 30 are slightly closer to the heater wires 30a, 30a.
b and three parallel portions of the farthest line 30c. Therefore, the position of the center of gravity of both temperature sensor wires 18 and 30 is
Almost agree. Therefore, when a current is applied to the heater wire 16 to generate a uniform temperature distribution on both sides, the temperature sensor wires 1
The resistance values of 8, 30 are kept almost equal. The temperature sensor wires 20 and 28 are also symmetrical with respect to the temperature sensor wires 18 and 30 and the heater wire 16 and similarly have substantially the same resistance. Therefore, at zero flow velocity, the four resistances are kept approximately equal.

FIG. 7 is a schematic configuration diagram when the present invention is applied to a tube type flow sensor. Since the cross-sectional area of the thin tube 40 is fixed, if the flow velocity is detected, the flow rate is simultaneously detected from the flow velocity × cross-sectional area. In the case of the tube type, the heater wire 42 is wound around the outside of the thin tube 40. Further, the temperature sensor wires 4 are symmetrically provided on both sides of the heater wire 42.
4 (R11) and 46 (R12) and the temperature sensor line 48 (R
13), 50 (R14). The temperature sensor wires 44 (R11) and 46 (R12) are wound several times in parallel and maintained at the same temperature. Similarly, the temperature sensor wires 48 (R13) and 50 (R14) are wound several times in parallel and maintained at the same temperature.

The detection circuit in this tube type flow sensor is a circuit to which resistors R11 to R14 are connected as in FIG. Therefore, as in the case of the micro flow sensor, the tube type is a flow sensor having high sensitivity and no detection error.

When wound around the thin tube 40 in the pattern of the temperature sensor lines shown in FIG. 6, the center of gravity of the temperature sensor lines on both sides coincides with each other, and a flow sensor with higher sensitivity can be realized.

[0032]

As described above, according to the present invention, a pair of temperature sensor wires are provided on both sides of a heater wire, and two resistors whose resistance changes are in anti-phase relationship are connected in series. Since the voltage difference at the connection point of the series circuit is detected, the voltage is amplified by a change in resistance and changes due to a slight change in flow rate or flow velocity. Can be.

Further, since the four resistors are placed under the same temperature environment, by using the same material, the resistance at the time of zero flow rate can be obtained.
Two resistance relationships can be maintained. Therefore, a detection error corresponding to the environmental temperature can be eliminated. If the four resistances at the time of zero flow velocity are set to be equal, a flow sensor that always operates at the highest sensitivity without depending on the environmental temperature can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a conventional micro flow sensor.

FIG. 2 is a diagram showing a detection circuit of a conventional flow sensor.

FIG. 3 is a plan view of the micro flow sensor according to the embodiment.

FIG. 4 is a detection circuit diagram of the embodiment.

FIG. 5 is a graph showing a relationship between a flow rate and a voltage difference between the conventional example and the present invention.

FIG. 6 is a partially enlarged plan view of a micro flow sensor according to another embodiment.

FIG. 7 is a schematic configuration diagram when applied to a pipe-type flow sensor.

[Description of Signs] 16 Heater wire 18, 20 Temperature sensor wire 28, 30 Temperature sensor wire V0 Constant voltage 26 Differential amplifier

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fumihiko Sato 10th Hanazono Todocho, Ukyo-ku, Kyoto-shi, Kyoto Inside (72) Inventor Toshihiko Tanmura 10th Hanazono-Todocho, Ukyo-ku, Kyoto-shi, Kyoto Inside the corporation

Claims (4)

[Claims] 1. A flow sensor for providing a temperature sensor wire on both sides of a heater wire and detecting the flow rate or flow rate in accordance with the resistance value of the temperature sensor wire that changes according to the flow rate or flow rate of the fluid, wherein one of the heater wires First and second temperature sensor lines provided on the other side, and third and fourth temperature sensor lines provided on the other side of the heater wire, wherein the first temperature sensor line and the fourth temperature sensor line are provided. A predetermined constant voltage is applied to a first series circuit of the temperature sensor lines and a second series circuit of the second temperature sensor line and the third temperature sensor line. A flow sensor for detecting the flow rate or the flow velocity according to a potential difference between a first potential at a connection point of a sensor line and a second potential at a connection point of the second and third temperature sensor lines. 2. The flow sensor according to claim 1, wherein the first to fourth temperature sensor lines are made of materials having the same temperature coefficient. 3. The first to Nth (N is an odd number of 3 or more) parallel portions of the first and second temperature sensor lines, wherein the first and second temperature sensor lines are arranged in parallel with each other. A flow sensor comprising: 4. The apparatus according to claim 1, further comprising a tube having a constant cross-sectional area, wherein said heater wire and said first to fourth temperature sensor wires are wound around said tube. Flow sensor.