JP3163558B2 - Flow velocity detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate detecting device for detecting a flow rate of an extremely small gas.

[0002]

2. Description of the Related Art FIG. 7 is a perspective view showing a conventional microbridge flow sensor. In the figure, a through hole 4 communicating the left and right openings 2 and 3 is formed at the center of the semiconductor base 1 by anisotropic etching, and a bridge-like shape is formed above the through hole 4 from the semiconductor base 1. Thus, a bridging portion 5 is formed which is spatially isolated from the semiconductor base 1 and is thermally insulated from the semiconductor base 1 as a result. On the surface of the bridging portion 5, thin-film heater elements 7 and thin-film temperature-measuring resistance elements 8, 9 sandwiching the heater elements 7 are arranged. In the corners on the semiconductor base 1, a temperature measuring resistance element 10 around the thin film is provided.
Are formed. FIGS. 8A and 8B are explanatory diagrams showing the operation of the microbridge flow sensor shown in FIG. 7A shows a temperature distribution of each element, and FIG. 7B shows a cross section taken along line VIIIB-VIIIB in FIG. Reference numeral 6 denotes a protective film made of a material having low thermal conductivity.

The heater element 7 is heated to a certain temperature th4, th5 (for example, 63) higher than the ambient temperature.
8C, the temperatures t6 and t7 of the temperature-measuring resistance elements 8 and 9 (for example, 35 ° C .: ambient temperature reference) become the temperatures th4 and th5 of the heater element 7 as shown in FIG. It is almost symmetric about. At this time, for example, when the gas moves from the direction of arrow 11 shown in FIG.
Lower the temperature by 6. On the other hand, the downstream temperature measuring resistance element 9
The heat conduction from the heater element 7 is promoted using the gas flow as a medium, and the temperature rises by ΔT7, so that a temperature difference occurs. Therefore, by incorporating the temperature measuring resistance elements 8 and 9 on the two sides of the Wheatstone bridge and using the output of this Wheatstone bridge as the sensor output, the temperature difference can be converted into a voltage, and a voltage output according to the flow velocity can be obtained.
As shown in FIG. 9, the flow velocity of the gas can be detected.

As described above, the conventional micro-bridge flow sensor has a thin-film bridging structure having an extremely small heat capacity formed by a thin-film technique and an anisotropic etching technique, and has a very high response speed, high sensitivity, and low sensitivity. It has excellent features such as power consumption and good mass productivity.

Incidentally, in order to obtain a high-precision numerical value in the detection of the gas flow velocity, it is necessary to confirm and initialize (correction processing) the initial values of the temperature measuring resistance elements 8 and 9 before the flow velocity detection. That is, the temperature measuring resistance elements 8 and 9 are formed by making full use of a photolithography technique, a film forming technique, and an etching technique, but it is extremely difficult to make the two characteristic values (for example, resistance temperature coefficient and the like) the same. . For this reason, it is necessary to adjust the electric circuit to which the temperature measuring resistance elements 8 and 9 are connected in advance to make the two values the same (zero point adjustment).

Normally, it is ideal to adjust the values of the temperature measuring resistance elements 8 and 9 by heating the heater element 7 and stopping the flow of gas (zero point).
However, it is actually difficult to stop the gas flowing in the actual use condition of the flow sensor at every measurement, and it is necessary to correct the temperature measurement resistance elements 8 and 9 while the gas is flowing. In this case, the zero point adjustment (substitute zero point adjustment) can be performed by subtracting from the sensor output a value obtained from the difference between the resistance values of the temperature measuring resistance elements 8 and 9 in a state where the heating of the heater element 7 is stopped. Is being done. Thus, there is a difference between the zero adjustment and the substitute zero adjustment.

[0007]

However, in such a conventional microbridge flow sensor, a heater element 7 is formed on one bridge 5 as shown in an enlarged plan view of a main part in FIG. Alternatively, as shown in FIG. 11, two bridge portions 5 having a slit-shaped central opening 12 are provided.
a and 5b are formed, and the heater element 7 is formed with the center opening 12 interposed therebetween, and the temperature measuring resistance elements 8 and 9 are formed outside the heater element 7. When heated, heat is transmitted through the base material of the bridging portions 5a and 5b in addition to the heat transmitted through the air, which has the disadvantage that the sensitivity of flow velocity detection is reduced.

Further, as shown in FIG. 8A, the temperatures t6 and t7 of the temperature measuring resistance elements 8 and 9 used in the actual flow velocity detection are the temperature th4 and th5 (6) of the heater element 7, respectively.
3 ° C .: based on the ambient temperature) (for example, 35 ° C .: based on the ambient temperature), the difference between the zero point adjustment and the substitute zero point adjustment becomes large, and there is a disadvantage that an accurate detected value cannot be obtained. Was. Further, if dust or the like adheres to the temperature measuring resistance elements 8 and 9, the surface of the dust becomes a heat sink or a radiation fin, so that the temperature of the temperature measuring resistance elements 8 and 9 changes and accurate flow velocity cannot be detected. there were.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to suppress the difference between zero point adjustment and substitute zero point adjustment without lowering the sensitivity of flow velocity detection. An object of the present invention is to provide a flow velocity detecting device capable of accurately detecting a flow velocity even when dust or the like adheres.

[0010]

In order to achieve the above object, a first invention (an invention according to claim 1) includes a first temperature measuring resistor, a heat generating element, and a heat generating element. Body and a second resistance temperature detector are sequentially provided, and a value obtained from a difference in resistance between the first resistance temperature detector and the second resistance temperature detector is set as a sensor output corresponding to the gas flow rate. In the detection device, a heat insulating material having a low thermal conductivity is provided between the first temperature measuring resistor and the heating element and between the heating element and the second temperature measuring resistor to supply power to the heating element. Means is provided for performing a substitute zero point correction by subtracting a value obtained from the difference between the resistance values in the stopped state from the sensor output.
According to the present invention, the space between the first temperature measuring resistor and the heating element and the space between the heating element and the second temperature measuring resistor are thermally insulated, and power supply to the heating element is stopped. The substitute zero point correction is performed by subtracting the value obtained from the difference between the resistance values in the state from the sensor output.

The second invention (the invention according to claim 2) provides a first temperature measuring resistor, a first heating element, a second heating element, and a second temperature measuring element from upstream to downstream in which gas flows. In a flow rate detecting device, a resistor is sequentially provided, and a value obtained from a difference between resistance values of the first and second temperature measuring resistors is set as a sensor output according to a gas flow rate. RTD and 1st
A heat-insulating material having a low thermal conductivity is provided between the first heating element and the second heating element, and between the second heating element and the second resistance thermometer. Means is provided for performing a substitute zero point correction by subtracting from the sensor output a value obtained from the difference between the resistance values when power supply to the first and second heating elements is stopped. According to the present invention, between the first temperature measuring resistor and the first heating element, between the first heating element and the second heating element, and between the second heating element and the second temperature measuring resistor. The value obtained from the difference between the resistance values when the power supply to the first and second heating elements is stopped is subtracted from the sensor output, thereby providing a substitute zero point. Correction is performed.

The third invention (the invention according to claim 3) is the first invention.
In the invention and the second invention, the first temperature measuring resistor and the second
Are mounted on two sides of a Wheatstone bridge, and the output of the Wheatstone bridge is used as a sensor output. According to the present invention, the output of the Wheatstone bridge in which the first resistance temperature detector and the second resistance temperature detector are incorporated on two sides thereof is a sensor output corresponding to the gas flow rate.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. [Embodiment 1] FIG. 1 shows an embodiment (first embodiment) of the present invention.
2 is an enlarged plan view of a main part of a flow sensor according to an embodiment of the present invention. In the figure, the same or corresponding parts as those in FIG. 7 are denoted by the same reference numerals.

Now, a through hole 4 formed in the semiconductor base 1 will be described.
On the upper side, a membrane portion 5 ′ is formed, which is spatially isolated from the semiconductor base 1 in a bridge shape, and is consequently thermally insulated from the semiconductor base 1. The membrane portion 5 ′ has two slit-shaped openings 1 communicating with the through holes 4 at the center.
It comprises a first membrane part 5c, a second membrane part 5d and a third membrane part 5e separated by 3 and 14. A temperature-measuring resistance element (first temperature-measuring resistor) 8 is provided on the surface of the first membrane portion 5c, a heater element (heating element) 7 is provided on the surface of the second membrane portion 5d, and a third membrane portion is provided. A resistance temperature element (second resistance temperature detector) 9 is formed on the surface of 5e.

FIGS. 3A and 3B are explanatory diagrams showing the operation of the flow sensor shown in FIG. Here, FIG. 7A shows a temperature distribution of each element based on the ambient temperature, and FIG. 7B shows a cross section of the first embodiment corresponding to FIG.

Now, as in FIG. 8, the heater element 7
At a certain higher temperature th1 than the ambient temperature (for example,
63 (C: ambient temperature reference), the temperatures t1 and t2 of the temperature-measuring resistance elements 8 and 9 are centered on the temperature th1 of the heater element 7 as shown in FIG.
It is symmetric at a lower temperature (for example, 20 ° C .: ambient temperature reference) than the temperatures t6 and t7 shown in FIG.

This is because the temperature-measuring resistance element 8 formed on the first membrane part 5c and the temperature-measuring resistance element 9 formed on the third membrane part 5e are formed on the second membrane part 5d. The heater element 7 is thermally insulated (air serves as a heat insulating material) through the slit-shaped openings 13 and 14, and the heated heat of the heater element 7 is reduced to the second as shown in FIG. 10 or 11. 1st and 2nd
This is because there is no direct conduction to the membrane part.

In this state, when the gas moves from the direction of arrow 11 shown in FIG. 1, the upstream temperature measuring resistance element 8 is cooled and its temperature is decreased by ΔT1. On the other hand, in the downstream temperature-measuring resistance element 9, heat conduction from the heater element 7 is promoted using the gas flow as a medium, and the temperature rises by ΔT2, so that a temperature difference occurs. Therefore, by incorporating the temperature-measuring resistance elements 8 and 9 on two sides of the Wheatstone bridge and using the output of this Wheatstone bridge as a sensor output, the temperature difference can be converted into a voltage, and a voltage output according to the flow velocity can be obtained. Can be detected. Further, a substitute zero point adjustment is performed by subtracting from the sensor output a value obtained from the difference between the resistance values of the resistance temperature elements 8 and 9 in a state where the heat generation of the heater element 7 is stopped.

As described above, in the first embodiment, the heat of the heater element 7 is conducted to the temperature measuring resistance elements 8 and 9 only by using the gas as a medium, and as shown in FIG. Because there is no heat transmitted through the base material,
The sensitivity of the flow velocity detection can be improved.

Further, the temperature t of the temperature measuring resistance elements 8 and 9
Since the rise of 1, t2 from the ambient temperature can be reduced to about 20 ° C., the difference between the zero point adjustment and the substitute zero point adjustment accompanying the temperature rise can be suppressed.

Further, even if dust adheres to the temperature measuring resistance elements 8 and 9, the amount of temperature change caused by the adherence of the dust is suppressed to be small due to the low temperature, and the influence of the detection error due to the adherence of the dust can be suppressed. it can.

[Embodiment 2] FIG. 2 shows a second embodiment according to the present invention.
FIG. 4 is an enlarged plan view of a main part of the flow sensor showing the embodiment. In the figure, the same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals. Here, the differences from the first embodiment are as follows.
Three slit-like openings 13 to 15 in the membrane part 5 ″
To form a first membrane 5f, a second membrane 5g, a third membrane 5h, and a fourth membrane 5i. Then, a temperature-measuring resistance element 8 is provided on the surface of the first membrane portion 5f, and one heater element (first heating element) 7 is provided on the surface of the second and third membrane portions 5g. In the figure, the other heater element (second heating element) 7 is formed, and in the fourth membrane portion 5i, a resistance temperature measuring element 9 is formed.

FIGS. 4A and 4B are explanatory diagrams showing the operation of the flow sensor shown in FIG. Here, FIG. 7A shows a temperature distribution of each element on the basis of the ambient temperature, and FIG. 7B shows a cross section of the second embodiment corresponding to FIG.

In the second embodiment, substantially the same operation as that of the first embodiment is performed, but it should be noted that two membrane portions on which the heater elements 7 are formed are formed. .

That is, in FIG. 4A, since the two membrane portions 5g and 5h forming the heater element 7 are thermally insulated from each other, an arrow 11 shown in FIG.
When the gas moves from the direction of, a temperature gradient of ΔT0 + ΔT5 is generated between the temperature th2 of the heater element 7 and the temperature th3 of the heater element 7.

Therefore, the temperature measuring resistance element 8 on the upstream side is cooled to a temperature difference ΔT1 or more shown in FIG.
The temperature of the downstream temperature measuring resistance element 9 is further promoted by the temperature gradient of the heater element 7 using gas as a medium, and the temperature difference Δ shown in FIG.
As a result, a large temperature difference ΔT4 is generated as compared with T2.
Thereby, a large voltage output difference can be obtained between the resistance temperature element 8 and the resistance element 9.

Third Embodiment FIG. 5 shows a third embodiment according to the present invention.
FIG. 4 is an enlarged plan view of a main part of the flow sensor showing the embodiment. In the figure, the same or corresponding parts as those in FIG. Here, the difference from the first and second embodiments is that the semiconductor base 1 is not provided with a thermally insulated membrane portion.

That is, in the above-described embodiment, two temperature-measuring resistance elements and a heater element are formed in the membrane portion, and air is used as a heat insulating material. On the other hand, in the third embodiment, the heat insulating material 16a that thermally insulates the temperature measuring resistance element 8 and the heater element 7 and the heater element 7 and the temperature measuring resistance element 9 are formed on the same semiconductor base 1. Is provided with a heat insulating material 16b. Thus, heat conduction to the heater elements 8 and 9 can be prevented as in the first and second embodiments.

FIG. 6 is a sectional view showing a section taken along line VI-VI in FIG. As shown in FIG.
b is formed sufficiently deep from the upper surface of the semiconductor base 1 to prevent heat conduction from the heater element 7 indicated by the arrow 17. In the third embodiment, the heat insulating materials 16a and 16a
Although b is provided in the semiconductor base 1, the semiconductor base 1 may be used as a heat insulating material.

[0030]

As is apparent from the above description, according to the present invention, according to the first invention, the distance between the first temperature measuring resistor and the heating element and the distance between the heating element and the second temperature measuring resistor are increased. Are electrically insulated from each other, and a value obtained from a difference between the resistance values of the first and second temperature measuring resistors in a state where power supply to the heating element is stopped is a sensor output. , The substitute zero point correction is performed, and the following excellent effects are obtained. (1) Since the heating element is thermally insulated from the first and second resistance temperature detectors, the temperatures of the first and second resistance temperature detectors at the time of detecting the flow velocity can be kept low. Therefore, the difference between the zero point adjustment and the substitute zero point adjustment can be suppressed. (2) Even if dust adheres to the resistance temperature detector, the influence of errors due to heat dissipation can be suppressed because the surface temperature is low,
Accurate flow rate detection can be performed. (3) There is almost no heat conduction from the heating element to the RTD through a portion other than the gas (for example, a semiconductor base), and the flow is measured only by the gas that actually flows and changes the temperature of the RTD. Since heat is conducted to the thermal resistor, it becomes more sensitive to gas flow. Therefore, it is possible to improve the sensitivity of the flow velocity detection particularly at a low flow velocity.

Further, in the second invention, between the first heating element and the first heating element, between the first heating element and the second heating element, and between the second heating element and the second heating element. Are electrically insulated from each other with respect to the first and second temperature measuring resistors in a state where power supply to the first and second heating elements is stopped. By subtracting the value obtained from the difference between the resistance values from the sensor output, the substitute zero point correction is performed, and has the following excellent effects in addition to the effects of the first invention. The flow causes a temperature difference between the first and second heating elements, and the temperature difference between the first and second temperature measuring resistors can be further increased. For this reason,
A large voltage output difference can be obtained between the first resistance temperature detector and the second resistance temperature detector.

[Brief description of the drawings]

FIG. 1 is an enlarged plan view of a main part of a flow sensor according to a first embodiment of the present invention.

FIG. 2 is an enlarged plan view of a main part of a flow sensor according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an operation of the flow sensor shown in FIG.

FIG. 4 is an explanatory diagram showing an operation of the flow sensor shown in FIG.

FIG. 5 is an enlarged plan view of a main part of a flow sensor according to a third embodiment of the present invention.

6 is a sectional view showing a section taken along line VI-VI in FIG. 5;

FIG. 7 is a perspective view showing a conventional microbridge flow sensor.

FIG. 8 is an explanatory diagram showing the operation of the microbridge flow sensor shown in FIG.

FIG. 9 is a characteristic diagram showing a relationship between a voltage output and a flow velocity.

FIG. 10 is an enlarged plan view of a main part showing a configuration of a detection unit of a conventional microbridge flow sensor.

FIG. 11 is an enlarged plan view of a main part showing a configuration of a detection unit of a conventional microbridge flow sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor base, 2, 3 ... Opening, 4 ... Through-hole, 5c, 5
f: first membrane portion, 5d, 5g: second membrane portion, 5e, 5h: third membrane portion, 5i: fourth membrane portion, 6: protective film, 7: heater element,
8, 9 ... resistance temperature element, 13, 14 ... opening, 16
a, 16b: heat insulating material.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/68-1/68 203 G01P 5/12

Claims (3)

(57) [Claims] 1. A first temperature measuring resistor, a heating element, and a second temperature measuring resistor are sequentially provided from upstream to downstream of a gas flow, and the first temperature measuring resistor and the second temperature measuring resistor are provided. In a flow velocity detecting device that sets a value obtained from a difference in resistance between the temperature measuring element and a sensor output according to a flow velocity of the gas, between the first temperature measuring resistor and the heating element and the heating element. A heat insulating material having a low thermal conductivity is provided between each of the second temperature measuring resistors, and a value obtained from the difference between the resistance values in a state where power supply to the heating elements is stopped is calculated from the sensor output. A flow velocity detecting device comprising means for performing a substitute zero point correction by subtraction. 2. A first temperature measuring element, a first heating element, a second heating element, and a second temperature measuring element are sequentially provided from an upstream to a downstream where gas flows, and the first temperature measuring element is provided. In a flow velocity detecting device, a value obtained from a difference between resistance values of a temperature resistance element and the second resistance temperature element is set as a sensor output according to a flow velocity of the gas, wherein the first resistance temperature element and the second 1 heating element, between the first heating element and the second heating element, and between the first heating element and the second heating element.
A heat insulating material having a low thermal conductivity is provided between each of the heating elements and the second resistance thermometer, and the resistance value in a state where power supply to the first and second heating elements is stopped. A flow velocity detecting device comprising means for performing a substitute zero point correction by subtracting a value obtained from the difference from the sensor output. 3. The Wheatstone bridge according to claim 1, wherein the first resistance temperature detector and the second resistance temperature detector are incorporated into two sides of a Wheatstone bridge, and the output of the Wheatstone bridge is used as a sensor output. A flow velocity detector characterized by the above-mentioned.