JPH09243423A - Flow rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow rate measuring apparatus wherein characteristics of flow rate measurement of fluid exhibit linearity. SOLUTION: A first temperature sensor 8, a second temperature sensor 9 and a heat-generating resistor 1 are sequentially positioned in a flowing direction of fluid, the heat-generating resistor 7 is drive-controlled to a higher temperature than the fluid by a predetermined temperature, and a flow rate of the fluid is measured from difference between detected temperatures by the first temperature sensor 8 and the second temperature sensor 9. The first and second temperature sensors 8, 9 are similarly heated by the heat-generating resistor 7 and similarly cooled by the fluid, but since a degree of the cooling differs due to arrangement and this is linearly proportional to the flow rate of the fluid, the flow rate of the fluid can be correctly measured.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a flow rate measuring device for measuring a flow rate of a fluid.

[0002]

2. Description of the Related Art At present, a flow rate measuring device for accurately detecting a flow rate without impeding the flow of fluid has been put into practical use.
It is used for gas meters and air conditioner air flow sensors. As such a flow rate measuring device, there is one called a heat-sensitive flow sensor, which is described in Japanese Patent Publication No. 03-38545 and Japanese Patent Publication No. 06-43906.

In the flow rate measuring device disclosed in Japanese Examined Patent Publication No. 03-38545, the heat generating resistor is driven to generate heat so that the temperature of the heat generating resistor is higher than the fluid by a constant temperature, so that the heat generating resistor is driven according to the flow rate of the fluid. The electric power is changed, and the flow rate of the fluid is measured from the electric power change.

Further, in the flow rate measuring device described in Japanese Patent Publication No. 06-43906, temperature sensors are arranged upstream and downstream of the heating resistor, and the flow rate of the fluid is calculated from the difference between the temperatures detected by these temperature sensors. To measure. In other words, considering that the heat quantity of the heating resistor is transferred to the temperature sensors on both sides by the fluid, the temperature sensor located downstream of the heating resistor is heated according to the flow rate of the fluid, and is placed upstream of the heating resistor. The temperature sensor is cooled according to the flow rate of the fluid. On the other hand, since the temperature of the fluid itself affects the two temperature sensors similarly, it is considered that the temperature of the fluid does not affect the difference between the temperatures detected by the two temperature sensors. Therefore, if the difference between the temperatures detected by the two temperature sensors is detected by the structure as described above, the flow rate of the fluid can be measured from this.

Japanese Patent Publication No. 06-43906 and Japanese Patent Publication No. 03-5
2028 discloses that a crosslinked structure is formed by anisotropic etching of a silicon substrate, and a heating resistor and a temperature sensor are formed therein. In such a structure,
Since the heat capacity of the heating resistor and the temperature sensor is reduced, its sensitivity and responsiveness are improved.

[0006]

In the flow rate measuring device described in Japanese Patent Publication No. 06-43906, the flow rate of the fluid is measured from the difference in the temperature detected by the temperature sensors arranged upstream and downstream of the heating resistor. can do.

However, as shown in FIG. 6 (a), the temperature detected by the temperature sensor located downstream of the heating resistor does not actually correspond to the flow rate of the fluid. Therefore, as shown in FIG. 6 (b), The difference between the temperatures detected by the two temperature sensors is not linearly proportional to the flow rate of the fluid. In other words, the temperature sensor located downstream of the heating resistor is initially heated when the flow rate of the fluid increases, but this heating saturates at a constant flow rate, and thereafter it is cooled corresponding to the flow rate of the fluid. .

Therefore, since the difference between the temperatures detected by the two temperature sensors is not linearly proportional to the flow rate of the fluid, it is difficult to accurately detect the flow rate of the fluid. In particular, since the temperature of the fluid actually affects the flow rate measurement result, the flow rate measurement result is compensated according to the temperature.However, if the flow rate measurement characteristic is not linear as described above, this is It is also difficult to compensate for.

Further, in the flow rate measuring device as described above, it is necessary to heat the heating resistor to a temperature higher than the fluid by a constant temperature regardless of the flow rate of the fluid. For this reason, for example, a dedicated fluid temperature sensor whose resistance value changes according to the temperature of the fluid is provided, and a bridge circuit is formed by this fluid temperature sensor and the heating resistor to feedback control the driving power of the heating resistor. are doing. However, since the resistance value of the heating resistor also changes depending on the heating temperature, it is difficult to accurately control the heating resistor to an appropriate temperature with the drive circuit having the above-described structure, and the thermal time constant of the driving circuit is also high. It becomes longer and consumes more power.

[0010]

According to the first aspect of the present invention,
A heating resistor arranged at a position where a fluid flows, a first temperature sensor arranged upstream of the heating resistor, and a second temperature arranged in a gap between the first temperature sensor and the heating resistor. A sensor, a heat generation control circuit that drives and controls the heat generation resistor to a temperature higher than the fluid by a predetermined temperature, and a flow rate measurement circuit that measures the flow rate of the fluid from the difference between the detected temperatures of the first temperature sensor and the second temperature sensor. Have and. Therefore, the first temperature sensor and the second temperature sensor are similarly heated by the heating resistor via the fluid when the fluid does not flow, and are cooled corresponding to the flow velocity when the fluid flows. At this time, the first temperature sensor separated from the heating resistor has a greater degree of cooling due to the flow of the fluid than the adjacent second temperature sensor, and therefore the difference between the detected temperatures of the first temperature sensor and the second temperature sensor is Linearly proportional to flow rate. Note that the flow rate in the present invention means the flow rate of the fluid for a certain period of time, and therefore has the same meaning as the flow velocity.

According to a second aspect of the present invention, a heating resistor arranged at a position where a fluid flows, a first temperature sensor arranged upstream of the heating resistor, and a surface of the heating resistor are arranged. A second temperature sensor, a fluid temperature sensor that is arranged at a position not affected by the heating resistor to detect the temperature of the fluid, and a difference between the temperature detected by the fluid temperature sensor and the second temperature sensor is a predetermined temperature. And a flow rate measuring circuit for measuring the flow rate of the fluid from the difference between the detected temperatures of the first temperature sensor and the second temperature sensor. Therefore, the first temperature sensor is heated by the heating resistor through the fluid,
The second temperature sensor is directly heated by the heating resistor.
When the fluid flows, the first temperature sensor is cooled according to the flow velocity, but since the second temperature sensor is maintained at a constant temperature by the heating resistor, the temperature detected by the first temperature sensor and the second temperature sensor. The difference of corresponds to the flow rate of the fluid. The heating temperature of the heating resistor is directly detected by the second temperature sensor,
The temperature of the fluid is directly detected by the fluid temperature sensor, and the heating resistor is driven and controlled by the heating control circuit based on these detected temperatures, so that the heating resistor is accurately controlled to an appropriate temperature.

According to a third aspect of the present invention, a heating resistor arranged at a position where a fluid flows, a first temperature sensor arranged upstream of the heating resistor, and a surface of the heating resistor are arranged. A second temperature sensor, a fluid temperature sensor that is arranged at a position not affected by the heating resistor to detect the temperature of the fluid, and a difference between the temperature detected by the fluid temperature sensor and the second temperature sensor is a predetermined temperature. And a flow rate measuring circuit for measuring the flow rate of the fluid based on the temperature detected by the first temperature sensor. Therefore, the first temperature sensor is heated by the heating resistor via the fluid, while the second temperature sensor is directly heated by the heating resistor. When the fluid flows, the first temperature sensor is cooled corresponding to the flow velocity, so the temperature detected by the first temperature sensor corresponds to the flow rate of the fluid. The heating temperature of the heating resistor is directly detected by the second temperature sensor, the temperature of the fluid is directly detected by the fluid temperature sensor, and the heating control circuit drives and controls the heating resistor based on these detected temperatures. , This heating resistor is accurately controlled to a proper temperature.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, a cavity is formed in the substrate to form a support portion having a crosslinked structure, and the first temperature sensor and the first temperature sensor are formed on the surface of the support portion. A second temperature sensor and a heating resistor were formed. Therefore, the first temperature sensor, the second temperature sensor, and the heating resistor are formed in a shape having a small heat capacity and being well cooled by the fluid.

[0014]

FIG. 1 shows a first embodiment of the present invention.
1 to 3 will be described below. First, the flow rate measurement device 1 of the present embodiment has a flow sensor 2, a heat generation control circuit 3, and a flow rate measurement circuit (not shown).

As shown in FIG. 1, the flow sensor 2 has one substrate 4 made of single crystal silicon or the like, and a tunnel-shaped cavity 5 is formed in this substrate 4, so that A support portion 6 having a crosslinked structure is formed on the cavity 5. Since the opening direction of the cavity 5 is parallel to the flow direction of the fluid (not shown), the bridging direction of the support portion 6 is perpendicular to the flow direction of the fluid.

A heating resistor 7, a first temperature sensor 8 and a second temperature sensor 9 are provided on the surface of the support portion 6, and these are formed in an elongated shape orthogonal to the fluid flow. There is. The first temperature sensor 8 is arranged upstream of the heating resistor 7, and the second temperature sensor 9 is arranged in a gap between the first temperature sensor 8 and the heating resistor 7. The surface of the substrate 4 upstream of the cavity 5 is
A fluid temperature sensor 10 is provided, and these temperature sensors 8 to 10 are formed of thin film resistors having a large resistance temperature coefficient.

As shown in FIG. 2, the heat generation control circuit 3 has a bridge circuit 11, and the bridge circuit 11 includes the second temperature sensor 9 and the fluid temperature sensor 1.
0, fixed resistors 12 and 13 for current control, and fixed resistor 14 for temperature setting. A direct current power supply 15 and a differential amplifier 16 are connected to the bridge circuit 11, and a control transistor 17 is connected to the differential amplifier 16. Since the DC power supply 15 is connected to the heating resistor 7 via the control transistor 17, the heating resistor 7 is driven and controlled to a temperature higher than the fluid by a predetermined temperature by the heating control circuit 3.

Further, the flow rate measuring circuit is, for example, a bridge circuit including the first temperature sensor 8 and the second temperature sensor as a part, a differential amplifier, an A / DC (Analog / Digita).
l Convertor), arithmetic processing circuit. The difference between the temperatures detected by the first temperature sensor 8 and the second temperature sensor 9 is output from the bridge circuit 11 or the like by the differential amplifier, and the difference is A / D converted by the A / DC before calculation. It is converted into the flow rate of the fluid by the processing circuit. In addition,
The arithmetic processing circuit is also connected to the fluid temperature sensor 10, and compensates the measurement result of the fluid flow rate in accordance with the measurement result of the temperature.

In such a structure, the flow rate measuring device 1 of this embodiment is used for a gas meter or the like and measures the flow rate of a fluid. In that case, the heat generation control circuit 3 drives and controls the heat generation resistor 7 to a temperature higher than the fluid by a predetermined temperature. Therefore, if the fluid does not flow, the first temperature sensor 8 and the second temperature sensor 9 are fluidized by the heat generation resistor 7. Is similarly heated through. In this case, since the temperatures detected by the first temperature sensor 8 and the second temperature sensor 9 are the same, the difference "0" allows the flow rate measurement circuit to accurately detect that the fluid is stopped.

When the fluid flows from such a state, the first and second temperature sensors 8 located upstream of the heating resistor 7,
Both 9 are cooled, but as shown in FIG.
The first temperature sensor 8 separated from the heating resistor 7 has a greater degree of cooling due to the fluid flow than the second temperature sensor 9 adjacent thereto. In other words, the first and second temperature sensors 8 and 9 are similarly heated by the heating resistor 7 and similarly cooled by the fluid, but the degree of this cooling is different due to the arrangement,
The difference is proportional to the fluid flow rate.

Therefore, as shown in FIG. 3 (b), the difference between the temperatures detected by the first temperature sensor 8 and the second temperature sensor 9 is linearly proportional to the flow rate of the fluid. Since the circuit detects, the flow rate of the fluid is accurately measured.
Since the characteristics of the heating resistor 7 and the temperature sensors 8 and 9 also change when the temperature of the fluid changes, the flow rate measurement circuit actually changes the flow rate according to the temperature of the fluid detected by the fluid temperature sensor 10. Although it is set to compensate the measurement result, this compensation is also easy because the flow rate measurement characteristic is linear.

The present invention is not limited to the above-mentioned form, and allows various modifications. For example, although the second temperature sensor 9 close to the heating resistor 7 is used for the heat generation control circuit 3 here, the first temperature sensor may be used for this heat generation control circuit. It is also possible to form the heat generation control device 19 by a feedback loop with the heat generation resistor 7 as a part of the bridge circuit 18, as shown in FIG.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described below based on Regarding the flow rate measuring device 21 of the present embodiment, the same parts as those of the flow rate measuring device 1 described above are denoted by the same names and reference numerals, and detailed description thereof will be omitted. The flow rate measuring device 21 of the present embodiment also has a flow sensor 22, a heat generation control circuit 3, and a flow rate measurement circuit, and the second temperature sensor 9 is used in the heat generation control circuit 3, but this second temperature sensor 9 is used. A temperature sensor 9 is formed on the surface of the heating resistor 7. Actually, the second temperature sensor 9 is formed on the surface of the heating resistor 7 through an insulating film (not shown). Such insulating films include silicon nitride, SiO ₂ , Ta. ₂ O ₅ etc. are used.

In the flow rate measuring device 21 of the present embodiment having such a configuration, the first temperature sensor 8 is heated by the heating resistor 7 via the fluid, but the second temperature sensor 9 is used.
Is directly heated by the heating resistor 7. When the fluid flows, the first temperature sensor 8 is cooled according to the flow velocity,
The second temperature sensor 9 is maintained at a constant temperature by the heating resistor 7. Since the difference between the temperatures detected by the first temperature sensor 8 and the second temperature sensor 9 corresponds to the flow rate of the fluid,
Based on this, the flow rate measuring circuit measures the flow rate of the fluid.

Since the temperature detected by the second temperature sensor 9 corresponds only to the temperature of the fluid and does not correspond to the flow rate, the above-described flow rate measurement result corresponds to the temperature detected by the first temperature sensor 8. In this case, the detection characteristics of the first temperature sensor 8 corresponding to the flow rate and the temperature of the fluid are known, and the temperature of the fluid is also accurately detected by the fluid temperature sensor 10. Therefore, the flow rate measurement circuit determines the flow rate of the fluid. It is possible to measure accurately.

In the flow rate measuring device 21 of the present embodiment, the heat generation temperature of the heat generating resistor 7 is directly detected by the second temperature sensor 9, and the fluid temperature is directly detected by the fluid temperature sensor 10. Since the heating resistor 7 is driven and controlled by the heating control circuit 3 based on the temperature, the heating resistor 7 can be accurately controlled to an appropriate temperature.
In particular, since the second temperature sensor 9 is located on the surface of the heating resistor 7, the heating control circuit 3 has a small thermal time constant and reduced power consumption.

In the flow rate measuring device 21 of this embodiment, the flow rate of the fluid is measured by the difference between the temperatures detected by the first and second temperature sensors 8 and 9, but as described above, the second temperature sensor is used. Since the temperature detected by 9 corresponds only to the temperature of the fluid and does not correspond to the flow rate, it is also possible to measure the flow rate of the fluid only by the temperature detected by the first temperature sensor 8. However, if the flow rate of the fluid is measured by the difference between the temperatures detected by the first and second temperature sensors 8 and 9, for example, the noise similarly generated in the first and second temperature sensors 8 and 9 due to disturbance may be offset. It is possible.

[0028]

According to the first aspect of the present invention, a heating resistor arranged at a position where a fluid flows, a first temperature sensor arranged upstream of the heating resistor, and the first temperature sensor and heat generation From the difference between the second temperature sensor arranged in the gap with the resistor, the heat generation control circuit that drives and controls the heat generating resistor to a temperature higher than the fluid by a predetermined temperature, and the difference between the detected temperatures of the first temperature sensor and the second temperature sensor. By having a flow rate measuring circuit that measures the flow rate of the fluid, the difference in the detected temperature between the first temperature sensor and the second temperature sensor is linearly proportional to the flow rate of the fluid, so that the flow rate of the fluid can be accurately measured. Therefore, it is easy to compensate the measurement result corresponding to the fluid temperature.

According to the second aspect of the present invention, the heating resistor arranged at the position where the fluid flows, the first temperature sensor arranged upstream of the heating resistor, and the surface of the heating resistor are arranged. The second temperature sensor, the fluid temperature sensor which is arranged at a position not affected by the heating resistor to detect the temperature of the fluid, and heats so that the difference between the temperature detected by the fluid temperature sensor and the second temperature sensor becomes a predetermined temperature. By having a heat generation control circuit that drives and controls the resistor and a flow rate measurement circuit that measures the flow rate of the fluid from the difference between the detected temperatures of the first temperature sensor and the second temperature sensor, The temperature of the fluid is directly detected by the temperature sensor, the temperature of the fluid is directly detected by the fluid temperature sensor, and the heating resistor is driven and controlled by the heating control circuit based on these detected temperatures.
This heating resistor can be controlled accurately to an appropriate temperature, and since the second temperature sensor is located on the surface of the heating resistor, the thermal time constant of the heating control circuit is small and power consumption can be reduced.

According to the third aspect of the present invention, the heating resistor arranged at a position where the fluid flows, the first temperature sensor arranged upstream of the heating resistor, and the surface of the heating resistor are arranged. The second temperature sensor, the fluid temperature sensor which is arranged at a position not affected by the heating resistor to detect the temperature of the fluid, and heats so that the difference between the temperature detected by the fluid temperature sensor and the second temperature sensor becomes a predetermined temperature. The temperature of the heating resistor is directly detected by the second temperature sensor by having the heat generation control circuit for driving and controlling the resistor and the flow rate measurement circuit for measuring the flow rate of the fluid based on the temperature detected by the first temperature sensor. The temperature of the fluid is directly detected by the fluid temperature sensor, and the heating resistor is driven and controlled by the heating control circuit based on these detected temperatures, so that the heating resistor is accurately controlled to an appropriate temperature. It can be, because the second temperature sensor located on the surface of the heating resistor can be thermal time constant of the heating control circuit to reduce the power consumption reduced.

According to the fourth aspect of the invention, a cavity is formed in the substrate to form a support portion having a bridge structure, and the first temperature sensor, the second temperature sensor, and the heating resistor are formed on the surface of the support portion. As a result, the first temperature sensor, the second temperature sensor, and the heating resistor can be formed in a shape having a small heat capacity and being favorably cooled by the fluid, so that the sensitivity and responsiveness can be improved.

[Brief description of drawings]

FIG. 1 is a plan view showing a flow sensor of a flow rate measuring device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a heat generation control circuit.

FIG. 3A is a characteristic diagram showing detected temperatures of a first temperature sensor and a second temperature sensor, and FIG. 3B is a characteristic diagram showing a measurement result of a fluid flow rate.

FIG. 4 is a circuit diagram showing a heat generation control circuit of a modified example.

FIG. 5 is a plan view showing a flow sensor of a flow rate measuring device according to a second embodiment of the present invention.

FIG. 6A is a characteristic diagram showing detected temperatures of a first temperature sensor and a second temperature sensor of a flow rate measuring device of a conventional example,
(B) is a characteristic diagram showing the measurement result of the flow rate of the fluid.

[Explanation of symbols]

 1, 21 Flow rate measuring device 3, 19 Heat generation control circuit 4 Substrate 5 Cavity 6 Support part 7 Heating resistor 8 First temperature sensor 9 Second temperature sensor 10 Fluid temperature sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 391025741 Mitsuteru Kimura 56, 3-2 Shiomidai, Shichigahama-cho, Miyagi-gun, Miyagi Prefecture 56 (72) Inventor Hiroyuki Horiguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Company, Ltd. (72) Inventor Mitsuteru Kimura 56, 3-2 Shiomidai, Shichigahama-cho, Miyagi-gun, Miyagi Prefecture

Claims (4)

[Claims] 1. A heating resistor disposed at a position where a fluid flows, a first temperature sensor disposed upstream of the heating resistor, and a gap disposed between the first temperature sensor and the heating resistor. Second temperature sensor, and a heat generation control circuit for driving and controlling the heat generation resistor to a temperature higher than the fluid by a predetermined temperature,
A flow rate measuring device, comprising: a flow rate measuring circuit that measures a flow rate of a fluid based on a difference between detection temperatures of the first temperature sensor and the second temperature sensor. 2. A heating resistor arranged at a position where a fluid flows, a first temperature sensor arranged upstream of the heating resistor, and a second temperature sensor arranged on the surface of the heating resistor. , A fluid temperature sensor arranged at a position not affected by the heating resistor to detect the temperature of the fluid, and the heating resistor so that the difference between the temperature detected by the fluid temperature sensor and the second temperature sensor becomes a predetermined temperature. And a flow rate measuring circuit for measuring the flow rate of the fluid from the difference between the temperatures detected by the first temperature sensor and the second temperature sensor. 3. A heating resistor arranged at a position where a fluid flows, a first temperature sensor arranged upstream of the heating resistor, and a second temperature sensor arranged on the surface of the heating resistor. , A fluid temperature sensor arranged at a position not affected by the heating resistor to detect the temperature of the fluid, and the heating resistor so that the difference between the temperature detected by the fluid temperature sensor and the second temperature sensor becomes a predetermined temperature. And a flow rate measurement circuit for measuring the flow rate of the fluid based on the temperature detected by the first temperature sensor. 4. A substrate is provided with a cavity to form a support portion having a cross-linking structure, and a first temperature sensor, a second temperature sensor and a heating resistor are formed on the surface of the support portion. Item 1, 2 or 3 of the flow rate measuring device.