JPH0516530B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a flow rate detector that detects the flow rate of a flowing fluid, and particularly relates to a flow rate detector that detects the flow rate using heat transfer between a heating element and a flowing fluid. This relates to a type of flow rate detector.

[Prior art]

Conventionally, there is a heat-sensitive flow rate detector as one of the devices for detecting the flow rate of a flowing fluid. FIG. 1 is a schematic diagram of this heat-sensitive flow rate detector.

In Fig. 1, 1 is a bulk heating element mainly made of silicon semiconductor, and 2 is this bulk heating element 1.
an electrode lead for supplying power to and supporting the same; 3;
is a support corresponding to, for example, a transistor package for fixing the electrode lead 2; 4 is an extraction lead connected to the electrode lead 2; 5 is a plumbing pipe made of stainless steel, for example; and 6 is the inside of this plumbing pipe 5. 7 is a differential bridge that detects the amount of heat generated from the bulk heating element 1, a detection circuit including an amplifier, etc., and 8 is a detection output output from this detection circuit 7. It is a signal line.

The operation of the heat-sensitive flow rate detector configured as described above will be explained. First, the power Pin supplied to the heating element 1 is expressed as Pin=Is ² ·Rs=Vs ² /Rs (1). Here, Is is the current flowing through the heating element 1, Rs is the resistance of the heating element 1, and Vs is the voltage of the heating element 1. If the amount of heat transfer between the heating element 1 and the mineral spirits 6 is Pout, the following equation holds true in a state of thermal equilibrium: Pin=Pout=h・As・ΔT (2). Here, h is the heat transfer coefficient between the heating element 1 and the mineral spirits 6, As is the surface area of the heating element 1, and ΔT is the temperature between the heating element 1 and the mineral spirits 6. Also, under laminar flow conditions where the Ray noise number Re, which generally represents the characteristics of fluid flow, is 1<Re<2000, the heat transfer coefficient h between the heating element 1 and the mineral spirits 6 is ha+b・v _0.5 ...( 3) The following empirical formula is established. Here a, b are constants, v
indicates the average flow velocity of mineral spirits 6. Therefore, from equations (1), (2), and (3), by detecting the electrical impedance Rs of this heating element 1 with the detection circuit 7, the mineral The flow velocity v (or flow rate Q) of the spirits 6 is output as a detection output signal. However, for example, as the heating element 1, an N-type homogeneous material in which a 0.7 x 0.7 x 0.15 mm ³ silicon chip is doped with 10 ¹⁵ cm ^-13 of phosphorus (P) is used, and as the support 3, a TQ-46 transistor package is used. , stainless steel plumbing pipe 5 has a diameter of 0.767 cm and a length of 30 cm.
cm, and this heating element 1 is installed approximately 25.3 cm behind the inlet of the mineral spirits 6. In this state, the heat-sensitive flow rate detector generates a unique temperature drift because a large amount of heat flows out to the support body 3 side through the electrode lead 2. In other words, the electric power Pin supplied to the heating element 1 is expressed as the sum of P _FLOW , which exchanges fluid with it, and P _LEAK flowing out to the support 3 side, Pin = P _FLOW + P _LEAK , so P _LEAK changes with time. As a result, the Pout also changes, and this heat-sensitive flow rate detector has the disadvantage of causing the aforementioned temperature drift. However, since this outflow P _LEAK to the support body 3 side always exists no matter what wire diameter and material is used, the temperature drift has an unavoidable problem.

[Summary of the invention]

This invention was made for the purpose of eliminating the above-mentioned drawbacks of the conventional system.In addition to the first heating element for detecting the flow velocity of the fluid, this invention is surrounded by a first heating element to make the outflow of heat flow to the support side zero or constant. By disposing the second heating element, a highly accurate heat-sensitive flow rate detector without temperature drift is provided.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 2 is a schematic enlarged configuration diagram of the element section of a heat-sensitive flow rate detector according to the first embodiment of the present invention, and FIG. 3 is a schematic diagram of a heat-sensitive flow rate detector using the element shown in FIG. FIG. 3 is a circuit configuration diagram.

In Fig. 2, 2 is an electrode lead for wiring thin wires of gold (Au), aluminum (Al), etc. by bonding, etc., 4a and 4b are extraction leads, and 9
10 is a thin plate-like diaphragm mainly made of a semiconductor such as silicon; 10 is a contact electrode made of aluminum (Al) or the like formed by vapor deposition; and 11a is a first diffusion layer made of the thin-plate diaphragm 9 with impurities diffused therein. The heating element 11b is a second heating element made of a diffusion layer in which impurities are diffused so as to surround the first heating element.

The diaphragm 9 of the element part of the heat-sensitive flow rate sensor constructed as described above is made by selectively etching the central part of a silicon substrate of approximately 150 μm to approximately 50 μm. It has a length of about 3 mm (horizontal direction on the paper) and is extremely thin at about 1:60 compared to the thickness of this central part, so it has a structure that makes it difficult to generate temperature distribution in the thickness direction.

Next, detection by the heat-sensitive flow rate detector using the first and second heating elements 11a and 11b will be explained based on the schematic circuit diagram of FIG. 3.

In FIG. 3, 12 is a temperature compensation element, 13, 1
4 is a bridge resistor, 15 is a differential amplifier, 16 is a linearizer, and 17 is a constant temperature difference control circuit. The temperature compensating element 12 and the bridge resistor 13 are connected to each other, and the first heating element 11a and the bridge resistor 14 are connected to each other, and a signal line drawn out from this connection point is connected to the differential amplifier 1.
Connected to 5. One terminal of the first heating element 11a and the temperature compensation element 12 is connected to the extraction leads 4a and 4b.
This bridge resistor 13, 14 is grounded through
One terminal of each is connected to a power supply. And a second heating element 11 that surrounds this first heating element 11a.
A control signal line from a constant temperature difference control circuit 17 is connected to b, and a signal line drawn out from the connection point between the first heating element 11a and the bridge resistor 14 is connected to this constant temperature difference control circuit 17. are doing. The other end of the second heating element 11b connects the lead 4b to the first
Like the heating element 11a, it is grounded. On the other hand, the output of the differential amplifier 15 is input to a linearizer 16 that corrects nonlinearity of the detection characteristics. Although the piping pipe 5 through which the fluid passes is not shown, the first
Same as the figure. Moreover, the first heating element 11a of the heat-sensitive flow rate detector having the above-mentioned configuration is the piping pipe 5.
The second heating element 11b is arranged not to be located upstream of the first heating element 11a with respect to the flow direction of the fluid to be measured.

In order to detect the flow rate or flow rate of the fluid with the above configuration, the fluid that has passed through the inside of the piping pipe 5 is
It collides with the heating element 11a and brings about a cooling effect according to the flow rate or flow rate. As a result, the first heating element 1
1a will change its electrical resistivity. Then, this change in electrical resistivity is taken out from the takeout lead 4 shown in FIG. At this time, the second heating element 11
b surrounds the first heating element 11a and is in contact with the support 3, so that heat flows out to the support 3 side. As a result, the resistivity of the second heating element 11b changes differently from that of the first heating element 11a. Therefore, the constant temperature difference control circuit 17 replaces the second heating element 11b with the first heating element 11a using fluid.
What is controlled so that it changes as well as the change or amount of change in the electrical resistivity of. This so-called second heating element 1
1b is controlled by a constant temperature difference control circuit 17 provided externally so as to have the same temperature or a constant temperature difference as that of the first heating element 11a. Therefore, the amount of heat flowing out from the first heating element 11a to the support body 3 side P _LEAK
will not depend on the flow rate or flow rate of the fluid over time. Under the condition that the first heating element 11a and the second heating element 11b are controlled to the same temperature by the constant temperature difference control circuit 17, the amount of heat P _LEAK becomes 0, and the first heating element 11a and the second heating element 11b
Under conditions where the and are controlled to a constant temperature difference, the amount of heat
P _LEAK = constant. As described above, by providing the second heating element on the diaphragm 9, time-dependent drift and flow velocity-dependent drift due to the temperature of the flow rate detector are eliminated, and highly accurate measurement is achieved.

In addition, in this first embodiment, the first and second heating elements 1
1a and 11b are made by forming two impurity diffusion layers on the same thin silicon plate.
The second heating element is formed by bonding a temperature-sensitive semiconductor such as silicon, a metal such as gold (Pu), copper (Cu), or an alloy such as copper-nickel (Cu-Ni) on a thin plate such as ceramic. Even if it is fixed by vapor deposition, the same operation and effect can be obtained.

FIG. 4 is a schematic enlarged configuration diagram of an element portion of a heat-sensitive flow rate detector according to a second embodiment of the present invention.

In FIG. 4, 18 indicates the first heating element 11a and the second heating element 11a.
a coupling member for coupling and supporting the heating element 11b; 4;
a' is an extraction lead formed on this coupling member 18 by adhesion or vapor deposition and feeding power to the first heating element 11a;
Reference numeral 4b' designates an extraction lead which is formed similarly to the extraction lead 4a' and supplies power to the second heating element 11b.

The element portion of the heat-sensitive flow rate detector having the above configuration is connected to the external circuit shown in FIG. 3, as in the first embodiment, to constitute a circuit of the heat-sensitive flow rate detector.
The first heating element 11a and the second heating element 11b are controlled by the constant temperature difference control circuit 17 so that the temperature difference due to collision with the fluid is maintained at zero or zero. The heat flow flowing from the first heating element 11a to the supporting body, which is the coupling member 18, is zero or constant, and no temperature drift occurs during measurement by the first heating element 11a. Therefore, effects similar to those of the first embodiment can be obtained. In addition, since the surface area of the first and second heating elements 11a and 11b can be increased, a large amount of heat can be exchanged between the first and second heating elements 11a and 11b, even at a small flow rate. Stable detection is achieved. Furthermore, the spatially averaged flow velocity of the fluid can be detected. The first and second heating elements 11a and 11b are made of a temperature-sensitive semiconductor such as silicon, but are not limited to silicon, and are made of metal such as platinum (Pt), copper (Cu), or Cu-Ni. The same effect can be obtained even with alloys, etc. Moreover, these first and second heating elements 11a, 11
Although b is shown as a bulk thin plate, it may also be a platinum (Pt) film deposited on an alumina/ceramic substrate, or copper (Cu) or Cu−
The same function as described above can be achieved by forming an alloy such as Ni, a thermistor, etc. by adhesion or vapor deposition.

FIG. 5 is a schematic enlarged configuration diagram of an element portion of a heat-sensitive flow rate detector according to a third embodiment of the present invention.

19 is a ceramic bobbin around which the first heating element 11a and the second heating element 11b are wound; 20
a is a connection end drawn out from the first heating element 11a;
20b is a connection end drawn out from the second heating element 11a. The ceramic bobbin 19 is made of a magnet made of alumina, steatite, etc., and is hollow inside. Note that the ceramic bobbin 19 does not need to be hollow if it is so thin that the temperature distribution in the radial direction can be ignored.

The first and second heating elements 11a and 11b are each made of platinum (Pt) for a predetermined number of times on the ceramic bobbin 19.
It is used to wind thin wire. And this first and second
The connection ends 20a and 20b of the heating elements 11a and 11b are connected to the external circuit shown in FIG. 3 shown in the first embodiment,
It can be operated in the same manner as the previous embodiment. That is, the first heating element 11a and the second heating element 11b are controlled by the constant temperature difference control circuit 17 so that the temperature difference is maintained at zero or constant. Since the amount of heat flowing from the first heating element 11a to the ceramic bobbin 19, which is a support, does not depend on time, no temperature drift occurs and the measurement output value is not adversely affected. Therefore, the same effects as in the previous embodiment can be obtained. Furthermore, since the element having such a heating element structure can be made small, it has the advantage of not only being compact as a whole but also providing quick response. In this third embodiment, thin platinum (Pt) wires are used as the first and second heating elements 11a and 11b, but the wires are not limited to such thin wires, and platinum (Pt), copper ( The same effect as described above can also be obtained with a structure in which a thin alloy film such as Cu) or Cu-Ni is formed by adhesion or vapor deposition.

As described above, the first to third embodiments each provide a highly accurate heat-sensitive flow rate detector in which the heat flow flowing from the heating element to the support body is independent of time and does not cause temperature drift.

〔Effect of the invention〕

As explained above, in this invention, a second heating element for temperature drift correction is provided surrounding a first heating element for detecting the flow velocity or flow rate of fluid, thereby preventing fluid from flowing to the support of the first heating element. Since the amount of heat generated can be corrected, time-dependent drift due to temperature and flow velocity-dependent drift can be removed, which has the great effect of enabling highly accurate detection.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a conventional heat-sensitive flow rate detector, FIG. 2 is a schematic enlarged block diagram of an element section of a heat-sensitive flow rate detector according to the first embodiment of the present invention, and FIG. 3 is a second embodiment of the heat-sensitive flow rate detector. A schematic circuit configuration diagram using a heat-sensitive flow rate detector using the elements shown in the figure, FIG. 4 is a schematic enlarged configuration diagram of the element part of the heat-sensitive flow rate detector according to the second embodiment of the present invention, and FIG. FIG. 7 is a schematic enlarged configuration diagram of an element portion of a heat-sensitive flow rate detector according to a third embodiment of the present invention. 1... Bulk heating element, 2... Electrode lead, 3
...Support, 4, 4a, 4b, 4a', 4b', 20
a, 20b...Extraction lead, 5...Piping pipe, 6...Mineral spirits, 7...Detection circuit, 8...Detection output signal line, 9...Diaphragm, 10...Contact electrode, 11a...No. 1 heating element, 11b...second heating element, 12...temperature compensation element, 13, 14...bridge resistor, 15...differential amplifier, 16...linearizer, 17...constant temperature difference control circuit, 18... ...Connecting member, 19...ceramic bobbin. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In a heat-sensitive flow rate detector that detects flow velocity and flow rate from the amount of heat transfer between a heating element and a flowing fluid, a first heating element that is in contact with the fluid and whose electrical resistivity changes depending on the temperature; , a support member that supports the first heating element, a second heating element that surrounds the first heating element and is supported by the support member, and a temperature difference between the first heating element and the second heating element. 1. A heat-sensitive flow rate detector characterized by comprising constant temperature difference control means that makes the temperature constant or zero. 2. The heat-sensitive flow rate detector according to claim 1, wherein the first heating element and the second heating element are comprised of impurity diffusion layers formed within a diaphragm of a temperature-sensitive semiconductor such as silicon. 3. The first heating element and the second heating element are formed of a thin plate-shaped temperature-sensitive semiconductor such as silicon, a metal such as platinum or copper, or an alloy such as Cu-Ni, and the first heating element and the second heating element 2. The heat-sensitive flow rate detector according to claim 1, further comprising a coupling member that electrically insulates and supports the heating elements. 4. The first heating element and the second heating element are heating elements made by adhering or vapor-depositing a temperature-sensitive semiconductor such as silicon, a metal such as platinum, copper, or an alloy such as Cu-Ni on a thin plate such as ceramic. A heat-sensitive flow rate detector according to claim 3. 5 The first heating element and the second heating element are formed of a cylindrical or columnar metal such as platinum or copper, or an alloy such as Cu-Ni, and the first heating element and the second heating element
2. The heat-sensitive flow rate detector according to claim 1, further comprising a coupling member that electrically insulates and supports the heating elements. 6. The first heating element and the second heating element are thin wires made of platinum, copper, etc. wound around the periphery of a bobbin made of a heat-resistant insulator such as ceramic. Thermal flow rate detector. 7. Platinum, which the first heating element and the second heating element are deposited on or adhered to a heat-resistant insulator such as ceramic;
6. The heat-sensitive flow rate sensor according to claim 5, wherein the heat-sensitive flow rate detector is a thin film body made of a metal such as copper or an alloy such as Cu-Ni.