JPH08145751A - Mass flowmeter - Google Patents

Abstract

PURPOSE: To provide a mass flowmeter which has excellent corrosion resistance and strength, and is easy to manufacture with a simple structure by providing such a constitution that a chip sensor having a temperature measuring resistor and a heating element never directly make contact with a fluid. CONSTITUTION: A base 11 formed of a material having poor heat conductivity but a certain mechanical strength is provided, and two gold-plated plate members 18S, 18R having good heat conductivity are soldered to a pad part 17, whereby the B-surface 11B side of holes 12, 13 is blocked. A chip sensor 20 formed of a temperature measuring resistor 53S and a heating element 54 for heating it is mounted on the surface never opposed to the passage of one plate member 18S, and a chip sensor 21 formed of a temperature measuring resistor 53R is mounted on the surface never opposed to the passage of the other plate member 18R. A corrosion resisting resist is applied to the B-surface 11B side of the base 11 and the lower surfaces of the plate members 18S, 18R to form a corrosion resisting layer 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter for measuring the flow rate of fluid such as gas and liquid.

[0002]

2. Description of the Related Art In a conventional thermal mass flowmeter, as shown in FIG. 6, a chip sensor 50 having a heating element is provided in a flow path 61 through which a fluid F such as gas or liquid flows, and a holder 62 is provided. Heating element 54 provided through the chip sensor 50
(See FIG. 5) The change in the amount of heat due to the flow of the fluid F is measured,
The flow rate is converted by converting this into an electric signal.

As the chip sensor 50 used here, as shown in FIGS. 5A and 5B, for example, an oxide film 52 such as SiO ₂ is formed on the surface of a silicon substrate 51, and this oxide film 52 is formed. On the upper surface of, for example, platinum, nickel,
The temperature measuring resistor 53 is formed using a metal having a high temperature coefficient of resistance such as aluminum, and the heating element 54 made of, for example, nichrome is formed. Further, the upper surface of each of these is covered with a silicon oxide film, a nitride film, or a polyimide film. For example, there is an indirectly heated type covered with a passivation film 55. In addition to the chip sensor 50, there are a method of self-heating a thermistor and a method of using a platinum thin wire called a hot wire.

[0004]

However, in the above-described conventional mass flowmeter, since the chip sensor 50 including a heating element is provided in the flow passage 61 through which the fluid F flows,
There were the following inconveniences. That is, since the chip sensor 50 directly contacts the fluid F,
Due to the corrosive components contained in the fluid F, the chip sensor 5
0 or the holding body 62 holding the same is corroded to cause a problem in durability, and when the fluid F containing the corrosive component or the fluid F itself has corrosiveness, the measurement should be substantially performed. I can't. The chip sensor 50 and the holder 62 are made as small as possible in order to make their heat capacities as small as possible. However, due to insufficient strength when an excessive flow rate occurs or when the fluid F contains a solid substance. May be destroyed. Since the entire shape including the holding body 62 is a three-dimensional structure, it is difficult to manufacture. And so on.

The present invention has been made in consideration of the above-mentioned matters. By preventing a chip sensor equipped with a resistance temperature detector or a heating element from directly contacting a fluid, a better corrosion resistance and An object of the present invention is to provide a mass flowmeter which has strength, has a simple structure, and is easy to manufacture.

[0006]

In order to achieve the above object, the mass flowmeter of the present invention is provided with a substrate having poor thermal conductivity so as to face a flow path of a fluid, and two holes formed in the substrate. Each of the sides of the plate facing the flow path is closed by a plate member having good thermal conductivity, and a surface of one plate member not facing the flow path is provided with a resistance temperature detector and a heating element for heating it. And a chip sensor made of a resistance temperature detector is attached to the surface of the other plate member not facing the flow path.

In the above mass flowmeter, a corrosion resistant layer may be formed on the side of the substrate and the plate member which is in contact with the fluid.

[0008]

In the mass flowmeter, since the chip sensor is provided in a state of not contacting the fluid flowing in the flow channel,
The above problems are solved. And since the chip sensor is provided in a non-contact state with the fluid flowing through the flow channel,
The above problems are solved. Further, since the shape of the sensor portion is flat and the sensor portion can be manufactured by a method similar to the method of mounting an ordinary IC or resistor on the substrate, it can be easily manufactured.

Further, when the corrosion-resistant layer is formed on the surfaces (outer surfaces) of the substrate and the plate member which are in contact with the fluid, the durability can be further improved.

[0010]

1 to 4 show an embodiment of the present invention. First, FIG. 1 and FIG. 2 are an exploded perspective view and a longitudinal sectional view showing the structure of the mass flowmeter of the present invention, respectively, in which, 1 is a flow path block, which is made of, for example, polyphenylene sulfide (PPS) resin. . A concave portion 2 having a circular shape in plan view for forming a sensor portion 6 (described later) is formed on the upper surface of the main body portion 1A of the flow path block 1, and one end of the concave portion 2 is formed inside the main body portion 1A. Two mutually independent flow paths 3 and 4 (hereinafter referred to as an introduction path 3 and a derivation path 4) that are continuous with each other and open at the end surface of the base portion 1B of the flow path block 1 are formed. Reference numeral 5 denotes a holding step portion for fitting and fixing the sensor portion 6, which has a shape similar to the outer shape of the sensor portion 6 and has openings 3 of the introduction path 3 and the discharge path 4.
a and 4a have been opened.

Reference numeral 6 is a sensor portion provided on the holding step portion 2. The configuration of the sensor unit 6 and the mounting structure for the flow path block 1 will be described later. Reference numeral 7 is a printed circuit board having one end inserted in a groove formed in the flow path block 1 and the other end screwed.
Is equipped with a signal processing / power supply unit that supplies power to the sensor unit 6 and receives an electric signal from the sensor unit 6. Reference numeral 8 denotes a case made of aluminum, for example, which is detachably provided so as to cover the main body 1A, the sensor portion 6 and the printed circuit board 7. In addition, 2a is a threaded portion formed on the peripheral wall of the recess 2, and 3b and 4b are threaded portions formed on the inner walls of the end portions of the introduction path 3 and the outflow path 4. Further, 9 is a straightening plate provided on the side of the openings 3a and 4a of the introduction path 3 and the exit path 4, respectively, and 10 is a pressing member thereof. 9
Reference numeral a is a straightening plate which is held on the inlet side of the introduction path 3 (on the screw portion 3b side by an appropriate pressing member 10a).

Here, an example of the configuration of the sensor section 6 will be described.
The mounting process will be described with reference to FIG. 11
Is a substrate made of a material having poor thermal conductivity but having some mechanical strength. In this embodiment, it is made of a glass fiber-containing epoxy resin plate having a thickness of 1 mm, and has a shape obtained by cutting a part of a disk (orifera). Is formed in. The substrate 1
As the material of No. 1, in addition to epoxy resin containing glass fiber, polyimide resin, ceramics, or the like can be used.

As shown in FIG. 3A, the substrate 11 is provided with holes 12 and 13 having a diameter of, for example, about 4 mm at appropriate intervals. An appropriate circuit pattern 14 and a plurality of electrodes 15, 16 are formed on one surface (hereinafter, referred to as A surface) 11A of the substrate 11, and holes on the other surface (hereinafter, referred to as B surface) 11B. Pad portions 17 are formed around 12 and 13 as shown in FIG.

Then, as shown in FIG. 1C, two plate members 18S, 18R having one surface (the upper surface in this embodiment) having good heat conductivity are preliminarily plated with gold and the pad portion 17 is provided. By soldering to the hole 1
B side 11B side of 2 and 13 is closed. Here, it is preferable that the plate members 18S and 18R have appropriate strength. In this embodiment, the thickness is 0.2 mm and the diameter is 5 mm.
mm stainless steel plate. The plate members 18S,
18R may be formed of a metal such as aluminum or titanium. Further, the soldering is performed, for example, by applying solder to the pad portion 17 and then performing heat treatment in a reflow furnace to fuse the solder.

Then, as shown in FIG.
1 is coated with a corrosion resistant resist on the B surface 11B side and the lower surfaces of the plate members 18S and 18R, and heat treatment is performed to form the substrate 1
The corrosion resistant layer 19 is formed on the B surface 11B of No. 1 and the lower surfaces of the plate members 18S and 18R.

Further, as shown in FIG. 6E, the chip sensors 20 and 21 are soldered to the upper surfaces of the plate members 18S and 18R, that is, to the holes 12 and 13 side using a reflow furnace. The chip sensors 20 and 21 used here have the same structure as that shown in FIG. 5, and are, for example, 0.2 mm thick and 1.5 mm square. Then, as shown in FIG. 6F, when wire bonding is appropriately performed with the electrode 15 formed on the substrate 11, in one chip sensor 20, the temperature measuring element 53 and the heat generating element 54 are connected to the electrode 15. To the S side, and the other chip sensor 21
In, the temperature measuring element 53 alone is connected to the electrode 15 and is on the R side. That is, one substrate 11 has an S side having a heat generating portion and an R side having a temperature reference portion.

Then, as shown in FIG. 3G, the sensor portion 6 is completed by connecting the jumper wire 22 to the electrode 16 formed on the substrate 11 by soldering. The other end of the jumper wire 22 is connected to the signal processing / power supply unit on the printed circuit board 7 side.

FIG. 4 shows the chip sensor 2 of the sensor section 6.
It is a figure which shows the circuit structure which incorporated 0 and 21, and in this figure, 23, 24, and 25 are resistors for forming the bridge circuit 26 with the temperature measuring element 53S of S side, and the temperature measuring element 53R of R side. Is. Reference numeral 27 is a control circuit including an operational amplifier, and a transistor 28 as a current limiting element is provided so that the output V _B of the bridge circuit 26 becomes equal to V _A.
Drive. 29 is a reference power source for the bridge circuit 26, 30
Is a DC power source connected to the heating element 54 on the S side via the transistor 28. 31 is an output point. The members represented by reference numerals 23 to 30 are provided on the printed board 7.

The sensor section 6 configured as described above is attached to the recess 2 formed in the main body section 1A of the flow path block 1 in the following manner, for example. That is, first, the rectifying plate 9 is provided in the openings 3 a and 4 a of the introduction path 3 and the extraction path 4 in a state of being fixed by the pressing member 10. Then
For example, the sensor portion 6 is fitted into the holding step portion 5 of the recess 2 via the seal member 32 made of fluororesin. In this case, since the substrate 11 is provided with an orifice, it serves as a guide for positioning, and in a predetermined state, that is, the S side corresponds to the opening 3a on the introduction path 3 side, and the R side corresponds to the opening 4a of the derivation path 4. Easy to set up. And the cap screw 33
Is screwed into the threaded portion 2a of the recess 2 to press the sensor portion 6 from above.

In this way, the sensor portion 6 is attached to the main body portion 1A of the flow path block 1, but since the seal member 32 is interposed between the sensor portion 6 and the holding step portion 5, A slight gap (flow path) 34 is formed between the sensor portion 6 and the holding step portion 5. This gap 34 is, in the embodiment,
It is about 1 mm. Therefore, the fluid F introduced into the flow path block 1 from the opening side of the introduction path 3 is directly blown to the S side of the sensor unit 6 via the two flow regulating plates 9a, 9. Then, this fluid F passes through the flow path 34,
It passes while coming into contact with the R side of the sensor unit 6 and goes out of the flow path block 1 via the lead-out path 4.

In the mass flowmeter having the above structure, one of the chip sensors 20 and 21 is used as a heating element and the other is used as a temperature reference. By constructing a constant temperature difference circuit as shown in FIG. Control is performed so that a constant temperature difference constantly occurs with respect to the temperature. When the flow of the fluid F occurs, the heater power increases to maintain a constant temperature difference,
The mass flow rate can be obtained based on this increase amount.

In the above mass flowmeter, since the tip sensors 20 and 21 are provided in a state of non-contact with the fluid F flowing in the flow path 34, the tip sensors 20 and 21 are provided.
Since the fluid F having an excessive flow rate does not come into direct contact with the solid substance in the fluid F, there is no possibility of damaging the chip sensors 20 and 21.

Further, the shape of the sensor portion 6 is flat,
Since it can be manufactured by a method similar to the method of mounting an ordinary IC or resistor on a substrate, it can be easily manufactured. The cost can be reduced accordingly, and high quality products can be manufactured stably.

Further, in the above-mentioned embodiment, the board 11 and the plate member 18 for mounting the chip sensors 20 and 21.
The corrosion-resistant layer 19 is formed on the surface (outer surface) of each of S and 18R that is in contact with the fluid F, and the chip sensors 20 and 21 are provided in a state of non-contact with the fluid F flowing through the flow path 34. Therefore, the substrate 11 and the plate members 18S, 18
The sensor unit 6 including the R and the chip sensors 20 and 21 is not corroded by the fluid F.

In particular, since the substrate 11 has a certain degree of mechanical strength, when it is mounted as a wall facing the flow path 34, its mounting structure is not limited, and it can be easily mounted by the cap screw 33. it can.

The present invention is not limited to the above-described embodiments, but can be implemented by being modified in various ways. For example, the flow path block 1 may be made of fluororesin or stainless steel. The seal member 32 may be made of a rubber material or a metal material.

Although the chip sensors 20 and 21 have the same structure, the chip sensor 21 on the R side may be the one having only the resistance temperature detector from the beginning.

In addition, resistors and capacitors for forming an electric circuit can be integratedly arranged on the substrate 11, which allows further miniaturization and cost reduction.

Furthermore, the flow velocity of the fluid F can be increased and an arbitrary flow rate output can be obtained by changing the diameter of the portion where the fluid F is directly blown to the S side of the sensor section 6, and an arbitrary flow rate from a small flow rate to a large flow rate can be obtained. Can be measured. Further, the size of the flow path 34 can be set arbitrarily.

[0030]

As described above, according to the present invention, since the chip sensor equipped with the resistance temperature detector and the heating element does not come into direct contact with the fluid, the mass flowmeter having more excellent corrosion resistance and strength. Is obtained. In addition, the structure of the sensor unit is flat, and the structure is simple, so that the mass flow meter can be manufactured in large quantities and high performance and high quality can be obtained.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an example of a mass flowmeter of the present invention.

FIG. 2 is a vertical cross-sectional view of an introduction path portion of the mass flow meter.

FIG. 3 is a diagram showing an example of a mounting process of a sensor unit incorporated in the mass flowmeter.

FIG. 4 is a circuit configuration diagram of the mass flowmeter.

FIG. 5 is a diagram showing an example of a chip sensor forming the sensor unit.

FIG. 6 is a diagram schematically showing a conventional mass flow meter.

[Explanation of symbols]

11 ... Substrate, 12, 13 ... Hole, 18S, 18R ... Plate member, 19 ... Corrosion resistant layer, 20, 21 ... Chip sensor, 3
4 ... Channel, 53S, 53R ... Resistance temperature detector, 54 ... Heating element, F ... Fluid.

Claims (2)

[Claims] 1. A substrate having inferior thermal conductivity is provided so as to face a flow path through which a fluid flows, and two sides of the two holes formed in the substrate facing the flow path are made of plate members having good thermal conductivity. A chip sensor consisting of a resistance temperature detector and a heating element for heating the same is attached to the surface of one plate member that does not face the flow path, and the other surface of the other plate member does not face the flow path. A mass flowmeter having a chip sensor made of a resistance temperature detector attached. 2. The mass flowmeter according to claim 1, wherein a corrosion-resistant layer is formed on the side of the substrate and the plate member that comes into contact with the fluid.