JPH01207634A - Differential pressure type flowmeter - Google Patents

Abstract

PURPOSE:To measure a fine flow rate by allowing a gauge made of a semiconductor formed on a diaphragm of silicon itself to detect differential pressure across a differential pressure hole bored in the center of the strain inducing part of the diaphragm. CONSTITUTION:When fluid Q flows in through a hole 32 as shown by an arrow, a pressure drop is generated at the differential pressure hole 21 at the center part of the strain inducing part 32 which functions as the orifice of the diaphragm 20 made of silicon, thereby generating differential pressure across the hole 21. This differential pressure causes the strain inducing part 32 to be strained, which is detected by a shear type gauge 38 as a piezoelectric resistance element. A computing element which calculates the flow rate is formed integrally with the fixed part 37 of the diaphragm 20 by semiconductor technology so as to satisfy a specific expression of the detected differential pressure and flow rate, and its electric signal is led out through lead wires 29 and 30.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a differential pressure type flowmeter that detects a flow rate by measuring the differential pressure generated above and below a restriction formed in a fluid passage, and particularly relates to a small-sized This paper relates to a differential pressure type flow meter that can measure minute flow rates.

<Prior Art> Flowmeters that measure minute flow rates include differential pressure flowmeters, thermal flowmeters, and area flowmeters. Of these, the hole diameter of the orifice where the orifice and converter are integrated is 0.5 m.
There are integral type differential pressure flowmeters with a size of about 1.5 m, but they are quite large.

FIG. 3 shows the principle structure of a differential pressure detecting section of a conventional differential pressure flowmeter. Reference numeral 10.11 is a fluid conduit, each end face of which is provided with a flange portion 12.13. A disk-shaped orifice plate 14 having a circular hole in the center is inserted and fixed between the flange portions 12,13.

Then, the fluid conduit 10.11 is connected to the Oriais plate 14.
Pressure extraction holes 15 and 16 are opened in the upstream and downstream pipe walls,
From here, each pressure is introduced into the differential pressure converter 17, and these differential pressures are measured.

In Fig. 3, the differential pressure converter is shown as a U-tube type differential pressure converter for simplicity, but in reality, for example, both ends are sealed with diaphragms and a center diaphragm is arranged in the center. The respective pressures taken out through the differential pressure extraction holes 15 and 16 are applied to each diaphragm of the differential pressure detection unit, which has two filled chambers, and the center diaphragm is displaced based on the differential pressure generated. The differential pressure converter is configured to electrically detect this displacement as a change in capacitance. This detection principle is the same regardless of size.

Using the differential pressure detected by this differential pressure converter, a flow rate calculator (not shown) executes flow rate calculation and outputs the result.

<Problem to be solved by the invention> However, as micro flowmeters for measuring micro flow rates, thermal flowmeters, area flowmeters, etc. have drawbacks such as insufficient accuracy and troublesome handling. In addition, in a differential pressure flowmeter, there is no difference in the size of the converter whether it is small or large, so a small-sized differential pressure flowmeter has a relatively large converter, and a flowmeter with a minute flow rate has a large converter. However, it has the drawbacks of a large shape and weight, lack of simplicity, and increased cost.

Means for Solving the Problems> In order to solve the above problems, the present invention provides a silicon diaphragm having a thin strain-generating part with a differential pressure hole in the center and a fixing part around it; 5 A semiconductor gauge that is formed in this diaphragm and detects the distortion of the strain-generating part that is distorted in response to the differential pressure on both sides of the differential pressure hole, a substrate that supports the diaphragm, and an electrical signal related to the output of the gauge that is connected to the outside. It is equipped with a base to which a lead wire to be taken out is fixed, a tube that connects this base and a substrate and serves as a passage for the fluid to be measured, and a cover that is coupled to the base so as to cover the diaphragm and serves as a passage for the fluid. The flow rate is calculated using electrical signals related to the flow rate.

A gauge measures the strain caused by the differential pressure generated in response to the measured flow rate in the differential pressure hole drilled in the center of the strain-generating part of the diaphragm, which is placed between the tube that serves as the fluid passage and the cover. The detected detection signal is used to calculate the flow rate.

<Embodiment> FIG. 1 is a longitudinal sectional view showing the configuration of one embodiment of the present invention.

Reference numeral 20 denotes, for example, a circular diaphragm made of a single crystal semiconductor such as silicon, which will be described in detail in FIG. A differential pressure hole 21 for generating a differential pressure is opened in this central portion. The diaphragm 20 is attached to one end of a ring-shaped substrate 22 made of, for example, Pyrex glass. They are joined by a method such as bonding. A cylindrical tube 24 having a circular step 23 on its outer peripheral surface, which serves as a passage for the fluid Q, is joined to the other end of the substrate 22 .

A base 25 is made of metal and has a cylindrical outer surface as a whole, and a circular step 26 is formed on a part of the outer surface.

The inside of the base 25 has a cylindrical space with a step that accommodates the tube 24, the substrate 22, and the diaphragm 20, and the base 25 is fixed in a liquid-tight manner by contacting the step 23 of the tube 24. A through hole 27 through which a lead wire is passed in the axial direction is provided in the thick wall portion located on the outside of this columnar shape.
28 is formed, and lead wires 29.30 from the diaphragm 20 are inserted and fixed into the through holes 27.28 while being liquid-tightly sealed with a sealing material such as glass.

Reference numeral 31 denotes a cover made of metal and having a cylindrical outer diameter, the inside of which has a circular hole 32 that serves as a fluid passage, and the lower part of which is a housing for storing the diaphragm 20, the substrate 22, the tube 24, and the base 25. A hole 33 is formed, and the lower end of the hole 33 abuts against a step 26 formed on the outer surface of the base 25 and is fixed in a liquid-tight manner.

Next, parts related to the diaphragm 20 will be explained in detail with reference to FIG. 2.

FIG. 2(a) is a plan view of the diaphragm with the insulating film removed, and FIG. 2(b) is a cross-sectional view of the diaphragm fixed to the substrate.

Reference numeral 34 denotes a diaphragm made of n-type silicon single crystal, which has a concave portion 35, and a strain-generating portion 36 in which the thickness of the single crystal is reduced due to the formation of the concave portion 35, and a fixed portion 3 around it.
7. A differential pressure hole 21 is provided in the center of the strain-generating portion 36.
is opened through the strain-generating portion 36.

The strain-generating portion 36 is made of a (100) plane of a single crystal, and a shear shape as a piezoresistive element is formed on the surface near the boundary between the strain-generating portion 36 and the fixed portion 37 in the <001> direction of the crystal axis passing through the center thereof. The conductivity type of the gauge 38 is P type due to the diffusion of impurities. The top of this shear type gauge 38 is covered with an oxide film 39 such as 5102.

The lower end of the fixed portion 37 of the diaphragm 34 is for example.

For example, it is bonded to a ring-shaped substrate 22 made of glass and having a hole 40 in the center by a method such as anodic bonding.

Next, the operation of the differential pressure type flowmeter configured as described above will be explained.

Now, as shown in Fig. 1, the fluid Q is flowing into the hole 32 from the direction of the arrow.
When the fluid flows through the inside, a pressure loss occurs at the differential pressure hole 21 which functions as an orifice of the diaphragm 20, and a differential pressure ΔP is generated before and after the hole. This differential pressure ΔP causes strain in the strain-generating portion 36 (FIG. 2) of the diaphragm 20, and this strain is detected by the shear type gauge 38.

The relationship between the differential pressure ΔP detected here and the flow RQ+ is: (hOc(AP)V2 It can be expressed as

Therefore, the diaphragm 34 is designed to satisfy this relationship.
By integrally forming an arithmetic element that calculates the flow rate using semiconductor technology in the fixed part 37, etc., and outputting the electric signal to the outside via the lead wires 29 and 30, a small and differential pressure type A flow meter can be realized.

In addition, when measuring the flow rate of gas, the flow rate of the gas to be measured changes depending on the temperature and pressure of the measuring fluid.
It is necessary to make this correction. In such a case, a temperature sensor and a pressure sensor may be formed on the diaphragm 20 using, for example, semiconductor technology, just as the arithmetic element for flow rate calculation is formed on the fixed part 37, and the outputs of these sensors may be used to determine the temperature of the gas flow rate. , can perform pressure correction. With this configuration, since a semiconductor sensor is used, an ultra-small differential pressure type flowmeter for measuring gas flow rate can be realized.

Note that although the shape of the differential pressure hole 21 shown in FIG. 1 is formed as a round hole, it may also be a square hole.
is configured to flow from the hole 32 side, but it may also flow from the tube 24 side.

Further, although the description has been made based on a shear type gauge as a gauge for detecting differential pressure, the present invention is not limited to this, and other types of gauges may be used.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, the differential pressure generated at both ends of the differential pressure hole opened in the center of the strain-generating portion of the silicon diaphragm is absorbed by the diaphragm itself. In other words, the orifice and differential pressure detection part are integrally formed using semiconductor technology, resulting in an ultra-compact differential pressure flowmeter that can measure minute flow rates. can do. As a result,
The weight of the flowmeter itself can be reduced, and as a result, cost can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing one embodiment of the present invention, Fig. 2 is a configuration diagram showing details when the diaphragm in Fig. 1 is fixed to a substrate, and Fig. 3 is a diagram of a conventional differential pressure type flowmeter. FIG. 3 is a vertical cross-sectional view showing the configuration. 10.11... Fluid pipe line, 14... Orifice plate,
20...Diaphragm, 21...Differential pressure hole, 22...
・Substrate, 24...Tube, 31...Cover, 36
... Strain part, 37... Fixed part, 38... Shear type gauge.

Claims (1)

[Claims] A silicon diaphragm having a thin strain-generating part with a differential pressure hole in the center and a fixed part around it, and a strain-generating part formed on the diaphragm that distorts in response to the differential pressure on both sides of the differential pressure hole. A semiconductor gauge that detects the strain of the diaphragm, a substrate that supports the diaphragm, a base to which a lead wire for extracting an electrical signal related to the output of the gauge to the outside is fixed, and this base and the substrate are coupled together for measurement. A differential pressure type flow rate comprising a tube serving as a passage for fluid, and a cover coupled to the base so as to cover the diaphragm and serving as a passage for the fluid, and calculating the flow rate using the electric signal. Total.