U.S. patent application number 11/536925 was filed with the patent office on 2007-02-01 for ultra-precision micro-differential pressure measuring device and ultra-precision differential pressure measuring device.
This patent application is currently assigned to Kotohiko Sekoguchi. Invention is credited to Kotohiko SEKOGUCHI.
Application Number | 20070022817 11/536925 |
Document ID | / |
Family ID | 32911408 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070022817 |
Kind Code |
A1 |
SEKOGUCHI; Kotohiko |
February 1, 2007 |
Ultra-precision micro-differential pressure measuring device and
ultra-precision differential pressure measuring device
Abstract
The ultra-precision micro-differential pressure measuring device
comprises a device body 1 having an inner space part therein, a
pressure receiving plate 3 which is installed inside the inner
space of the device body 1 and divides the said inner space
hermetically into a lower space 7 and an upper part space 8, an
electronic weighing and pressure converting device 2 which is
installed in the lower space 7, and supports and secures the
pressure receiving plate 3, and a liquid sealing part R which
liquid-seals the outer peripheral part of the afore-mentioned
pressure receiving plate 3 and maintains the air-tightness between
the lower space 7 and the upper space 8. A micro-differential
pressure between a pressure P1 inside the upper space 8 and a
pressure P2 inside the lower space 7 is measured by the electronic
weighing and pressure converting device 2 through the pressure
receiving plate 3.
Inventors: |
SEKOGUCHI; Kotohiko;
(Ikeda-shi, Osaka, JP) |
Correspondence
Address: |
GRIFFIN & SZIPL, PC
SUITE PH-1
2300 NINTH STREET, SOUTH
ARLINGTON
VA
22204
US
|
Assignee: |
Sekoguchi; Kotohiko
3-2, Itachibori 2-chome Nishi-ku
Osaka
JP
FUJIKIN INCORPORATED
Osaka
JP
|
Family ID: |
32911408 |
Appl. No.: |
11/536925 |
Filed: |
September 29, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10546159 |
Aug 22, 2005 |
|
|
|
11536925 |
Sep 29, 2006 |
|
|
|
Current U.S.
Class: |
73/736 |
Current CPC
Class: |
G01L 13/06 20130101 |
Class at
Publication: |
073/736 |
International
Class: |
G01L 15/00 20060101
G01L015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2003 |
JP |
2003-042247 |
Sep 25, 2003 |
JP |
2003-332600 |
Claims
1-9. (canceled)
10. An ultra-precision differential pressure measuring device
comprising a device body having an inner space inside; a pressure
receiving plate installed in the inner space of the device body and
that divides the inner space hermetically into a lower space and an
upper space; an electronic weighing and pressure converting device
installed inside the lower space on which the pressure receiving
plate is supported and secured; and a dividing film is provided in
a space between the outer periphery of the pressure receiving plate
and the inner wall face of the device body to keep air-tightness
between the lower space and the upper space, wherein a differential
pressure between a pressure P1 inside the upper space and a
pressure P2 inside the lower space is measured by the electronic
weighing and pressure converting device via the pressure receiving
plate.
11. An ultra-precision differential pressure measuring device as
claimed in claim 10, wherein the device body is constructed so that
a lower part body provided with a pressure introducing hole in
communication with the lower space and an upper part body provided
with a pressure introducing hole in communication with the upper
space are placed opposite to each other and combined to form the
device body; and a first fitting groove is formed on the outer
periphery of the pressure receiving plate at a right angle relative
thereto so that the inner periphery of the dividing film is
inserted into the first fitting groove while a second fitting
groove is formed on the inner face of the device body at a right
angle relative thereto and at the position as high as the position
of the first fitting groove so that the outer periphery of the
dividing film is inserted into the second fitting groove.
12. An ultra-precision differential pressure measuring device as
claimed in claim 10, wherein the dividing film is a brim-shaped
dividing film formed of a resin film or a thin metal film, and an
outer peripheral part of the dividing film and an inner peripheral
part thereof are hermetically inserted into a second fitting groove
of the device body and a first fitting groove of the pressure
sensing plate, respectively.
13. An ultra-precision differential pressure measuring device as
claimed in claim 10, wherein measurement values are continuously
taken out from the electronic weighing and pressure converting
device in the form of electric signals, and converted to the
differential pressure by a computer and outputted.
14. An ultra-precision differential pressure measuring device as
claimed in claim 10 wherein the electronic weighing and pressure
converting device comprises an electronic weighing device and a
computer that converts measurement signals from the electronic
weighing device into the differential pressure and outputs the
differential pressure.
15. An ultra-precision differential pressure measuring device as
claimed in claim 10 wherein a supporting body is provided on a base
on the electronic weighing and pressure converting device so that
the pressure receiving plate is supported by and fixed to the
supporting body.
16. An ultra-precision differential pressure measuring device as
claimed in claim 10, wherein the electronic weighing and pressure
converting devices is constructed so that the pressure receiving
plate is supported and fixed by the supporting body whose upper
ends or lower ends or both are pointed.
Description
FIELD OF THE INVENTION
[0001] The present invention is concerned with an ultra-precision
micro-differential pressure measuring device and an ultra-precision
differential measuring device in which a high-performance
electronic weighing and pressure converting device is employed. The
present invention is also concerned with an ultra-precision
micro-differential pressure measuring device which is used as a
standard instrument for a differential pressure gauge, and also
used as a tool for measuring the pressure drop characteristics of a
low-resistance filter, monitoring the filter characteristics, and
assessing the flow characteristics of the fluid equipment which
deals with gases under a reduced pressure, and further an
ultra-precision differential pressure measuring device widely used
for the measurement of the differential pressure of approximately
2-5 atmospheric pressure.
BACKGROUND OF THE INVENTION
[0002] The Askania type micro-manometer and the liquid column
manometer in which the liquid column height is measured visually
have been commonly used as standard instruments to measure a
micro-pressure or micro-differential pressure. A model in which a
force that acts on the ram mechanism of a cylinder is weighed by an
electronic weighing device has been also used.
[0003] Furthermore, a method in which the differential pressure is
electrically detected by a strain gauge, a semiconductor gauge or
the like is also used, but not widely.
[0004] However, for example, with the former, i.e., the Askania
type micro-manometer in which the liquid column height is measured
visually, the maximum resolution power of the measuring is
approximately 0.01 mm. This means that it is totally impossible to
continuously and accurately measure the micro-differential pressure
of the water column of a nanometer (nmAq) order lower than 0.01 mm.
And, the measured values cannot be outputted as electric signals
continuously.
[0005] With the latter, i.e., the electronic differential pressure
measuring device wherein an electronic weighing device is employed,
the measurement result can be outputted as electric signals
continuously. However, this device has a problem that the
occurrence of measurement errors arising from the friction of
moving or sliding parts and a low degree of mechanical machining
precision is unavoidable because the device is so constituted that
a force generated by the pressure to be measured is transmitted to
an electronic weighing and pressure converting device by way of a
stem, a ram and the like with the result that a high-precision
measurement of the micro-differential pressure can not be achieved.
(The JITSU-KOU-HEI No. 6-76937 and the TOKU-KOU-HEI No. 2-52975 and
others)
[0006] The problem is shared by a wide-use type electronic
differential pressure measuring device which is aimed to measure
the differential pressure of approximately 2.about.5 atmospheric
pressure. Measurement errors due to friction of moving parts are
also unavoidable, thus resulting in failure of the high-precision
measurement. TABLE-US-00001 Patent Literature 1 Public Bulletin
JITSU-KOU-HEI No. 6-76937 Patent Literature 2 Public Bulletin
TOKU-KOU-HEI No. 2-52975
DISCLOSURE OF THE INVENTION
Object of the Invention
[0007] The present invention is intended to solve the
afore-mentioned problems of the conventional measuring devices for
micro-pressure and micro-differential pressure and widely used
electronic differential pressure measuring devices: that is, (1)
according to the device in which the liquid column height is
detected visually, the measurement precision is low and the
measured values can not be outputted continuously, and (2)
according to the electronic type weighing device, the occurrence of
the measurement errors is unavoidable due to friction of movable
parts in the mechanism to convert the pressure into a force and
transmit the same to the electronic weighing device with the result
that it is difficult to measure the micro-differential pressure
while the measuring precision is low. It is a primary object of the
present invention to provide an ultra-precision micro-differential
pressure measuring device and an ultra-precision differential
pressure measuring device in which an electronic weighing and
pressure converting device is installed in the space in which a
pressure to be measured is applied, and the afore-mentioned space
to which the pressure to be measured is applied and the other space
in which a pressure is measured are divided and isolated
hermetically from each other with a sealing liquid or by a dividing
film in cooperation with a pressure receiving plate, thus making
possible the high-precision measurement of the micro-differential
pressure of the water column of a nanometer (nmAq) order having
three effective digits, and the ultra-precision measurement of the
differential pressure of approximately 2.about.5 atmospheric
pressure.
Means of the Invention
[0008] The inventors of the present invention have noted that
according to the conventional method in which a force applied on
the pressure receiving plate forming a pressure receiving face is
transmitted to the electronic weighing device with the pressure
receiving plate being supported by a sliding (moving) mechanism, a
frictional resistance generated at the afore-mentioned sliding part
causes errors such that it is inappropriate for measuring the
micro-differential pressure. Thus, the inventors of the present
invention have come to an idea in which to avoid the errors caused
by the frictional resistance, the pressure receiving plate forming
the pressure receiving face is supported by and fixed to the base
of the electronic weighing and pressure converting device without
restraining the pressure receiving plate and a liquid sealing
method is adopted to air-tightly divide the two spaces, to which
the pressures are applied, on the upper and lower sides of the
pressure receiving plate.
[0009] At the same time, the inventors of the present invention
have come to an idea that, in the event of measuring the
differential pressure of approximately 2.about.5 atmospheric
pressure a thin resin film or a metal-made film body is employed as
a dividing film to replace the afore-mentioned liquid sealing
method such that a higher precision differential pressure
measurement is achieved.
[0010] The present invention is created based on the
afore-mentioned ideas and measuring test results. The device
according to the present invention in claim 1 comprises a device
body 1 having an inner space inside, a pressure receiving plate 3
which is installed in the inner space inside the device body 1 and
air-tightly divides the said inner space into a lower space 7 and
an upper space 8, an electronic weighing and pressure converting
device 2 which is installed inside the lower space 7 and on which
the pressure receiving plate 3 is supported and fixed, and a liquid
sealing part R which liquid-seals the outer peripheral part of the
afore-mentioned receiving plate 3 and air-tightly separates the
lower space 7 and the upper space 8 so that a micro-differential
pressure between a pressure P1 inside the upper space 8 and a
pressure P2 inside the lower space 7 is measured by an electronic
weighing and pressure converting device 2 via the pressure
receiving plate 3.
[0011] The present invention in claim 2 relates to a device as
claimed in claim 1 wherein the device body 1 is so constructed that
a lower part body 1a provided with a pressure introducing hole 7a
in communication with the lower space 7 and an upper part body 1b
provided with a pressure introducing hole 8a in communication with
the upper space 8 are placed opposite to each other and combined,
and the device body 1 is provided with a ring-shaped sealing liquid
storage groove 9 at the inner wall face in the inner space.
[0012] The present invention in claim 3 relates to a device as
claimed in claim 1 wherein the pressure receiving plate 3 comprises
a flat-shaped disc plate 3a and a sealing wall 3b extending
downwardly from the outer periphery of the disc plate 3a.
[0013] The present invention in claim 4 relates to a device as
claimed in claim 1 wherein the electronic weighing and pressure
converting device 2 is so constructed that the measurement values
are continuously taken out of the electronic weighing and pressure
converting device 2 in the form of electric signals and transmitted
to a computer to be converted into differential pressures and
outputted.
[0014] The present invention as claimed in claim 5 relates to a
device as claimed in claim 4 wherein the electronic weighing and
pressure converting 2 comprises an electronic weighing device and a
computer which converts measurement signals from the electronic
weighing device to differential pressures.
[0015] The present invention as claimed in claim 6 relates to a
device as claimed in claim 1 wherein the electronic weighing and
pressure converting 2 has a supporting base 5 on which a supporting
body 4 is provided so that the pressure receiving plate 3 is
supported by and fixed to the supporting body 4.
[0016] The present invention as claimed in claim 7 relates to a
device as claimed in claim 1 wherein the electronic weighing and
pressure converting 2 is so constructed that the pressure receiving
plate 3 is supported by and fixed to the supporting body 4 whose
upper and/or lower ends are pointed.
[0017] The present invention as claimed in claim 8 relates to a
device wherein a liquid sealing part R comprises a ring-shaped
sealing liquid storage groove 9 formed at the inner wall face of
the inner space of the device body 1, a sealing liquid 6 filled in
the sealing liquid storage groove 9, and the ring-shaped sealing
wall 3b extending downwardly from the periphery of the pressure
receiving plate a lower end of which is inserted into the sealing
liquid 6 from above.
[0018] The present invention as claimed in claim 9 relates to a
device as claimed in claim 8 wherein the liquid sealing part R is
surface-treated so that uniform wettability is secured entirely or
partly on the liquid contacting part.
[0019] The present invention as claimed in claim 10 relates to an
ultra-precision differential pressure measuring device wherein the
device comprises a device body 1 having an inner space inside, a
pressure receiving plate 3 which is installed in the inner space of
the device body 1 and divides the said inner space hermetically
into a lower space 7 and an upper space 8, an electronic weighing
and pressure converting device 2 installed inside the lower space
on which the pressure receiving plate 3 is supported and secured,
and a dividing film 10 which is provided in a space between the
outer periphery of the pressure receiving plate 3 and inner wall
face of the device body 1 to keep air-tightness between the lower
space 7 and the upper space 8 wherein the differential pressure
between a pressure P1 inside the upper space 8 and a pressure P2
inside the lower space 7 is measured by the electronic weighing and
pressure converting device 2 via the pressure receiving plate
3.
[0020] The present invention in claim 11 relates to a device as
claimed in claim 10 wherein the device body 1 is so constructed
that a lower part body 1a provided with a pressure introducing hole
7a in communication with the lower space 7 and an upper part body
1b provided with a pressure introducing hole 8a in communication
with the upper space 8 are placed opposite to each other and
combined; and a fitting groove 3d is formed on the outer periphery
of the pressure receiving plate 3 at a right angle relative thereto
so that the inner periphery of the dividing film 10 is inserted
into the fitting groove 3d while a fitting groove 1d is formed on
the inner wall face of the device body 1 at a right angle relative
thereto and at the position as high as the position of the
afore-mentioned fitting groove 3d so that the outer periphery of
the dividing film 10 is inserted into the fitting groove 1d.
[0021] The present invention as claimed in claim 12 relates to a
device as claimed in claim 10 wherein the dividing film 10 is a
brim-shaped dividing film formed of a resin film or a thin metal
film, and an outer peripheral part of the said dividing film 10 and
an inner peripheral part thereof are hermetically inserted into the
fitting groove 1d of the device body and the fitting groove 3d of
the pressure receiving plate 3 respectively.
[0022] The present invention in claim 13 relates to a device as
claimed in claim 10 wherein the measurement values are continuously
taken out from the electronic weighing and pressure converting
device 2 in the form of electric signals, and converted to the
differential pressure by a computer and outputted.
[0023] The present invention in claim 14 relates to a device as
claimed in claim 10 wherein the electronic weighing and pressure
converting 2 comprises an electronic weighing device and a computer
which converts the measurement signal from the electronic weighing
device into the differential pressure and outputs the same.
[0024] The present invention in claim 15 relates to a device as
claimed in claim 10 wherein a supporting body 4 is provided on a
base 5 on the electronic weighing and pressure converting device 2
so that the pressure receiving plate 3 is supported by and fixed to
the supporting body 4.
[0025] The present invention in claim 16 relates to a device as
claimed in claim 10 wherein the electronic weighing and pressure
converting device 2 is so constructed that the pressure receiving
plate 3 is supported and fixed by the supporting body 4 whose upper
ends or lower ends or both are pointed.
Effects of the Invention
[0026] According to the ultra-precision micro-differential pressure
measuring device in accordance with the present invention, the
pressure receiving plate 3 is never affected by a meniscus formed
by the sealing liquid 6 because there is no involvement of up and
down movements of the pressure receiving plate 3.
[0027] Although the heights of the liquid levels of the sealing
liquid 6 which forms two ring-shaped liquid surfaces differ
depending on the differential pressure .DELTA.P between the
pressure spaces 7 and 8, as will be explained later, it is not
mandatory that the areas A1 and A2 of the liquid surfaces should be
the same.
[0028] Furthermore, in the event that the shape of the liquid
surface changes due to a micro-change of the differential pressure
.DELTA.P between the pressure spaces 7 and 8, a change of the
meniscus formed by the sealing liquid 6 is caused such that a force
that acts on the pressure receiving plate 3 in the upward and
downward directions is induced.
[0029] However, precision of the measuring of the differential
pressure is not affected because the force is counterbalanced
between the ring-shaped liquid levels of the inside and the outside
(the two liquid faces).
[0030] With the present invention, the electronic weighing and
pressure converting device 2 is installed inside the lower space 7
in the device body 1, and the inside of the device body is divided
hermetically into the lower space 7 and the upper space 8 by the
pressure receiving plate 3 and the liquid sealing part R at the
periphery of the pressure receiving plate 3. Further, the force
applied by the differential pressure between the spaces 7 and 8 on
the afore-mentioned pressure receiving plate 3 is continuously
measured with the electronic weighing and pressure converting
device 2, and converted into the differential pressure and
outputted in the form of the electric signals.
[0031] As a result, the force exerted by the differential pressure
is directly transmitted to the electronic weighing and pressure
converting device 2 through the pressure receiving plate 3 fixed on
the electronic weighing and pressure converting device 2. Because
there exists no mechanical friction part in the transmission route
of the force exerted by the differential pressure, precision of the
measuring of the differential pressure is remarkably improved. By
employing the electronic weighing and pressure converting device 2
with the minimum measurement capacity as suitably chosen, a
continuous high-precision measurement of the micro-differential
pressure having effective figures of three digits or more becomes
possible with the ultra-precision micro-differential pressure
measuring device in accordance with the present invention. For
example, in the case of the electronic weighing and pressure
converting device 2 having a minimum measurement capacity of 0.0001
g, a continuous high-precision measurement of the differential
pressure of the water column of a few hundred nanometer order
becomes possible.
[0032] Any kind of liquid can be used as the sealing liquid because
the density of the sealing liquid 6 which forms the liquid sealing
part R is irrelevant to the measurement of the differential
pressure.
[0033] As a result, the manufacturing costs are significantly
reduced because the selection of the sealing liquid is easy and the
structure of the measuring device itself is simple.
[0034] Furthermore, with the ultra-precision differential pressure
measuring device in accordance with the present invention, since
the dividing film 10 is made of a flexible thin film, a force in
the upward and downward directions applied on the pressure
receiving plate 3 is not induced by the insertion of the dividing
film 10 into the fitting groove 1d of the device body 1 and the
fitting groove 3d of the pressure receiving plate 3.
[0035] In addition, because the form or weight of the pressure
receiving plate 3, that is, its material, thickness or shape is
irrelevant to the measurement of the differential pressure, the
material, thickness or shape of the pressure receiving plate 3 can
be chosen as desired, thus further making it possible to reduce the
manufacturing costs of the differential pressure measuring
device.
[0036] With the conventional differential pressure measuring
device, a standard instrument and the like has been required for
correction or test. Further, an actual occurrence of the
differential pressure has been needed at the time of the test.
However, the differential pressure measuring device in accordance
with the present invention is extremely advantageous in that the
correction and test can be performed easily requiring no
differential pressure because a dead weight equivalent to the
differential pressure (pressure) can be used instead.
[0037] As described above, the present invention is capable of
continuously measuring the micro-differential pressure with high
precision and continuously outputting the measurement values in the
form of electric signals using the device which has a simple
construction and can be produced at a low cost. Therefore, the
present invention has excellent, practical advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a cross-sectional schematic view of the
ultra-precision micro-differential measuring device in accordance
with the first embodiment of the present invention.
[0039] FIG. 2 is a cross-sectional schematic view of the
ultra-precision micro-differential measuring device in accordance
with another embodiment of the present invention.
[0040] FIG. 3 is a cross-sectional view to illustrate the state of
the ring-shaped liquid sealing part R at the time when differential
pressure is zero.
[0041] FIG. 4 is a cross-sectional view to illustrate the state of
the ring-shaped liquid sealing part at the time when there exists
differential pressure.
[0042] FIG. 5 is a cross-sectional schematic view of an
ultra-precision differential pressure measurement in accordance
with the second embodiment of the present invention.
[0043] FIG. 6 is a partially enlarged cross-sectional view to
illustrate the state of the upper and lower space parts isolated by
the dividing film.
LIST OF REFERENCE CHARACTERS AND NUMERALS
[0044] 1 Device body [0045] 1a Lower part body [0046] 1b Upper part
body [0047] 1d Fitting groove [0048] 2 Electronic weighing and
pressure converting device [0049] 3 Pressure receiving plate [0050]
3a Flat-shaped disc plate [0051] 3b Sealing wall [0052] 3c
Receiving groove [0053] 3d Fitting groove [0054] 4 Supporting body
[0055] 4a Pointed end [0056] 5 Base for supporting body [0057] 6
Sealing liquid [0058] 7 Lower space [0059] 7a Pressure introducing
hole [0060] 8 Upperspace [0061] 8a Pressure introducing hole [0062]
9 Sealing liquid storage groove [0063] R Ring-shaped liquid-sealing
part (Sealing wall 3b, Sealing liquid 6 and Storage groove 9)
[0064] A1 Area of outer ring-shaped part [0065] A2 Area of inner
ring-shaped part [0066] S1 Area of upper surface of pressure
receiving plate [0067] S2 Area of lower surface of pressure
receiving plate [0068] Se Effective pressure receiving area [0069]
De Effective diameter [0070] .rho. Density of sealing liquid [0071]
g Gravitational acceleration [0072] Po Pressure inside upper and
lower spaces shown when differential pressure is zero [0073] hbo
Distance between lower end surface of sealing wall 3b and liquid
level shown when differential pressure is zero [0074] Pbo Liquid
pressure at position of lower end surface of sealing wall 3b shown
when differential pressure is zero [0075] P1 Pressure inside upper
space 8 [0076] P2 Pressure inside lower space 7 [0077] hb Distance
between lower end face of sealing wall 3b and liquid level of outer
ring-shaped part shown when there exists differential pressure
[0078] h1 Distance between liquid level of outer ring-shaped part
shown when there exists differential pressure and liquid level
shown when differential pressure is zero [0079] h2 Distance between
liquid level of inner ring-shaped part shown when there exists
differential pressure and liquid level shown when differential
pressure is zero [0080] Pb Liquid pressure at lower end face of
sealing wall 3b shown when there exists differential pressure
[0081] 10 Dividing film [0082] D Diameter of pressure receiving
plate [0083] .delta. Space between end face of pressure receiving
plate 3 and inner wall face of lower part body 1a
BEST MODE OF CARRYING OUT THE INVENTION
[0084] The following embodiments of the present invention are
described with reference to the drawings hereunder.
[0085] FIG. 1 is a cross-sectional schematic view of an
ultra-precision micro-differential pressure measuring device in
accordance with the present invention. With reference to FIG. 1, 1
designates a device body, 2 an elctronic weighing and pressure
converting device, 3 a pressure receiving plate, 4 a supporting
body, 5 a base for the electronic weighing and pressure converting
device, and 6 a sealing liquid.
[0086] The afore-mentioned device body 1 is made of metal or an
engineering plastic in the shape of a box in which an inner space
is provided. With the present embodiment, the device body 1 is made
up of a lower part body 1a and an upper part body 1b which are
placed opposite to each other and combined together in an air-tight
manner.
[0087] With the embodiment in FIG. 1, the lower part body 1a and
upper part body 1b which are both disk-shaped in the plane
configuration are placed opposite to each other and air-tightly
combined so that the device body 1 is formed. However, there is no
need to say that any form or structure of the device body 1 can be
chosen as desired.
[0088] The afore-mentioned lower part body 1a is provided with a
pressure introducing hole 7a in communication with the lower space
7 while the upper part body 1b is provided with a pressure
introducing hole 8a in communication with the upper inner space
8.
[0089] At the inner peripheral wall of the device body 1 a
ring-shaped storage groove 9 for storing a sealing liquid 6 which
has predetermined width and depth is formed and is open in the
upward direction. The sealing liquid 6 is stored inside the said
storage groove 9.
[0090] With the embodiment in FIG. 1, the storage groove 9 is
formed at the upper part of the inner peripheral wall face of the
lower part body 1a. However, the storage groove 9 can be formed at
the inner peripheral wall face of the upper part body 1b instead as
illustrated in FIG. 3 and FIG. 4.
[0091] The afore-mentioned electronic weighing and pressure
converting device 2 is installed inside the pressure space on one
side (the inner space 7 of the lower part body 1a), and supported
by and fixed to the lower part body 1a,
[0092] The afore-mentioned electronic weighing and pressure
converting device 2 comprises an electronic weighing device and a
computer by which the weight value from the electronic weighing
device is converted into a differential pressure and outputted.
[0093] A detailed description of the electronic weighing device is
omitted here because it is publicly known. To measure a
micro-differential pressure .DELTA.P to be measured in the range of
the water column of a few hundred nanometer order having effective
figures of three digits, the electronic weighing device having the
minimum display of approximately 0.0001 g is used as described
hereunder. Regarding the maximum measurement capacity, one suitable
for the maximum differential pressure to be measured can be
chosen.
[0094] With the present embodiment, one of the AND-made HX series
with an electronic even balance HX-100 having the minimum display
of 0.0001 g and the maximum measurement capacity of 101 g is
employed for the electronic weighing device.
[0095] The afore-mentioned pressure receiving plate 3 is made of a
plastic material and formed in an inverted dish-shape by processing
the plastic material. A sealing wall 3b extends in the downward
direction at a right angle downward from the outer periphery of a
flat-plate-shaped circular disc 3a. The pressure receiving plate 3
can be made of not only plastic materials but also metal
materials.
[0096] The said pressure receiving plate 3 is horizontally
supported by and fixed to the base 5 of the electronic weighing and
pressure converting device 2 via the supporting body 4 with the
sealing wall 3b at the outer periphery being inserted into the
sealing liquid 6 in the storage groove 9 as illustrated in FIG. 1
such that the pressure receiving plate 3 is never allowed to move
up and down.
[0097] With the present embodiment, the pressure receiving plate 3
is formed of 2 mm-thick plastic, and its diameter D is chosen to
fit the maximum and minimum values of the differential pressure
.DELTA.P to be measured as will be explained hereunder.
[0098] Furthermore, the afore-mentioned supporting body 4 is made
of metal in the shape of a cylinder or a circular truncated cone,
and its height is appropriately decided depending on the external
dimensions of the device body 1. The supporting body 4 can be made
of any material. With the present embodiment, the supporting body 4
is made of brass. The shape of the supporting body 4 is not limited
to a cylinder or a circular truncated cone. For example, it can be
a rectangular parallelepiped and the like such as a trapezoid a
rectangle, a square and the like in the side view.
[0099] The storage height of the afore-mentioned sealing liquid 6
can be appropriately decided depending on the level of the
differential pressure .DELTA.P to be measured as stated
hereinafter.
[0100] The weight measurement operation can be so effected that the
density of the sealing liquid 6 is not directly related to the
downward thrust Fa applied on the electronic weighing and pressure
converting device 2 by the differential pressure .DELTA.P to be
measured. Hence, any kind of liquid (such as water, oil and the
like, for example) can be used for the sealing liquid 6. With the
present embodiment, silicon oil is utilized for the sealing liquid
6.
[0101] As apparent in FIG. 1, the inside of the device body 1 is
hermetically divided into a lower space 7 in communication with a
pressure introducing hole 7a and an upper space 8 in communication
with a pressure introducing hole 8a by the afore-mentioned pressure
receiving plate 3 and the sealing liquid 6. The electronic weighing
and pressure converting device 2 is installed inside the lower
space 7. The force F corresponding to the pressure difference
.DELTA.P=P1-P2>0 (or .DELTA.P=P2-P1>0) between the spaces 7
and 8 applied on the pressure receiving plate 3 is continuously
measured by the said electronic weighing and pressure converting
device 2, and the weight values as measured are converted to the
differential pressures by the computer and outputted as electric
signals continuously.
[0102] FIG. 2 is a cross-sectional schematic view of the
ultra-precision micro-differential pressure measuring device in
accordance with the second embodiment of the present invention. The
device in accordance with second embodiment is the same as the
first embodiment illustrated in the afore-mentioned FIG. 1 except
for the following, i.e. (1) the upper part body 1b and the lower
part body 1a are hermetically coupled without using flanges, (2)
ends of the supporting body 4 are pointed, and (3) the electronic
weighing and pressure converting device 2 is not equipped with the
base. Except for these differences, all the other constructions of
the device are identical to those of the device in accordance with
the first embodiment.
[0103] Namely, the upper end of the afore-mentioned supporting body
4 is in the pointed end shape 4a, and the pointed end 4a is engaged
in the receiving groove 3c formed on the lower face side of the
pressure receiving plate 3 so that the lateral movement of the
pressure receiving plate 3 is prevented. The shape and number of
the supporting body 4 can be chosen as desired as long as the
pressure receiving plate 3 is securely supported.
[0104] With the embodiment in FIG. 2, only the upper end part of
the supporting body 4 is formed in the pointed end shape. However,
it is possible that both the upper and lower end parts are in the
pointed end shape.
[0105] Furthermore, with the embodiment in FIG. 2, the electronic
weighing and pressure converting device 2 is installed inside the
lower space 7. However, the electronic weighing and pressure
converting device 2 is installed in the upper space 8 and faces in
the downward direction while the pressure receiving plate 3 is
suspended and fixed by way of the supporting body 4. When the
construction is adopted in which the pressure receiving plate 3 is
suspended for support, the weight of the pressure receiving plate 3
is included and considered when determining the offset amount of
the electronic weighing and pressure converting device 2.
[0106] Next, the principle of the operation of the ultra-precision
micro-differential pressure measuring device in accordance with the
present invention is described.
[0107] FIG. 3 and FIG. 4 are explanatory drawings relating to the
differential pressure .DELTA.P applied on the electronic weighing
and pressure converting device 2 in the ultra-precision
micro-differential pressure measuring device in accordance with the
present invention illustrated in FIG. 1. FIG. 3 shows the state of
the ring-shaped liquid sealing part R (the sealing wall 3b of the
pressure receiving plate 3 and the sealing liquid 6 inside the
storage groove 9) shown when the differential pressure .DELTA.P
between the lower space 7 and the upper space 8 is zero. FIG. 4
shows the state of the ring-shaped liquid sealing part R shown when
there exists the differential pressure P1-P2>0 between the lower
space 7 and the upper space 8.
[0108] Referring now to FIG. 3 and FIG. 4, S1 designates an area of
the upper face of the pressure receiving plate 3, S2 an area of the
lower face of the pressure receiving plate 3, .rho. a density of
the sealing liquid 6, g gravitational acceleration, A1 an area of
the outer ring-shaped part of the ring-shaped liquid sealing part
R, A2 an area of the inner ring-shaped part of the ring-shaped
liquid sealing part R, P0 pressures inside the upper and lower
spaces 7 and 8 shown when the differential pressure is zero, hbo a
distance between the lower end face of the sealing wall 3b and the
liquid level of the sealing liquid 6. Then, the sealing liquid
pressure at the lower end face of the sealing wall 3b in the
sealing liquid 6 is expressed by the equation, Pbo=Po+.rho. g
hbo.
[0109] As shown in FIG. 4, in the event that the pressure of the
upper space 8 and pressure of the lower space 7 are P1 and P2
respectively with the differential pressure P1-P2 (P1>P2) being
caused, the liquid level of the outer ring-shaped part descends,
while the liquid level of the inner ring-shaped part ascends.
Referring to FIG. 4, hb is a distance between the lower end face of
the sealing wall 3b and the liquid level of the outer ring-shaped
part shown when there exists the differential pressure, h1 is a
distance between the liquid level of the outer ring-shaped part
shown when there exists the differential pressure and the liquid
level shown when the differential pressure is zero, h2 is a
distance between the liquid level of the inner ring-shaped part
shown when there exists the differential pressure and the liquid
level shown when thte differential pressure is zero, and Pb is the
liquid pressure at the lower end face of the sealing wall 3b shown
when there exists the differential pressure.
[0110] The liquid pressure Pb at the lower end face of the sealing
wall 3b shown when there exists the differential pressure is
expressed by the following equation (1): Pb=P1+.rho. g hb=P2+.rho.
g(h1+h2+hb) (1) Also, P1-P2=.rho. g(h1+h2) (2) A1 h1=A2 h2 (3) So,
from Equation (2) and Equation (3), the differential pressure P1-P2
is expressed by Equation (4). P1-P2=.rho. g(1+A2/A1)h2 (4) Also,
hbo=hb+h1 (5) So, a difference F between forces exerted by the
pressures applied to the upper and lower faces of the pressure
receiving plate 3 is expressed by the following equations
(6).about.(9). F=S1P1-{S2P2+(S1-S2)Pb} (6) Here, (S1-S2) is
represented by .DELTA.S=(S1-S2) (7)
[0111] Pb in Equation (1) is substituted in Equation (6) to obtain
Equation (8) F = S 1 .times. P 1 - ( S 2 .times. P 2 + .DELTA.
.times. .times. SPb ) = S 1 .times. P 1 - [ S 2 .times. P 2 +
.DELTA. .times. .times. S .times. { P 2 + .rho. .times. .times. g +
( h 1 + h 2 + hb ) } ] = S 1 .times. P 1 - { ( S 2 + .DELTA.
.times. .times. S ) .times. P 2 + .DELTA. .times. .times. S .times.
.times. .rho. .times. .times. g .function. ( h 1 + h 2 + hb ) } = S
1 .times. P 1 - S 1 .times. P 2 - .DELTA. .times. .times. S .times.
.times. .rho. .times. .times. g .function. ( h 1 + h 2 + hb ) = S 1
.function. ( P 1 - P 2 ) - .DELTA. .times. .times. S .times.
.times. .rho. .times. .times. g .function. ( h 1 + h 2 + hb ) ( 8 )
##EQU1##
[0112] The second term of the above Equation (8) can be rewritten
using Equation (5) to obtain Equation (9). F = S 1 .function. ( P 1
- P 2 ) - .DELTA. .times. .times. S .times. .times. .rho. .times.
.times. g .function. ( h 2 + hb + h 1 ) = S 1 .function. ( P 1 - P
2 ) - .DELTA. .times. .times. S .times. .times. .rho. .times.
.times. g .function. ( h 2 + hbo ) = S 1 .function. ( P 1 - P 2 ) -
.DELTA. .times. .times. S .times. .times. .rho. .times. .times. gh
2 - .DELTA. .times. .times. S .times. .times. .rho. .times. .times.
ghbo ( 9 ) ##EQU2##
[0113] The third term of the above Equation (9) is not counted,
that is to say, the term is zero, at the time of measuring the
differential pressure by resetting the weight of the pressure
receiving plate 3 and the electronic weighing and pressure
converting device 2 where the differential pressure is zero.
Accordingly, the force Fa actually detected by the electronic
weighing and pressure converting device 2 is expressed by Equation
(10). Fa=S1(P1-P2)-.DELTA.S.rho. gh2 (10)
[0114] When h2 is eliminated by substituting Equation (4) in
Equation (10), Equation (11) is obtained. Equation (12) for
calculating the differential pressure P1-P2, which is ultimately
needed, is obtained from Equation (11). Se in Equation (12) is an
effective pressure receiving area defined in Equation (13).
Fa=S.sub.1(P.sub.1-P.sub.2)-.DELTA.S(P.sub.1-P.sub.2)/(1+A.sub.2/A.sub.1)-
=S.sub.1(P.sub.1-P.sub.2){1-(.DELTA.S/S.sub.1)/(1+A.sub.2/A.sub.1)}
(11) (P.sub.1-P.sub.2)=Fa/Se (12)
Se=S.sub.1/{1(.DELTA.S/S.sub.1)/(1+(A.sub.2/A.sub.1))} (13)
[0115] To determine the differential pressure (P1-P2), which is the
object of the measurement, from the force Fa measured by the
electronic weighing and pressure converting device 2, Fa is divided
by the effective receiving area Se.
[0116] There is no need at all to make .DELTA.S particularly small
comparing with S1, or to make A2 equal to A1 when the said
ultra-precision micro-differential pressure measuring device is
designed.
[0117] When the differential pressure (P1-P2) is slightly changed,
there is seen a slight deformation in the meniscus formed between
the liquid level of the sealing liquid 6 and the wall face of the
sealing wall 3b. However, because the way the said deformation
occurs is opposite between the upper space 8 side (P1 side) and the
lower space 7 side (P2 side) with the result that the surface
tension resulting from the deformation of the meniscus is
compensated, thus not resulting in the lowering of the measuring
accuracy of the differential pressure.
[0118] If wettability is uneven due to stains and the like on the
wall face, there may be a possibility that the wetting state
changes over time such that the shape of the meniscus between the
liquid surface of the sealing liquid 6, the sealing wall 3b and the
sealing liquid storage groove 9 becomes an external factor
disturbing the force Fa exerted by the differential pressure
(P1-P2).
[0119] In such a case, an effective countermeasure is to apply an
appropriate treatment onto the liquid-contacting wall face in
advance.
[0120] As stated above, with the ultra-precision micro-differential
measuring device, the differential pressure (P1-P2) can be obtained
using Equation (12) by converting the output of the electronic
weighing device into the differential pressure by the computer. Any
kind of material, shape and the like can be chosen for the sealing
liquid 6 and pressure sensing plate 3 for the reason that the above
mentioned Equation (12) is irrelevant to the density .rho. of the
sealing liquid 6 and the weight of the pressure receiving plate
3.
[0121] Next, described hereunder is the relation between the
external dimensions of the pressure receiving plate 3, the minimum
differential pressure measurable with the ultra-precision
micro-differential pressure measuring device in accordance with the
present invention, and the air flow velocity indicated when the
said minimum differential pressure is expressed in terms of the
dynamic pressure of the air flow.
[0122] Now, if the effective pressure receiving area is designated
Se, the differential pressure .DELTA.P, and the force applied to
the electronic weighing device F, the afore-mentioned force F can
be expressed by Equation F=Se.DELTA.P.
[0123] Here, assuming that the weight F as applied by the force
caused by the differential pressure .DELTA.P is 0.1 g, the value of
the differential pressure .DELTA.P to be measured is:
.DELTA.P=F/Se=0.1/Se(g/mm.sup.2)=0.01/Se
(kg/cm.sup.2)=0.01.times.10.sup.4/Se(mmAq)=100/Se (mmAq)
[0124] If the velocity of the air flow at the room temperature and
normal atmospheric pressure having the dynamic pressure
corresponding to the above mentioned differential pressure .DELTA.P
is designated u (m/s),
[0125] The following equation is obtained:
.DELTA.P=.rho.u.sup.2/2g=(1.25/1000)u.sup.2/2g=0.06378u.sup.2(mmAq)
[0126] When the differential pressure .DELTA.P is calculated with
Se in the afore-mentioned Equation .DELTA.P.apprxeq.100/Se (mmAq)
being a parameter, and the velocity u of the air flow having the
dynamic pressure corresponding to the differential pressure is
obtained, the results are shown in Table 1 below. TABLE-US-00002
TABLE 1 An effective diameter of 100 200 400 the pressure receiving
surface equivalent to the effective pressure receiving area Se: De
mm Measured differential 0.01273 0.003183 0.0007958 pressure:
.DELTA.P mmAq The velocity of the air 0.4468 0.2234 0.02793 flow at
room temperature & normal pressure: u m/s (The velocity of the
air flow having the dynamic pressure corresponding to .DELTA.P)
[0127] In Table 1 above, the effective pressure receiving area Se
is converted to the effective diameter De mm of the pressure
receiving plate.
[0128] As stated above, in the event that, for example, the
effective diameter De of the circular pressure receiving plate is
100 mm, using the electronic weighing and pressure converting
device 2 having the weight measurement capacity F of 0.1 g, the
measured differential pressure .DELTA.P is 0.01273 mmAq. The
measured differential pressure .DELTA.P is 795.8 nmAq in the event
that the effective diameter De is 400 mm. In this case, the
differential pressure .DELTA.P of the water column of a few hundred
nanometer having effective figures of about three digits can be
measured.
[0129] As described above, with the ultra-precision
micro-differential pressure measuring device in accordance with the
present invention, the micro-differential pressure having effective
figures of three or more digits can be measured with a high
accuracy by employing the electronic weighing and pressure
converting device 2 whose weight measurement capacity F is 0.1
g.about.0.0001 g.
[0130] FIG. 5 is a cross-sectional schematic view of an
ultra-precision differential pressure measuring device in
accordance with the embodiment of the second invention. The second
invention differs from the first invention in that a dividing film
10 is used instead of the liquid sealing used in the
ultra-precision micro-differential pressure measuring device in
accordance with the first invention illustrated in FIG. 1 to FIG. 4
inclusive.
[0131] Namely, with FIG. 5, 1 designates the device body, 2 the
electronic weighing and pressure converting device, 3 the pressure
sensing plate, 4 the supporting body (a conical body for the load
transmission), 7 the lower space, 8 the upper space, and 10 a
dividing film. All the other constructions except for the dividing
film 10 are identical to those of the afore-mentioned first
invention illustrated in FIG. 1 to FIG. 4 inclusive.
[0132] With the second invention in the said FIG. 5, the dividing
film 10 is utilized to isolate the upper space pressure P1 (a
primary pressure) from the lower space pressure P2 (a secondary
pressure) so that the measurable upper limit value of the
differential pressure is raised to 2.about.5 atmospheric
pressure.
[0133] It is desirable that the dividing film 10 has the following
characteristics:
(a) a thin film having flexibility (characteristics of being
flexible),
(b) a force to work on the electronic weighing and pressure
converting device 2 is not exerted when the dividing film 10
expands or contracts with the temperature change and the like,
and
(c) air-tightness is maintained over a long period of time, and
excellent corrosion resistance is exhibited. With the present
embodiment, a resin film or a thin metal film with thickness of
5.about.200 .mu.m is used.
[0134] To prevent the force to be applied to the electronic
weighing and pressure converting device 2 due to an expansion or
contraction of the afore-mentioned dividing film 10 owing to the
temperature change and the like, both ends of the dividing film 10
are secured to the pressure receiving plate 3 and the lower part
body 1a at the same lateral level, that is, height. Furthermore, to
reduce a chance that a force to be applied to the afore-mentioned
electronic weighing and pressure converting device 2 is induced,
the dividing film 10 is somewhat slackened as shown in FIG. 6.
[0135] FIG. 6 is a partially enlarged cross-sectional view to show
how the upper and lower space 8 and 7 are divided by the dividing
film 10. The outer and inner peripheral parts of the narrow-width
brim- (or ring-) shaped dividing film 10 are inserted into the
fitting grooves 3d and 1d formed at a right angle relative to the
end face of the pressure receiving plate 3 and the inner
surrounding wall face of the lower part body 1a respectively, and
hermetically bonded to (or pressed in) them.
[0136] Referring to FIG. 6, D designates the diameter of the
pressure receiving plate 3, .delta. a space between the end face of
the pressure receiving plate 3 and the inner wall face of the lower
part body 1a, Fa a force applied to the electronic weighing and
pressure converting device 2 through the supporting body 4 out of a
force exerted by the differential pressure (P1-P2, P1>P2), FD a
force applied to the pressure receiving plate 3, and Fp a force
exerted on the dividing film 10.
[0137] The afore-mentioned Fp is equally transmitted to the
pressure receiving plate 3 and the lower part body 1a because the
space .delta. is relatively small compared to the diameter D of the
pressure receiving plate 3.
[0138] Then, the force Fa to be transmitted to the electronic
weighing and pressure converting device 2 through the
afore-mentioned supporting body 4 is shown as Fa=FD+Fp/2. Here,
FD=(P1-P2).times..pi.D.sup.2/4, and,
Fp=(P1-P2).times..pi.(D+.delta.).times..delta.. Then, Fa can be
expressed by the following equation (14). Fa = ( P 1 - P 2 )
.times. .pi. .times. .times. D 2 / 4 + ( P 1 - P 2 ) .times. .pi.
.function. ( D + .delta. ) .times. .delta. / 2 = ( P 1 - P 2 )
.times. .pi. .times. .times. D 2 / 4 .times. { 1 + 2 .times.
.delta. / D + 2 .times. ( .delta. / D ) 2 } ( 14 ) ##EQU3##
[0139] Now, with the diameter D of the pressure receiving plate 3
and the breadth of the dividing film 10 (or the space 6) being
given, (P1-P2)=Fa/[(.pi.D.sup.2/4).times.{1+2.delta./D+2
(.delta./D).sup.2}]=Fa/K . . . (15) is obtained from the
afore-mentioned Equation (14). Here,
K=(.pi.D.sup.2/4).times.[1+2.delta./D+2(.delta./D.sup.2)] . . .
(16) The differential pressure (P1-P2) can be obtained by dividing
Fa detected by the electronic weighing and pressure converting
device 2 by the constant K of the denominator.
FEASIBILITY OF INDUSTRIAL USE
[0140] The ultra-precision micro-differential pressure measuring
device in accordance with the present invention is used as a
standard instrument for a differential pressure gauge, and also
used for measuring the pressure drop characteristics of a
low-resistance filter, monitoring the filter characteristics,
assessing the flow characteristics of the fluid equipment which
deals with gases under a reduced pressure. The ultra-precision
differential pressure measuring device in accordance with the
present invention is widely used for the measurement of the
differential pressure of approximately 2.about.5 atmospheric
pressure in the industries and the like.
* * * * *