Abstrict An electromagnetic flow meter using pairs of concentric electrodes
mounted through a pipe line in an opposed facing relationship. The
output flow signals from the electrodes are first differentially
amplified with respect to a common reference signal and then the
output signals from the first differential amplification are differentially
amplified in two successive operations to produce a final flow signal
having a value "n" times the output signal from a single
pair of "n" facing electrodes.
Claims The embodiments of the invention in which an exclusive property
or privilege is claimed are defined as follows:
1. An electromagnetic flow meter comprising
electrodes opposingly disposed on the wall of a pipe for guiding
fluid including a plurality of concentric electrode assemblies each
having a plurality of electrodes arranged coaxially, and
differential amplifier means for flow signal values detected by
respective facing pairs of electrodes of said opposing concentric
electrode assemblies operative that the values amplified once are
successively and differentially amplified further, whereby the flow
representative value attained in the final differential amplification
is an integral multiple of the voltage difference between said respective
pairs of electrodes.
2. An electromagnetic flow meter as set forth in claim 1 wherein
each of said electrode assemblies have two electrodes.
3. An electromagnetic flow meter as set forth in claim 1 wherein
said differential amplifier means includes a first plurality of
AC differential amplifiers for comparing respective ones of the
electrode output flow signal with a common reference level.
4. An electromagnetic flow meter as set forth in claim 3 wherein
said differential amplifiers means includes a second plurality of
AC differential amplifiers for comparing pairs of output signals
from said first plurality of amplifiers.
5. An electromagnetic flow meter as set forth in claim 4 wherein
said differential amplifier means includes a third AC differential
amplifier for comparing output signals from said second plurality
of amplifiers.
6. An electromagnetic flow meter as set forth in claim 5 wherein
each of said electrode assemblies have two electrodes, said first
plurality of amplifiers has four amplifiers, said second plurality
of amplifiers has two amplifiers and said third amplifier is a single
amplifier.
7. An electromagnetic flow meter as set forth in claim 6 wherein
said common reference signal is a ground reference level.
8. An electromagnetic flow meter as set forth in claim 7 and including
magnetic field producing means arranged to respond to an energizing
signal to produce a magnetic field at right angles to a centerline
passing through said coaxial electrodes and to the flow path of
the fluid in the pipe.
Description CROSS-REFERENCE TO RELATED APPLICATION
Subject matter shown but not claimed herein is shown and claimed
in a copending application of Norikazu Wada, Ser. No. 832872 filed
on even date herewith and assigned to the same assignee as the present
application.
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates to an electromagnetic flow meter
and more particularly to an electromagnetic flow meter wherein a
signal-to-noise (S/N) ratio is improved.
2. Description Of The Prior Art
In order to increase an electromotive force between detecting electrodes
of the electromagnetic flow meter without increasing the density
of magnetic flux applied to the flow meter, the following method
has been adopted in the prior art flow meter of this kind. Namely,
a plurality of electrode pairs are arranged along the wall of a
fluid flow pipe along the axis of the same, and electromotive forces
obtained by respective electrode pairs are composed, or summed,
to establish an increased electromotive force of the detecting electrode
configuration. According to the prior art flow meter of this kind,
however, it is often observed that the electromotive forces of the
electrode pairs are different from each other which creates a summing
conflict. Further, there is another disadvantage in that the input
terminal, and the leads of a converter, which is a circuit for composing
the electrode signals, are apt to pick up external noise signals.
Therefore, various kinds of complicated matching circuits are needed
to overcome such disadvantages.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved electromagnetic
flow meter.
Another object of the present invention is to provide an improved
electromagnetic flow meter having a high signal-to-noise ratio.
In accomplishing these and other objects, there has been provided,
in accordance with the present invention, an electromagnetic flow
meter in which a pair of electrodes opposing to each other in the
fluid flow pipe are constituted with concentric electrode assemblies
comprising a plurality of electrodes arranged coaxially and the
flow signal values detected between corresponding electrodes of
opposing electrode assemblies are differentially amplified.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the present invention may be had when
the following detailed description is read in connection with the
accompanying drawings, in which:
FIG. 1 is a diagrammatical representation of an embodiment of an
electromagnetic flow meter according to the present invention,
FIG. 2 and FIG. 3 are cross-sectional views of a part of the electrode
assembly used in this invention as illustrated in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 in more detail, there is shown an electromagnetic
flow meter embodying the present invention and using the electrodes
shown in FIGS. 2 and 3. This electromagnetic flow meter includes
a signal detector 1 and a signal converter 2. The detector 1 includes
a pipe having a pipe wall 3 for guiding the fluid to be measured,
an excitation coil 4 for generating a magnetic field in response
to an energizing current which intersects the axis of the fluid
pipe at a right angle, and a pair of concentric electrode assemblies
5 and 5' which are mounted through the wall 3 of the fluid pipe
opposite each other. Further, the pipe wall 3 has a lining 6 for
electrical insulation formed on its inner wall. The concentric electrode
assembly 5 comprises a rod shaped inner electrode 51 an electrically
insulating tube 52 and a hollow center electrode 53. These three
electrode constituents are assembled in a coaxial relation.
The electrode assembly 5' has the same construction as the electrode
assembly 5 and includes an inner electrode 51', an electrically
insulating tube 52' and an outer hollow electrode 53'. The inner
electrodes 51 and 51' are used as an opposing electrode pair while
the outer electrodes 52 and 52' are also used as another opposing
electrode pair.
A more detailed illustration of the concentric electrode assembly
is shown in FIGS. 2 and 3. The complex electrode assembly shown
in FIG. 2 is an external mounting type which is mounted through
a hole in the pipe wall 3 in water-tight fashion by using a spring
57 that is located between a lower plate 55 and an upper plate 56
and compressed by fastening bolts 54 threaded into the pipe wall
3. The bolts 54 pass through the plates 55 and 56 while the bolt
heads bear against the outer plate 56. A reference numeral 58 designates
an electrode connecting rod which has an electrically insulating
coating on its outer surface. The rod 58 is connected to the outer
electrode 53 while the inner electrode 51 is extended through aligned
holes in the plates 55 and 58 to a connection terminal past the
outer plate 56. An insulating coating 59 on the extended part of
the electrode 51 serves to electrically isolate the electrode 51
from the plates 55 56 and the concentric spring 57. The electrodes
53 and 51 are provided with radially outwardly extended collars
with the tube 52 having a matching collar positioned therebetween.
The insulating coating 6 is extended through the hole in the pipe
wall 3 and on the outside surface of the pipe wall 3 surrounding
the hole in the pipe wall 3 to electrically insulate the collar
of the outer electrode 53 from the pipe wall 3. When the bolts 54
are tightened into the pipe wall 3 the bolt heads bear against
the outer plate 56 to compress the spring 57 whereby the inner plate
55 is urged against the collars of the electrodes 51 and 53 the
tube 52 and the insulating coatings 6 and 59. Thus, the collars
and insulating coatings are compressed into a layered structure
to provide fluid-tight seals along with electrical insulation of
the electrodes 51 and 53.
FIG. 3 shows a concentric electrode assembly of an internal mounting
type wherein the complex electrode assembly 5 is inserted from the
inside of the pipe 3. A center electrode 51A is formed from a straight
rod having a tapered head at one end and a threaded portion at the
other end. The center electrode 51A is located within an electrically
insulating sleeve 52A which extends from the threaded portion to
the tapered head. An electrically conductive wedge ring 62 having
a raised inner lip is located on the insulating coating 6 which
is extended through the hole in the pipe wall 3 and onto the pipe
wall outer surface surrounding the hole in the pipe wall 3. An insulating
washer 59 is located on top of the wedge ring 62. A flatened nut
60 is threaded onto the center electrode 51A while a concentric
spring 61 is located between the washer 59 and the nut 60. Finally,
an outer hollow cylindrical electrode 53A is located on the sleeve
52A and extends from the tapered head of the center electrode to
the raised lip of the wedge ring 62. Electrical conncetions to the
inner electrode 51A and the outer electrode 53A may be made at any
suitable point by well-known techniques. When the nut 60 is turned
down on the center electrode 51A, the spring 61 is located between
insulating washer 59 and the nut 60 is compressed urge the washer
59 and ring 62 against the outer electrode 53A and to draw the tapered
head of the center electrode 51A into the end of the sleeve 52A
and the electrode 53A. Thus, the end of the sleeve 52A and the electrode
53A are distorted to fix the assembly 5A to the pipe wall 3 in a
water-tight fashion.
The detector 1 comprising the electrode assembly 5 and 5' as constructed
above is electrically connected to the converter 2 as shown in FIG.
1. More particularly, the inner electrode 51 is connected to one
input of a first alternating current, i.e., AC, differential amplifier
21 while the inner electrode 51' is connected to one input of a
second AC differential amplifier 22. The outer electrode 53' is
connected to one input of a third AC differential amplifier 23 while
the outer electrode 53 is connected to one input of a fourth AC
differential amplifier 24. The other inputs of these differential
amplifiers 21 through 24 are supplied with an earth potential as
a reference voltage through a head 30. The outputs of amplifiers
21 and 22 are received by a fifth AC differential amplifier 25 at
corresponding ones of its inputs while the outputs of amplifiers
23 and 24 are received by a sixth AC differential amplifier 26 at
corresponding ones of its inputs. In the same manner, the outputs
of these fifth and sixth amplifiers 25 and 26 are received by respective
inputs of a seventh AC differential amplifier 27. A reference numeral
28 designates a direct current, i.e, DC, amplifier which amplifies
the output of the seventh AC differential amplifier 27 to generate
a DC output proportional to the fluid flow while reference numeral
29 designates a signal converter or transmitter for converting the
output of said DC amplifier 28 for further transmission in a manner
well-known in the art.
In the operation of the circuit constituted as set forth above,
assume that the voltage induced at the inner electrode 51 of the
assembly 5 is e.sub.1 that the voltage induced at the outer electrode
53 is e.sub.2 that the voltage induced at the inner electrode 51'
of the assembly 5' is e.sub.1 and that the voltage induced at the
outer electrode 53' is e.sub.2 '. The outputs of AC differential
amplifiers 21 through 24 become e.sub.1 e.sub.2 e.sub.3 and e.sub.4
respectively because the input reference voltages of those amplifiers
are similar earth potentials. As a consequence, the output of the
amplifier 25 becomes (e.sub.1 -e.sub.1 ') while the output of the
amplifier 26 becomes (e.sub.2 -e.sub.2 '). Accordingly, the output
of the amplifier 27 is expressed as (e.sub.1 -e.sub.1 ') (e.sub.2
-e.sub.2 '). Since the detecting electrode of this invention is
formed as the concentric electrode assembly, the inner and outer
electrodes detect the fluid which is in almost same area so that
the signals induced at two electrodes are considered as being generated
at almost same time and being equal in their values. Therefore,
the following relation can be established among the signals induced
as above.
As a consequence, the output of the AC differential amplifier 27
is expressed as follows.
As is apparent from the above equations, the input of the DC amplifier
28 in this embodiment is a signal which is twice as large as the
difference between the voltages induced at respective facing electrodes.
In the embodiment as set forth above, the complex electrode assembly
is constituted with two electrodes in coaxial relation so that the
input of the DC amplifier 28 becomes twice as large as the difference
of the voltage between the facing electrodes. However, where the
assembly is constituted with n-facing electrodes, it is apparent
that the input of the DC amplifier 28 is made "n" as large
as the difference of the voltage between n-facing electrodes.
As explained above, according to this invention, the detecting
electrode is constituted with the electrode assembly having a plurality
of coaxial electrodes, and the outputs by the corresponding electrodes
of the complex electrode assemblies are differentially amplified
whereby it becomes possible to obtain the flow meter output which
is in integral multiples of the voltage difference between the electrodes
in response to the number of the electrodes constituting the electrode
assembly. Therefore, it becomes possible to obtain a novel electromagnetic
flow meter which has high S/N ratio.
Accordingly, it may be seen that there has been provided in accordance
with the present invention, an improved electromagnetic flow meter
having a signal-to-noise ratio. |