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Патент USA US3040580

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31 (‘2-11
FIPQSGZ
KR
June 26, 1962
A. KOLlN
3,0405 71
ELECTROMAGNETIC FLOWMETER FOR CONDUCTIVE FLUIDS
Filed July 29, 1957
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3 Sheets-Sheet 1
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l2,
INVENTOR
MW Kiwi .
June 26, 1962
3,040,571
A. KOLIN
ELECTROMAGNETIC FLOWMETER F OR CONDUCTIVE FLUIDS
Filed July 29, 1957
3 Sheets-Sheet 3
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AMPLIFIER
INVENTOR
W \W‘
United States Patent 0 ”
3,040,571
Patented June 26, 1962
2
1
?ow in either direction. A source of energizing electric
voltage is indicated at the connection points 17 which are
3,040,571
ELECTROMAGNETIC FLOWMETER FOR
connected by electrical leads 18 and 19 to the metallic
CONDUCTIVE FLUIDS
conduit ?ange bolts 20 and 21.
Alexander Kolin, Los Angeles, Calif., assignor to the 5
An electrode 14 is provided for insertion into a thread
United States of America as represented by the Secre
ed
hole in the dielectric conduit 10 and is mounted with
tary of the Navy
its inner surface ?ush, or substantially so, with the inner
Filed July 29, 1957, Ser. No. 674,904
wall of the conduit section. Elongated metal electrode
5 Claims. (Cl. 73-194)
15 is of a su?icient length to reach from the axis of the
This invention relates generally to apparatus for sens 10 conduit section to a location beyond the outer wall
thereof. This electrode 15 is coated with an externally
ing ?uid ?ow by electromagnetic means and particularly
threaded insulating covering 16 which covers all portions
to an electromagnetic ?owmeter for conductive ?uids.
of the electrode inside of the conduit except at its very
While electromagnetic ?owmeters of various types and
tip 22 where electric contact with the ?uid at the conduit
designs are well known in the prior art, such meters are
axis is made. The covering 16 with its electrode 15 may
generally characterized by having large and weighty ex
be inserted through a threaded hole in the conduit section
ternal magnets for creating a homogeneous magnetic
10, spaced from the electrode 14. While these electrodes
?eld further utilized in measuring the ?ow of ?uid passing
are shown in parallel relationship in the same plane and
through said meter in the vicinity of the poles of the ex
installed fairly close together, they may be installed at any
ternal magnet. Where the ?owmeter comprises a conduit
distance apart and in any manner so that electrode 14
or throat through which the ?uid is passed, this homo
contacts the ?uid at the inner conduit wall and tip 22 of
geneous magnetic ?eld is established transverse to the di
electrode 15 contacts the ?uid at its axial center.
rection of ?uid ?ow so that the ?owing ?uid passes there
Electrodes 14 and 15 are connected by electrical leads
through. The volume rate of ?uid ?ow is then found by
25 and 26, respectively, to an instrument 24 which may
measuring the voltage induced in the ?uid integrated over
a conduit diameter perpendicular to the conduit axis and 25 be a sensitive voltmeter calibrated to read in units of
volume ?ow.
to the magnetic ?eld vector. Such types of ?owmeters
The principle of operation of the embodiment of the
are in?uenced greatly by the velocity pro?les of the ?uid
invention shown in FIGS. 1 and 2 is described as follows:
passing therethrough and various complex means are re
The diameter of conduit section 10 is preferably small
quired to properly compensate for variations in these
velocity pro?les.
30 as compared to its length. Under these conditions, a uni
directional current derived from a voltage source 17
It has now been found that in the sensing of the ?ow of
conductive ?uids through a conduit, an instrument read
ing may be obtained which is linearly proportional to the
volume rate of ?ow and independent of the velocity pro
passed through the ?uid conductor in the conduit section
10 will give rise to a magnetic ?eld represented by circu
lar ?eld lines of a magnetic ?ux density B(r) which is
?le. This instrument reading is obtained by measuring
given in the interior of the conduit as a function of the
the induced voltage in a ?uid moving through a substan~
radial distance r from the conduit axis by the expression:
tially axially symmetrical non-uniform magnetic ?eld
B(r)=%O[-I><rl
generated by a current passing through the ?uid in the
conduit parallel to the conduit axis.
An object of this invention, therefore, is to dispense
(1)
where J is the current density in amp./m.2; B(r) the mag
netic ?ux density in Webers/m.2; ,u0=41r.l0—'7, the per
with the bulky external magnets employed in previous
electromagnetic ?owmeters.
meability of space; and r is measured in meters.
As the ?uid conductor moves through this magnetic
Another object of this invention is to provide an im
?eld, a potential gradient is induced in it which varies
proved electromagnetic ?owmeter for conductive ?uids
45 from point to point due to the fact that the magnetic ?ux
embodying the advantages set forth above.
density B(r), as well as the ?uid velocity V, varies in
Other objects, special features, and advantages of the
space in an axially symmetrical fashion. The induced
electric ?eld is given as the gradient of the potential V
invention will become more apparent in view of the fol
lowing detailed description and accompanying drawings
by the expression:
wherein:
FIGURE 1 is a schematic diagram of one embodiment 50
of the invention showing the conduit in cross-section;
FIG. 2 is an enlarged cross-sectional partial elevation
of a section of conduit wall showing the electrode con
struction of FIG. 1;
FIG. 3 is a schematic diagram of another embodiment 55
of the invention;
FIG. 4 is an enlarged cross-sectional elevation of the
modi?ed electrode shown in FIG. 3;
FIG. 5 is a schematic diagram of another embodiment
of the invention;
FIG. 6 is a schematic diagram showing a modi?ed form
of sensing circuitry and electrode structure from that
shown in FIG. 5; and
grad V=[V><B]
(2)
This reduces in cylindrical coordinates to the following
expression for the induced radial ?eld:
60
where Vz designates the ?uid velocity in the direction of
the conduit axis and B0 the magnetic ?ux density which,
at any particular point, is perpendicular to the conduit
radius and to the conduit axis.
The potential difference V measured between the cen
ter and the periphery of the ?uid in the conduit under the
speci?ed conditions is given by the integral:
FIG. 7 is a cross-sectional plan view taken on the line
65
7—7 of FIG. 6.
With reference to FIGS. 1 and 2, a dielectric conduit
where R is the inside radius of the conduit 10; B(r) =B0;
section 10 is shown connected between two metallic con
and )‘(r) =VZ. No other assumptions are made about the
duit sections 12 and 13. The system of conduits is ?lled
velocity distribution Vz=f(r) except that it is axially
with a ?uid conductor such as a liquid metal or a strong
symmetrical.
electrolyte. While for purposes of description we may 70 The expression under the integral on the right side in
equation 4 has the signi?cance of Q, the volume rate of
consider the ?ow of conductive ?uid to be from left to
?ow in cubic meters per second traversing the conduit.
right, as shown by the arrow 11, actually the liquid may
3,040,571
3
4
Hence, we obtain for the potential difference V between
as indicated on the galvanometer, resulting in a
zero reading of that meter. The position of moving con
tact 41 at cancellation is indicated against a scale which
the center and the inside wall of the conduit:
serves as a measure of the rate of ?ow.
While the preceding embodiments have been illustrated
This equation 5 shows that, at a constant current den
sity J, the reading of the voltmeter 24in FIG. 1 is a linear
function of the volume rate of ?ow Q. If mere indica
tion rather than measurement of ?ow is sufficient, any
means of sensing or detecting the potential difference be
tween the pick-up electrodes 14 and 15 may be used. As
ing through the measuring conduit sections, it may be
the preceding calculation indicates, the induced voltage
of an AC. source for the previous D.C. source with the
and described as utilizing a constant or pulsating source
of DC. current for energizing the conductive ?uid ?ow
more convenient to use an AC. source, particularly _where
larger energizing currents are required. The substltutlon
attendant changes in circuitry are indicated in FIGS. 5,
is independent of the electrical conductivity of the ?uid
6, and 7.
conductor and, hence, the calibration at any given con
With reference to FIG 5, a dielectric conduit section
stant value of J is independent of the conductivity of
the ?uid conductor.
15 50 is coupled in the usual manner to the two metallic con
duit sections 12 and 13. Two metallic plug contact elec
With further reference to FIG. 1, the source of electric
trodes 51 are threadedly installed near the ends of the
dielectric measuring section 50 so that their inner contact
faces are substantially ?ush with the inner Wall of the
means for producing a substantially constant unidirec
in the form of a
tional current including a source of pulsating E.M.F. pro 20 conduit. A source of AC.
step-down transformer 52 is shown connected to the two
ducing a pulsating current of. constant average value.
voltage connected to connection points 17 may be a stor
age battery, a DC. motor generator, or any other suitable
plug electrodes 51.
Two forms of pick-up electrodes are shown, by way
of illustration, as centrally disposed with relation to the
contact electrodes conveying the current derived from the
voltage source to the conductive ?uid in conduit 10.
25 measuring conduit section. Pick-up electrode 53 is a hol¢
low metallic threaded cylinder threadedly inserted in a
With reference to FIGS. 3 and 4, the measuring conduit
hole provided in the wall of the conduit section 50.
section 30 may be made of any suitable metal. In this
Pick~up electrode 54 comprises a right-angle ‘bent rod
case, the conduit itself may constitute the peripheral pick
like core 55 covered by a dielectric or insulating cover
up electrode connected to the lead 31 of the sensing device
or instrument 32. A point of connection between the 30 56. The core 55 may be provided with a conical tip 57
Being electrically connected to connection points 17, the
metallic conduit sections 12 and 13 serve as energizing
lead 31 and the conduit 30 is indicated at 33 which con
which is positioned on the axis of the conduit section
nection may be a weldment or braze or any other suitable
and may be pointed facing against the direction of ?ow.
The upper portions of the core 55 and its covering 56
protrude externally of the conduit wall and pass through
form of connection. Metal conduit sections 12 and 13
are secured to the ?anges of the measuring conduit sec
tion 30 by means of the usual ?anges and ?ange bolts as
indicated by bolts 20 and 21. Connection points 17 are
provided for the connection of a source of DC. voltage.
the aperture formed in the hollow cylindrical electrode
These points 17 are connected by heavy electrical leads
of the stepdown transformer 52 connected to the con
ductive ?uid in conduit 50 through the energizing con
18 and 19 to their respective ?ange bolt connections 20
53.
The alternating current is supplied by the secondary
and 21. Thus, in this embodiment, the energizing current 40 tact electrodes 51. This alternating current traversing
longitudinally through the conductive ?uid gives rise to
is introduced at the ends of the measuring section 30 and
the current passes through the walls of the conduit section
30 as well as through the conductive ?uid passing there- ,
through.
The pick-up electrode 34 comprises a metallic rod-like
core 35 having a metallic washer 36 affixed thereto. The
electrode 35 is covered with cylindrical dielectric or in
sulating portion 37 and 38 which are separated and abut
against the washer 36. The upper portion 37 is shown as
having an external thread which is inserted into a thread
ed hole provided in the wall of the conduit section 30.
The lower portion 38 is provided with a pointed end which
?ts into a similarly shaped depression formed in the con
duit wall opposite the threaded hole. The periphery of
washer 36 is exposed to contact with the conductive ?uid
and is so positioned on its rod-like electrode core 35 as to
an alternating magnetic ?eld. The ?ow of the conductive
?uid through this ?eld induces an alternating E.M.F. which
is in phase with the magnetic ?eld and which is picked
up by the pick-up electrodes 53 and 55. The same rela
tions established for the induced
in the constant
magnetic ?eld hold also for the instantaneous average,
effective and/or maximum values of the induced alter
nating E.M.F. generated in the alternating magnetic ?eld.
The induced alternating voltage is conveyed to the input
of ampli?er 58 whose output is connected to a suitable
sensing device 59. If the signal induced by flow is strong
enough, the ampli?er may be omitted.
When the apparatus is energized with AC, there is a
transformer E.M.F. induced at zero ?ow in the input lead
circuit from the pick-up electrodes to the sensing devices.
be on the axis of the conduit. The outer end of the core
35 is electrically connected to the lead 39 which is con
This voltage must be compensated for so as to obtain a
zero instrument reading at zero ?ow. This compensation
41 and a source of constant
so the effective
may be accomplished in various ways. The preferred
nected to the sensing device 32 through its associated
method is shown in FIG. 5. A coil 60 comprising several
apparatus.
60
turns of wire is mounted on a shaft v61 so that it can be
The method of sensing the induced
in the con
rotated about the vertical axis of the shaft. This coil
ductive ?uid between the inner wall of the conduit section
is connected in series with the lead wire connecting the
30 and the centrally disposed contact washer electrode
pick-up electrode 53 to one side of the ampli?er input.
36, as shown in this embodiment, FIGS. 3 and 4, com
prises a galvanometer 32 or some other suitable null type 65 In the orientation shown, the magnetic ?eld surrounding
the conduit 50 penetrates the coil area perpendicularly
instrument, a potentiometer 40 having a moving contact
ocnnected to the con
induced in it is a maximum. This
nection points 42. This auxiliary
maintains a
to
induced
be compensated
is inbut
phase
the with
two E.M.F.’s
the transformer
have different
constant potential drop across the resistor portion of the
amplitudes.
By
rotating
the
coil
60
about
the axis of
potentiometer. The moving or sliding contact 41 is con 70
shaft 61, the amplitude of the
induced in the coil
nected through the galvanometer to the measuring conduit
can be diminished until it equals the amplitude of the
section at 33. One end of the potentiometer resistor por
unwanted transformer
Since rotation of the coil
tion is connected to the external end of the pick-up elec
60 through 180° causes a phase reversal, the E.M.F.
trode 35. At a given rate of ?uid ?ow, the moving con
derived from coil 60 can be put in phase opposition to
tact 41 is set so as to cancel out the conductive ?uid 75
the transformer
and thus made to cancel it.
3,040,571
5
FIG. 6 illustrates another circuitry for the same objec
tive, i.e., the elimination of the undesired transformer
E.M.F. Here the coil 60 may be ?xed in a plane sub
stantially parallel to the conduit axis. The current de
6
ductive ?uid ‘through said selected length of conduit
in volume units per unit of time.
3. ‘Electromagnetic ?ow sensing means comprising a
dielectric conduit with metallic energizing electrodes pass
ing through its wall, one near each end of said conduit,
means of generating an alternating current ‘connected to
said electrodes so as to communicate electrically with the
rived from coil 60 is passed through a divider or po
tentiometer circuit 62 Where a fraction of the voltage de
veloped across the resistor 63 may be used in phase oppo
sition to the transformer
to cancel it. The elec
conductive ?uid ?owing through the conduit, a ?rst pick
trode 54 in FIG. 6 is provided with .a rounded right-angle
bend instead of the sharp angular bend shown in FIG. 5. 10 up electrode passing through the wall of said dielectric
conduit, an insulating coating covering said electrode
FIG. 7 shows a cross-sectional View of the two pick-up
electrodes used in FIGS. 5 and 6 as installed in a section
of the wall of conduit 50.
everywhere except near the central axis of said conduit, a
concentric metal ring insulated from said electrode and
surrounding it at its point of passage through said wall so
While certain speci?c embodiments of the invention
have been illustrated and described, it should be realized 15 as to e?ect an electric contact between said ring and the
conductive ?uid ?owing through said conduit thus serving
that the parts are interchangeable from one embodiment
as the second pick-up electrode, a ‘coil rotatably mounted
to another. Furthermore, while the pick-up electrodes
on the outside of said conduit, said coil being connected at
have been shown close together, they may be installed
anywhere in the measuring conduit section, regardless
of its length so long as one makes contact with the
periphery of the column of conductive ?uid passing there
through and the other makes ?uid contact at the longitu
one end to the second pick-up electrode and an alternating
current voltmeter connected to the ?rst pick-up electrode
and to the other end of said coil.
4. An electromagnetic ?ow meter for measuring the
?ow of a conductive ?uid through a conduit comprising,
dinal axis of the conduit section. The measuring con
in combination:
duit sections 10, 30‘, and 50 may be either metallic or
non-metallic. The voltage sources for the conductive 25
a selected portion of said conduit having a longitudinal
?uid energizing currents may be either direct or alternat
axis;
ing current sources. The whole conduit system may be
means connected to the ends of said selected portion for
of dielectric material so long as two contact electrodes
passing an electric current longitudinally through the
are provided to conduct the energizing currents to a se
lected portion of the conductive ?uid passing there 30
through. The contact electrodes 51 shown in FIG. 5
could be two concentric rings mounted on the inner Wall
at the ends of the measuring section, each ring being
provided with an external electrical connection leading
to the main voltage source. Many other modi?cations 35
may suggest themselves to those skilled in the art. All
such modi?cations would undoubtedly fall within the
spirit of the invention and within the scope of the ap
pended claims, wherein I claim:
1. Electromagnetic ?ow sensing means comprising a 40
dielectric conduit, energizing electrodes spaced apart
along the conduit and adjacent to the ends of the conduit,
through which electrodes a current can ‘be passed through
the conductive ?uid in the conduit, a pick-up electrode
passing through the conduit wall ?ush with its inside wall 45
so as to make contact with the periphery of the ?uid
?owing through the conduit, a pick-up electrode passing
through the conduit wall covered with dielectric ma
terial except at its tip which is located along the conduit
axis and makes contact with the center of the ?uid column
?owing through the conduit and a device connected to
both pick-up electrodes to sense the potential di?erence
between the center and the periphery of the ?uid column
in the conduit.
2. An electromagnetic ?ow meter for measuring the
?ow of a conductive ?uid through a conduit comprising,
in combination:
means for passing an electric current longitudinally
through the conductive ?uid ?owing through a select
ed length of said conduit whereby an axially sym 60
metrical non-homogeneous magnetic ?eld is estab
lished in the conductive ?uid and whereby a potential
di?erence is created radially through said conductive
conductive ?uid ?owing in said selected portion
whereby an axially symmetrical non-homogeneous
magnetic ?eld is established in the conductive ?uid
in said portion, said magnetic ?eld having zero in
tensity at the longitudinal axis of said portion of con
duit and a maximum intensity at the inner wall of
said portion of conduit whereby a potential difference
is created radially through said conductive ?uid be
tween the axis and the inner wall of said portion of
conduit;
means located at the axis and wall of said portion of
conduit for sensing the magnitude of said potential
di?erence; and
indicating means for converting said potential di?erence
to a measure of the ?ow of said conductive ?uid
through said conduit.
5. Electromagnetic ?ow sensing means comprising, in
combination:
a conduit through which conductive ?uid ?ows;
means for passing an electric current through the con
ductive ?uid in a selected portion of said conduit,
said means including conductive ?uid contact elec
trodes disposed longitudinally with relation to said
selected portion and said electric current being passed
substantially parallel to the longitudinal axis of said
conduit portion;
the longitudinal axis of said conduit; and
means for sensing and indicating the voltage generated
between said electrode means.
References Cited in the ?le of this patent
UNITED STATES PATENTS
?uid between the geometric center of said conduit
65 2,637,208
and the Wall of said conduit;
means for sensing the magnitude of said potential dif
2,691,303
2,733,604
ference; and indicating means for converting said po
tential difference to a measure of the ?ow of said con
.
electrode means for contacting said conductive ?uid
at the inner wall of said conduit and substantially at
2,746,291
Mellen _______________ .. May 5,
De Boisblanc __________ __ Oct. 12,
Coulter _______________ __ Feb. 7,
Swengel ____________ ._- May 22,
1953
1954
1956
1956
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