Electromagnetic flowmeter usable in less-than-full fluid lines

An electromagnetic flowmeter having a flow tube interposed in a normally less-than-full fluid line. A pair of arcuate electrodes are mounted in the flow tube at opposed positions spanning a substantial portion of the total circumference of the inner wall of the tube, whereby the electrodes are operative with respect to fluid in the tube in a range extending from a level close to empty to completely full. The electrodes which are in direct contact with the fluid have an inverted T formation, whose vertical leg conforms to the inner circumference of the tube, and whose horizontal base extends along the bottom of the tube, thereby maintaining a large portion of the electrode area in contact with the fluid at all times. Associated with the flow tube is an electromagnet that is excited by a periodically interrupted direct current to establish a magnetic field in the tube which is intercepted by the fluid passing therethrough to induce a signal in the electrodes.

BACKGROUND OF INVENTION 
This invention relates generally to electromagnetic flowmeters for 
measuring the flow rate of fluids passing through a pipe line, and more 
particularly to a flowmeter whose electrode structure is adapted to 
provide accurate flow measurement in open channels as well as in pipe 
lines which normally run at less than full capacity. 
In an electromagnetic flowmeter, the liquid whose flow rate is to be 
measured is conducted through a flow tube provided with a pair of 
diametrically opposed electrodes, a magnetic field normal to the direction 
of flow being established by an electromagnet. When the flowing liquid 
intersects this field, a signal is induced therein which is transferred to 
the electrodes. This signal, which is proportional to the average velocity 
of the liquid and hence to its average volumetric rate, is then amplified 
and processed to actuate a recorder or indicator. 
Electromagnetic flowmeters of the type heretofore known, including those 
disclosed in U.S. Pat. Nos. 3,550,446; 3,329,018 and 3,786,687, are 
effectively restricted to pipe lines which run full. Indeed, the 
instruction books which accompany such flowmeters usually admonish the 
user that major inaccuracies would be experienced should the flow tube be 
interposed in a pipe line that is less than full. 
Because of this limitation, existing types of electromagnetic flowmeters 
are not applicable for measurement in storm sewers, plant effluent lines 
and in other open-channel and pipe line situations in which less-than-full 
pipes are normally encountered. The exclusion of electromagnetic 
flowmeters from such applications is a serious drawback when one takes 
into account the many advantages to be gained by an electromagnetic 
flowmeter which is free of moving parts and which introduces no obstacle 
in the flow path. 
There are at least four reasons why known types of electromagnetic 
flowmeters are incapable of providing accurate measurement with 
less-than-full pipes, and these will now be briefly considered. 
POINT I 
A standard, full pipe electromagnetic flowmeter in which an electromagnetic 
field is established by means of sinusoidal a-c power exhibits large zero 
shifts as the pipe becomes partially full. This is caused by variations in 
the geometry of the pick-up loop formed by the electrode leads and the 
fluid-conducting path therebetween. 
POINT II 
A standard, full-pipe electromagnetic flowmeter makes use of a pair of 
button-shaped electrodes mounted at diametrically opposed positions in a 
horizontal plane passing through the center of the meter tube, this plane 
defining the half-full level. When, therefore, the fluid in the flow tube 
falls below the half-full level, the electrodes lose contact with the 
fluid and the meter is unresponsive to fluid flow. 
POINT III 
In the standard meter, the magnetic field established therein has a flux 
distribution in which the flux intensity is symmetrical from the top to 
the bottom of the flow tube. With this magnetic field, the signal-to-flow 
rate ratio increases as the level of the fluid in the meter drops, whereas 
for accurate measurement it is vital that the signal be independent of 
fluid level. 
POINT IV 
In a conventional flowmeter in which the electrodes are exposed and in 
electrical contact with the fluid passing through the flow tube, it has 
been found that as soon as any portion of the electrodes becomes uncovered 
as the fluid level drops, large d-c potential variations are encountered. 
These variations are often of greater amplitude than that of the 
flow-induced signal, giving rise to erroneous indications of flow rate. 
To provide a flowmeter which is effective in measuring flow rate in 
less-than-full pipes, the above-identified Mannherz et al. copending 
application discloses an arrangement wherein mounted within the flow tube 
interposed in the fluid line at opposed positions therein is a pair of 
arcuate electrodes spanning a considerable portion of the total tube 
circumference to render the electrodes operative with respect to the fluid 
passing through the tube in a range extending from a level approaching the 
empty state to a level approaching the full state. 
In Mannherz et al., the electrodes are embedded in a dielectric liner and 
are therefore not in contact with the fluid being metered as in a 
conventional magnetic flowmeter but are electrically insulated therefrom, 
thereby dictating the use of a high impedance amplifier for the signal 
derived from these electrodes. 
Associated with the flow tube in the Mannherz et al. meter is an 
electromagnet whose coils are excited by a periodically interrupted direct 
current to establish a magnetic field that is intercepted by fluid passing 
through the tube to induce a signal in the electrodes. This signal is 
sampled during the steady state intervals of the magnetic flux to provide 
an output free of zero shift error and of interference voltages. The 
distribution of magnetic flux in the field is made such as to 
progressively decrease in intensity as one goes from the top to bottom of 
the tube, thereby providing an output signal which is indicative of flow 
rate and independent of flow level. 
SUMMARY OF INVENTION 
The main object of the present invention is to provide a flowmeter capable 
of accurately measuring flow rate when interposed in a line passing fluid 
through the flow tube at a level below its full capacity, which flowmeter 
makes use of electrodes which are in direct contact with the fluid but are 
so shaped as to obviate the drawbacks that normally attend the use of 
direct-contact electrodes. 
More particularly, in the electrode arrangement disclosed in the Mannherz 
et al. application, the electrodes are insulated from the fluid being 
metered but are capacitively coupled thereto to obviate the generation of 
galvanic potentials, whereas in the present invention, the electrodes are 
so shaped as to reduce the noise level to a degree which renders 
unnecessary the use of insulated electrodes as well as a high-impedance 
input amplifier and other expedients dictated by capacitively coupled 
electrodes. 
A significant advantage of a flowmeter in accordance with the invention 
which includes shaped electrodes in direct contact with the fluid is that 
it is less expensive than a meter of the Mannherz et al. type, for it 
permits the use of a conventional primary structure designed for standard 
electrodes, the shaped electrodes being secured to the bosses normally 
provided for the standard electrodes. 
Also an object of this invention is to provide a flowmeter of the 
above-type in which the electrodes in direct contact with the fluid are 
shaped to span a substantial portion of the total circumference of the 
flow tube so that the electrodes are fully operative with respect to fluid 
passing through the tube even when the fluid level is very low, the shape 
being such as to minimize variations in DC potential. 
Briefly stated, these objects are accomplished in a flowmeter having a flow 
tube which is interposable in a fluid line, such as a sewer pipe, that is 
normally less-than-full. Mounted within the flow tube at opposed positions 
therein in direct contact with the fluid is a pair of arcuate electrodes 
spanning a considerable portion of the total tube circumference to render 
the electrodes operative with respect to the fluid passing through the 
tube in a range extending from a level approaching the empty state to a 
level approaching the full state. Each electrode has an inverted 
T-formation whose vertical leg conforms to the inner circumference of the 
tube and whose horizontal base extends along the bottom of the tube, 
thereby maintaining a large portion of the total area of the electrode in 
contact with the fluid at all times. 
Associated with the tube is an electromagnet whose coils are excited by a 
periodically-interrupted direct current to establish a magnetic field that 
is intercepted by fluid passing through the tube to induce a signal in the 
electrodes. This signal is sampled during the steady state intervals of 
the magnetic flux to provide an output free of zero shift error and of 
interference voltages. The distribution of magnetic flux in the field is 
made such as to progressively decrease in intensity as one goes from the 
top to bottom of the tube, thereby providing an output signal which is 
indicative of flow rate and independent of flow level.

DESCRIPTION OF INVENTION 
METER PRIMARY 
Referring now to FIG. 1, there is shown in section a flow tube 10 which is 
included in a flow measuring system in accordance with the invention. Tube 
10, when fabricated of conductive material, is provided with an inner 
insulating liner 11. Mounted on the surface of liner 11 in direct contact 
with the fluid passing through the tube is a pair of arcuate electrodes 12 
and 13 which occupy opposed positions in the tube and together span a 
considerable portion of the total circumference thereof. In practice, each 
electrode spans about 170.degree.. 
The horizontal plane X passing through the center of tube 10 represents the 
level of the fluid when it is half full. It will be evident from FIG. 1 
that the actual level of fluid 14 is well below the half-way point. It 
will also be evident that electrodes 12 and 13 will remain in operative 
relation with this fluid even when the level is close to empty. In 
practice, therefore, the level would have to drop below a level of about 
0.01 D before effective contact is lost with the electrodes. Since a flow 
rate creating a level this low would be almost negligible, the fact that 
it cannot be measured is immaterial in practical terms. 
Associated with flow tube 10 is an electromagnet having coils 15 and 16 
which in practice may be saddle-shaped. The coils are placed on the top 
and bottom of the tube to establish a magnetic field therein whose lines 
of flux are perpendicular to the direction of fluid flow, whereby when the 
fluid passes through the flow tube, a signal is induced in the electrodes 
as a function of flow rate. 
In order, therefore, to render the output signal independent of the fluid 
level, the flux density of the magnetic field established by coils 15 and 
16 is set up so that this density decreases progressively as one goes from 
the top of the meter tube to the bottom thereof. As explained in detail in 
the copending Mannherz application, the flow signal induced in the 
electrodes is the resultant of an infinite number of generators dispersed 
in the fluid. The circuit surrounding the generator may be represented by 
a network of fluid-equivalent shunting resistors. The decrease in density 
causes the generator output to decrease as one moves from the top to the 
bottom of the tube to an extent compensating for the loss of the 
fluid-equivalent shunting resistors as the fluid level drops. 
This progressive decrease in flux density may be effected by adjusting the 
relative amount and the direction of excitation current applied to coils 
15 and 16, or by providing a larger coil at the top section of the meter 
tube than at the bottom thereof. 
THE ELECTRODES 
As pointed out previously, in a situation in which the electrodes of 
conventional design are in direct electrical contact with the fluid and 
are partially uncovered as the fluid level drops, large d-c potential 
variations take place. These variations are at a frequency close to the 
frequency of the flow-induced signal and are often of much greater 
amplitude than the flow-induced signal. Hence they result in large output 
indication variations. Moreover, the d-c potential variations act, most of 
the time, to saturate the signal converter coupled to the electrodes, 
giving rise to errors because of operation in the saturated condition. The 
objectionable d-c potentials are due to the galvanic potentials that exist 
between the electrodes and ground. 
Whenever two metals (electrodes) are immersed in an electrolytic solution, 
a potential difference will exist between them. These potentials are 
described by the Nerst equation: 
##EQU1## 
where: E.sub.o is the potential that would exist if the reaction products 
were at equilibrium conditions, V 
e is the potential existing under non-equilibrium conditions, V 
t is the absolute temperature, K 
n is the number of gram-atoms/gram-mole 
a.sub.+ is the activity quotient established by concentrations of the 
reaction products at the electrodes 
R is the gas constant = 8.314 J/K. mol 
F is the Faraday constant - 96,500 coulombs/gram-atoms 
At equilibrium a.sub.+ = 1 so that 1n a.sub.+ = 0 and E - E.sub.o = 0. Any 
dynamic condition producing non-equilibrium concentrations of reaction 
products at the electrodes causes a.sub.+ .noteq. 0 and, therefore, E - 
E.sub.o .noteq. 0. In the case of the partially full magnetic flowmeter, 
it is this E - E.sub.o voltage which appears as noise on the flow signal. 
A fuller discussion of the behavior of metals immersed in an electrolyte 
may be found in Outlines of Physical Chemistry, Daniels, F., Wiley 1950, 
Chapter XVI. 
Though the area of the electrodes does not directly enter into the Nerst 
equation, rapid changes in the area will, in a dynamic situation, 
influence the value of the activity coefficient a.sub.+. Thus, during 
non-equilibrium conditions, the potential difference of the electrodes (E) 
will be a function of the change in area that is immersed in the 
electrolyte. 
EQU .DELTA.E = f (.DELTA.A) 
in a partially full electromagnetic flowmeter with arcuate electrodes, the 
condition exists that the area of the electrode exposed to the electrolyte 
is continually changing. This is typical of any open channel turbulent 
flow. Thus the .DELTA.E observed at the electrodes will be a function of 
both the turbulence of the flow and the geometric configuration of the 
electrodes which will determine the .DELTA.A for a given flow condition. 
It becomes important, therefore, to configure electrodes 12 and 13 so as to 
minimize rapid changes in the electrode area that makes contact with the 
fluid. FIG. 2 illustrates in connection with electrode 13 a preferred 
electrode configuration which is adapted to maintain a large portion of 
the total area of the electrode in contact with the fluid electrolyte at 
all times regardless of changes in fluid level. 
The shaped electrode 13 has an inverted T-formation constituted by a 
vertical leg 13A which is curved to conform to the inner circumference of 
the flow tube and a horizontal straight-line base or strip 13B which 
extends along the bottom of the flow tube. Base 13B represents a 
substantial portion of the total area of the electrode and is always in 
contact with the fluid regardless of the level of the fluid in the flow 
tube, whereas the area of vertical leg 13A representing the remaining 
portion of the total area of the electrode is more or less in contact with 
the fluid, depending on fluid level. Thus the percentage change in the 
total electrode due to rapid changes in the fluid level is minimized. As a 
consequence, changes in DC potential at the electrodes will be minimal. 
It will be appreciated that the inverted T formation is not the only 
electrode shape that will accomplish the desired result. The geometrical 
requirement is such that a substantial portion of the overall area of the 
electrode must always stay in contact with the fluid, changes in fluid 
contact being restricted to the remaining portion of the electrode area. 
This may also be accomplished by a pear-shaped or other configuration in 
which most of the total area is adjacent the bottom of the tube. 
The magnetic field may be either direct or alternating, for in either event 
the amplitude of signal induced in the liquid passing through the field 
will be a function of its flow rate. However, when operating with direct 
magnetic flux, the d-c signal current flowing through the liquid acts to 
polarize the electrodes, the magnitude of polarization being proportional 
to the time integral of the polarization current. With alternating 
magnetic flux operation, polarization is rendered negligible, for the 
resultant signal current is alternating and therefore its integral does 
not build up with time. 
Though a-c operation is clearly advantageous in that polarization is 
obviated and the a-c flow-induced signal may be more easily amplified, it 
has distinct drawbacks. The use of an alternating flux introduces spurious 
voltages that are unrelated to flow rate and, if untreated, give rise to 
inaccurate indications. The two spurious voltages that are most 
troublesome are: 
1. stray capacitance-coupled voltages from the coil of the electromagnet to 
the electrodes, and 
2. induced loop voltages in the input leads. The electrodes and leads in 
combination with the liquid extending therebetween constitute a loop in 
which is induced a voltage from the changing flux of the magnetic coil. 
The spurious voltages from the first source may be minimized by 
electrostatic shielding and by low-frequency excitation of the magnet to 
cause the impedance of the stray coupling capacitance to be large. But the 
spurious voltage from the second source is much more difficult to 
suppress. 
The spurious voltage resulting from the flux coupling into the signal leads 
is usually referred to as the quadrature voltage, for it is assumed to be 
90.degree. out of phase with the A-C flow-induced voltage. Actual tests 
have indicated that this is not true in that a component exists in-phase 
with the flow-induced voltage. Hence, that portion of the "quadrature 
voltage" that is in-phase with the flow-induced voltage signal constitutes 
an undesirable signal that cannot readily be distinguished from the 
flow-induced signal and whose change produces a changing zero shift 
effect. 
Existing a-c operated electromagnetic flowmeters are also known to vary 
their calibration as a function of temperature, fluid conductivity, 
pressure and other effects which can alter the spurious voltages both with 
respect to phase and magnitude. Hence, it becomes necessary periodically 
to manually re-zero the meter to correct for the effects on zero by the 
above-described phenomena. 
All of the adverse effects encountered in a-c operation of electromagnetic 
flowmeters can be attributed to the rate of change of the flux field 
(d.phi./dt), serving to induce unwanted signals in the pick-up loop. If, 
therefore, the rate of change of the flux field could be reduced to zero 
value, then the magnitude of quadrature voltage and of its in-phase 
component would become non-existent and zero drift effects would 
disappear. When the magnetic flux field is a steady state field, as, for 
example, with continuous d-c operation, the ideal condition d.phi./dt=0 is 
satisfied. 
But d-c operation to create a steady state field is not acceptable, for 
galvanic potentials are produced and polarization is encountered. In a 
system in accordance with the invention for measuring flow in 
less-than-full pipes, the coils of the electromagnet periodically 
interrupt d-c power and the signal is sampled during intervals in which a 
steady-state condition exists so that one retains the advantages of a-c 
operation without its concomitant disadvantages. 
THE SYSTEM 
Referring now to FIG. 3, there is shown a flowmeter system in accordance 
with the invention, constituted by a primary in the form of an 
electromagnetic flowmeter adapted to produce a low-level, a-c signal 
output whose amplitude is proportional to the flow rate of the liquid 
being measured, and a secondary which converts this low level a-c signal 
to a proportional d-c current output signal. 
The flowmeter primary includes the flow tube 10 through which the liquid 14 
to be measured is conducted, the liquid only partially filling the tube. 
The electromagnet, including coils 15 and 16, establishes a magnetic field 
transverse to the direction of flow and which is perpendicular to the axis 
of the electrodes. 
As is well known, a voltage is induced in liquid 14 whose flow intersects 
the magnetic field, this voltage being transferred to electrodes 12 and 13 
to produce a signal at flowmeter output terminals that reflects the flow 
rate. This signal is referred to as the flow-induced signal to distinguish 
it from spurious signal components that are independent of flow rate. 
Coils 15 and 16 are energized by a relatively low-frequency square wave 
derived from a full-wave rectifier power supply constituted by a 
transformer 17 whose primary is connected to an a-c power line through a 
regulator 17A, the line supplying the usual 50 or 60 Hz current. The 
secondary of transformer 17 is connected to the input junctions of a 
full-wave rectifier bridge 18, whose output junctions are connected to the 
respective movable contacts of two single-pole single-throw switches 19 
and 20 whose fixed contacts are both connected to one end of the 
series-connected coils 15 and 16, the other end being connected to the 
center tap of the secondary of transformer 17. 
When switch 19 is closed and switch 20 is simultaneously open, the 
rectified output is applied to the magnet coil in one polarity, and when 
switch 19 is open and switch 20 is simultaneously closed, the polarity is 
reversed. Alternatively, rather than reversing polarity, the switch may be 
arranged to periodically interrupt the d-c power to provide a single-sided 
on-off operation. 
While for purposes of explanation, switches 19 and 20 are shown as 
mechanical devices, in practice these switches are in electronic form and 
may be constituted by triacs or any other type of electronic switching 
device in vacuum tube or solid-state form. 
Switches 19 and 20 are activated at a rate which is low relative to the 
frequency of the a-c line. This is accomplished by means of a presettable 
scaler or frequency divider 21 to which the 60 Hz line voltage is applied 
as a clock signal, the scaler yielding low frequency pulses in the order 
of 17/8, 33/4 or 71/2 Hz. 
The low-frequency pulses from the scaler are applied to the firing 
electrodes of the two triac switches (or whatever other electronic 
switching devices are used) to alternately turn on the triacs and thereby 
connect either the positive or the negative side of the full-wave 
rectified 60 Hz voltage to the magnet coils. Thus when switch 19 is 
closed, current flows through the magnet coil in one direction, and when 
switch 20 is closed, the current flows in the reverse direction. 
Because the output of the full-wave rectifier is a raw, unfiltered direct 
voltage, it is composed by a continuous train of half-cycle pulses, all of 
the same polarity. But with the low-frequency switching action in 
accordance with the invention, the voltage applied to the coils is 
periodically reversed in polarity, as a result of which the current 
passing through the coil has a 120 Hz ripple component. 
Because the electromagnet has a relatively high inductance, it functions as 
a filter choke, and, in practice, it takes out as much as 75 percent of 
the ripple component. The remaining portion of the 120 Hz ripple component 
that appears in the flow-induced signal is smoothed out at the summing 
junction of the secondary via the filter action of the associated error 
amplifier, to be later described. This obviates the need for filter 
capacitors associated with the choke, as in conventional filters. Thus, 
the system functions as it it were excited by a "square wave equivalent" 
having a substantially constant amplitude. 
The flow-induced signal appearing across electrodes 12 and 13 of the 
flowmeter primary is fed to a secondary constituted by a converter. This 
converter is essentially a solid-state feedback system producing a 
frequency output (and optional current) proportional to flow. 
In the converter shown in FIG. 3, the flow-induced signal is applied to the 
first stage of the converter which is an a-c pre-amplifier 22. This signal 
has a generally square-wave formation but for the spikes appearing at the 
points of polarity reversal. These spikes are the result of switching 
transients or surges, and have a duration depending on the 
inductance-resistance time constant of the electromagnetic circuit. 
The constant level portion of the square wave reflects the steady state 
condition of the magnetic field, and has an amplitude that is directly 
proportional to the velocity of liquid passing through the flow-tube. 
Hence it is only this portion of the signal which is of interest for 
accurate measurement purposes. 
The output of pre-amplifier 22 is applied through a blocking capacitor 23 
to one input of a summing junction 24 to whose other input is fed the 
output of a range attenuation circuit 25 from an error signal type of 
feedback loop. The error signal produced by a comparison of the flow 
signal and the feedback signal in the summing junction is amplified in a-c 
error amplifier 26, which is provided with a negative feedback circuit 27 
adapted to attenuate all frequencies lower and higher than that of the 
error signal. 
The a-c output of the error amplifier is applied to an inverting 1:1 
amplifier 28, whose output is applied to a full-wave demodulator 29. The 
operation of the demodulator is synchronized with the low-frequency 
switching rate of the magnet coil and is so gated as to block the applied 
error signal at those points corresponding to the point of polarity 
reversal, the blockage being maintained for the duration of the 
inductance-resistance time constant of the electromagnetic circuit. In 
this way, the d-c output of the demodulator reflects only the steady state 
magnetic flux condition, the spiked portions of the flow-induced signal 
being suppressed. 
In order to synchronize the demodulator, the frequency divider 21, which 
responds to the 50 or 60 cycle signal to produce low-frequency control 
pulses for governing the electromagnet switching action, is provided with 
suitable logic to produce gating pulses at the same low-frequency rate. 
These gating pulses are coincident with the steady-state portion of the 
flow-induced signal. Thus, the demodulator is activated only during the 
steady state intervals and is otherwise blocked. As a consequence, the 
secondary only looks at the flow-induced signal during the period that 
d.phi./dt is equal to zero. 
The d-c output pulses produced by demodulator 29 are applied to a 
resistance-capacitance integrating circuit 30 to produce a direct-voltage 
error signal whose magnitude is a function of flow rate. This error signal 
is applied to a direct-current amplifier 31, whose output is used as a 
controlled bias for a d-c to frequency converter 32. 
The d-c-to-frequency converter translates the d-c error signal level to a 
variable frequency pulse train which exhibits a duty cycle that is 
proportional to the error signal. (Duty cycle is defined as the pulse 
width or on-time interval (t) divided by the total period (.tau.). This 
variable duty cycle error signal VD is used to drive the output circuits 
of the system as well as serving as the take-off point for the error 
signal feedback circuit. 
For purposes of feedback, the variable duty cycle error signal must first 
be restored to a proportional low-frequency signal (i.e., 17/8 Hz or 
whatever low frequency is in effect). This is accomplished by means of a 
sampling circuit 33 coupled to the dc-to-duty cycle converter 32 and 
acting to sample an in-phase reference voltage RV derived from the 
electromagnetic circuit. 
To generate this reference voltage, a fractional-ohm resistor 34 is 
interposed between the series-connected coils and the center tap of the 
secondary of transformer 17, the voltage drop thereacross depending on 
current flow through the magnet coil. This voltage is applied to an 
operational amplifier 35 to produce reference voltage RV at its proper 
level. 
The output of sampler 33 is constituted by the duty-cycle pulses derived 
from the d-c to frequency converter, enveloped by the low-frequency square 
wave reference voltage RV. This output is fed to summing junction 24 
through the range attenuator 25. Inasmuch as this feedback signal depends 
on the amplitude of reference voltage RV, any variation in the voltage as 
a result of line fluctuations will proportionately change the feedback 
signal. Since it is the ratio of the flow-induced signal to the feedback 
signal that constitutes the measurement criterion, no loss of accuracy 
will be experienced with variations in line voltage (within reasonable 
limits). 
The signal from the dc-to-duty cycle converter 32 is applied to a 
duty-cycle-to-dc converter 36, which converts the pulses of the former 
into an analog d-c output that is proportional to fluid flow rate. The 
signal from the dc-to-duty cycle converter is also applied to a pulse 
scaler 37 which converts the applied pulses into engineering units which 
are available to drive an external counter. 
While there has been shown and described a preferred embodiment of an 
electromagnetic flowmeter in accordance with the invention usable in 
less-than-full fluid lines, it will be appreciated that many changes and 
modifications may be made therein without, however, departing from the 
essential spirit thereof.