Fluidic volumetric fluid flow meter

Fluidic volumetric flow meter method and apparatus wherein undesirable dynamic interaction (ringing) which could appear in an output signal is inhibited. Electrical isolation and shielding also contribute to a high quality output signal in accordance with the invention. Particularly advantageous housing structures adapt the flow measurement device to a variety of applications as a complete flow meter.

BACKGROUND OF THE INVENTION 
The field of the invention is apparatus and methods for measurement of 
volumetric flow rate of flowing fluid. More particularly, the invention 
relates to dynamic or inferential measurement devices, as opposed to 
positive displacement measuring devices, which former devices are 
additionally of fluidic operation. 
Conventional fluidic measuring devices in the field to which the present 
invention relates are disclosed in the following U.S. Pat. Nos. 
______________________________________ 
U.S. Pat. No. 
ISSUED INVENTOR(S) 
______________________________________ 
3,690,171 12 September 1972 
Tippetts, et al 
3,889,534 17 June 1975 J. Grant 
4,050,304 27 September 1977 
A. Thomas 
4,107,990 22 August 1978 
C. Ringwall 
4,404,859 20 September 1983 
Ohsawa, et al 
______________________________________ 
These teachings establish that the possibility of measuring fluid flow 
rate, either on a volume or mass basis, has been recognized for a number 
of years. The first three teachings listed above are believed to apply 
wall-attachment type fluidic oscillators to, respectively, measurement of 
volumetric flow rate as a function of oscillator frequency, to measurement 
of mass flow rate as a function of oscillator amplitude and frequency, and 
to measurement of mass flow rate as a function of oscillator frequency and 
total pressure drop across the oscillator. 
The Ringwall U.S. Pat. No. 4,107,990 recognizes the deficiencies of 
wall-attachment fluidic oscillators in the application to flow rate 
measurement. Accordingly, the Ringwall patent teaches use of a 
differential pressure proportional fluidic oscillator to provide a 
volumetric flow rate meter. However, to extend the measurement range of 
the Ringwall teaching beyond that obtainable with a single oscillator, 
multiple amplifier stages must be utilized. Additionally, it is believed 
that the signal quality which is obtained from an oscillator as taught by 
Ringwall may be less than optimum. This output signal is believed to be 
contaminated with dynamic oscillation, or ringing, noise which is 
internally self-generated by the oscillator as a result of internal fluid 
inductances and capacitances. 
An alternative approach to fluid mass flow rate measurement is presented by 
U.S. Pat. No. 4,508,127 issued 2 April 1985 to a coinventor of the present 
invention and assigned in common therewith. The disclosure of the '127 
patent is specifically incorporated herein by reference to the extent 
necessary for a complete disclosure and understanding of the present 
invention. The '127 patent teaches use of a dynamic volumetric flow rate 
meter, such as a turbine meter, to obtain a signal indicative of 
volumetric fluid flow rate. A fluidic oscillator having a regulated total 
pressure drop thereacross is employed to generate a second signal 
indicative of fluid density. The two signals are combined by 
multiplication to obtain an indication of fluid mass flow rate. 
However, it is desirable to provide a volumetric fluid flow rate meter 
which avoids the use of moving-part type flow meters. The fluidic 
oscillator because of its rugged, no-moving-parts construction is 
recognized as offering considerably improved service life over all flow 
meters having moving parts, such as the turbine flow meter, for example. 
Further, the limited flow measurement range and need for multiple 
oscillators of the Ringwall teaching should be avoided. Finally, it is 
highly desirable to provide such a volumetric flow rate meter with a 
"clean" output signal substantially free of both self-generated noise or 
ringing, and noise of electrical origin. 
SUMMARY OF THE INVENTION 
The inventors have discovered that internally self-generated noise in a 
fluidic oscillator may result from dynamic interaction between moving 
fluid in the feedback channels of the oscillator and the output signal 
generating apparatus. In other words, the feedback channels provide a 
fluid inductance, and the output transducers a fluid capacitance which 
under the influence of the pulsating, time-variant oscillations of the 
oscillator itself set up an internal self-generated noise or ringing. This 
ringing noise appears in the output signal of the flow meter and degrades 
the performance or measurement accuracy thereof. 
Accordingly, the invention provides a fluidic device having an inlet and a 
flow path extending from the inlet to the outlet. A part of the flow path 
defines a power jet nozzle upstream of and leading to an interaction 
chamber. The interaction chamber leads to the outlet. A splitter is spaced 
from the power nozzle across the interaction chamber and is in alignment 
therewith to separate a pair of feedback inlets leading from the 
interaction chamber. A pair of feedback channels extend from the pair of 
feedback inlets to respective feedback outlets. The feedback outlets are 
oppositely disposed perpendicularly to the power nozzle and intermediate 
the latter and the interaction chamber. A branch passage extends from each 
feedback channel to a respective variable-volume chamber which is bounded 
by a flexible diaphragm. The diaphragms are movable in response to 
pressure variations within the respective variable-volume chamber and are 
associated with means for producing an output signal in response to such 
movement. Fluid flow restriction means are provided in each branch passage 
for resisting dynamic oscillation (ringing) of fluid flow in the feedback 
channels with the variable volume of fluid in the variable-volume 
chambers. 
In a further aspect of the invention, second fluid flow restriction means 
are provided in each of the feedback channels between the branch passage 
and the feedback outlet of each. These second fluid flow restriction means 
have the effect of increasing the magnitude of the pressure fluctuations 
in the variable-volume chambers and thereby of increasing the magnitude of 
the output signal produced, notwithstanding the first fluid flow 
restrictions. 
According to still another aspect of the invention, a vent passage is 
provided opening outwardly of each variable-volume chamber to communicate 
with the outlet, and third fluid flow restriction means is provided in 
each vent passage. 
Yet another aspect of the invention provides fluid flow bypass means in 
fluid flow parallel with the first-described fluidic device. The bypass 
means provides a plurality of fluid flow parallel flow paths. Each of the 
flow paths of the bypass means replicates the power nozzle of the 
first-described fluidic device so that the same characteristic of 
coefficient of discharge is provided by the parallel plural flow paths. 
Additional aspects of the invention provide housing structure for receiving 
both the first-described fluidic device and a second-described bypass 
means, the two cooperatively defining a fluid volume flow rate module. The 
housing also provides for communication outwardly thereof of the output 
signal of the device. In one particularly described and depicted 
embodiment of the invention, redundant volume flow rate measurement 
modules are provided in a uniquely arranged structure which is 
particularly advantageous in the aerospace technologies. 
Still additionally, the invention provides a fluid volumetric flow meter 
wherein an output transducer includes an electrically conductive diaphragm 
bonded electrically with a piezoceramic disc. Both the diaphragm and the 
disc are electrically isolated from surrounding structure. Upon flexure of 
the diaphragm an electrical signal is produced across the piezoceramic and 
is conducted to a point of utilization in part by the diaphragm, but not 
by surrounding structure. Surrounding structure may effectively shield the 
output transducer from electrical interference. 
Additional objects and advantages of the present invention will appear from 
reading the following detailed description of several preferred 
embodiments of the invention taken in conjunction with the accompanying 
drawing figures. The following detailed description includes description 
of embodiments of the invention which may be employed as principal 
components of a liquid fuel volume flow rate sensor, a part of an 
electronic fuel controller for a turbine engine. However, the invention is 
not limited to such use and is not intended to be so limited. In fact, in 
many respects the invention has almost universal application to the art of 
flow measurement. This broad scope of the present invention will quickly 
appear to those skilled in the art of flow measurement in view of the 
following.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
FIG. 1 depicts schematically a fluidic liquid volumetric flow meter, which 
is generally referenced with the numeral 10. Flow meter 10 includes a flow 
sensing device 12 and a bypass unit 14. An inlet 16 to the flow meter 
communicates both with the flow sensing device 12 and with the bypass unit 
14, while an outlet 18 from the flow meter similarly communicates with 
both 12 and 14. The flow sensing device 12 includes a fluidic oscillator 
20 having an inlet 22 and outlet 24 and feedback channels 26,28. Connected 
with the feedback channels 26,28 via branch passages 30 and 32 are a pair 
of variable-volume sensing chambers 34,36. Each of the branch passages 
30,32 includes a fluid flow restriction 38,40, respectively. Similarly, 
each of the feedback passages 26,28 includes a fluid flow restriction 
42,44. Extending from each of the variable volume sensing chambers 36,38 
is one of a pair of vent passages 46,48, each having its respective fluid 
flow restriction 50 and 52. Each of the variable-volume chambers 34 and 36 
is bounded by a flexible and electrically conductive diaphragm 54 and 56, 
respectively, upon which is mounted a sensing transducer 58 and 60. As 
will be further described hereinafter, the diaphragms are responsive to 
pressure variations within the chambers 34 and 36 to flex, which results 
in the transducers 58 and 60 providing electrical output signals via 
conductors 62 and 64. 
While not depicted in FIG. 1, it will be seen that the fluidic oscillator 
20 includes a power jet nozzle which directs a stream of fluid from the 
inlet toward the outlet. The power jet nozzle of the fluidic oscillator 20 
results in a measurable pressure drop between the inlet 22 and the outlet 
24 of the oscillator 20. Turning for a moment to the structure of the 
bypass unit 14, it will be seen that this unit provides a plurality of 
flow paths each referenced with the numeral 66. Each flow path 66 is in 
fluid flow parallel with the flow path through the fluidic oscillator 20 
between inlet 22 and outlet 24 thereof. Each flow path 66 of the bypass 
unit 14 is provided with a fluid flow restriction 68 which replicates the 
coefficient of discharge characteristic of the power jet nozzle within the 
fluidic oscillator 20. As a result, because the pressure drop across the 
flow meter 10 between inlet 16 and outlet 18 is the same for the fluidic 
oscillator 20 as it is for the bypass unit 14, each of the flow paths 66 
within the bypass module 14 will flow substantially the same fraction of 
volume of fluid per unit time as that which flows through the fluidic 
oscillator 20. 
Turning to FIG. 2, it will be seen that the fluidic oscillator 20 includes 
a housing 70 defining the inlet 22, outlet 24 and other structures of the 
fluidic oscillator. The housing 70 defines a flow path generally 
referenced with the numeral 72 and extending between the inlet 22 and the 
outlet 24. The flow path 72 defines a power jet nozzle 74 opening into an 
interaction chamber generally referenced with the numeral 76. The 
interaction chamber 76 opens downwardly out of the plane of FIG. 2 to the 
outlet 24. Housing 70 also defines a knife-edged splitter member 78 which 
is aligned with the power jet nozzle 74 and is disposed oppositely thereof 
across interaction chamber 76. The splitter member 78 separates a pair of 
feedback inlets 80 and 82 which communicate respectively with the feedback 
channels 26 and 28. Each one of the feedback channels 26 and 28 
communicates respectively with one of a pair of feedback outlets 84,86 
which are oppositely disposed perpendicularly to the power jet nozzle 74, 
and between the latter and the interaction chamber 76. 
In order to reduce the effect of electrical interference upon the output 
signal produced by the transducers 58,60, an electrical insulation 55 is 
provided between the diaphragms 54,56 and the housing 70. As a result, 
both the diaphragms 54,56 and transducers 58,60 are electrically isolated 
from the housing 70. As will be further seen hereinafter, the housing 70 
may act to additionally shield the transducers 58,60 and diaphragms 54,56 
from electrical interference. 
Having observed the basic structure of the fluidic oscillator 20, it is 
well to now consider its method of operation. It will easily be understood 
that when fluid flows into the inlet 16 of the fluid flow meter a portion 
of this fluid must flow through the fluidic oscillator 20 via inlet 22, 
the flow path 76 leading to outlet 24 and vent passages 46,48. Fluid 
entering the inlet 22 upon flowing through the power jet nozzle 74 forms a 
stream of fluid referenced with the numeral 88 which projects across the 
interaction chamber 76 toward the splitter member 78. Upon encountering 
the splitter member 78, the fluid stream 88 divides so that a portion 
thereof is received by each of the feedback inlets 80 and 82. Inherently, 
a slightly greater portion of the fluid stream 88 will be received by one 
of the feedback inlets 80 and 82 than is received by the other of these 
feedback inlets. The velocity of the fluid stream 88 is partially 
reconverted to pressure at the feedback inlets 80 and 82 in proportion to 
the degree of split of the fluid stream 88. Fluid received by the feedback 
inlets 80 and 82 is communicated by the respective feedback channels 26 
and 28 to the respective feedback outlets 84 and 86. Because one of the 
feedback inlets will have received a slightly greater portion of the fluid 
stream 88, fluid issuing from the associated feedback outlet will exert a 
greater lateral pressure force upon the fluid stream issuing from power 
jet nozzle 74 than does the fluid from the other feedback outlet. As a 
result of the differential pressure effective at outlet 84,86, the fluid 
stream 88 will be urged toward the feedback inlet having received the 
lesser portion of the stream 88. This phenomenon results in oscillation of 
the fluid stream 88 between the two feedback inlets 80 and 82 on opposite 
sides of the splitter member 78. The period of oscillation is a function 
of the velocity of the fluid stream 88 and the effective transport and 
feedback distances of the oscillator 20. This transport distance in 
substance is the linear dimension from the area where the power jet nozzle 
74 opens to the interaction region 76 adjacent the feedback outlets 84 and 
86, across the interaction chamber 76 to the feedback inlets 80,82. The 
feedback distance is the dimension around the feedback channels 26 and 28 
to the feedback outlets 84 and 86. 
It will be understood that not all of the fluid stream 88 is received into 
the feedback inlets 80 and 82 and that the majority of the fluid is 
allowed to flow from the fluidic oscillator 20 via the outlet 24. 
Considering the fluid within the feedback channels 26 and 28, it will be 
seen that when the fluid stream 88 is received into either one of the 
feedback inlets 80 or 82, the associated channel receives a portion of 
fluid the kinetic energy of which is partially converted to a pressure 
which migrates through the fluid within the feedback channel at the 
acoustic velocity of the particular fluid. The pressure in the feedback 
channels communicates via the branch passages 30 and 32 into the 
variable-volume sensing chambers 34 and 36. As a result, the diaphragms 54 
and 56 flex in response to the pressure variations experienced within the 
sensing chambers 34 and 36. Flexing of the diaphragms 54 and 56 results 
both in variation of the volume defined within chambers 34,36, and in 
flexing of the transducers 58 and 60. Flexing transducers 58,60 result in 
an electrical signal conducted by conductors 62 and 64. It will be seen 
that as the diaphragms 54 and 56 flex, the volumes of the chambers 34 and 
36 increase and decrease so that the chambers 34 and 36 exhibit 
fluidically a capacitance. The channels 26,28 may be considered to exhibit 
a fluidic inductance which arises from the liquid density and the 
dimensions of these channels. 
In order to prevent the capacitance of the sensing chambers 34 and 36 from 
dynamically interacting with the inductance of the feedback channels 26 
and 28 to produce noise or ringing, the Applicants provide fluid flow 
restrictions 38 and 40 in the branch passages 30 and 32. However, the 
restrictions 38 and 40 would have the effect, the Applicants believe, of 
reducing the magnitude of the pressure variations experienced in the 
chambers 34 and 36 and available for sensing by flexing of the diaphragms 
54 and 56. In order to offset this reduction in the pressure variations 
experienced in the sensing chambers 34 and 36, the Applicants provide 
fluid flow restrictions 42 and 44 which are disposed downstream of the 
respective branch passages at each of the feedback channels 26 and 28. 
Further, in order to insure that all air or compressible gas is purged 
from the sensing chambers 34 and 36 and therefore does not interfere with 
flexing of the diaphragms 54 and 56 by fluid pressure variations 
experienced therein, the Applicants provide the vent passages 46 and 48 
having fluid flow restrictions 50 and 52 therein. These vent passages 
allow a relatively small but significant flow of fluid from the feedback 
passages 26 and 28 through the respective sensing chambers 34 and 36 so 
that all compressible gases are purged therefrom. 
Turning to FIG. 3, it will be seen that an oscillator according to an 
actual reduction to practice of the present invention displayed a high 
degree of linearity of oscillation frequency verses liquid flow rate 
passing therethrough. FIG. 3 shows the plotting points resulting from 
testing of the oscillator at various known liquid flow rates fall, in 
effect, perfectly on a straight line. The actual reduction to practice of 
the inventive oscillator was effected by the use of stacked fluidic 
laminae as are depicted by FIG. 4. These laminae are alphabetically 
designated "a" through "j" on FIG. 4 in stacking order. In order to 
promote continuity of description, features of the laminae which are 
analogous in structure or function to those which were depicted 
schematically in FIGS. 1 and 2 are referenced with the same numeral, 
perhaps with one or more primes added to distinguish portions of 
structure. 
Viewing FIG. 4 in greater detail it will be seen that lamina "h" defines an 
inlet 22 in conjunction with laminae "g" and "i" having notches 22' 
aligning with the inlet passage 22 in lamina "h" to define a convergent 
inlet opening. Lamina "h" likewise defines a pair of feedback passage 
portions 26' and 28'. These feedback passage portions communicate with 
openings 26",28" defined in laminae "g" and "f", as well as with 
restrictive orifices 42 and 44, the latter of which are defined only in 
lamina "f". Viewing laminae "e" and "d", it will be seen that the feedback 
channels are completed by a pair of aligning elongate openings 26'" and 
28'" communicating the openings 26" and 28" of lamina "f" with the 
restrictive orifices 42 and 44 thereof. Lamina "c" defines a pair of 
restrictive orifices 38 and 40 respectively communicating with the 
elongate openings 26'" and 28'" of laminae "d" and "e". The restrictive 
orifices 38 and 40 of lamina "c" align with holes 30 and 32 defined by 
lamina "b" to define the branch passages opening to the sensing chambers 
34 and 36, recalling the description of FIGS. 1 and 2. 
Viewing FIG. 4 once again, it will be seen that lamina "a" defines a pair 
of large openings 34',36' communicating with the holes 30 and 32 of lamina 
"b", and the function of which will be further described hereinafter. 
Lamina "a" also defines a pair of elongate notches 34",36" extending 
radially outwardly from openings 34',36', respectively. Lamina "b" defines 
a pair of holes 46',48' communicating also with the openings 34',36' of 
lamina "a" and further communicating with restrictive openings 50 and 52 
of lamina "c". The vent passages are substantially defined by lamina "d" 
which provides a pair of elongate slots 46 and 48 communicating with the 
restrictive openings 50 and 52 and extending to the edge of the laminae. 
In order to complete the description of the laminae stack shown in FIG. 4, 
it must be noted that lamina "i" defines four rather winged-shaped 
openings 76' in alignment with the interaction chamber 76 defined by 
lamina "h". The openings 76 of lamina "i" align with a collection chamber 
24' portion of outlet 24 defined by lamina "j" and communicating with an 
outlet slot 24 extending to the edge thereof. It will be understood that 
while lamina "a" is the top lamina of a fluidic laminae stack embodying 
the features of the present invention, the stack would ordinarily be 
bounded at its opposite side by a plain lamina having no fluidic openings 
therein and bounding the outlet chamber 24' and outlet 24 below lamina "j" 
and the plane of FIG. 4. 
FIGS. 5 and 6 in conjunction depict a fragment of the structure of the 
laminae stack shown in FIG. 4. Viewing FIG. 5 in particular it will be 
seen that the laminae "a", "b" and "c" in conjunction substantially define 
the sensing chamber 34, the branch and vent passages 30 and 46' 
respectively, and the flow restrictive orifices 38 and 50. The structure 
defining sensing chamber 36 is substantially similar, and so will not be 
further described. Recalling the description of FIG. 4, it will be seen 
that the restrictive opening 38 communicates with the opening 26'" in 
lamina "d" while the flow restrictive orifice 50 communicates with vent 
passage slot 46 in lamina "d". Received within the opening 34' of lamina 
"a" is an annular spacing and sealing member 92. The member 92 sealingly 
engages the surface of lamina "b". The flexible diaphragm 54 is received 
into opening 34' of lamina "a" and sealingly engages the sealing and 
spacing member 92. Because of the sealing and spacing member 92, the 
diaphragm 54 is spaced slightly away from the lamina "b" to cooperatively 
define the sensing chamber 34. An annular capture member 94 is also 
received in opening 34' in engagement with the outer surface of diaphragm 
54. The capture member 94 defines a chamber 96 on the outer diameter 
thereof. 
Viewing FIGS. 5 and 6 in conjunction, it will be seen that the material of 
lamina "a" is swaged radially inwardly at 98 toward the center of opening 
34' and against the shoulder 96 presented by ring 94 to capture the ring, 
the diaphragm 54 and the spacing member 92 within the opening 34'. FIG. 6 
depicts that the swaging of lamina "a" is performed as a substantially 
circumferentially continuous groove 98. Because of the swaging 98 of the 
material of lamina "a" into engagement with shoulder 96 of the capture 
ring 94, the ring 94 is held into tight engagement with the diaphragm 54, 
and the latter is likewise held in sealing engagement with the sealing 
ring 92. The groove resulting from swaging lamina "a" at 98 is interrupted 
by notch 34", which extends radially outwardly from opening 34' of lamina 
"a". Diaphragm 54 defines a radially outwardly extending portion 57 
extending into the notch 34" outwardly of ring 94. The portion 57 is bent 
upwardly out of the plane of diaphragm 54 to displace the outer end 
thereof toward the outer surface of lamina "a". One wire 62 is connected 
to the portion 57 adjacent the outer end thereof. 
Mounted upon the diaphragm 54 by use of an electrically conductive adhesive 
is a piezoceramic disc 58 which has previously been identified in the 
schematic representations of the invention as a transducer member. The 
piezoceramic disc conventionally responds to flexure of the diaphragm 54 
by producing an electrical output conducted to a point of utilization via 
the other conductor 62. In order to electrically isolate the diaphragm 54, 
and piezoceramic disc 58 mounted thereon, from the housing cooperatively 
defined by laminae "a"-"j", the radially outer peripheral portion of the 
diaphragm is provided with a relatively thin coating of dielectric 
polymer. This polymer coating may be tetrafluoroethylene, for example. 
While this insulative coating on diaphragm 54 is too thin to be 
effectively depicted in FIGS. 5 and 6, it is depicted schematically as 
insulation 55 on FIG. 2. The insulative coating 55 on diaphragm 54 is of 
sufficient thickness to effectively isolate the latter from electrical 
contact with lamina "a" or "b" via the spacing ring 92, as well as from 
lamina "a" via capture ring 94, viewing FIG. 6. 
Turning once again to FIG. 1, it will be recalled that the bypass unit 14 
defines a plurality of bypass passages 66, each provided with its own 
restriction 68 replicating the coefficient of discharge characteristic of 
the power jet within the fluidic oscillator 20. FIG. 7 depicts a pair of 
laminae 100,102 at an intermediate stage of manufacture for the bypass 
unit 14. It will be noted that each of the laminae 100,102 similarly to 
the laminae "a" through "j" depicted in FIG. 4 conventionally includes 
four unreferenced alignment holes which are used during the manufacture of 
a laminae stack, as will be readily understood by those skilled in the 
fluidic art. Viewing the laminae 100 and 102, it will be immediately noted 
that these laminae are substantially identical with one being simply 
flipped over or reversed top to bottom with respect to the other. Each 
laminae includes larger end portion a, and a smaller end portion b. Spaced 
between the end portions a and b are plural substantially identical 
boundary portions c. These end portions and boundary portions a, b, c, 
cooperatively define a; plurality of elongate openings 66 extending from 
near one edge to near the other edge. The plurality of openings 66 are, as 
a group, offset toward the one end b of the lamina 100, 102 and away from 
the other end a. This offset results in the end portions a and b being of 
different sizes. The offset of the group of openings 66 in each lamina 
results in the boundary portions c aligning with the openings 66 when 
successive ones 100, 102 of the substantially identical laminae as 
alternated end for end and stacked, as is seen viewing FIG. 7. 
Intermediate of the ends of the opening 66 each lamina defines a pair of 
confronting protrusions 68' which cooperate to define the fluid flow 
restrictions 68. Each of the elongate openings 66 defines a width 
dimension which is referenced on lamina 100 with the character W. Also, 
the elongate openings 66 are spaced apart by a dimension referenced on 
lamina 102 with the character S. That is, the boundary portions have a 
width dimension S perpendicular to the length of the openings 66. The 
dimension S exceeds the width W of the elongate openings 66 according to 
twice an interbonding dimension referenced between the laminae 100 and 102 
with the reference character I. 
It will be seen that when the laminae 100 and 102 are stacked one upon the 
other as depicted by arrow 104, an interbonding region is provided on each 
side of each elongate opening 66, which in width is equal to dimension I. 
Therefore, a plurality of laminae 100,102, each being substantially 
identical, may be stacked, with each one being reversed or flipped end for 
end respective to its immediately adjacent neighbors, and interbonded. The 
interbonded stack of laminae 100,102 is then trimmed at each side along a 
cutting line 106,108 to open the ends of the elongate openings 66. Thus, 
the openings 66 define bypass passages extending through the bypass unit 
14 from one face to the other. The end portions a and b of successive 
laminae in the stack bond to one another. Each end portion a bonds to the 
boundary portions c next in the stack of laminae, while adjacent boundary 
portions c bond to their neighbors in the laminae stack. Therefore, 
cutting off the parts of each laminae 100, 102 outside of the trimming 
lines 106, 108 simply opens the passages 66, but does not affect the 
structural integrity of the laminae stack after interbonding. Each bypass 
passage 66 is rectangular in cross section and is bounded on opposite 
sides by portions of a single lamina. These portions are either an end 
portion a or b, and adjacent boundary portion c; or a pair of boundary 
portions c. On the other two opposite sides, each passage 66 is bounded 
either by boundary portions c or end portions b of lamina adjacent in the 
stack of laminae. Those skilled in the fluidic art will recognize that a 
laminae stack for making a bypass unit 14 will also include at each end 
thereof for bounding the outermost bypass passages 66 a plain lamina 
having no openings other than the unreferenced alignment holes. 
Viewing FIG. 8, it will be seen that the resulting bypass unit 14 is 
essentially a prismatic solid having openings 66 extending therethrough 
from one face of the prism to the opposite face. Because of the way in 
which the laminae 100,102 were reversed or alternated in the stacking of 
bypass unit 14, the plurality of bypass passages 66 are arranged within 
the bypass unit in a regular grid-like pattern. Also, viewing FIG. 8 it 
will be noted that the previously unreferenced alignment holes which were 
conventionally used during manufacturing for stacking of the laminae 
preparatory to the interbonding process may advantageously be used for 
intersecuring a bypass unit 14 to a fluid flow rate sensing module 20. 
Each of the alignment holes which are referenced on FIG. 8 with the 
numeral 110 may, when a bypass unit 14 is stacked with an oscillator 
module 20, align with one another and removably receive a rolled spring 
steel pin 112. That is, the fluid flow rate sensing module 20 and the 
bypass unit 14 are congruent when placed side by side. The spring steel 
pin 112 is removably force-fitted into the aligned holes 110 of the bypass 
module 14 and oscillator module 20 to hold these two modules securely 
together while allowing optional disassembly thereof. 
FIG. 9 depicts a portion of a redundant fluid flow meter according to the 
invention. The redundant fluid flow meter of FIG. 9 includes a first meter 
10 having a bypass unit 14 and fluidic oscillator device 20, and a second 
fluid flow meter 10' having an associated bypass unit 14' and fluidic 
oscillator device 20'. The first and second fluid flow meters 10 and 10' 
are substantially identical and are arranged with their inlets and outlets 
like disposed. Interposed between the two fluid flow meters 10 and 10' is 
a spacing member 114 defining four through holes 116 which have the same 
spacing therebetween as the alignment holes 110 in the bypass units 14,14' 
and fluidic oscillator devices 20,20'. The spacing member 114 also defines 
a C-shaped through passage 118 opening outwardly in a downstream 
direction. The through passage 118 when the fluid flow meters 10 and 10' 
are assembled with the spacing member 114 provides liquid communication to 
the outer face of the flexible diaphragms 54 and 56 of each of the fluid 
flow meters 10 and 10'. The through passage 118 within spacing member 114 
also provides a chamber 120 within which the conductor 62,64 from the 
piezoceramic discs and diaphragms on each of the oscillator devices 20 and 
20' are received. The conductors 62 and 64 may advantageously be led 
outwardly from the piezoceramic discs 58,60 and chamber 120 through an 
opening 122 extending from the latter to open outwardly on the spacing 
member 114. Viewing FIG. 9 and considering the arrangement of the modules 
10 and 10' when sandwiching the spacing member 114 therebetween, it will 
be seen that the alignment holes 110 of each of the fluid flow meters 
aligns with one another and with the through holes 116 of the spacing 
member 114. Consequently, relatively long spring steel roll pins 124 may 
be forcibly inserted into the aligned holes 110 of the fluid flow meters 
10 and 10' and into the through holes 116 of spacing member 114 to secure 
these elements together. 
FIGS. 10 and 11 illustrate that a fluidic flow meter like that illustrated 
in FIG. 9 may be advantageously housed within a housing 126 providing a 
rectangular recess 128 therein for receiving the fluidic flow meters 10 
and 10' along with the spacing member 114. The housing 126 provides an 
inflow passage 130 extending to the recess 128 and flow meter 10,10' 
therein. Within the recess 128, the flow meter 10,10' is sealingly 
received upon a resilient gasket 132 disposed upon a shoulder 134 defined 
by the cooperation of recess 128 and inflow passage 130. In order to urge 
the flow meter 10,10' into sealing engagement with the gasket 132, a 
spacing member 136 and outlet coverplate 138 are provided. The spacing 
member 136 is rectangular in plan view to slidably be received within the 
recess 128 above the flow sensor 10. Spacing member 136 defines a through 
passage 140 leading from the outlets of the flow sensor 10,10' and of the 
bypass units 14 thereof. The outlet coverplate 138 is removably secured to 
the housing 126, as by fasteners 142 passing therethrough and threadably 
engaging the housing 126. The outlet coverplate 138 defines an outlet port 
144 opening from a chamber 146 defined by the cooperation of the spacer 
member 136, the through passage 140 thereof, the fluid flow sensor 10,10' 
and the outlet coverplate 138. The housing 126 also defines a passage 148 
aligning with the passage 122 (viewing FIG. 9) of the spacer member 114 of 
fluid flow sensor 10,10' and providing for passage of the conductors 62,64 
outwardly of the housing 126. 
Recalling the description of FIGS. 2, 5 and 6, particularly with reference 
to the electrically insulative coating 55 upon the diaphragms 54,56 and 
the purpose thereof, it will be noted that as installed in the cavity 128, 
the fluid flow meters 10,10', are electrically in contact with the housing 
126. On the other hand, the diaphragms 54,56, and piezoceramic discs 58,60 
thereon are electrically isolated from and surrounded by the housing 126 
and the remainder of the fluid flow meter. Additionally, viewing FIG. 9 it 
will be seen that the remainder of the fluid flow meters 10,10' along with 
the spacer member 114 virtually completely surround the diaphragms 54,56 
and piezoceramic discs 58,60. Consequently, the Applicants believe the 
remainder of the fluid flow meters 10,10' may electrically shield the 
electrical output portions of the invention from electrical interference. 
FIGS. 12 and 13 depict an alternative embodiment of the invention wherein 
the fluidic oscillator module 20 is received between a bypass plate 150 
and a bar-like retaining member 152. The bypass plate 150 provides a 
central inlet passage 154 leading to the inlet of the fluidic oscillator 
module 20. Also, the bypass plate provides a plurality of bypass passages 
extending therethrough, and each replicating the coefficient of discharge 
of the power jet nozzle within the fluidic oscillator module 20. The 
bypass plate 150, oscillator module 20, and retainer 152 are received 
within a three-part housing generally referenced with the numeral 158. The 
housing 158 includes a central portion 160 defining a through bore 162. 
Each of the bypass plate 150 and retainer member 152 define a reduced 
diameter portion cooperating with the remainder of each to define 
respective shoulders 164,166. The reduced diameter portion of each of the 
bypass member 150 and retainer member 152 are received into the through 
bore 162 of the central portion 160 so that the shoulder 164 sealingly 
engages the central portion 160. A pair of fasteners 168 extend between 
the bypass plate 150 and retainer 152 to urge the latter into engagement 
with the central portion 160 of housing 158. 
The spacing between the bypass plate 150 and retainer member 152 is 
selected to captively receive the fluidic oscillator module 20 
therebetween. A sealing member 170 is provided between the bypass plate 
150 and the fluidic oscillator module 20. The central portion 160 of 
housing 158 defines a radially extending boss 172 which defines a mounting 
surface 174 upon which is sealingly secured an electrical connector 176. 
The connector 176 provides for conduction outwardly of the housing 158 of 
the electrical signals originating with the piezoceramic transducers of 
the fluidic oscillator module 20. 
The housing 158 also includes a pair of end portions 178 and 180 which are 
substantially identical. The end portions 178 and 180 each define a 
threaded part 182 which is configured to sealingly mate with a standard 
tube fitting (not shown). The end portions 178, 180 provide an inlet for 
fluid flow to the fluidic oscillator member 20 and bypass plate 150, and 
flow therefrom, as is indicated by the arrow 184. Each of the end portions 
178 and 180 are sealingly secured to the center portion 160 of the housing 
158 as by a plurality of fasteners 186 passing therethrough via aligned 
holes in each. The embodiment of the invention depicted by FIGS. 12 and 13 
has been found by the Applicants to be particularly useful for in-line 
applications in which it is desirable to determine the volumetric fluid 
flow rate through a pipeline or conduit, for example. 
While the present invention has been depicted and described with reference 
to several preferred embodiments thereof, no limitation upon the invention 
is implied by such reference, and no such limitation is to be inferred. 
The invention is intended to be limited only by the spirit and scope of 
the appended claims, which also provide an additional definition of the 
invention.