Abstrict A flow meter particularly for receiving respiratory flows for pulmonary
function diagnoses has a perforated piezo-ceramic flow resistance
element and transducer in a flow tube for providing a highly-sensitive
flow measurement with little resistance to the flow. Electric contact
plates abut opposite planar faces of the piezo-ceramic material
plate and are spaced apart at the periphery of the piezo-ceramic
plate by an insulating disk. Frame members carry the piezo-ceramic
plate and electric contact plates and are spaced and protected within
a housing of the flow meter by soft, floating seal members. Contact
lugs connected to the electric contact plates conduct signals from
the meter which are a function of the bending of the piezo-ceramic
material plate under the differential flow pressures on an upstream
and a downstream side of the piezo-ceramic plate.
Claims We claim as our invention:
1. A flow meter for medical pulmonary function diagnoses comprising:
a flow tube having an interior cross-section;
a flow resistance element comprising a piezo-ceramic material having
through-flow passages for a respiratory gas; and
an electrical contact means associated operatively with said flow
resistance element for measuring electrical characteristics of the
piezo-ceramic material as a gas is passed through the meter.
2. A flow meter as defined in claim 1 wherein the piezo-ceramic
material comprises a plate and the through-flow openings comprise
perforations in the plate.
3. A flow meter as defined in claim 1 wherein the flow resistance
is disposed in the flow tube across the entire cross-section thereof.
4. A flow meter as defined in claim 1 wherein the piezo-ceramic
material is a flat sheet having opposite planar sides and the electrical
contact means comprise a pair of annular contact plates, each contact
plate fitted adjacent a periphery of one of said opposite planar
sides of said piezo-ceramic material.
5. A flow meter as defined in claim 4 each contact plate further
having a contact lug from which an electrical signal may be communicated,
as to a monitoring apparatus.
6. In a flow meter for pulmonary function diagnoses having a flow
tube with a cross-sectional area, the improvement of a flow resistance
element comprising:
a piezo-ceramic material formed in a plate having opposite first
and second sides to obstruct substantially the entire area of the
flow tube but having perforations therein for passage of respiratory
gases from one side of the plate to the other; and
a pair of electrically-conductive contact plates, each of said
contact plates being annular in form and contacting one of the first
and second sides of the piezo-ceramic material plate about a periphery
thereof.
7. A flow meter having an axis and adapted for use with a respiratory
gas and comprising:
a piezo-ceramic material plate formed with perforations therethrough
and having a periphery and opposite first and second planar faces;
first and second electrical contact plates each respectively coaxially
abutting said first and second faces of the piezo-ceramic plate
adjacent said periphery thereof, and each of said contact plates
having a connection lug extending therefrom;
coaxial first and second frame members respectively abutting the
first and second contact plates and respectively adjacent the first
and second sides of the piezo-ceramic plate, the frame members being
connected together about the contact plate and the piezo-ceramic
plate to form a flow resistance and transducing set with the connection
lugs extending therefrom;
first and second soft, floating seals, one disposed adjacent each
axial side of the flow resistance and transducing set frame members;
and
a pair of housing parts adapted to enclose the flow resistance
and transducing set and to engage the seals thereon to support the
piezo-ceramic material against shocks and vibrations transmitted
to the housing,
thereby to provide a compact, reliable, highly sensitive flow meter
assembly.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to flow meters for measuring flow volumes,
particularly in a flow of gas such as in pulmonary function diagnoses,
wherein a flow resistance comprises a mechanical-electrical transducer
disposed in a flow tube.
2. The Prior Art
Flow meters are known wherein the drop in pressure across a flow
resistance is measured by a differential pressure-sensitive device
connected by lines into opposite interior spaces of a flow tube
divided by the resistance element. The flow resistance is a fine-meshed
wire net. Such flow meter is complex since it is constructed into
two parts.
A one-piece flow meter is shown in U.S. Pat. No. 2989866 comprising
a wire resistance strain gage incorporated in the flow resistance
element. Although differential pressure is measured, the wire strain
gage complicates flow meter construction, is somewhat unreliable,
and provides more resistance to flow of air in one direction than
in the other flow direction through the tube.
SUMMARY OF THE INVENTION
In an air flow meter, a flow resistance element comprises a piezo-ceramic
transducer plate having apertures therethrough. The piezo-ceramic
plate is disposed within a flow tube and entirely occupies the axial
cross-section thereof. A pair of electrically-conductive contact
plates which are annular in form contact opposite sides of the piezo-ceramic
plate at the axial faces on peripheries thereof. Each of the contact
plates has a contact lug for communicating distortions in the piezo-ceramic
material to a remote point such as a monitoring apparatus. The piezo-ceramic
material and the contact plates are held within frame members which
are, in turn, supported within the flow meter housing upon soft,
floating seal members which cushion the piezo-ceramic material within
a housing member from shocks due to accident and from normal apparatus
vibrations. The invention thus provides a compact flow meter with
few individual parts through which gas flows symmetrically in both
directions, and having high reliability despite its use of the piezo-ceramic
transducer. The transducer sets can be standardized by use of a
capacitor in conjunction with the contact lugs of the contact plates.
THE DRAWING
The one drawing FIGURE is an exploded perspective view of the parts
of the flow meter of the present invention.
THE PREFERRED EMBODIMENTS
A flow meter according to the invention has a flow tube formed
by two coaxial housing parts 1 2. A piezo-ceramic material plate
3 forms a flow resistance and transducer element disposed in a longitudinal
center of the flow tube on the axis of the meter. The plate 3 has
a great plurality of small perforations 3a therein to permit through-flow
of a respiratory gas or other fluid. An insulating disk 4 surrounds
a circular periphery of the flow resistance plate 3 to ensure separation
of metal contact plates 5 6 which are annular in form and are placed
in adjoining axial relation to the plate 3. Contact lugs 7 8 extend
respectively from the contact plates 5 6 for connection to a remote
monitoring or recording device (not shown) for converting distortions
in the piezo-ceramic plate 3 as indicated by the electrical characteristics
thereof, into differential pressure terms and/or flow volume terms.
The piezo-ceramic plate 3 the insulating disk 4 and the contact
plates 5 6 are assembled into a flow resistance and transducing
set between opposite frame members 9 10. The frame members 9 10
are attached to one another by clamps or screws, not shown. The
elements 3-10 are flexibly suspended between seals 11 12 engaging
the frame members 9 10 within the housing parts 1 2. The seals
11 12 insulate the piezo-ceramic plate 3 from vibrations in the
housing 1 2 thus increasing the accuracy of the differential pressure
readings from the transducer element by reducing interference with
the piezo-ceramic plate 3. The seals 11 12 also protect the piezo-ceramic
material 3 from damage due to accidental shocks, such as dropping
the meter tube onto a hard floor.
Supporting mountings 13 14 for the flow meter are joined together
by screws 15 with the parts 1-12 clamped therebetween. The support
mountings 13 14 are readily attached to a housing, not shown, of
a pulmonary function monitoring and recording instrument. Tube connections
16 17 on the flow meter extend outwardly from the support mountings
13 14 and are adapted to receive thereover a respiratory tube connected
to a mouthpiece for a patient. The other of the tubes 16 17 not
connected to the mouthpiece may be connected to further apparatus
or be left open to atmosphere.
In operation, as the patient breathes through the respiratory tube,
the piezo-ceramic flow resistance element 3 distorts very slightly
under the differential flow pressure thereacross. The piezo-ceramic
material converts the pressure difference into an electrical signal.
The signal is passed by the contact plates 5 6 and the contact
lugs 7 8 to the monitoring apparatus. With the flow meter of the
present invention, a large output signal with a high limiting frequency,
in excess of 300 Hz, and with minimum superimposed interference
as from vibration, can be produced. Where a number of flow meters
are to be used interchangably, a significant advantage of the present
invention is that the output signals of each of the individual flow
meters can be standardized very easily by connecting a capacitor
to the transducer element output. The small flow resistance of the
meter together with its high output signal allows very small respiratory
flows to be measured.
Although various minor modifications may be suggested by those
versed in the art, it should be understood that we wish to embody
within the scope of the patent warranted hereon all such modifications
as reasonably and properly come within the scope of our contribution
to the art. |