Abstrict This invention relates to a flow meter of a fluidistor oscillator
type, which has its principal use when measuring the ventilation
of a moving human being or animal. Thanks to the special design
of the flow meter it can be made small, light and portable at the
same time as the pressure drop in it is minimal.
Claims We claim:
1. A flow meter of a fluidistor oscillator type with two interconnected
control inlets located on each side of the connection between an
inlet and two outlet ducts and with the inlet, the control inlets,
the control duct and the outlet ducts located in one and the same
plane and in which the oscillation is detected by the pressure waves
that are formed in the control duct, characterized in that the inlet
is fitted with a net over the orifice and is limited by two control
surfaces, which give a wedge formed inlet, that the control duct
runs circularly around the two outlet ducts, that the outlet is
perpendicular to the direction of inflow and the plane that is formed
by the inlet, the control inlets, the control duct and the outlet
ducts and is located in the centre of the circle that is formed
by the control duct, that a connecting duct between the rear ends
of the two outlet ducts is fitted with a crest, which helps to guide
the flow to the outlet, and that the oscillations are detected by
means of a transmitter and a receiver for ultrasonics placed in
the endpoints of the control duct and directed towards a point on
the symmetry plane of the flow meter located from the inlet somewhat
beyond the centre of the control duct and on one half of the height
between the top and the bottom of the meter.
Description This invention relates to a flow meter of a fluidistor oscillator
type. The object of the invention is to make a flow meter for above
all respiratory measurements. The flow meter according to the invention
has its principal use when measuring the ventilation of human beings
and animals when the measurement is carried out on a moving object.
In these cases it is of particular importance that the flow meter
is small, light and portable at the same time as the pressure drop
in the meter is minimal.
At present when making these measurements dry gas meters and gas
tight bags containing 10-20 l (i.e. Douglas bags) are used into
which the exhaled air is led at the same time as the collecting
time is measured. Both measuring devices are bulky and heavy compared
with the present invention. Possible solutions with flow meters
of other types than the one of the invention are also cumbersome
and heavy.
The invention relates to a special design for a flow meter of the
fluidistor type. A fluidistor consists of an inlet duct and two
outlet ducts that form a certain angle with each other. Between
the inlet duct and the outlets there is on each side a control inlet.
If one of the control inlets is closed a vortex arises at its orifice
and thereby a partial vacuum that directs the flow to the outlet
on this side. If then this control inlet is opened and the other
closed, the flow is in the same way directed to the other outlet.
By joining the two control inlets the flow will switch between the
two outlets. With a suitable dimensioning the switching frequency
is directly proportional to the flow.
To use a fluidistor flip-flop as a flow meter is previously known
from the Swedish Published Patent Application No. 349146 and the
U.S. Pat. Nos. 3238960 and 3802283.
The aimed qualities of the flow meter are according to the invention
achieved by giving the flow meter the special design that is evident
from the following claim.
A suitable embodiment of the flow meter according to the invention
will now be described with reference to the attached drawing where
FIG. 1 shows a section through a flow meter and
FIG. 2 a section along A--A in FIG. 1.
The flow meter comprises an inlet 1 two control inlets 5 and 6
a control duct 7 and two outlet ducts 8 and 9 located in one and
the same plane. In this way the flow meter can be made small.
The flow meter is designed as a box with flat top and bottom. Except
by top and bottom the inlet is limited by two guide surfaces 3 and
4 which give a wedge formed inlet. The inlet can thus be made short.
The angles between the guide surfaces 3 and 4 and the symmetry plane
A--A of the flow meter in FIG. 1 are each suitably between 40.degree.
and 50.degree.. Further the orifice of the inlet is covered by a
net 2. In this way is obtained that wind at outdoor use does not
disturb the function of the meter. Without the net the inlet would
have to be considerably longer. The two control inlets 5 and 6 are
located on each side of the connection between the inlet 1 and the
outlet ducts 8 and 9. The control inlets are interconnected through
the control duct 7 which runs circularly around the two outlet
ducts 8 and 9. In comparison with the usual design with a more cornered
control duct a better signal-to-noise ratio is achieved. The design
also helps to make the meter small. The outlet 10 is perpendicular
to the direction of inflow and the plane that is formed by the inlet
1 the control inlets 5 and 6 the control duct 7 and the outlet
ducts 8 and 9 and is located in the centre of the circle that is
formed by the control duct 7. The outlet takes up all the space
between the outlet ducts 8 and 9 so that the pressure drop in the
meter will be minimal. A connecting duct between the rear ends of
the two outlet ducts 8 and 9 is fitted with a crest 11 which helps
to guide the flow to the outlet 10. The oscillations are detected
by the pressure waves that are formed in the control duct by means
of a transmitter 12 and a reciever 13 for ultrasonics placed in
the endpoints of the control duct and directed towards a point 14
on the symmetry plane of the flow meter located from the inlet somewhat
beyond the centre of the control duct and on one half of the height
between the top and the bottom of the meter. By aiming the transmitter
and reciever in this way the ultrasonic signal will go through the
control duct with wall reflections.
In one embodiment the flow meter had the folowing data: length
110 mm, width 85 mm, height 44 mm, weight 80 g, pressure drop 4
mm H.sub.2 O at 100 l/min and 28 mm H.sub.2 O at 200 l/min, measuring
range 16-250 l/min and error in measurement less than 2% RMS of
the indicated value over the entire measuring range.
By changing the geometry in a linear way the measuring range can
be moved upwards or downwards. |