A method of urine flow measurement where liquid in the form of
a free-fall jet is collected in a collecting vessel and the vertical
force produced by the collecting vessel on a measuring device, for
example a scale or the like, is sensed, and the change in time of
said force is utilized for obtaining a measure of the flow corresponding
to the jet. The method is especially characterized in that the effect
of the impulse of the jet on the sensed force is eliminated by deflecting
the vertical flow constituted by the jet to a substantially horizontal
flow by a rotating device before the liquid is caused to contact
the vessel. The invention also relates to a flow meter.
1. A method for measuring the rate at which urine is emitted without
interference from the impulse force of the urine stream comprising:
collecting urine in the form of a free-falling stream in a collecting
vessel having substantially vertical walls;
deflecting the free-flowing stream of urine using a rotating device
contained within the collecting vessel but mounted separately therefrom,
said device being rotated at a speed sufficient to generate a centrifugal
force such that the vertical velocity of the urine is converted
into horizontal velocity;
causing the deflected urine stream to flow downward from the rotating
device into a measuring chamber, said chamber being equipped with
means for measuring the amount of urine contained in said measuring
determining the rate of change of said amount of urine in the measuring
chamber, whereby the rate of urine emission can be accurately measured
without interference from the impulse force of the urine stream.
2. A method as defined in claim 1 further comprising the step
of weighing the collecting vessel by means of a vetically moveable
disc on which the vessel is supported, which disc is operably connected
to means which measures the rate of change of said weight.
3. A method as defined in claim 2 further comprising the step
of generating a signal voltage from the means for measuring the
rate of change in weight, wherein the signal voltage is directly
proportional to the time derivative of force.
4. A method according to claim 2 further comprising the step of
generating an output signal from a piezoelectric crystal proportional
to the rate of change of said weight, wherein said disc via a cam
affects the piezoelectric crystal which is attached to a spring,
which is clamped at both ends and, respectively, freely supported.
5. A method as defined in claim 1 further comprising the step
of braking air movement induced by rotation of said device using
discs provided below said device.
6. An apparatus for measuring the rate at which urine is emitted
without interference from the impulse force of the urine stream
a collecting vessel for receiving urine in the form of a free-falling
stream, said vessel having a base and generally cylindrical vertical
mounting means to support the weight of the vessel and urine collected
a rotatable device positioned within the vessel such that after
entering the collecting vessel, the free-falling stream of urine
will strike the rotatable device, said rotatable device having an
outer edge substantially adjacent to but not touching the interior
of said vertical walls of the vessel, and said rotatable device
dividing the vessel into an upper urine receiving chamber and a
lower urine measuring chamber;
means for rotating the rotatable device at a rate sufficient to
cause the free-falling stream of urine striking the rotatable device
to be deflected toward the vertical walls such that the vertical
velocity of the urine stream is converted to horizontal velocity;
means for measuring the weight of the vessel and the urine collected
in the urine measuring chamber, and determining therefrom the rate
of urine emission, wherein the rotatable device is mounted separately
from the collecting vessel such that neither the rate of rotation
of the device nor the impulse force of the free-falling stream of
urine contributes to the measured weight of the urine collected.
7. An apparatus as defined in claim 6 further comprising a vertically
movable plate on which the weight of the collecting vessel is taken
up, means for measuring the rate change of said weight and a heavy
chassis on which said plate and means are mounted.
8. An apparatus as defined in claim 7 characterized in that the
rotatable device is operably connected to a motor located on a bottom
plate, which via a cellular rubber plate is resiliently attached
to the heavy chassis of the apparatus.
9. An apparatus as defined in claim 7 characterized in that said
plate via intermediate member is attached resiliently to said chassis
by means of upper springs and by means of rods extending vertically
downward from the plate via a ring connecting the rods and attached
to the chassis also by lower springs.
10. An apparatus as defined in claim 6 characterized in that it
includes means for emitting a signal voltage which is directly proportional
to the rate of change of the weight of said vessel.
11. An apparatus as defined in claim 6 further comprising a cam
and a piezoelectric means, said cam being mounted to transmit force
from said disc to said piezoelectric means, and said piezoelectric
means being attached to a spring which is clamped at both ends and,
respectively, freely supported.
12. An apparatus as defined in claim 6 wherein the base of said
vessel includes a central hole, from which a flange projects upward
to a height intended at measurement not to be exceeded by the liquid
level in the vessel, through which hole an axle extends for driving
said rotary device.
13. An apparatus as defined in claim 6 further comprising free
standing rigidly attached discs located below said rotary device
and intended to brake air movements induced by the rotation of said
14. An apparatus as defined in claim 6 wherein said rotary device
has an upper surface that is at least partially conical.
15. An apparatus as defined in claim 6 characterized in that said
rotary device has a hydrophobic surface.
BACKGROUND OF THE INVENTION
This invention relates to a method for urine flow measurement wherein
liquid in the form of a free-falling jet is collected in a collecting
vessel, and the weight of the vessel as a vertically acting force
is continuously sensed and utilized for yielding a measure of the
The invention also relates to a flow meter for carrying out the
During examination of the function of the lower ureters of a human
being, the measurement of the urine flow as a function of the time,
is the objective examination method which offers the greatest potential
possibilities for obtaining copious information. Based upon the
urine flow and the hydrostatic pressure in the bladder of a person,
the elastic properties of the urethra determining the urine flow
can be obtained. It is a prerequisite, however, that this flow and
pressure can be measured accurately. Known urine flow meters, however,
yield serious errors in measurement.
In a usual method of flow measurement, a scale with a collecting
vessel is used. The force, F, recorded by such a scale is given
by the equation ##EQU1## where m.sub.o is the initial mass of the
vessel, g is the acceleration of gravity, p is the density of the
urine, t is the time, Q the volume flow for the urine, and v the
corresponding flow rate. The integral term in equation 1 corresponds
to the volume. The last term in the expression is the reaction force
due to the kinetic energy of the urine jet.
In order to receive an output signal corresponding to the flow,
the first derivative of the force signal is determined, whereby
##EQU2## The first term of the derivative, i.e. gpQ, is proportional
to the desired flow. The remaining two terms are false signals occurring
as a result of flow variations. The effect of these false terms
can be illustrated by the recorded flow at an imagined pulse shaped
uring flow. When the flow starts and ceases, due to said reaction
force in principle infinitely large derivative terms are obtained
which yield large overshoots in the measured valves. These overshoots
can be filtered out, but the system then receives a very slow response.
Some of the problems with the kinetic energy of the urine jet can
be overcome by collecting the urine in a funnel intended to take
up the reaction force. The funnel, however, introduces a problem
which potentially is still more serious, viz. a variable delay of
the flow. This delay depends on where the urine jet meets the funnel.
When a jet with constant flow is caused to oscillate over the funnel,
this variable delay gives rise to a false variation in the flow
which is recorded by the equipment.
In a known type of flow meter the flow is related to the effect
which is required to accelerate the liquid to the circumferential
speed of a rotating plate. The urine, however, here is collected
by a funnel, and therefore the method and meter are afflicted with
the errors in measurement involved therewith. When the urine jet
is caused to directly meet the rotating plate, the reaction force
of the jet affects the necessary effect for maintaining the rotation
of the plate constant.
SUMMARY OF THE INVENTION
The present invention relates to a flow meter substantially designed
according to the aforesaid scale principle. In the flow meter according
to the invention, the problems referred to above have been substantially
eliminated so that the flow can be measured with very high accuracy.
The present invention, thus, relates to a method of urine flow
measurement where liquid in the form of a free-falling jet is collected
in a collecting vessel, and the vertical force produced by the collecting
vessel on a measuring member, for example a scale or the like, is
sensed. The change in time of said force is utilized to determine
the flow corresponding to the jet.
The method is especially characterized in that the influence of
the impulse of the jet on the sensed force is eliminated by deflecting
the vertical flow constituted by the jet to a substantially horizontal
flow by means of a rotating device before the urine is caused to
contact the vessel.
The invention also relates to a flow meter for urine flow measurement,
wherein urine in the form of a free-falling jet is continuously
collected in a collecting vessel, and wherein means, for example
a scale or the like, are provided for sensing a vertical force produced
by the vessel. The change in time of said force is intended to be
utilized for determining the flow corresponding to the jet.
The flow meter according to the invention is especially characterized
in that it comprises a rotary device free from said vessel, by means
of which device the vertical flow constituted by the jet is deflected
to a substantially horizontal flow prior to the urine striking the
wall or base of the vessel, so that the influence of the impulse
of the jet on the sensed force is eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail in the following,
with reference to an embodiment and the accompanying drawings, in
FIG. 1 schematically shows a known arrangement for flow measurement
FIGS. 2a-c schematically show by way of curves real flow, recorded
volume and recorded flow at a known flow meter substantially according
to FIG. 1.
FIG. 3 respectively, shows recorded flow as a function of the time,
where the flow is maintained constant while the liquid jet is caused
to oscillate over a collecting funnel comprised in the flow meter,
FIG. 4 is a schematic vertical section through a part of an apparatus
according to the invention,
FIG. 5 is a schematic vertical central section A--A according to
FIG. 6 through an embodiment of an apparatus according to the invention,
FIG. 6 is a section B--B according to FIG. 5
FIG. 7 shows an electric output signal as a function of applied
constant flow at a flow meter according to the invention, and
FIG. 8 shows the response on an applied pulse shape flow at a flow
meter according to the invention.
In FIG. 1 the numeral 1 designates a collecting vessel, and 2 is
a scale, on which the vessel 1 is placed. An arrangement of this
known type involves errors in measurement as referred to above.
In FIG. 2c overshoots 3' from the actual pulse shape flow 3 FIG.
2a, are observed as a result of the jet impulse. In FIG. 3 pulsations
in the recorded flow at the use of a funnel are shown, through which
funnel the liquid is caused to pass prior to the arrival at the
collecting vessel at a flow meter according to FIG. 1 which pulsations
are obtained from liquid jet oscillating over the funnel.
In the embodiment of an apparatus according to the invention shown
partially and schematically in FIG. 4 the numeral 4 designates a
collecting vessel, to which a liquid flow in the form of a jet 5
is intended to enter. 6 designates a rotary, substantially horizontal
and preferably circular disc located in, but not in contact with
the vessel 4 and preferably substantially adjoining the inner wall
7 of the vessel. The rotary disc 6 substantially divides the interior
of the vessel 4 into an upper urine receiving chamber 41 and a lower
urine measuring chamber 42. The jet 5 strikes the disc 6 whereby
the vertical flow constituted by the jet is deflected to a substantially
horizontal flow prior to the supply of the liquid to the lower urine
measuring chamber 42 of the vessel 4 and, in applicable cases, of
liquid 8 in the vessel. The disc 6 is capable of rotation at high
speed, so that the horizontal flow rate of the liquid after the
deflection of the flow is high.
According to a preferred embodiment, the disc 6 has a hydrophobic
coating to ease the flow of liquid therefrom.
The vessel 4 is preferably substantially cylindrical and designed
so that its bottom 9 includes a central hole 10 from which a flange
11 projects upward to a height intended at measurement not to be
exceeded by the liquid level in the vessel 4. An axle 12 for driving
the disc 6 extends through the hole 10.
In the embodiment of a flow meter according to the invention shown
in FIGS. 5 and 6 the collecting part of the meter is designed substantially
as in FIG. 4. The axle 12 is mounted in a pipe 13 by bearings 14
and extends to a motor 15 located beneath the vessel on a bottom
plate 16 which via a cellular rubber disc 17 is resiliently, elastically
attached to the relatively heavy chassis 18 of the meter in order
to minimize the transfer of vibrations from the motor 15 and rotating
disc 6 to the chassis 18. In the embodiment shown, the chassis 18
comprises a circular bottom 19 and a wall arrangement 20 projecting
in a cylindric configuration from the bottom 19. 21 designates a
vertically movable thin metal plate, on which the vessel 4 is placed
and via which the vertical force from the vessel 4 is intended to
be taken up. The plate 21 includes a central hole 22 for extending
the pipe 13 and axle 12 therethrough. The plate 21 is resiliently
supported via intermediate members in the form of metal blocks 23
on the chassis 18 by means of three upper soft springs 24 which
extend radially inward from the circumference 25 of the upper portion
of the chassis, and by means of six rods 26 extending from the plate
21 vertically downward at a ring 27 which connects the rods 26
and is resiliently attached also to the lower portion of the chassis
by three soft springs 28. The plate 21 hereby is fixed horizontally.
The plate 21 has on its lower surface 29 a cam 30 on which the
plate in the embodiment shown is intended to rest and thereby to
affect a piezoelectric ceramic crystal 31. According to a preferred
embodiment, the crystal has a length of 20 mm and is of the type
marketed under the designation PXE 5 multimorph, Philips. The crystal
is longitudinally and symmetrically glued on the upper surface of
a spring 32 which is 60 mm long, 10 mm wide and 1 mm thick.
The spring is rigidly clamped at both its ends 3334 to a beam
35 and, respectively, resting freely on an edge (not shown). The
said cam 30 extends diametrically in the chassis, and the beam 35
with the spring 32 and crystal 31 are arranged as a chord perpendicular
to the cam, as shown in FIG. 6.
According to a preferred embodiment, beneath the disc 6 a disc
36 supported by the outer pipe 13 is provided with discs 37 intended
to brake air movements induced by the rotation of said disc 6.
According also to a preferred embodiment, discs or the like (not
shown) are provided at the bottom of the vessel 4 for braking movements
of the liquid collected in the vessel.
The method and the way of operation of the arrangement according
to the invention substantially should have become apparent from
The reaction force from the impulse of the jet 5 thus, is absorbed
by the rapidly rotating disc 6 free from the vessel 4. The jet is
deflected by the disc, and the liquid flow is accelerated to a horizontal
speed v.sub.1 FIG. 4 at the circumference of the disc. When the
liquid meets the wall of the collecting vessel, a horizontal force
is obtained which, however, is distributed uniformly over the inner
surface of the vessel. By the design described for sensing the force,
the force is sensed only in vertical direction. The flow meter,
therefore, is not sensitive to the horizontal force. After having
met the inner surface 7 of the vessel, the liquid moves slowly with
the speed v.sub.2 downward along the vessel wall, and as m.sub.2
dv.sub.2 /dt<<m.sub.2 g only a force contribution is recorded
which corresponds to m.sub.2 g. The resulting force, therefore,
with the designations according to FIG. 4 is
The signal voltage emitted by the piezoelectric crystal arranged
in the way described above is directly proportional to the derivative
of the applied force. The arrangement described for measuring the
force, therefore, eliminates the problems involved with electric
By means of the design described, comprising upper and lower springs
and rods for suspending the plate 21 a stable anchoring of the
plate is obtained, so that movement is permitted only in vertical
direction, and as mentioned the output signal from the crystal in
principle is independent of horizontal forces. Vibrations of the
chassis due to movements of the motor can give rise to an interference
signal, because the collecting vessel and plate 21 and the attachment
constitute a seismic transmitter. This interference has been minimized
due to small mass of the vessel/plate and rigid force transmitter.
By means of said discs for braking air movements and liquid movements
the size of interference signals has been reduced still more.
As should be obvious from the aforesaid, the invention offers essential
advantages over the known art. By means of the disc 6 interferences
as a result of the jet meeting directly the vessel are eliminated.
The effect of both impulse and wave formation is eliminated. Due
to the rapid rotation of the disc, the liquid arrives very rapidly
at the collecting vessel wall after the jet has met the disc, and
thereby the meter is insensitive to the place where the jet meets
the disc. The output signal. therefore, is not interfered by oscillating
movement of the jet, as shown in FIG. 3.
In FIGS. 7 and 8 measurement results obtained with a flow meter
according to the invention are shown. They show a linear relation
between applied flow and output signal. The response to applied
pulse shape flow is rapid and does not show overshoots. When the
pulse shape flow is recorded with an electric time constant of 0.1
sec.. a response time is obtained which from the start of the flow
to its arrival at 63% of the final value is about 0.2 sec.
The invention has been described above with reference to substantially
one embodiment. Several more embodiments and minor alterations,
of course, can be imagined without therefore abandoning the invention
Other configurations of the rotating member 6 than the disc shape
shown, for example, can be imagined. In FIG. 5 a central cone-shaped
portion is shown. The rotating member, however, can be designed
so that the cone shape entirely dominates.