Abstrict A flow meter is disclosed which comprises a rotary piston carrying
at least one magnet, and a measuring transducer. The transducer
comprises a multiplicity of magnetic field-sensitive components
arranged in correspondence with the path of motion of the magnet.
The magnetic field-sensitive components are arranged in groups which
are coupled to a respective pulse edge-sensitive circuit such as
a monostable multivibrator. The flow meter of the invention is particularly
applicable as a liquid flow meter for foods.
Claims What is claimed is:
1. A flow meter comprising a piston rotatably mounted in the flow
meter, at least one magnet carried by the piston, a measuring transducer
arranged adjacent to the piston and comprising a plurality of magnetic
field-sensitive components arranged in correspondence with the path
of motion of the magnet carried by the piston so as to be sequentially
sensitive to the field of the magnet as the piston rotates, each
magnetic field-sensitive component being operative to generate a
pulse as the magnet is carried past the respective magnetic field-sensitive
component, non-adjacent magnetic field sensitive components being
coupled together according to a predetermined order to arrange the
magnetic field-sensitive components in groups, the predetermined
order depending on the number of groups, and an electric pulse edge-sensitive
circuit coupled to each group of magnetic field-sensitive components
for generating a pulse of relatively short duration in response
to an edge of each pulse generated by the magnetic field-sensitive
components.
2. The flow meter according to claim 1 wherein the magnetic field-sensitive
components are disposed in numerical order corresponding to the
path of motion of the magnet, the magnetic field sensitive components
being connected in three groups, a first and fourth of the field-sensitive
components being coupled together, a second and a fifth of the magnetic
field-sensitive components being coupled together, and a third and
a sixth of the magnetic field-sensitive components being coupled
together, and so on.
3. The flow meter according to claim 1 wherein spacings between
the magnetic field-sensitive components along the path of motion
of the magnet are so chosen that each pulse is proportional to an
equal part of the volume flowing through the flow meter.
4. The flow meter according to claim 1 and including a magnetically
conductive plate disposed adjacent the magnetic field-sensitive
components on the side thereof facing away from the magnet, the
plate having a flat surface disposed perpendicularly to the axis
of polarization of the magnet.
5. The flow meter according to claim 1 and including an OR circuit,
the output of each of said electric circuits being coupled to a
respective input of the OR circuit.
6. The flow meter according to claim 1 wherein the magnetic field-sensitive
elements comprise Hall switches having a Hall probe and a switching
amplifier coupled thereto.
7. The flow meter according to claim 6 wherein the probe and amplifier
are integrated.
8. A flow meter comprising a piston rotatably mounted in the flow
meter, at least one magnet carried by the piston, a measuring transducer
arranged adjacent to the piston and comprising a plurality of magnetic
field-sensitive components arranged in correspondence with the path
of motion of the magnet carried by the piston so as to be sequentially
sensitive to the field of the magnet as the piston rotates, a magnetically
conductive plate disposed adjacent the magnetic field-sensitive
components on the side thereof facing away from the magnet, the
plate having a flat surface disposed perpendicularly to the axis
of polarization of the magnet, each magnetic field-sensitive component
being operative to generate a pulse as the magnet is carried past
the respective magnetic field-sensitive component, and means coupled
to the magnetic field-sensitive components for generating pulses
of relatively short duration in response to an edge of the pulses
generated by the magnetic field-sensitive components.
9. The flow meter according to claim 8 wherein said means comprises
an electric pulse edge-sensitive circuit coupled to each magnetic
field-sensitive component.
Description BACKGROUND OF THE INVENTION
The present invention relates to a liquid or gas flow meter which
includes a rotary piston carrying at least one magnet, and a magnetic
transducer.
In a known flow meter (see for example U.S. Pat. No. 3874235)
which comprises a rotary piston carrying a magnet and a magnetic
transducer, the magnetic field-sensitive parts are arranged at the
center of the path of motion of the exciter magnet and are provided
with U-shaped magnetic conductor strips for guiding the magnetic
field lines, the poles of which are diametrically opposite each
other in the path of motion. To increase measuring accuracy, several
poles are provided in this type of flow meter. However, the central
arrangement of the magnetic field-sensitive parts at the center
of the path of motion and the relatively large dimensions of the
poles and the magnetic conductor strips require narrow tolerance
limits in order to increase measuring accuracy for reasons of space.
If relatively numerous, closely adjacent poles are arranged, there
is a further danger of spuriously generated signals by the magnetic
field-sensitive parts.
OBJECT AND SUMMARY OF THE INVENTION
Objects of the present invention are to increase the measuring
accuracy and resolution of a flow meter while avoiding measuring
errors due to spuriously generated signals by the magnetic field-sensitive
parts.
According to the invention, a multiplicity of magnetic field-sensitive
components is provided in a flow meter comprising a rotary piston
carrying a magnet, and a magnetic transducer. The transducer includes
magnetic field-sensitive components arranged to correspond to the
path of motion of the magnet. The outputs of the magnetic field-sensitive
components are coupled to electric pulse edge-responsive circuits
which generate an electric output pulse of relatively short width
in response to a leading (positive) or trailing (negative) edge
of an input pulse. The components are sequentially arranged so that
the pulses they generate follow each other in sequence.
Arranging a multiplicity of magnetic field-sensitive components
according to the invention can increase the resolution and thereby
the measuring accuracy of the flow meter without increasing measuring
errors due to spurious signals. According to the invention, any
deleterious effect of an overlap of adjacently generated pulses
is eliminated and such overlap is not detrimental to resolution
since only the leading or trailing edge of the output signals of
the magnetic field-sensitive components are used. The magnetic field-sensitive
components can therefore be arranged directly adjacent to each other
according to the path of motion of the magnet. Since only one magnetic
field-sensitive component generates a pulse of relatively short
pulse width at any one time, measuring errors due to spurious signals
are prevented.
To each magnetic component, an electric edge-responsive circuit
or module can be assigned and each electric circuit can be identical.
To decrease the amount of circuitry, the magnetic field-sensitive
components can advantageously be combined in groups; non-adjacent
magnetic field-sensitive components spaced, for example, by an equal
number of magnetic field sensitive components, can be connected
together, the number of groups determining which components are
connected together and the spacing between components which are
connected together.
For evaluating the electric pulses, the outputs of the electric
circuits can advantageously be coupled to an OR gate and thereby
interlinked, so that at the output of the OR gate, a signal is available
which can be fed to a counting device.
According to one aspect of the invention, the measuring accuracy
of the flow meter can be increased still further by choosing the
spacings between adjacent magnetic field-sensitive components along
the path of motion so that the same width is assigned to each pulse
to compensate for flow meter system errors. For example, system
errors caused by the non-linear relationship of the liquid or gas
flowing through the meter and the angle of rotation of the rotary
piston can be compensated by a suitable arrangement of the magnetic
field-sensitive components. With such an arrangement, the number
of the electric pulses is proportional to the volume of the liquid
or gas flowing through the flow meter.
According to another aspect of the invention, there can advantageously
be provided on the side of the magnetic field-sensitive components
facing away from the magnet, a plate which is highly magnetically
conductive and has a flat surface which is perpendicular to the
axis of polarization of the magnet carried by the piston. The arrangement
of the highly magnetically conducting plate at the magnetic field-sensitive
components advantageously provides a concentration of the magnetic
field of the magnet in the vicinity of the magnetic field-sensitive
components so that the reliability of the response of the magnetic
field-sensitive components and thereby the measuring accuracy of
the flow meter can be increased.
According to still another aspect of the invention, the magnetic
field-sensitive components in the flow meter according to the invention
can advantageously be Hall switches which comprises a Hall probe
and an integrated switching amplifier.
Due to the small dimensions of the Hall switches, which contain
an extremely magnetic field-sensitive Hall probe, a large number
of magnetic field-sensitive components can be arranged in the path
of motion of the magnet. In addition, the integrated switching amplifier
ensures that the output signal of the Hall switch, which is fed
to the electric circuits, is of adaquate magnitude.
More particularly, a flow meter according to the invention comprises
a piston rotatably mounted in the flow meter, at least one magnet
carried by the piston, and a measuring transducer arranged adjacent
to the piston and comprising a plurality of magnetic field-sensitive
components arranged in correspondence with the path of motion of
the magnet carried by the piston so as to be sequentially sensitive
to the field of the magnet as the piston rotates. Each magnetic
field sensitive component is operative to generate a pulse as the
magnet is carried past the respective magnetic field-sensitive component.
Means are coupled to the magnetic field-sensitive components for
generating pulses of relatively short duration in response to an
edge of the pulses generated by the magnetic field-sensitive components.
The pulse generating means comprises an electric pulse edge-sensitive
circuit coupled to each magnetic field-sensitive component. Non-adjacent
magnetic field sensitive components are coupled together according
to a predetermined order to arrange the magnetic field-sensitive
components in groups, an electric circuit being coupled to each
of the groups.
In a disclosed embodiment, the magnetic field-sensitive components
are disposed in numerical order corresponding to the path of motion
of the magnet. A first and fourth of the field-sensitive components
are coupled together, a second and a fifth of the magnetic field-sensitive
components are coupled together, and a third and a sixth of the
magnetic field-sensitive components are coupled together. A seventh
of the magnetic field sensitive components is coupled to the first
and fourth, an eighth to the second and fifth, a ninth to the third
and sixth, and so on.
The field-sensitive components are spaced along the path of motion
of the magnet to provide pulses generated by the magnetic field-sensitive
components of equal width, whereby system errors tending to give
unequal pulse widths can be compensated.
These and other aspects of the invention will be more apparent
from the following description of the preferred embodiment thereof
when considered with the accompanying drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not
limitation in the figures of the accompanying drawings in which
like references indicate similar parts and in which:
FIG. 1 is a cross-section view of part of a flow meter according
to an embodiment of the invention and a schematic wiring diagram
of the magnetic field-sensitive components, the monostable multivibrators
and the OR circuit of the embodiment; and
FIG. 2 is a waveform diagram of pulses generated by the magnetic
field-sensitive components, the multivibrators and the OR circuit
of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the flow meter shown in FIG. 1 the magnetic field-sensitive
components 1 form part of a measuring transducer 2 which is disposed
adjacent to a fixed wall 3 of the flow meter. The magnetic field-sensitive
components 1 are positioned along a curve in correspondence with
the path of motion 4 of a magnet 5 mounted on a rotary piston 6
of the flow meter. On the side of the components 1 facing away from
the magnet 5 a highly magnetically conductive plate 7 is disposed.
The magnetically field-sensitive components 1 which in the preferred
embodiment comprises Hall switches, are combined in groups by connecting
the components in a predetermined arrangement. As shown in FIG.
1 the compounds are connected into three groups; thus, the first
component is connected to the fourth component, the second to the
fifth, the third to the sixth, the seventh to the first and fourth,
etc, reference being had to a numerical order starting either from
the left side of the components and counting in a counterclockwise
direction or from the right side of the components and counting
in a clockwise direction. The lines connecting the components and
forming the three groups are designated 8 9 10.
Lines 8 9 10 are connected to the inputs 11 12 13 of electric
circuits or modules 14 15 16 to thereby connect the outputs of
respective groups to a respective module. The electric modules 14
15 16 in the preferred embodiment comprise monostable multivibrators.
The inputs 11 12 and 13 of the monostable multivibrators are trigger
inputs which respond to the respective leading (positive) or trailing
(negative) edge of a signal. Pulses of relatively short width are
generated at the outputs 17 18 19 of the monostable multivibrators
14 15 16 in response to the signals (edges) present at the trigger
inputs. The duration of the pulses is chosen so that the pulses
present at the different outputs occur sequentially. The outputs
17 18 19 are connected to respective inputs of an OR gate (circuit)
20. A shaped pulse output signal U is obtained at the output of
the OR gate 20 to which may be connected a counter circuit.
The pulse diagram of FIG. 2 shows the output signals a, b, c of
the first to third magnetic field-sensitive components, respectively.
The pulses a', b', c' represent the relatively short width pulses
of the three corresponding monostable multivibrators, where the
pulse a' occurs at the time of the leading (positive) edge of the
output signal a. The pulses b' and c' occur at the times of the
leading edge of the output signals b and c. The pulses d represent
the output signal U which is formed in this case from an interlinkage
of the pulses a', b', c' by means of the OR gate 20.
The operation of the flow meter according to the invention will
now be described. Referring to FIG. 1 the magnet 5 rotates with
the rotary piston 6 of the flow meter so that the magnetic field-sensitive
components sequentially enter the influence zone of the magnet.
At the instant a magnetic field-sensitive component is activated,
i.e., during the leading edge of the output signal of the component,
the respective electric module connected thereto is trigged and
produces at its output an electric pulse of relatively short width.
The width of the pulse is selected to be short enough so that the
pulse ends prior to the instant at which the magnet 5 activates
the next component in the direction of rotation. Optimum resolution
during the measuring process is thus assured and inaccurate measurements
due to spurious generation of pulses from the magnetic field-sensitive
components is prevented.
The advantages of the present invention, as well as certain changes
and modifications of the disclosed embodiments thereof, will be
readily apparent to those skilled in the art. It is the applicant's
intention to cover by his claims all those changes and modifications
which could be made to the embodiments of the invention herein chosen
for the purpose of the disclosure without departing from the spirit
and scope of the invention. |