Abstrict An electromagnetic pulse pick-up unit, particularly for use in
flow meters having small nominal width, comprises a pair of magnets
arranged at opposite locations and with opposite polarity in a measuring
gear of the flow meter. Concentrically arranged with the axis of
rotation of the gear, there is provided a sensing unit assembled
of a central pick-up cylinder, a sensing coil arranged around the
portion of the cylinder facing the magnet, and a plurality of Wiegand
wires distributed side by side in axial direction on the cylindrical
outer surface of the pick-up cylinder in close proximity to the
sensing coil. A pole ring of magnetically conductive material short
circuits the ends of the Wiegand wires remote from the magnets.
Claims What is claimed as new or desired to be protected by Letters Patent
is set forth in the appended claims:
1. An electromagnetic pulse pick-up arrangement in a flow meter
including a measuring chamber defining an inlet and outlet and a
front wall of a magnetically non-conductive material, a measuring
gear supported in the measuring chamber for rotation about an axis,
the pick-up arrangement comprising a pair of oppositely polarized
magnets secured to the measuring gear at opposite locations relative
to said axis, a cylindrical well formed in the front wall opposite
the measuring gear, a stationary Wiegand sensor including a central
pick-up cylinder arranged in the well in an axially spaced relationship
with the measuring gear, one end of said pick-up cylinder facing
said two magnets, a sensing coil surrounding a portion of the jacket
of the pick-up cylinder close to said one end, a plurality of Wiegand
wires arranged substantially parallel to each other and extending
in axial direction on the jacket of the pick-up cylinder, a portion
of each of said Wiegand wires overlapping said sensing coil, and
a pole ring of a magnetically conductive material inserted on another
portion of the jacket of the pick-up cylinder remote from said one
end, and a pole ring engaging another portion of each of said Wiegand
wires.
2. A pulse pick-up arrangement as defined in claim 1 wherein the
jacket portion of the pick-up cylinder adjacent to said one end
is provided with a circumferential annular groove for accommodating
the sensing coil, and the outer cylindrical surface of the jacket
of the pick-up cylinder being formed with axially directed elongated
grooves for accommodating the Wiegand wires.
3. A pulse pick-up arrangement as defined in claim 2 wherein the
Wiegand wires are secured in the longitudinal grooves by gluing.
4. A pulse pick-up arrangement as defined in claim 2 wherein the
opposite end of said pick-up cylinder is provided with an axial
blind bore for temporarily accommodating a holding magnet which
holds by its magnetic force the Wiegand wires in the longitudinal
grooves until the wires are secured by gluing and the pick-up cylinder
is inserted into the well.
5. A pulse pick-up arrangment as defined in claim 2 wherein the
longitudinal grooves together with the Wiegand wires extend to the
level of the one end face of the pick-up cylinder to contact the
bottom surface of the well.
6. A pulse pick-up arrangement as defined in claim 5 wherein the
circumferential annular groove for accommodating the sensing coil
is separated from the one end of the pick-up cylinder by a thin
collar, and the pole ring inserted on the other jacket portion of
the pick-up element engaging outer surface of the other portions
of the Wiegand wires.
7. A pulse pick-up arrangement as defined in claim 2 wherein said
annular groove and said axially directed grooves are filled with
a casting material and said Wiegand wires and said sensing coil
are embedded in said casting material.
8. A pick-up arrangement as defined in claim 1 wherein each of
the two magnets is arranged in a blind bore formed in the side of
the measuring gear remote from the front wall and extending to the
proximity of the front wall, and each blind bore being sealed by
a closing part.
9. A pulse pick-up arrangement as defined in claim 1 comprising
an oval measuring gear meshing with another oval gear, the two magnets
being rod magnets arranged in the end portions of the long axis
of the oval measuring gear, and the axially directed longitudinal
grooves on the pick-up cylinder being non-uniformly spaced one from
each other to compensate for irregular rotary speed of the oval
measuring gear.
Description BACKGROUND OF THE INVENTION
The present invention relates in general to flow meters and in
particular to an electromagnetic pick-up arrangement in flow meters
particularly in flow meters of small nominal width. The flow meter
is of the type which includes a measuring chamber, a measuring wheel
supported for rotation in the chamber and including a magnetic device
having pole surfaces directed against an end wall of the measuring
chamber. The end wall is of a magnetically non-conductive material
and is formed with a well or space in which a Wiegand sensor is
fixedly arranged in such a manner that during each rotation of the
measuring wheel electric pulses are generated in the sensor whereby
the number of pulses is a measure of flow of a medium streaming
through the measuring chamber.
A pulse pick-up of this kind is described for example in the German
publication DE-OS No. 3046804 which discloses a Wiegand sensor
for impeller type counters in flow meters with mechanism and indicator
operating in air. In this prior art arrangement, a ring magnet is
embodied in the hub of the impeller to rotate therewith and to act
on a single Wiegand wire which is surrounded by a sensing coil and
oriented transversely to the axis of rotation of the impeller and
closing the latter midway of its length. The Weigand wire is arranged
outside a separating wall. The disadvantage of this known arrangement
is the limited number of generated pulses inasmuch during each rotation
of the impeller only a single pulse is generated and consequently
resolution of the measured value low. Moreover this relatively large
ring magnet cannot be installed in flow meters of very small nominal
width because in such flow meters the measuring gears may be of
smaller size than the required dimensions of the ring magnet. In
this case, the ring magnet must be driven as a separate rotating
member by the measuring wheel and consequently the rotating mass
would be substantially increased.
In the German magazine "Electronic", 1980 copy 7 page
45 the application of Wiegand wires as a sensing module in flow
meters has been devised. In this article an arrangement is described
in which a number of Wiegand wires is arranged axis parallel on
the jacket of a sensing drum rotating together with the measuring
wheel. The sensing coil of the module together with magnets are
disposed in a separate structural unit which must be mounted on
the outer surface of a stationary housing part of the flow meter
and arranged on the sensing drum. The disadvantage of this solution
is the fact that the sensing drum which is necessary for supporting
and embodying the Wiegand wires rotates partially in the work space
of the counter and requires additional installation space. Furthermore,
the sensing drum introduces a relatively large additional rotating
mass exerting breaking action on the measuring wheel. Moreover,
in this known solution the sudden polarity change in the Wiegand
wires must be transmitted over a relatively large distance through
the housing jacket of the flow meter to the outer fixedly mounted
sensing coil and consequently only relatively weak pulses are produced.
Since the flow meter counters are usually made of metal an additional
damping of transmitted pulses occurs. The prior art pulse pick-up
arrangement is unsuitable for installation in flow meters of small
nominal diameters inasmuch the sensing drum carrying the Wiegand
wires is too large in relation to the diameter of the measuring
wheel and therefore it would make a compact construction of the
flow meter impossible.
SUMMARY OF THE INVENTION
It is therefore a general object of the present invention to overcome
the aforementioned disadvantages.
More particularly, it is an object of the invention to provide
an improved arrangement of Wiegand sensor suitable particularly
as a pulse pick-up for flow meters of small nominal width.
Another object of this invention is to provide such an improved
pulse pick-up arrangement which can be installed with minimum design
changes in time-tested flow meters of compact structure without
negatively affecting their measuring quality.
An additional object of this invention is to provide such an improved
pulse pick-up arrangement which guarantees a high measuring resolution
and a generation of strong measuring pulses.
In keeping with these objects and others which will become hereinafter,
one feature of the invention resides, in a pulse pick-up arrangement
in flow meters of the before described kind, in a combination which
comprises a pair of opposite polarized bar magnets secured to the
measuring wheel of the flow meter at diametrically opposite locations
near the circumference of the wheel, a stationary Wiegand sensor
arranged in the well in the non-magnetic front wall opposite the
measuring wheel and being axially spaced apart from the latter,
the Wiegand sensor including a concentric arrangement of a central
pick-up cylinder, a sensing coil surrounding a portion of the pick-up
cylinder facing the two magnets and a plurality of Wiegand wires
arranged substantially axial parallel along the cylindrical outer
surface of the pick-up cylinder and of the sensing coil, and a pole
ring of a magnetically conductive material surrounding a portion
of the pick-up remote from the two magnets and engaging the end
portions of the Wiegand wires.
Due to the fact that the two opposite polarized bar magnets in
the measuring wheel are spaced apart for a relatively large distance,
and since these magnets are aligned with the Wiegand wires arranged
on the outer jacket of the stationary pick-up cylinder and sensing
coil, the pick-up cylinder and the sensing coil can be designed
with a relatively large diameter and consequently an increased number
of Wiegand wires can be distributed on the outer jacket of the pick-up
cylinder. As a consequence, a large number of pulses is generated
during each rotation of the measuring wheel resulting in a substantially
increased measuring resolution. Since the Wiegand wires extend parallel
to the axis of rotation of the measuring wheel and engage the pole
ring at the side remote from the measuring wheel, a major part of
field lines of the magnet field generated by the two opposite polarized
magnetic surfaces, extend from the magnetic surface of one magnet
through the magnetically non-conductive end wall of the measuring
chamber and along a path constituted by the axial parallel Wiegand
wires situated in the effective range of the one bar magnet, then
via the magnetic pole ring and back through the Wiegand wires and
end wall in the effective range of the other bar magnet.
By virtue of this axial extension of the magnetic field through
the pole ring, the Wiegand wires are exposed to magnetic fields
over a substantially increased length in comparison with prior art
arrangements which do not employ the pole ring and where the field
line would extend along the path of the least magnetic resistance
through the magnetically non-conductive space between the two magnets.
Due to the magnetic excitation of a substantially larger section
of each Wiegand wire, a higher magnetic pulse is produced in the
Wiegand wires and induces in the sensing coil which is concentrically
arranged in close proximity to the parallel Wiegand wires, a high
signal voltage.
In a preferred embodiment, the cylindrical surface of the pick-up
cylinder is formed with an annular groove for accommodating the
sensing coil and with axially directed longitudinal grooves for
accommodating the Wiegand wires in the close proximity to the sensing
coil. In this manner, the cylindrical jacket of the pick-up cylinder
is utilized for supporting a maximum number of Wiegand wires while
the diameter of the pick-up cylinder can be relatively small and
at the same time, the sensing coil is in immediate effective range
of the Wiegand wires.
The Wiegand wires are held in position in the longitudinal axially
directed grooves either by clamping or gluing or by embedding in
a plastic material together with the sensing coil.
In a particularly advantageous embodiment of this invention the
pick-up cylinder is also formed with an axial blind bore 12' in
which during installation of the pick-up assembly a holding magnet
is temporarily inserted whereupon the Wiegand wires are loosely
layed in the longitudinal grooves and are held in position by the
holding magnet. Thereafter the Wiegand wires are either glued to
the grooves or embedded together with a sensing coil in a cast plastic
material and the holding magnet is removed.
Preferably the longitudinal axial parallel grooves on the outer
surface of the cylindrical pick-up member extend up to the end face
of the latter so that the ends of the Wiegand wires can be shifted
into engagement with the thin walled bottom of the well in the non-magnetic
end wall. In this manner, the Wiegand wires are arranged as close
as possible to the bar magnets in the measuring wheel and consequently
a sufficient magnetic induction is produced in the Wiegand wires
even if the bar magnets are of small size. Especially in the case
of counters having reduced width there is frequently no room for
installing larger magnets in the measuring wheel and only by this
arrangement it can be achieved a reliable sensing even in minute
measuring wheels.
Preferably, the annular groove for accommodating the sensing coil
is located as close as possible to the end of the pick-up cylinder
facing the measuring wheel so that only a thin rim portion separates
the groove from the end face of the pick-up cylinder. At the same
time, the pole ring at the opposite end of the pick-up cylinder
is in contact with end portions of the Wiegand wires which overlap
the sensing coil. In this way a particularly strong magnetic flux
is concentrated in the longitudinal direction of the Wiegand wires
which in turn enables the generation of very strong pulses. At the
same time, the pole ring serves as a holder for the Wiegand wires
laying in the axial grooves and can be also employed as an installation
aid. The pick-up cylinder together with Wiegand wires, the sensing
coil and the pole ring thus forms a compact structural unit which
can be easily inserted in the cylindrical well or recess in the
end wall of the measuring chamber.
The two bar magnets are preferably accommodated in two blind bores
formed in the side of the measuring wheel remote from the end wall
of the measuring chamber and having its bottom in close proximity
to the end wall. The blind bores are sealed by a stopper or plug.
This sealing of the two magnets in the measuring wheel guarantees
that the flow meter employing the pick-up arrangement of this invention
is not subject to any limitations as regards to the applicable media
and consequently the arrangement of this invention can be used also
in flow meters for strongly aggressive media.
The measuring wheel can be an oval gear which during its rotation
drive the two magnets at a non-uniform speed. In order to produce
uniformly spaced measuring pulses during each rotation, that is
a pulse sequence of constant frequency, the Wiegand wires are distributed
on the jacket of the pick-up cylinder at non-uniform spacings from
each other so as to compensate for the non-uniformity of the rotation.
This arrangement is of particular importance in flow meters in which
the output pulses are employed for regulating purposes requiring
a constant frequency.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself however both as to its construction and its method
of operation together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a longitudinal section of a flow meter, shown on an enlarged
scale, having oval measuring gears of small nominal width and embodying
the pulse pick-up arrangement of this invention;
FIG. 2 is a schematic front view of oval measuring gears arranged
in the measuring chamber of the flow meter;
FIG. 3 is a front view of a cut-away part of the pick-up cylinder
in the arrangement of this invention, shown with axial parallel
grooves on its jacket with inserted Wiegand wires; and
FIG. 4 shows schematically a non-regular distribution of Wiegand
wires on the jacket of the pick-cylinder.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The oval gear counter of small width is illustrated in FIGS. 1
through 3. It consists of a counter housing 1 defining a measuring
chamber 2 in which two oval gears 3 and 4 rotate on fixed shafts
5 and 6. The open front side 7 of measuring chamber 2 is closed
by a housing cover 8 of a non-magnetic material which forms the
front end wall of the measuring chamber. The housing cover 8 is
formed with a cylindrical well 11 whose axis 13 is in alignment
with the axis of rotation of the counting or measuring gear 3. The
well 11 extends to such a depth that the partition 15 between the
bottom wall 14 of the well and the front end wall 7 of the measuring
chamber is relatively thin, considering the strongly enlarged scale
of the illustration.
The two bar magnets 9 and 10 are diametrically opposed relative
to the shaft 5 and are located in the end portions of the large
axis of the oval gear 3. The diameter of a pick-up cylinder 12
as mentioned before, corresponds or exceeds the range of the two
bar magnets 9 and 10. The end portion of the pick-up cylinder 12
facing the two magnets 9 and 10 is provided with a circumferential
annular groove 17 in which sensing coil 18 is accommodated. Between
the end face 14 of the pick-up cylinder 12 and the annular groove
17 is only a thin collar or flange 20 left for supporting the ends
of Wiegand wires 21 as it will be explained below. In the cylindrical
jacket of pick-up cylinder 12 adjoining the opposite end of the
annular groove 17 there are provided axis parallel longitudinal
grooves 22 for supporting outer parts of the Wiegand wires 21. The
outer end of the pick-up cylinder 12 remote from the measuring gear
supports a pole ring 23 of a magnetically conductive material which
is inserted on the outer end of the pick-up cylinder and snugly
engages the end portions of Wiegand wires 21. The pole ring together
with Wiegand wires, sensing coil and the pick-up cylinder form a
compact structural unit which is as a one piece insertable into
the well 11. After insertion of the pick-up unit into the well,
the latter is sealed by a sealing ring 25 and closed by a cover
plate 24 which is secured to the housing cover 8 by screws.
The bar magnets 9 and 10 are inserted into the blind bores 26 in
the oval gear 3 with opposite polarities and the pole surfaces of
these magnets extend to the close proximity of the front end wall
7 of the measuring chamber. The magnets are sealed in the assigned
blind bores 26 by stoppers or closing plugs 27.
Referring to FIG. 2 the counter housing 1 is provided with an
inlet 28 and an opposite outlet 29 communicating with the measuring
chamber 2 midway between the shafts 5 and 6. The measured medium
flowing through the measuring chamber in the direction indicated
by arrow sets the two oval gears 3 and 4 into rotation about the
fixed shafts 5 and 6. The oval gears are provided with bearing bushings
30 and 31 (FIG. 1). Rotary magnetic field produced by magnet 9 is
conducted by successive Wiegand wires 21 and closed by the magnetic
short-circuit in the pole ring 23 and returned along the opposite
Wiegand wires into the other magnet 10. Due to this resulting magnetic
loop extending along the Wiegand wires 21 and continuously changing
in fast sequence its polarity, strong magnetic pulses are generated
in the Wiegand wires which in turn induce strong electric voltage
pulses in the sensing coil 18. The coil 18 is connected via connection
wire 32 to electrical terminals 33 and to a connection cable 34.
FIG. 3 shows an embodiment where the Wiegand wires 21 are uniformly
distributed in the longitudinal grooves 20 22 on the jacket 16
of the pick-up cylinder 12.
In the case of oval measuring gears where the rotary speed of the
magnets is not uniform, a non-uniform distribution of the Wiegand
wires 21 on the outer surface of the pick-up cylinder is used so
that the non-uniform rotation of the oval gears 3 and 4 is neutralized.
The central angle between respective radii 35 passing through the
wires varies in synchronism with the variation of the circumferential
speed of the oval gear 3 during one revolution, namely twice between
a minimum and a maximum value.
It will be understood that each of the elements described above
or two more together may also find a useful application in other
types of constructions differing from the types described above.
While the invention has been illustrated and described as embodied
in a specific example of a pulse counter for use with flow meters
of flat design, it is not intended to be limited to the details
shown since various modifications and structural changes may be
made without departing in any way from the spirit of the present
invention.
Without further analysis the foregoing will so fully reveal the
gist of the present invention that others can by applying current
knowledge, readily adapt it for various applications without omitting
features that from the standpoint of prior art fairly constitute
essential characteristics of the generic of specific aspects. |