Abstrict A bulk flow meter having an inclined baffle plate disposed within
a conveying space in the path of a bulk material to be measured
is provided. The meter includes a measuring chamber that is separated
from the conveying space by a partition. The baffle plate is carried
by a baffle plate support which is horizontally movable under the
impact of the bulk material and which includes a rod-shaped connecting
member that extends through an opening in the partition. A dust
protector is provided for preventing dirt and dust from entering
the measuring chamber from the conveying space. The dust protector
includes a rigid tube that surrounds a portion of the length of
the rod-shaped connecting member on the baffle-side of the partition.
Flexible diaphragms are provided for connecting the rigid tube to
the partition and to the rod-shaped connecting member.
Claims I claim:
1. Bulk flow meter comprising a measuring chamber separated from
the conveying space by a partition, a baffle plate disposed in the
conveying space inclined in the fall path of the bulk material to
be measured, a horizontally movable baffle plate support which comprises
a rod-shaped connecting member projecting through an opening in
the partition for supporting the baffle plate, rigid tube means
disposed on the baffle plate side of the partition and surrounding
a portion of the rod-shaped connecting member, the inner diameter
of said rigid tube means being greater than the outer diameter of
the rod-shaped connecting member, a first flexible diaphragm connecting
one end of said rigid tube means in dust-tight manner to the partition,
and a second flexible diaphragm connecting the other end of said
rigid tube means in dust-tight manner to the rod-shaped connecting
member.
2. Bulk flow meter according to claim 1 in which the rigid tube
means is connected by the first diaphragm to the edge of the opening
in the partition and the outer diameter of the rigid tube means
is less than the diameter of the opening.
3. Bulk flow meter according to claim 1 in which an annular first
flange surrounding the opening is connected to the partition in
dust-tight manner and the rigid tube means is connected by the first
diaphragm to the periphery of the first annular flange.
4. Bulk flow meter according to claim 3 in which a second flange
is connected to the rod-shaped connecting member in dust-tight manner
and the rigid tube means is connected by the second diaphragm to
the periphery of the second flange.
5. Bulk flow meter according to claim 4 in which the outer diameter
of the rigid tube means is less than the outer diameter of each
flange.
6. Bulk flow meter according to claim 5 in which the two flanges
are provided with plate-shaped recesses at the end surfaces facing
each other.
7. Bulk flow meter according to claim 4 in which the inner diameter
of the second flange is less than the inner diameter of the first
flange and the outer diameter of the rigid tube means lies between
the inner diameter of the first flange and the outer diameter of
the second flange.
8. Bulk flow meter according to claim 1 in which the rigid tube
means comprises a plurality of tube sections of different diameter
and the tube sections are connected together in dust-tight manner
by flexible diaphragms.
9. Bulk flow meter according to claim 1 comprising a covering a
flexible diaphragm material which surrounds the outer surface of
the rigid tube means, the two ends of said covering being connected
in dust-tight manner to the partition and the rod-shaped connecting
member, the covering having radially extending sections forming
the diaphragms.
10. Bulk flow meter according to claim 1 in which the diaphragms
have free annular surfaces having radial widths, with the radial
widths very small compared with a total axial length of the rigid
tube means.
11. Bulk flow meter according to claim 1 in which the diaphragms
are formed from a material consisting essentially of silicone rubber.
12. Bulk flow meter according to claim 4 comprising a covering
of flexible diaphragm material which surrounds the outer surface
of the rigid tube means, the two ends of said covering being connected
in dust-tight manner to the partition and the flanges disposed on
the rod-shaped connecting member, the covering having radially extending
sections forming the diaphragms.
Description The invention relates to a bulk flow meter comprising a measuring
chamber separated from the conveying space by a partition, a baffle
plate disposed in the conveying space inclined in the fall path
of the bulk material to be measured and a horizontally adjustable
baffle plate support which comprises a rod-shaped connecting member
projecting through an opening in the partition.
A bulk material flow meter of this type is known for example from
DE-PS No. 3149715. The purpose of separating the measuring chamber
from the conveying space is to protect the sensitive components
of the bulk flow meter accommodated in the measuring chamber from
the dirt and dust obtaining in the conveying space because these
sensitive components can be greatly impaired in their function by
dirt and dust and this can lead to measurement errors or even to
complete failure of the device.
However, in bulk flow meters of the type mentioned at the beginning
there is the problem that in the partition an opening must be provided
for the passage of the rod-shaped connecting member carrying the
baffle or impact plate. This opening must be large enough to permit
the maximum displacement of the connecting member. Thus, there is
necessarily a gap through which dirt and dust can still penetrate
into the measuring chamber if no additional sealing is provided.
The sealing of the opening in the partition is problematical in
particular when the adjustment of the connecting member takes place
transversely of the opening as is in particular the case in bulk
flow meters in which the baffle plate support is linearly displaceable
by a straight-line guide mechanism and the baffle plate is disposed
laterally adjacent the baffle plate support. In this case the sealing
must be formed such that it permits the transverse movement of the
rod-shaped connecting member without exerting thereon a resistance
falsifying the measured quantity.
It has however been found in particular that the measuring accuracy
of such bulk flow meters is impaired when the pressure fluctuations
generated in the conveying space by the falling bulk material are
transmitted to the measuring chamber. However, conventional seals
which offer little resistance to the movement of the rod-shaped
connecting member, such as flexible bellows, transmit pressure fluctuations
practically without any attenuation.
The problem underlying the invention is to provide a bulk flow
meter of the type mentioned at the beginning which has a very simple
and robust dust protection means which provides complete separation
of the measuring chamber from the conveying space, substantially
prevents transfer of pressure fluctuations between the conveying
space and the measuring chamber and permits any displacement of
the baffle plate support, in particular also transversely of the
axis of the opening, without appreciable resistance or return forces
which could falsify the measurement result.
According to the invention this problem is solved in a bulk flow
meter of the type mentioned at the beginning in that the portion
of the rod-shaped connecting member projecting through the opening
in the partition is surrounded over a part of its length by a rigid
tube whose diameter is greater than the diameter of the rod-shaped
connecting member, that the one end of the rigid tube is connected
by a first flexible diaphragm in dust-tight manner to the partition
and that the other end of the rigid tube is connected by a second
flexible diaphragm in dust-tight manner to the rod-shaped connecting
member.
In the bulk flow meter according to the invention the opening provided
in the partition is completely sealed by the dust protection means
consisting of the tube and the two diaphragms so that any penetration
of dirt or dust from the conveying space into the measuring chamber
is prevented. The two diaphragms are offset with respect to each
other by the length of the tube so that they permit without appreciable
resistance any movement of the rod-shaped connecting member relatively
to the opening, in particular also transversely of the axis of the
opening. Such a transverse movement causes only a tilting of the
tube which is allowed by bending of the two diaphragms. Diaphragms
are particularly suitable for performing such bendings with small
force expenditure and almost unlimited frequency without their strength
being impaired.
Pressure differences obtaining between the conveying space and
the measuring chamber can be transmitted only via the annular diaphragm
surfaces present on the one hand between the rigid tube and the
partition and on the other between the rigid tube and the rod-shaped
connecting member. These annular diaphragm surfaces can be kept
very narrow because they need only take up the tilting movement
of the rigid tube corresponding to the maximum displacement of the
baffle plate support. The maximum displacement of the baffle plate
support in conventional bulk flow meters of this type is only a
few millimeters so that the radial width of the annular diaphragm
surfaces can also be kept to the order of magnitude of a few millimeters.
On the other hand, no pressure can be transferred via the surface
of the rigid tube which forms by far the greater part of the area
of the dust protection means subjected to the pressure difference
.
Further features and advantages of the invention will be apparent
from the following description of an example of embodiment illustrated
in the drawings, wherein:
FIG. 1 is a schematic side view of a bulk flow meter in which the
invention can be used,
FIG. 2 is a plan view of the bulk flow meter of FIG. 1 with the
upper side of the housing enclosing the metering chamber removed,
FIG. 3 is an enlarged illustration of a first example of embodiment
of the dust protection means of the bulk flow meter of FIGS. 1 and
2 in the rest position of the impact or baffle plate,
FIG. 4 is a corresponding illustration of the dust protection means
of FIG. 3 at maximum displacement of the baffle plate,
FIG. 5 is an enlarged illustration of a second example of embodiment
of the dust protection means and
FIG. 6 is an enlarged illustration of a third example of embodiment
of the dust protection means.
The bulk flow meter 10 illustrated very schematically in FIGS.
1 and 2 has a housing 12 which encloses a measuring chamber 14 and
an impact or baffle plate 16 which is arranged outside the housing
12 in a conveying space 18. The baffle plate 16 lies inclined in
the fall path of bulk material 20 the throughput of which is to
be measured and which is supplied to the conveying space 18 in any
suitable manner, for example via a chute 22. The baffle plate 16
is carried by a baffle plate support 24 which is disposed in the
interior of the housing 12 and which is formed so that it permits
a horizontal displacement of the baffle plate 12. The baffle plate
support 24 illustrated as example in FIG. 2 comprises for this purpose
a beam 26 which is axially displaceably disposed in a frame 36 formed
from frame-like side members 28 30 and connecting members 32 34.
Springs 42 and 44 connecting the beam 26 to the frame 36 tend to
hold the beam 26 in a defined rest position and oppose a movement
of the beam 26 out of this rest position with a progressive spring
force.
The baffle plate support 24 further includes a support rod 46 which
extends transversely of the longitudinal axis of the beam 26 through
an opening 48 in the front wall 50 of the housing 12. The support
rod 46 is connected in the measuring chamber 14 rigidly to the beam
26 whilst at the end of the support rod 46 projecting outwardly
into the conveying space 18 the impact or baffle plate 16 is secured.
The support rod 46 thus serves as rod-shaped connecting member between
the beam 26 and the baffle plate 16.
Corresponding to the known mode of operation of bulk flow meters
of this type the bulk material falling onto the inclined baffle
plate 16 exerts an impact force I which is directed perpendicularly
to the baffle plate and which can be broken down into a horizontal
component H and a vertical component V (FIG. 1). The horizontal
force component H tends to move the baffle plate 16 and the baffle
plate support 24 connected rigidly thereto against the force of
the springs 42 44. The magnitude of the horizontal force component
or the travel caused thereby is a measure of the impact force or
momentum exerted on the baffle plate which in turn with a known
drop and density of the bulk material 20 is a measure of the throughput.
The force or travel sensor 52 disposed in the measuring chamber
14 responds to the horizontal force component exerted or the travel
caused thereby and thus furnishes an output signal which is a measure
of the throughput.
The purpose of the housing 12 is to protect the measuring chamber
14 and the components of the bulk flow meter disposed therein from
the dust and dirt obtaining in the conveying space 18. Settlements
of bulk material, dirt and dust can cause measurement errors or
lead to total failure of the device.
The sole connection between the measuring chamber 14 and the conveying
space 18 is at the point of the opening 48 in the front partition
50. This opening must be large enough to permit maximum displacement
of the support rod 46.
To prevent penetration of dirt and dust through the opening 48
a dust protection means 60 is provided of which various embodiments
are illustrated to an enlarged scale in FIGS. 3 to 6.
Apparent in FIGS. 3 to 6 are the portion of the front wall 50 of
the housing 12 surrounding the opening 48 and forming the partition
between the measuring chamber 14 and the conveying space 18 and
the support rod 46 passing through the opening 48.
In the embodiment illustrated in FIGS. 3 and 4 the dust protection
means 60 is formed by a rigid tube 62 and two flexible diaphragms
64 and 66. The rigid tube 62 consists of metal or a rigid plastic
and surrounds over a certain length the portion of the support rod
46 projecting out of the opening 48. Its diameter is greater than
the diameter of the support rod 46 but less than the diameter of
the opening 48. The diaphragm 64 connects the end of the tube 62
facing the opening 48 in dust-tight manner to the edge of said opening
48. The diaphragm 66 connects the other end of the tube 62 in dust-tight
manner to the support rod 46. Each of the two diaphragms 64 and
66 is thus annular and dimensioned such that it completely covers
the annular gap between the tube 62 and the edge of the opening
48 or the periphery of the support rod 46.
FIG. 3 shows the parts of the dust protection means 60 in the rest
position of the baffle plate support 24 i.e. when no fcrce is exerted
by bulk material on the baffle plate 16. The support rod 46 is then
substantially in the centre of the opening 48 and the diaphragms
64 and 66 hold the tube 62 substantially coaxially to the support
rod 46.
In FIG. 4 the same parts assume the position corresponding to the
maximum adjustment of the baffle plate support 24. The support rod
46 is then laterally offset with respect to the centre axis of the
opening 48. The longitudinal axis of the tube 62 is tilted with
respect to its rest position through an angle .alpha.. This tilting
is made possible by the flexibility of the diaphragms 64 and 66.
The diaphragms exert on the support rod 46 a certain return force
which opposes the measuring force and is undesirable because it
falsifies the measurement result. The return force is a function
of the properties of the diaphragm, in particular the diaphragm
material employed, the weight of the tube and the geometrical dimensions
of the entire system.
With regard to the geometrical dimensions it can be seen from FIG.
4 that the internal diameter of the tube 62 must be so dimensioned
that the support rod 46 in the position of maximum displacement
still does not strike the tube 62.
To obtain the minimum possible return forces the use of very flexible
diaphragms is favourable but there are limits in this respect due
to the requirements of adequate mechanical strength and continuous
loadability. Preferably, the diaphragms consist of silicone rubber.
Their edge portions may be connected to the partition 50 the tube
62 and the support rod 46 by clips.
Under otherwise identical conditions the return forces are the
smaller the longer the tube 62. The tube length L can however not
be made of any desired magnitude because of the space conditions
obtaining. Moreover, the reduction of the return force with increasing
tube length becomes progressively smaller so that from a certain
tube length onwards no appreciable gain is obtained.
If there is a pressure difference between the measuring chamber
14 and the conveying space 18 on either side of the partition 50
the free annular surfaces of the diaphragms 64 and 66 are the sole
surfaces of the dust protection means 60 via which the pressure
difference can be transferred because a pressure transfer is not
possible via the surface of the rigid tube 62. It is therefore favourable
as regards the problem of pressure transfer to keep the radial widths
of the free annular surfaces of the diaphragms 64 and 66 i.e. the
width B1 of the diaphragm 61 and the width B2 of the diaphragm 66
as small as possible. These widths B1 and B2 also depend on the
maximum displacement of the support rod 46. It is pointed out in
this connection that the illustration in FIGS. 3 and 4 is not true
to scale and in particular the displacement of the support rod 46
shown in FIG. 4 has been very much exaggerated for clarity. In reality
it is only a few millimeters when the sensor 52 is a displacement
sensor and practically zero when the sensor 42 is a force sensor.
The radial widths B1 and B2 of the diaphragms 64 and 66 may therefore
also be kept to the order of magnitude of a few millimeters. They
are in any case very small compared with the length L of the rigid
tube 62. For example, with a tube length L of about 200 mm each
width B1 and B2 may be between about 5 and 15 mm.
FIG. 5 shows another example of embodiment of the dust protection
means. In this case at the edge zone of the partition 50 surrounding
the opening 48 an annular flange 70 is connected in dust-tight manner
to the partition 50. This can be done by any known manner of connecting
ensuring a dust-tight seal. The flange 70 is so arranged that its
opening 72 aligns with the opening 48 of the partition 50. The end
side of the flange 70 remote from the partition 50 has a plate-shaped
recess 74.
A further annular flange 76 is connected in dust-tight manner to
the support rod 46. The end side of the flange 76 facing the flange
70 has a plate-shaped recess 78. The two flanges 70 and 72 have
about the same external diameter.
Between the two flanges 70 and 72 a rigid tube 80 surrounding the
support rod 46 is disposed and the length of said tube is substantially
equal to the distance between the two flanges 70 and 76. The internal
diameter of the tube 80 is substantially greater than the diameter
of the support rod 46 and its external diameter is less than the
external diameter of each flange 70 72.
A hose-like covering 82 of flexible material, for example silicone
rubber, surrounds in tight engagement the rigid tube 80 and the
outer surfaces of the two flanges 70 and 76 to which the hose-like
covering 82 is connected in dust-tight manner round the periphery.
The hose-like covering or envelope 82 thus forms a continuous dust-tight
seal from the partition 50 up to the flange 76.
An annular portion of the covering 82 which extends substantially
radially between the outer surface of the flange 79 and the rigid
tube 80 and which covers the plate-shaped recess 74 of the flange
70 forms a first flexible diaphragm 84. In the same manner, an annular
portion of the covering 82 extending substantially radially between
the outer surface of the flange 76 and the rigid tube 80 and covering
the plate-shaped recess 78 of the flange 76 forms a second flexible
diaphragm 86.
It is immediately apparent that the suspension of the rigid tube
80 at the two flexible diaphragms 84 and 86 permits a transverse
displacement of the support rod 46 with tilting of the rigid tube
80 in the same manner as illustrated in FIG. 4 for the first embodiment.
The tilting of the rigid tube 80 is permitted by the plate-shaped
recesses 72 and 78 in the flanges 70 76.
In the embodiment of FIG. 5 the two diaphragms 84 and 86 lie at
the outer side of the rigid tube 80 and at the facing end sides
of the flanges 70 76. The radial widths B1 of the diaphragm 84
and B2 of the diaphragm 86 which are cf equal magnitude in the
example of embodiment illustrated, should again be kept as small
as possible to reduce the problem of pressure transfer, as explained
above with reference to the example of embodiment of FIGS. 3 and
4.
FIG. 6 shows a third example of embodiment of the dust protection
means which is formed by modifying the example of embodiment of
FIG. 5. As in the latter, at the partition 50 the annular flange
70 provided with the plate-shaped recess 74 is arranged in dust-tight
manner such that its opening 72 aligns with the opening 48 in the
partition 50. Furthermore, a second flange 88 is again connected
in dust-tight manner to the support rod 46 but in this case the
external diameter of the second flange 88 is less than the external
diameter of the first flange 70.
The rigid tube 90 is divided into several (three in the example
illustrated) annular tube sections 91 92 93 of different diameters.
The diameters of the tube sections decrease stepwise with increasing
distance from the partition 50 the greatest diameter, i.e. the
diameter of the tube section 91 being less than the diameter of
the annular flange 70 and the smallest diameter, i.e. the diameter
of the tube section 93 being greater than the diameter of the flange
88. The sum of the lengths of the tube sections 91 92 and 93 is
substantially equal to the distance between the flanges 70 and 88.
The external surfaces of the tube sections 90 92 93 and the surfaces
of the flanges 70 and 88 are again enclosed by a closely engaging
hose-like covering or envelope 94 of flexible diaphragm material,
for example silicone rubber, and the end portions of the hose-like
covering 94 are connected to the outer surfaces of the flanges 70
and 88 in dust-tight manner round the periphery thereof. The annular
sections of the hose-like covering 94 which extend substantially
radially and which cover the intermediate spaces between the outer
surfaces of the flanges and the outer tube sections 91 93 and the
intermediate spaces between the individual tube sections 91-92 and
92-93 form flexible annular diaphragms 95 96 97 98 which again
permit transverse displacement of the support rod 46 with tilting
of the tube sections 91 92 93. The effective diaphragm area in
this case depends on the sum of all the radial widths B1 B2 B3
B4 of the diaphragms 95 96 97 98 for which once again the dimensioning
rule explained above applies.
The dust protection means described is of course not limited to
use in the bulk flow meter chosen only by way of example. In particular,
it is independent of the construction of the baffle plate support
usedand the nature dependent thereon of the movement of the rod-like
connecting member passing through the opening 48. In particular,
it is equally well suited to bulk flow meters in which the baffle
plate support is not displaced parallel but executes a rotational
movement about an axis lying in the measuring chamber. |