Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
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Field of the Invention
The invention relates to a tank level measur-
ing device comprising a probe fixed to a rope paid
5 out by a drum and including a take-up motor enga2ing
the shaft of the drum and maintaining the rope under
tension, and further including an electrical indicat-
ing means acted by the shaft of the drum.
Tank level measuring devices of this kind are
10 ~enerally known and are employed, for instance, for
the continuous moni-toring o~ the level in petroleum
tanks. The probe of such tank level measuring devices
consists e.g. of an axially magnetized permanent mag-
netic rod suspended from a rope within a tube inside
15 the tank and adapted to be lifted and lowered therein,
or of a float or a sensing plate having a correspond-
ing guide means. Lifting is effected by means of a
motor acting on the drum shaft which in turn carries
the drum taking up the rope. The motor is designed
20 SUCh that it will continuously tension the rope support-
ing the probe.
On the tube, which passes vertically through the
the tank and receives the probe, for instance a spheri-
cal float is movably supported. The spherical float
consists of a hollow sphere in which there is disposed
an annular body of similarly axially magnetized permanent
magnetic columns which are oriented ~ertically. As the
spherical float is lifted and lowered the probe will be
taken along and will thus indicate the level of the liquid
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in the tank. In another embodiment a float which is
directly coupled to the rope slides up and down along
a vertical ~uide means in the tank and indicates the
liquid level in the tank.
A similar embodiment in employed for sensing
the liquid level by means of a sensing plate.
In a measuring device disclosed ln DE-OS
24 26 085 the drum shaft drives an angle coder through
a reducing gear unit capable of transforming the angular
10 position of the shaft into a digital electrical signal
which in parallel bit, binary coded form may be trans-
ferred to receivinæ and displaying means.
DESCRIPTION OF THE PRIOR ART
Level indication by means of the prior art tank
15 level measuring devices is extremely inaccurake and thus
unsatisfactory. For instance, the interaction between
spherical float and probe results in offsets of the meaY
ured value which are unavoidable because of slippage.
Measurement errors due to the variation~ in density of
20 the medium to be measured in case of major temperature
fluctuations are also unavoidable. Further errors are
due to tooth clearance and friction in the reducing
gear unit, to the conversion of the rotary motion into
electrical analog values because of linearity and trans-
25 ducer errors, to the conversion of current in the powerconverter, and finally toan additional tolerance error
in the A~D-converter. Due to these numerous tolerances
and error sources the errors in measurement are considerable,
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so that the stock contained in a tank can be de-termined only
very inaccurately.
It is the object of the present invention to provide
a tank level measuring device having a higher measuring accu-
racy.
In accordance wi-th the invention, there is provided
a liquid level measuring system, comprising a hollow spherical
float for following the level of said liquid, said Eloa-t having
a plurality of magnets surrounding a cylindrical passage dia-
metrically through said float, a probe comprising a magnetfor being retained in the field of said float magnets to Eollow
vertical movement of said float, a flexible line attached to
said probe, a drum having said flexible line wound thereon,
a hollow tube located beneath said drum to permit said flexible
line to extend therein, means for biasing said drum for rotation
to take up slack in said flexible line, said drum having a
shaft fixed thereto for rotation therewith, a rotary pulse
generator having a shaft and comprising a slotted disc and
light detectors for scanning said disc, and means for direct]y
coupling said generator shaft to said drum shaf-t whereby said
pulse generator may be employed for providing digital readings
of said liquid level, said hollow tube having a closed lower
end to exclude said liquid and extending through said Eloat
cylindrical passage for permitting free vertical movement oE
said float while confining it to a substantially vertical path.
Due to the direct coupling of -the drum shaEt -to the
generator shaft the -tooth clearance and friction and -therewith
the measurement errors caused by the insertion of -the reducing
gear are avoided. The ro-tary pulse generator equipped with
the flying spot scanned slotted disc permits an extremely high
sequence and thereby an extraodrinary accuracy. The rapid
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pulse sequence has a definite influence on the accuracy of
the measurement. It is possible without difEiculties to operate
with a pulse sequence of one pulse per 1 mm ropeway. Too fast
changing of the display can be avoided by using a Ram-Memory
in the digital display.
For transmittance only four lines (two for the voltage
supply and one each for the counting back and forth) as compared
to eighteen lines with the angle coder.
From DE-GB 7003885 it is known to use an electrical
transmitter for display, e.g. an pulse generator, a potentio-
meter or a synchro system. There is no disclosure as tothe con-
structional features of the electrical display.
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With increased accuracy the manufacturing costs of
the present measuring device are considerably reduced.
The ~oregoing and other objects and benefits of
the invention will be more fully set forth below in con
nection with the best mode contemplated by the inven-
tors of carrying out the invention, and in connection
with which there are illustrations provided in the draw~
ings, wherein:
The figure of drawings is a schematic showing
of the apparatus mounted on the top of a tank contain-
ing liquid the level of which is being measured.
DESCRIPTION OF THE PREFERRED EMBODIMENT
., . . . .. . _ _ ~ . . . _ . _
Referring to the drawing figure, there is illustra~
ted a measuring device 7 which is mounted on the cover
3 of e.g. a petroleum or water tank. This measuring
device 7 comprises a casing 9 seated on the top 11 of
the cover 3. A tube 15, which extends to the bottom
17 of the tank, is passed through a bore 13 in the tank
cover. The tube 15 is resiliently supported on the bot-
tom 17 by means of a pad 19. A probe 23 is suspended
from a rope 21 within the tube. This probe 23 is a
permaner.t magnetic rod which is axially magnetized and
suspended vertically.
A spherical float 25 is mounted for up- and
downward sliding movement along the tube 15. The sphe-
rical float i3 floating in the respective region o~ the
surface of the liquid in the tank 5.
The spherical float 25 consists of a hollow sphere 27
through which a sleeve-like through-passage 29 extends.
An annular array of further permanent magnet rods 33
is vertically ai3posed on the sleeve wall ~1. In this
5 way the permanent magnet rods 23 of the spherical float
25 will take along the probe 23 as the spherical float
25 moves longitudinally along the tube 15. Buoyancy is
imparted to the spherical float 25 by gas or air charge
in the hollow space 35.
Inside the casing 9 of the measuring device 7
a rope drum 39 is supported with its drum shaft 41
between two supporting walls 37. A spring motor 49
acts on the drum shaft 41, said drum shaft extending
through the supporting walls 37. The spring motor 39
15 is capable of always keeping the rope tensioned.
By means of a stub shaft 51 the drum shaft 41
also drives a reducing gear unit 53 which turns a pair
of pointers 55 in front of an indicating dial 57. The
reducing gear unit 53, the pair of pointers 55 and the
20 indicating aial 57 form an indicatinæ means 61 within
a casing 59.
The drive shaft 65 of a rotary pulse generator
67 is directly coupled to the drum shaft 41 via a coupl-
ing 63. The rotary pulse gererator 67 is a component
in which, for instance a slotted disk is scanned by
means of one or several light detectors. The light
pulses produced during the scanning operation are con-
verted into electrical pulses from which the built-in
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electronic circuit forms digital readings. Display
is effected, for instance, by means of a digital dis-
play device 69 disposed either in the viscinity of, or
remote from, the measuring device. Further pulses may
be transmitted via lines 71 to a central unit where
the measured values can be continually stored and
processed.
The counter has to operate with a rapid pulse
se~uence to accomplish the measurements with accuracy.
For this reason, the pulse generator is layed out such
that per 1 mm ropeway at least one pulse is released.
A Ram-Memory being provided in the digital display
69 retain~ the obtained measured values. The retained
values in turn serve as basis data when the measured
values very to higher or lower values.
While a particular embodiment of the invention
has been described above in considerable detail, in
accordance with the applicable statutes, this is not
to be taken as limiting the invention but merely as
being descriptive thereof.
