Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SENSOR
Background of the invention
The invention relates to a sensor for an appara-
tus for measuring the level and/or the quantity of a liquid
medium in a vessel, for examp:Le a pressure vessel, provided
with a carrier which may be mounted in the wall of the
vessel, a first pipe fastened to the carrier and a second
pipe positioned concentrically and insulated within the
first pipe, which second pipe may be connected through a
bushing member positioned in the carrier.
A sensor of this type may for example be applied
for measuring the level in a pressure vessel for liquid gas
in a motor car. The two pipes together form a capacitor,
of which the capacity value is dependent on the presence
of the liquid gas between the two pipes. By means of an
electronic circuit the level or the quantity of gas which
is still present in the pressure vessel may be determined
on the basis of the capacity value, so that the supply of
fuel may be indicated to the user.
It is also possible to apply a sensor of this
kind for determining the level and/or the quantity of the
liquid gas in a storage tank with a fuelling station. Although
the known sensor in practice functions satisfactorily for
the application in a fuel tank, the accuracy for application
in storage tanks may leave much to be desired, whereas with
such applications it is moreover desirable to obtain a clear
signalling at certain levels.
Summ~y of the invention
t is an object of the invention to provide a
sensor of the above-mentioned type, which is particularly
suitable for application in storage tanks and the like.
For this purpose the sensor according to the invention
is characterized in that a conductor is wound at least locally on
the first pipe the pitch of the winding of the sensor attentively
increasing and decreasing along the length of the horn pipe the
portions of said winding having increased pitch at preselected
positions, which conductor is insulated with respect to the first
pipe and may be connected through a bush~ng member positioned in
the carrier.
In this manner a second capacitor is obtained, by which
with a varyiny level a larger capacity variation is attained, so
that a more accurate measuring is possible as the capacitate
increases in a step like fashion to clearly signal the level
reaching the preselected positions.
This clear level signalling is especially important
with the application in storage tanks. In this case the filler
valve should be closed at a filling of 90%, whereas at 85%
filling a presignalling for closing the filler valve should be
given. Furthermore with the sensor according to the invention it
is possible to give a first warning, sig~al at a filling of 30%,
by which it is signalled to the user that it is necessary to
order a new supply. Hereafter for example a second signal may be
given at 20~, whereas at a filling of 10~ the take-off valve can5 be closed. srief description of the drawinqs
Th~ invention will hereinafter be further elucidated
with reference to the drawings, in which two embodiments are
shown.
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1 2~47~3
Fig. l shows schematically a first embodiment of the
sensor according to the inv~ntion.
Fig. 2 shows schematically a second embodiment of the
sensor according to the invention.
Referring to fig. 1, there is shown a sensor 1 to be
used in an apparatus for measurlng the level and/or the quantity
of a liquid medium in a vessel, for example for measuring ~he
quantity of liquid gas in a supply tank. The sensor 1 is
provided with a carrier 2 which may be mounted in the wall of the
supply tank, a first pipe 3 fastened to the carrier 2 and a
second pipe 4 positioned concentrically within the first pipe 3.
This second pipe 4 is mounted in the first pipe 3 by means of two
insulating centering caps 5. The two pipes 3, 4 consist of metal
and together iorm a capacitor. The first pipe 3 is connected to
mass electrical earth by means of its fastening to the carrier 2,
whereas the second pipe 4 may be connected to a schematically
indicated electronic circuit 7 through a bushing member 6
positioned in the carrier Z. The bushing member 6 preferably
consists of a so-called glass bushing, which has particularly
favourable mechanical properties.
The capacity value of the capacitor formed by the two
pipes 3, 4 is dependent on the level o~ the liquid gas in the
supply tank, so that the electronic circuit 7 can in a simple
manner determine the quantity of liquid gas present in the supply
tank from this capacity value.
With the sensor shown an insulated conductor 8 is wound
locally on the first pipe 3, which conductor may be connected to
the electronic circuit 7 through a second bushing member 9
mounted in the carrier 2. The bushing member
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g preferably consists oE a glass bushing. The local windings of
the conductor 8 are obtained by winding the conductor with a
variable pitch on the pipe 3. As an alternative it is also
possible to wind the conductor with a fixed pitch on the pipe 3.
In this case a second capacitor is obtained, by which the total
capacity value is increased and a more accurate measuring is
possible. The conductor 8 may also be connected to the bushing
member 6 of the second pipe 4.
The local application of the windings of the conductor
8 have the advantage that in a particularly accurate way certain
important levsls of the liquid gas in the supply tank may be
signalled. In the embodiment shown in the drawing; hlgh pitch
positions of windings hava been provided successively at selected
filling levels of for example 6, 10, 20, 30, 50, 80, 85, and 90%
with the lower level being at the bottom as shown in Figure 1.
By this the electronic circuit 7 receives a clear signalling of
these various levels. At 85% for example a presignalling for
closing the filler valve may be given, whereas at 90% the filler
valve is automatically closed. Lower levels may be used to
indicate that the stock of liquid gas has to be replenished,
whereby at a certain minimum level of for example 10 or 6% the
take- off valve is closed.
In order to prevent damage of the insulated conductor 8
a protection pipe 10 has been applied, which encloses the
insulated conductor 8.
Fi~. 2 shows a sensor 20, which mainly corresponds with
the sensor 1 of fig. 1. The sensor 20 is in particular to be
used as measuring means for measurin~ the contents of a supply
tank for example liquid gas, with
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which a protection has been provided, which during filling
when reaching a filling level of 90% closes the filler valve
of the supply tank, so that no dangerous situations may arise.
The sensor 20 in the same manner as the sensor 1
is provided with a carrier 21, a first pipe 22 mounted in
a central opening of the carrier 21 and a pipe 23 mounted
concentrically in the first pipe 22. The second pipe 23 is
centred with respect to the first pipe 22 and insulated by
a wire 24 from plastic material helically fastened on the
second pipe 23. The bottom end of the two pipes 22, 23 is
cast into an epoxy material 25. In the bottom end of the
first pipe 22 openings 26 are provided through which the
liquid medium may enter the space between the two pipes
22, 23. The capacity value of the capacitor formed by the
two pipes 22, 23 varies dependent on the level of the liquid
medium in the supply tank and just as with the sensor 1
may be determined by an electronic circuit 27.
In order to avoid dangerous situations when
filling the supply tank, it is necessary to stop the
filling at a filling level of 90~. For this purpose at the
height of this 90% filling level the sensor 20 is provided
with a winding 28, which is mounted on the first pipe 22
and which is insulated with respect to this pipe 22. The
winding 28 together with the pipe 22 forms a second capacitor,
which is connected to a separate protection circuit of the
electronic circuit 27.
The winding 28 is enclosed by a housing 29,
which in the end 30 xemote from the carrier 21 has a number
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of small openings 31. At some distance from the openings
31 in the direction of the carrier 21 one or more large
openings 32 are provided. During filling the liquid medium
when reaching the small openings 31 will first slowly
penetrate in the space between the pipe 22 and the housing
29, by which the capacity value of the capacitor formed by
the pipe 22 and the winding 23 slowly increases. However,
as soon as the medium reaches the openings 32, the said
space is rapidly filled, so that a rapid increase of the
capacity value occurs, which is detected with certainty by
the electronic circuit 27. The sharp increase of the capacity
value means that the maximum filling level of 90~ is attained
and for the sake of safety the filler valve is automatically
closed. By this it is attained that even in the case of
inattention of the operating people no overfilling of the
supply tank is possible.
The second pipe 23 and the winding 28 are in the
same manner as with the sensor 1 connected with the circuit
27 through bushing members in the carrier 21. In this case
the upper end of the pipe 22 is filled with an epoxy material.
For the protection of the sensor 20 a protection
pipe 33 has been mounted around the unit.
The invention is not restricted to the embodi-
ments described hereinbefore, which may be varied in several
ways within the scope of the invention.
It is for example also possible to apply a not
insulated conductor instead of an insulated conductor. In
this case between the pipe 3 and the conductor insulating
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means are provided, which for example are made as axially
extending insulating ribs, which are fastened on the outside
of the pipe 3.
Although in the drawing the conductor has been
; shown with a circular cross-section, the conductor may also
be constructed as a conductive belt.
