DE19925185C2 - Level measuring device - Google Patents

Description

The invention relates to a level measuring device for a Tank.

Level measuring devices have been used for more than 20 years Tanks known in which the buoyancy body of a rotatable gela the float in the area of the liquid level in the liquid in the tank in question is floating. The spin axis of the swimmer, which is usually below the highest possible liquid level is with the input side a mechanical transmission (or a transmission) the one on the output side of which a magnet is mounted. The ones from Level of the liquid dependent angular position of the swim mers is thus transferred to the magnet, its angular position is a measure of the level. The magnet is in close to the outside of the tank. Its turning position is at older embodiments of the known level measuring device device through a housing wall by a second rotation bar mounted magnet detects the mechanically with an pointing device is coupled. This level measuring device  is suitable for tanks in which flammable or explosive any liquids must be stored. Because with the gearbox that is located in the potentially explosive area, none is there visibly their tightness problematic implementation by the Tank wall required.

In later embodiments, the previously known level measuring device direction is the magnet stored outside the tank interior replaced by a magnetic field sensor that works with an electronic the evaluation device is connected. This sensor detects the magnetic field depending on the angular position of the magnet, which is a measure of the level and with the help of the evaluation direction can be converted into a level value.

The used in the known level measuring devices mechanical transmission or the transmission can in the long term need to cause interference. Simple maintenance work is not possible because the gearbox is in the potentially explosive area located. Almost inevitable properties of a mechanical Gearboxes such as slip, lost motion, hooks and above all an im Gear wear occurring over the course of the operating time to measurement inaccuracies.

DE 39 17 497 A1 describes a level sensor with a Permanent magnets. At the end of one in a container for a medium descending pipe is on a pivot bearing two-armed lever mounted, on one lever arm a swim mer is attached, while the other lever arm a permanent carries magnets. Inside the tube is in action area of the permanent magnet a magnetically actuated con contact switch. Depending on the pivoting position of the lever arm, this con Tact switch switched on or off. The known one Level sensors can therefore only detect whether a predetermined level the medium is reached; he is unable to make a con to measure continuous level.  

A level indicator to determine the presence of a liquid speed is shown in DE-OS 20 05 927. This level indicator is structurally very similar to that from DE 39 17 497 A1 known level sensors. At the bottom of a pipe that reaching into a liquid tank from above is a two-armed one Lever rotatably mounted. One sits at the end of one lever arm Float, at the end of the other a permanent magnet. Internally of the tube is in the area of the permanent magnet Reed switch contact arrangement. How this level works the indicator is the same as that of DE 39 17 497 A1 known level sensor.

In DE 26 27 865 A1 a level measuring device is be wrote that is able to maintain a continuous level to eat. In one embodiment it is located outdoors End of an angled lever a float while in the loading realm of the other end, in which the fulcrum of the Lever is located, a permanent magnet is arranged. The Perma Magnet acts on a field plate (Hall probe) with its Help that from the position of the swimmer and thus the perma Magnetic magnetic field is measured to be a measure of to deliver the level. In another embodiment a float moves translationally, its vertical Displacement via a sub formed from two coil springs is transferred to a permanent magnet, which is in near a field plate. In all embodiments the magnetic field sensor (field plate) is in the area of the Medium, which makes maintenance work considerably more difficult. At which he Most embodiment, the swimmer requires a lot of room to move, high accuracy is not expected in the second.

It is an object of the invention to provide a level measuring device create that lie accurate measurement results even in long-term operation finished, low maintenance and inexpensive.  

This object is achieved by a level measuring device with the features of claim 1. Advantageous refinements the invention emerge from the subclaims.

The level measuring device according to the invention for a tank has a float rotatably mounted about an axis of rotation and a tube with a first end and a second end. The Pipe is set up with its second end up to Reach the outside of the tank and is opposite the interior of the tank sealed. In the area of the first end of the tube and outside of the tube is on the axis of rotation of the float Magnet mounted. Opposite the magnet is inside the tube a magnetic field set up for measuring a magnetic field arranged sor, which is set up one of the angle position of the float-dependent signal via an electrical Output line to an evaluation device.

The fact that the pipe abge against the interior of the tank is sealed, the interior of the tube is not in the ex explosive area of the tank. The magnetic field sensor that the angular position of the float and thus the level of the Detected liquid in the tank is therefore not an extreme condition exposed and in particular does not need explosion-proof to be protected. Because the magnetic field sensor has one in the tube Running electrical line with the evaluation device connected, there is no need for a mechanical Transmission. The level measuring device according to the invention is therefore easy to maintain and not disturbing even in continuous operation susceptible. The above mentioned, with a mechanical gear associated disadvantages do not occur. For this reason, lets himself with the level measuring device according to the invention achieve a high measuring accuracy. Furthermore, they are relatively absent high costs for a mechanical transmission or a transmission sion.  

The level measuring device according to the invention is suitable especially for tanks in which flammable or reactive liquid that an explosive Ge can form mixed. The vapor pressure above the liquid level can, depending on the type of tank, well above the atmosphere pressure. Examples are tanks for motor vehicles, rivers siggas tanks and stationary tanks, for example for heating oil, Che micro or fuel. But also for use with non-explosive liquids is the fiction appropriate level measuring device well suited.  

In a preferred embodiment of the invention, the Magnetic field sensor via a probe guide in a defined position positionable. The probe guide preferably has an in the tube insertable rod with a first end and a two th end, which via a stop in a defined position in the Pipe can be positioned and in the area of its first end Magnetic field sensor carries. The rod extends into the tube led state with its second end preferably up to second end of the tube. With the help of the rod, the magnetic field sensor can be easily removed from the pipe, if necessary, for example for a repair or to replace the magnetic field sensor. Because the magnetic field sensor can be positioned in a defined position, it is ensured that he the magnetic field of the mounted on the axis of rotation of the float Magnets in a reproducible way, what the measurement is accurate benefits.

The level measuring device preferably has a bearing direction on which the axis of rotation of the float is rotatable is the and in the area of the first end of the tube at the Tube is attached. In this case, the pipe can be considered mechanical Serve bracket for the float. The second end of the pipe is preferably for mounting in the upper area of the tank set up. In this case it runs largely vertically and hangs in the interior of the tank, so that it essentially Chen only has to absorb tensile forces. Refinements in which the Pipe runs obliquely, but are also conceivable. The evaluations device is preferably arranged outside the tube. The electrical line between the magnetic field sensor and the evaluation device in a simple and easy to maintain way in the interior of the tube. In one preferred The th embodiment is a supply unit that needs the other electrical voltages or currents for the magnet provides field sensor, integrated in the evaluation device. The evaluation device also contains the circuits for Amplify and decode the swimmer's angular position  corresponding signal of the magnetic field sensor. Because the angle of rotation of the float in a non-linear manner from the level of the rivers liquid in the tank, it is advisable to direction using a microprocessor increase, so that a level or alternatively that Volume of the liquid still in the tank indicated can be. In the latter case, the geometric shape also works of the tank in the calculation. The result for the level is preferably shown or saved in a display.

Conventional magnetic field sensors can be used as a magnetic field sensor use that are sufficiently sensitive to pass through the front preferably non-ferromagnetic conversion of the tube through the magnetic field of the magnet (which is a permanent magnet) on the To address the swimmer's axis of rotation. Eligibility comes into play play a hall effect sensor. Another option is a Magnetic field sensor, which is a GMR component (Giant Magneto Resistance Pickup). In the following the invention is based on a Embodiment described in more detail. The drawings show in

Fig. 1 is a schematic view of a level measuring device according to the invention, which is installed in a tank, wherein the axis of rotation of the float of the level measuring device is in the paper plane, and

Fig. 2 is a schematic view of the level measuring device of FIG. 1, wherein the axis of rotation of the float is oriented perpendicular to the paper plane and the two extreme positions of the float are shown.

In Figs. 1 and 2 in schematic form a filling is stand-measuring apparatus 1 shown. The level measuring device 1 is installed in a tank 2 , the interior of which is denoted by 3 net. In the upper area of the tank 2 there is a dome 4 with a cover plate 5 . In Fig. 1 the level of a liquid in the tank 2 is indicated by a dashed line 6 te. In the exemplary embodiment, the tank 2 is sealed off from the surroundings, since the liquid is combustible and can form an explosive mixture with air. This liquid can also be a liquid gas.

The fill level measuring device 1 has a float 10 with a buoyancy body 12 . The buoyancy body 12 sits at the end of an arm 14 which is laterally attached to a rotary bearing 16 , see also FIG. 2. A counterweight 18 is located opposite the buoyancy body 12 . The pivot bearing 16 is held by a bearing device 19 which allows a rotational movement of the drive body 12 on the axis of rotation D of the pivot bearing 16 . In FIG. 2, the two extreme positions are illustrated (with an arc B between them), which may take 12 of the buoyant body. The lowest position is shown in solid lines, the highest position in dash-dotted lines. The buoyancy body 12 of the float 10 floats in the area of the liquid level of the liquid in the tank 2 . The float 10 therefore rotates when the level 6 changes about the axis of rotation D. Therefore, the angular position of the float 10 is a measure of the level 6 .

The bearing device 19 is fastened to a tube 20 , specifically in the region of the first end 21 of the tube 20 . The tube 20 ver runs in the embodiment substantially in the vertical direction and extends with its second end 22 to the outside of the tank, see Fig. 1. In the area of its second end 22 , the tube 20 is by means of a screw 24 in abge sealed way out through the cover plate 5 and BEFE Stigt. The interior of the tube 20 is completely sealed off from the interior 3 of the tank 2 . Therefore, the tank 2 may be under pressure and may contain a combustible liquid or a liquefied gas, while the interior of the tube 20 contains air at atmospheric pressure without the risk of an explosive mixture being formed.

As can be seen in FIG. 1, a magnet 30 is mounted on the axis of rotation D of the float 10 . The magnet 30 , which is a permanent magnet, is fastened to the rotary bearing 16 symmetrically to the axis of rotation D and takes part in the rotary movement of the buoyant body 12 . The magnet 30 is located outside the tube 20 .

Opposite the magnet 30 , a magnetic field sensor 32 is arranged in the interior of the tube 20 , which detects the magnetic field of the magnet 30 which is dependent on the angular position of the float 10 . In the exemplary embodiment, the magnetic field sensor 32 is a Hall effect sensor.

The magnetic field sensor 32 is attached to a rod 34 serving as a probe guide, specifically in the region of the first end 36 of the rod 34 . The rod 34 extends with its second end 37 to the second end 22 of the tube 20 . The rod 34 can be positioned via a stop (not shown in the figures) in a defined position in the tube 20 and allows the magnetic field sensor 32 to be pulled up out of the tube 20 , for example for repair, maintenance or calibration work , The stop ensures a reproducible position with respect to the magnet 30 . An electrical line 38 , which connects the magnetic field sensor 32 to an evaluation device 40 , runs along the rod 34 in the interior of the tube 20 .

The supply voltage for the magnetic field sensor 32 is provided by the evaluation device 40 . The magnetic field sensor 32 supplies an output signal to the evaluation device 40 via the electrical line 38 , which corresponds to the magnetic field detected by the magnetic field sensor 32 and depends on the angular position of the float 10 and thus on the fill level 6 of the liquid. This signal is processed in the evaluation device 40 , it being possible to take into account, for example, that the magnetic field depends on the fill level 6 in a non-linear manner due to various influences. In the exemplary embodiment, the evaluation device 40 also has a display, with the aid of which the determined fill level 6 is displayed.

Claims (9)

1. Level measuring device for a tank, with a float ( 10 ) rotatably mounted about an axis of rotation (D) and with a first end ( 21 ) and a second end ( 22 ) pointing pipe ( 20 ), which is set up for this , with its second end ( 22 ) to the outside of the tank ( 2 ), and which is sealed off from the interior ( 3 ) of the tank ( 2 ), wherein in the region of the first end ( 21 ) of the tube ( 20 ) and outside the tube ( 20 ) on the axis of rotation (D, 16 ) of the float ( 10 ), a magnet ( 30 ) is mounted and a magnetic field sensor arranged to measure a magnetic field opposite the magnet ( 30 ) in the interior of the tube ( 20 ) 32 ) is arranged, which is set up to output a signal dependent on the angular position of the float ( 10 ) via an electrical line ( 38 ) to an evaluation device ( 40 ). 2. Level measuring device according to claim 1, characterized in that the magnetic field sensor ( 32 ) via a probe guide ( 34 ) can be positioned in a defined position. 3. Level measuring device according to claim 2, characterized in that the probe guide has a guide rod ( 34 ) in the tube ( 20 ) with a first end ( 36 ) and a second end ( 37 ) which has a stop in Defi ned position in the tube ( 20 ) can be positioned and carries the magnetic field sensor ( 32 ) in the region of its first end ( 36 ). 4. Level measuring device according to claim 3, characterized in that the rod ( 34 ) in the tube ( 20 ) inserted state extends with its second end ( 37 ) to the second end ( 32 ) of the tube ( 20 ). 5. Level measuring device according to one of claims 1 to 4, characterized by a bearing device ( 19 ) on which the axis of rotation (D, 16 ) of the float ( 10 ) is rotatably mounted and in the region of the first end ( 21 ) of the tube ( 20 ) is attached to the tube ( 20 ). 6. Level measuring device according to one of claims 1 to 5, characterized in that the evaluation device ( 40 ) is arranged outside the tube ( 20 ). 7. Level measuring device according to one of claims 1 to 6, characterized in that the second end ( 22 ) of the tube ( 20 ) is set up for mounting in the upper region of the tank ( 2 ). 8. Level measuring device according to one of claims 1 to 7, characterized in that the magnetic field sensor ( 32 ) has a Hall effect sensor. 9. Level measuring device according to one of claims 1 to 7, characterized in that the magnetic field sensor is a GMR Has component.