DE202005005418U1 - Liquid level sensor for at least weakly conducting liquids, e.g. brake fluid, has two electrodes connected to evaluation and control electronics, with the electrodes functioning alternately as cathode and anode - Google Patents

Abstract

Sensor (10) for determining the level (N) and or the condition of an at least weakly conducting liquid (12) , e.g. brake fluid, contained in a container (14). The sensor comprises two electrodes (16, 18) that are immersed in the liquid and evaluation and control electronics (20). The at least two conducting electrodes are controlled by the electronics so that they are alternately cathode and anode. The invention also relates to a corresponding reservoir container with sensor electrodes.

Description

The The invention relates to a sensor for determining the level and / or the state of an at least slightly electrically conductive liquid like brake fluid in a container, comprising at least two electrodes intended for immersion in the liquid and an evaluation and control electronics.

A sensor of the type mentioned is for example from the DE 38 12 687 A1 known. This is a capacitive sensor in which at least one of the two electrodes has a cover layer of electrically insolating material which insulates the electrically conductive core of the electrode from the liquid.

Either Production, control and evaluation of the capacitive sensor are with increased effort connected.

From that Based on the present invention, the problem underlying by electronic means without mechanically moving components a sensor for level monitoring to develop such a simple and cost-effective Structure has, reliable works and arranged in a simple manner in a liquid container can be.

The Problem is inventively achieved in that at least two conductive electrodes for measuring the conductivity the liquid immerse themselves in them, with the individual electrodes passing through the evaluation and control electronics alternately as a cathode and / or anode are controllable. By the embodiment of the invention is a level monitoring achieved by electronic means, in which no mechanically moving Parts are necessary. In this solution, the conditionally existing conductivity the liquid the brake fluid recorded and evaluated by means of active electronic switching technology.

In order to There is no sacrificial electrode in this galvanic element, is the anode / cathode constantly changed with an electronic circuit, so that effectively no material flow can occur. This changing Potential or frequency can be generated in sine or digital form.

The at least two conductive electrodes make up the properties use the brake fluid. For example, the electrodes dip at a high liquid level almost complete into the liquid a, with the result that the conductance between the electrodes a low value. This can be used electronically to record the level be evaluated. With decreasing liquid level, the dive Electrodes less and less into the liquid, so a higher conductance is detected.

The Basic principle of the present invention comprises at least two conductive bars, which in the brake fluid dive in and over an applied voltage and current a high-resistance conductivity the liquid Measure by means of the evaluation and control electronics.

According to one preferred embodiment the electrodes as conductive rods formed, which extend parallel to each other at a distance A and get inside the liquid receiving container extend.

at too low resistance of the liquid are either foreign particles due to aging or water present in the liquid. This can also be recognized and evaluated.

there it is provided that first ends of the rod-shaped electrodes substantially lie in a plane which the minimum level of the container Are defined.

Prefers the electrodes are made of a corrosion-free, electrically conductive metal like stainless steel preferably made of V4A.

Around To ensure a simple production of the sensor, the electrodes in a related to the liquid level arranged upper housing wall as molded, wherein second ends of the rod-shaped electrodes as terminal contacts are formed.

The Drive signal may preferably be an alternating voltage or an alternating current be, which has a sine or rectangular shape. Also can the drive signal may be formed as a digital signal.

Of Furthermore, it is provided that the evaluation and control electronics via leads is connected to the electrodes, wherein the evaluation and control electronics together with the supply lines, the electrodes and the liquid form a closed, evaluable circuit with the result that, for example, errors in the supply lines and / or the evaluation and control electronics can be detected.

For more details, advantages and features of the invention will become apparent not only from the claims, the features to be taken these features - alone and / or in combination - but also from the following description of the drawing to be taken preferred embodiment.

The single figure shows a sensor 10 for determining a level N and / or the state of an at least slightly electrically conductive liquid 12 like Bremsflüs fluid in a container 14 , preferably a brake fluid reservoir, comprising at least two for immersion in the fluid 12 certain electrodes 16 . 18 and an evaluation and control electronics 20 that have leads 22 . 24 with the sensor 10 connected is.

The electrodes 16 . 18 are formed as conductive rods which extend parallel to each other at a distance A and inside the container 14 extend and into the liquid 12 plunge.

About the evaluation and control electronics, the electrodes 16 . 18 then controlled with a control signal and measured the high-resistance conductivity of the liquid.

So that there is no sacrificial anode in this galvanic element, the polarity of each electrode 16 . 18 changed, ie the anode cathode is connected to the evaluation and control electronics 20 constantly changed, so that effectively no material flow can occur. This alternating potential (frequency) can be generated in sine or digital form.

A current flow between the electrodes 16 . 18 is of a variable conductance of the liquid 12 dependent. The higher the liquid level, ie the deeper the conductive rod electrodes 16 . 18 into the liquid 12 immerse, the lower the ohmic resistance. The resistance also decreases as, for example, water in the liquid 12 intercalates.

Below the brake fluid 12 a minimum level MIN, the resistance becomes almost infinitely high, which falls short of the brake fluid 12 is detected below a minimum level.

Of course, the evaluation and control electronics 20 also able to detect a short circuit, for example in case of a fault in the sensor 10 or the supply lines 22 . 24 can occur. For evaluation and / or control of the sensor 10 has the evaluation and control electronics very accurate amplifier circuits such as operational amplifier.

All components of the arrangement shown in the figure, such as leads 22 . 24 and sensor 10 are part of the electronic circuit and are automatically monitored.

In the illustrated embodiment, the sensor 10 in an upper container wall 26 of the brake fluid reservoir 14 arranged. The rod-shaped electrodes are 16 . 18 into the container wall 26 molded, with first ends 28 . 30 the rod-shaped electrodes 16 . 18 lie substantially in a plane which the minimum level MIN of the liquid 12 defined and second ends 32 . 34 the rod-shaped electrodes 16 . 18 Connection contacts for the supply lines 22 . 24 form. This allows a very simple and cost-effective implementation of the sensor.

Overall, it should be noted that the position of the sensor 10 is arbitrary, ie the sensor 10 may for example also be arranged in the region of the brake cylinder. As a drive signal, a sinusoidal or rectangular AC voltage or an alternating current can be used. Also, a digital control signal can be used.

Claims (10)

Sensor ( 10 ) for determining the level (N) and / or the state of an at least slightly electrically conductive liquid ( 12 ) like brake fluid in a container ( 14 ) comprising at least two for immersion in the liquid ( 12 ) certain electrodes ( 16 . 18 ) and an evaluation and control electronics ( 20 ), characterized in that at least two conductive electrodes ( 16 . 18 ) for measuring the conductivity of the liquid in which the individual electrodes ( 16 . 18 ) via the evaluation and control electronics ( 20 ) are each alternately drivable as the cathode and / or anode. Sensor according to claim 1, characterized in that the electrodes ( 16 . 18 ) are formed as conductive rods and extending at a distance (A) parallel to each other into the interior of the container ( 14 ). Sensor according to claim 1 or 2, characterized in that first ends ( 28 . 30 ) of the rod-shaped electrodes ( 16 . 18 ) lie substantially in a plane which the minimum level (MIN) of the container ( 14 ) Are defined. Sensor according to at least one of the preceding claims, characterized in that the electrodes ( 16 . 18 ) are made of a corrosion-free, electrically conductive metal such as stainless steel preferably V4A. Sensor according to at least one of the preceding claims, characterized in that the electrodes ( 16 . 18 ) in an upper housing wall ( 26 ) of the container ( 14 ) arranged as molded. Sensor according to at least one of the preceding claims, characterized in that the drive signal is an AC voltage or is an alternating current. Sensor according to at least one of the preceding claims, characterized characterized in that the drive signal is a sinusoidal or rectangular shape having. Sensor according to at least one of the preceding claims, characterized characterized in that the drive signal is a digital signal. Container ( 14 ) with a sensor ( 10 ) according to at least one of claims 1 to 8, characterized in that the container ( 14 ) is a brake fluid reservoir of a hydraulic brake system of a motor vehicle, wherein rod-shaped, conductive electrodes ( 16 . 18 ) in a housing wall ( 26 ) are formed and parallel or substantially parallel in the of the brake fluid reservoir ( 14 ) recorded brake fluid ( 12 ). Container ( 14 ) according to claim 9, characterized in that the container ( 14 ) is a brake cylinder.