WO2001081876A2

WO2001081876A2 - System for detecting a liquid level

Info

Publication number: WO2001081876A2
Application number: PCT/DE2001/001410
Authority: WO
Inventors: Julian De La Azuela; David Ortiz Sanchez
Original assignee: Robert Bosch Gmbh
Priority date: 2000-04-22
Filing date: 2001-04-10
Publication date: 2001-11-01
Also published as: WO2001081876A3; DE10020081A1

Abstract

The invention relates to a system for detecting a liquid level, wherein the electrodes (2, 3) of a sensor (S) are disposed in the area of the liquid level to be monitored and the electrodes (2, 3) are linked with an electronic evaluation circuit by which the change of resistance that occurs between the electrodes (2, 3) when they contact the liquid is convertible to an evaluation signal. A circuit element (Q1; Q2) signals that the level is surpassed, the sensor (S) being connected to the circuit element (Q1; Q2) together with a timer (R2, C1) so that when the supply current (U) for the evaluation circuit is switched on in an interval predetermined by means of the timer (R2, C1), a signal is output even when the electrodes (2, 3) do not contact the liquid.

Description

Arrangement for the detection of a liquid level

State of the art

The invention relates to an arrangement for the detection of a liquid level, in particular the water level in an aggregate, according to the preamble of the main claim.

From DE 30 00 585 AI an arrangement is known with which the level of a water level in a water separator for a fuel filter in a motor vehicle is to be monitored. Electrodes are provided for this purpose, which are enclosed by the water when the level to be monitored is exceeded, which causes a measurable change in resistance between the electrodes. This change in resistance can be evaluated with an electronic circuit in such a way that an alarm function is triggered when the predetermined level is exceeded. Advantages of the invention

The arrangement for detecting a liquid level mentioned at the outset has electrodes in the region of the liquid level to be monitored, the electrodes being connected to an electronic evaluation circuit by means of which the change in resistance between the electrodes upon contact with the liquid cannot be converted into an evaluation signal. The evaluation signal is used to signal that the level has been exceeded. According to the invention, the sensor is advantageously connected to the switching module together with a timing element, so that when the supply voltage for the evaluation circuit is switched on, signaling takes place in a time period predetermined with the timing element even without contact of the electrodes with the liquid.

The signaling when the arrangement is switched on, for example when starting a motor vehicle, serves to check that the arrangement is functioning properly. In a preferred embodiment, the timing element is a simple and space-saving R-C circuit which is connected to the control input of the switching module with its central connection and the sensor with the resistive electrode path is parallel to the capacitor of the R-C circuit. It is particularly advantageous if the switching module is a field effect transistor, preferably a MOSFET.

In a further particularly advantageous embodiment, the signal output of the field effect transistor is routed to the input of a Darlington circuit, with means that the signaling, for example with a lamp, can be carried out via very precisely adjustable switching times. In all embodiments, it is particularly advantageous that the time period of the signaling when the arrangement is switched on depends on the dimensioning of the timing element, in particular the RC circuit, but is not influenced by the length of the electrodes of the sensor.

It is also advantageous if the arrangement is installed in a compact sensor module which can be plugged or screwed onto a liquid container to be monitored. Simple assembly and a compact housing shape can be achieved if the electrodes are attached on the inner side facing the liquid and there is a circuit board in contact with the electrodes with the evaluation circuit. The contact can be made, for example, by welding and then encapsulated with silicone, for example, to protect the electronic components on the circuit board.

Furthermore, the previously described unit can be welded on the outer side to the plug pins of a plug so that a corresponding evaluation signal can be processed further. These preassembled components can then be easily extrusion-coated, for example with plastic, to produce the entire sensor module, so that the desired installation shape is produced.

These and further features of preferred further developments of the invention emerge from the claims and also from the description and the drawings, the individual features each individually or several in the form of sub-combinations in the embodiment of the invention and in other areas and can represent advantageous and protectable versions for which protection is claimed here.

drawing

An embodiment of an arrangement according to the invention for the detection of a liquid level is explained with reference to the drawing. Show it:

1 shows a schematic section through a sensor module for monitoring a water level;

FIG. 2 shows a circuit diagram of an evaluation circuit of the sensor module;

Figure 3 is a circuit diagram of an extended evaluation circuit of the sensor module with a Darlington power amplifier and

Figure 4 shows a curve of a voltage measured with the water level over time.

Description of the embodiment

FIG. 1 shows a cut-open sensor module 1 with two electrodes 2 and 3, which come to rest after installation in a liquid container (not shown here) and detect contact with the liquid, here water. The electrodes 2 and 3 are concludes contacted on a circuit board 4, on which the evaluation circuit explained below is attached. The other connections of the printed circuit board 4 are contacted with plug pins 5, which are located in a plug housing 6 as part of the sensor module 1.

A circuit diagram of an evaluation circuit according to FIG. 2 shows a field effect transistor Q1, which is supplied with a switching signal via an R-C circuit with a capacitor C1 in the size of approximately 1 μF and a resistor R2 in the size of approximately 2.2 M. A signal means L, e.g. a lamp, driven. The electrodes 2 and 3 are shown here schematically as a sensor S, which is parallel to the capacitor C1 with the resistance of the path between the electrodes 2 and 3. The evaluation circuit according to FIG. 2 is supplied with a supply voltage U, which is additionally stabilized here via a resistor Rl and a zener diode Dl, e.g. to about 5 V.

In addition to the circuit arrangement according to FIG. 2, an exemplary embodiment according to FIG. 3 also has a Darlington output stage Q2 connected downstream of the field effect transistor Q1 and via which the signaling means L is controlled.

After switching on the supply voltage U, the field effect transistor Q1, or also the Darlington output stage Q2 according to FIG. 2, is also controlled, so that the signaling means L is actuated, e.g. by lighting up a lamp. For a time period dependent on the dimensioning of Cl and R2, here for example approx. 2

Seconds, this state remains as if from one Diagram according to FIG. 4, which shows the profile of the voltage u1 on the signal means L, can be seen. The course in FIG. 4 shows the conditions in the circuit according to FIG. 3; the course in the circuit according to FIG. 2 would result in a flatter falling edge.

After the capacitor C1 has been charged, the signaling means L goes out provided that the resistance gap between the electrodes 2 and 3 in the sensor S is large enough. When the electrodes 2 and 3 come into contact with water, however, the resistance becomes so low that the field effect transistor Q1 is opened again and the signaling means L is actuated again until the water level drops and the electrodes 2 and 3 are released.

Claims

claims

1) Arrangement for the detection of a liquid level at which

- Electrodes (2, 3) of a sensor (S) are arranged in the area of the liquid level to be monitored and

-the electrodes (2, 3) are connected to an electronic evaluation circuit, by means of which the change in resistance between the electrodes (2, 3) can be converted into an evaluation signal upon contact with the liquid, with which a switching module (Q1; Q2 ) the excess level is signaled, characterized in that

the sensor (S) is connected to the switching module (Q1; Q2) together with a timing element (R2, C1), so that when the supply voltage (U) is switched on for the evaluation circuit, the switching element (R2, C1) During this period, signaling takes place even without the electrodes (2, 3) coming into contact with the liquid.

2) Arrangement according to claim 1, characterized in that the timer (R2, C1) is an RC circuit, which is connected to the control input of the switching module (Ql) with its central connection and the sensor with the resistance- adhered electrode path is parallel to the capacitor (Cl) of the RC circuit.

3) Arrangement according to claim 1 or 2, characterized in that

-The switching module is a field effect transistor (Ql), preferably a MOSFET.

4) Arrangement according to claim 3, characterized in that

-The signal output of the field effect transistor (Ql) is led to the input of a Darlington circuit (Q2), by means of which the signaling is carried out.

5) Arrangement according to one of the preceding claims, characterized in that

the arrangement is built into a compact sensor module (1) that can be plugged or screwed onto a liquid container to be monitored and that the sensor module (1) has the electrodes (2, 3) on the inside, facing the liquid a circuit board (4) contacted with the electrodes (2, 3) with the evaluation circuit and on the outer side has a plug (6) for contacting the signal or other evaluation means.