DE10020081A1 - Water level sensor for car fuel filters, has self test function through simple time delay circuit - Google Patents

Abstract

The water level sensor has an electrode sensor (S) connected to a time delay circuit (R2,C1) and MOSFET switch (Q) so that when the supply voltage (U) is connected during the time delay a signal is produced even if the electrodes do not contact the fluid.

Description

State of the art

The invention relates to an arrangement for the detection of a Liquid level, especially the water level in egg nem aggregate, according to the genus of the main claim.

From DE 30 00 585 A1 an arrangement is known with which is the level of a water level in a water separator over for a fuel filter in a motor vehicle to be watched. There are electrodes for this if the level to be monitored is exceeded be surrounded by water, creating a measurable Wi the change in level between the electrodes is effected. This change in resistance can be done with an electronic Circuit can be evaluated so that the over an alarm function occurs when the specified level is reached is solved.

Advantages of the invention

The arrangement mentioned above for the detection of a river liquid level has electrodes in the area of the monitor liquid level, the electrodes with are connected to an electronic evaluation circuit, by means of the change in resistance between the electro in the event of contact with the liquid in an extractor tesignal is unchangeable. With the evaluation signal Signaling of the levels via a switching module transgression. According to the invention is more advantageous Way the sensor together with a timer to the Switching module switched so that when the Supply voltage for the evaluation circuit in one a signal i with the time period predetermined even without contact of the electrodes with the liquid speed occurs.

The signaling when switching on the arrangement, at for example when starting a motor vehicle, the Check the correct functioning of the arrangement. The In a preferred embodiment, the timer is one simple and space-saving R-C circuit that with its central connection at the control input of Schaltbau stone lies and the sensor with the resistance adhered electrode path parallel to the capacitor of the R-C circuit lies. It is particularly advantageous if the switching module is a field effect transistor, preferably is a MOSFET.

In a further particularly advantageous embodiment form is the signal output of the field effect transistor led the input of a Darlington circuit, by means of the signaling, for example with a lamp, made via very precisely adjustable switching times can be. It is special in all embodiments  advantageous that the period of signaling at Switching the arrangement on from the dimensioning of the timing element, especially the R-C circuit but not on the length of the electrodes of the sensor being affected.

It is also advantageous if the arrangement in one compact sensor module is built in, which is too over waking liquid container plugged on or on is screwable. Easy assembly and compact Housing shape is feasible if on the inner, the Liquid-facing side, the electrodes attached are inside and one contacted with the electrodes Printed circuit board with the evaluation circuit is available. The Contact can be made, for example, by welding be put and then to protect the electronic Components on the circuit board, for example with silicone be encapsulated.

Furthermore, the previously described unit on the ver the outer side with the plug pins of a plug are welded so that a corresponding evaluation signal can be processed further. This pre-assembled construction elements can then be easily manufactured of the entire sensor module, for example with plastic overmolded, so that the desired installation form ent stands.

These and other features of preferred training gene of the invention go out not only from the claims the description and the drawings, the individual characteristics individually or for more ren in the form of sub-combinations in the execution form of the invention and realized in other fields his and advantageous as well as protectable execution represent representations for which protection is claimed here becomes.

drawing

An embodiment of an arrangement according to the invention for the detection of a liquid level is based on the Drawing explained. Show it:

Fig. 1 shows a schematic section through a sormodul Sen for monitoring a water level;

Fig. 2 is a circuit diagram of an evaluation circuit of the sensor module;

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

Fig. 4 shows a course of a ge measured with the water level voltage over time.

Description of the embodiment

Fig. 1 shows a cut sensor module 1 with two electrodes 2 and 3 , which come to rest after installation in a liquid container, not shown here, and detect the contact with the liquid, here water. The electrodes 2 and 3 are contacted with connections on a printed circuit board 4 , on which the evaluation circuit, which is explained below, is attached. The other connections of the circuit board 4 are contacted with pins 5 , which are in a connector 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 RC circuit with a capacitor C1 in the size of approximately 1 μF and a resistor R2 in the size of approximately 2.2 M. . Via the field effect transistor Q1, a signal means L, z. B. a lamp. 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 distance 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 R1 and a Zener diode D1, for. B. to approx. 5 V.

An embodiment according to FIG. 3 has, in addition to the circuit arrangement according to FIG. 2, a Darlington output stage Q2 connected downstream of the field effect transistor Q1, 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 turned on, so that the signaling means L is actuated, for. B. by lighting a lamp. For a period of time depending on the dimensioning of C1 and R2, here for example about 2 seconds, this state is maintained, as can be seen from a diagram according to FIG. 4, which shows the course of the voltage U1 on the signal medium L. 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 charging the capacitor C1, the signal means L goes out provided that the resistance distance between the electrodes 2 and 3 in the sensor S is large enough. When the electrodes 2 and 3 come into contact with water, 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 (5)

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

• - Electrodes ( 2 , 3 ) of a sensor (S) are arranged in the region 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) signaling that the level has been exceeded, 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 in a time period specified by the timing element (R2, C1) a signaling even without contact of the electrodes ( 2 , 3 ) with the liquid he follows.

2. Arrangement according to claim 1, characterized in that

• - The timing element (R2, C1) is an RC circuit with its central connection at the control input of the switching block (Q1) and the sensor with the resistive electrode path is parallel to the capacitor (C1) of the RC circuit.

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

• - The switching module is a field effect transistor (Q1), preferably a MOSFET.

4. Arrangement according to claim 3, characterized in that

• - The signal output of the field effect transistor (Q1) 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 ), which can be plugged or screwed onto a liquid container to be monitored and that
• - The sensor module ( 1 ) on the inner, liquid-facing side of the electrodes ( 2 , 3 ), inside ei ne with the electrodes ( 2 , 3 ) contacted circuit board ( 4 ) with the evaluation circuit and on the outer side a plug ( 6 ) for contacting the signal or other evaluation means.