DE20305598U1 - Electronic chip circuit, for detecting presence of any electrically conducting substance above or below given threshold, comprises logic circuit with chip inputs arriving via sensor contact - Google Patents

Abstract

An electronic circuit detects the presence or absence of a substance having electrical conductivity, above or below a given threshold. The circuit comprises a logic chip (13). All chip inputs (14, 15) arrive via a sensor contact (17) as the same type of square wave voltage, resulting in a pre-determined output signal (16) to a display unit. A single alternating square wave current is continually generated and is taken as the reference for all functions and measurements. Alternating current is continually fed each sensor contact (17) via a capacitor (18). During measurements an active signal voltage is continually supplied at the chip (13) output (16) and activates a static liquid crystal display and/or an acoustic signal. The chip is a four-function NAND-IC, or two two-function NAND-ICs and a four-function Exclusive-OR-IC, registering five different conditions.

Description

Wolfgang von Horsten
Potsdamer Str. 11
80 802 Munich

Munich, 31 March 2 003

Our reference: VH 12 02 G
Applicant: Wolfgang von Horsten

Circuit for detecting substances with electrical conductivity

The invention relates to a circuit for detecting substances with electrical conductivity, in particular water and aqueous solutions, according to the preamble of claim 1.

The circuit works with an electronic circuit that contains a sensor. The sensor consists of two electrical contact points. The circuit records the electrical contact resistance between the two contact points. The contact resistance is inversely related to the electrical conductivity of the medium between the contact points.

The circuit enables the registration and display of two different states on the sensor, namely a contact resistance (a conductivity) above a certain threshold value or a contact resistance (a conductivity) below a certain threshold value. Depending on the intended use of the circuit, the corresponding

States, for example, the values: substance present - not present, container empty - full, moisture present - not present.

The number of sensors to be used can be specified as desired. With several sensors at different heights in a container, different fill levels in the container can be displayed, for example.

As a result, the circuit can be used in a corresponding device to register and display, for example, the fill level of bulk materials or liquids, in particular water, provided that the substances to be controlled or one of their components have at least a low electrical conductivity. In particular, a corresponding device can also be used to register and display a moisture level in the medium surrounding the sensor.

Such a device is known from DE 40 17 314 A1. In the known device, a push button starts the measurement and display for a predetermined period of time, and the optical signals are generated as flashing signals from light-emitting diodes. However, the "electronic control circuit" mentioned in the known device does not contain any other specific features of the electronic circuit to be used.

Another device is known from DE 3 6 39 695 A1. There too, an "electronic circuit" is mentioned, but no further features of the circuit are described.

In DE 692 28 548 T2 an electronic measuring circuit is described in detail. This description makes the effort: Öeutii.cii,:implemented with ö.ejir'cias'measuring process

In a preferred embodiment, a Z-switching network, a sinusoidal resonant circuit, an amplifier and an inverter or a Schmitt trigger and filter are required to detect the change in capacitance of a sensor element when immersed in a substance to be measured.

For further explanation, in particular deepening and supplementing the technical background of the present invention, reference is made to the following prior art: DE 197 44 784 Al,
DE 199 27 687 Al,
DE 197 26 044 C2,
DE 198 49 706 Al,

DE 40 27 692 C2,
DE 200 12 404 Ul.

In summary, it can be stated that electronic devices for liquid or fill level measurement have been disclosed several times. However, either mainly only the applications and tasks are described and no solution for the electronic circuit is given (examples are DE 4017 314 Al, DE 36 39 695 Al, DE 200 12 404 Ul), or electronic measuring and evaluation methods are presented which require a high level of circuit complexity and special components or sensors (examples are DE 197 44 784 Al, DE 692 28 548 T2, DE 199. 27 687 Al, DE 197 26 044 C2, DE 198 49 706 Al, DE 40 27 692 C2).

In typical applications, for example for a liquid level indicator, a number of devices and circuits are known that describe details of the sensors and embodiments for the indicator. However, in view of the state of the art,

Technology to note that the electronics to be used al- ··· ···· ···· ···· ···· ···· ···· ·· ·· · · ·

if necessary, the class is denoted as ^:

In more detailed descriptions, complex circuits are described, often using microprocessors, for example.

Based on this state of the art, the invention aims to provide a novel electronic circuit that requires a minimum - which presumably cannot be reduced any further - of components and power consumption and therefore represents a unique optimum in terms of commercially favorable production and functionality.

In other words, the present invention also stands out from the current state of the art in that the features mentioned in detail in claims 2 to 4 and 8 are implemented jointly and continuously by the subject matter of claim 1. This means that the circuit according to the invention, which essentially consists of a digital logic switching element, already solves the problem of both querying a sensor (without a disadvantageous direct current load on the measuring point) and activating a display element, while at the same time using the lowest possible power, so that energy-saving continuous operation of the corresponding device is possible without any problems.

According to the invention, this object is achieved by the subject matter of claim 1.

The electronic circuit according to the invention is particularly simple and compact. It can be produced inexpensively, it is extremely easy to use, has a self-explanatory and clear display, and a particularly long service life with extremely low power consumption.

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elements, such as ζ. B. On-off switches or buttons. The electronic board contains only a single, inexpensive, commercially available CMOS IC for the application of one measuring point or only two standard CMOS ICs for the application of four measuring points, each together with a few other common components.

A button cell is sufficient for several years of operation. If the level indicator is in a position with sufficient light, a small solar cell is sufficient for a permanent power supply.

Preferably, a lithium battery with a voltage of 3 volts is used for the power supply. A lithium button cell with a capacity of 180 mAh can supply the circuit with power continuously during its own guaranteed lifespan of 5 years. The power requirement of the circuit depends on the level of the supply voltage. At a correspondingly low voltage, the power requirement according to claim 9 is extremely small and amounts to only a few microamperes.

In a preferred embodiment, the display is made by means of an LCD bar display with a vertical arrangement of the individual LCD segments, for example according to the successive height of the measuring points.

In a particularly preferred embodiment, an electronic circuit with 4 sensors and an LCD display with five different symbols is used. When the battery is inserted, at least one of the symbols is always activated, so that the operational readiness of the electronics or the battery is constantly visible. This function of the display is achieved by, for example, the lowest of the sensor contacts arranged vertically one above the other controlling two symbols alternatively, namely

for example with non-conductive sensor contact alone ··· ···· ·· ·· #·· ··· ···· ···· ···· ·· ·· · ·

the lowest:Symb*o.ii \jnd|b^i:-W5rh«.n<3e ₄ iiL§nf|Leiii?fajhigkeit

instead the next symbol above. In this arrangement, the lowest symbol is on the one hand a control signal for the circuit's readiness for measurement and on the other hand an indication signal for the "dry" or "no liquid" state or corresponding states.

The other symbols above are only activated if and for as long as the associated sensor contacts, which correspond to higher measuring points, measure conductivity.

In a preferred embodiment, the individual symbols of the LCD display are shown as black areas in the active state and are not visible in the inactive state.

The sensor contacts are metallic surfaces made of copper or silver or other preferably corrosion-resistant materials. The sensor contacts are either in compact form, for example as pieces of wire, or are applied as a coating or alloy to another metallic material or to a suitable surface.

In a preferred embodiment, the sensor contacts are applied as electrical conductor tracks on a suitable carrier material. The lower end of a conductor track can serve directly as a sensor contact surface. This area of the contact surface can be provided with a separate metallic coating made of gold, silver or other suitable materials (carbon, graphite) for better corrosion resistance. The remaining conductor track establishes the electrical connection to the electronic part; this part of the conductor track can be insulated, for example by a lacquer coating. The conductor tracks have the appropriate lengths that are intended for the positions of the sensor contacts.

In a further preferred embodiment, the electrical conductor tracks and the sensor contacts are applied to a flexible carrier. The flexible carrier can also be provided with an adhesive or bonding layer on its back. This enables the sensor and supply line part to be adjusted and, if necessary, fixed to flat and non-flat surfaces or walls.

The electrical load on the sensor contacts is extremely low. The voltage drop across the sensor contacts is typically less than 0.1 volts, and the measuring current is typically less than one microampere. According to claim 3, only an alternating voltage/square-wave voltage without a direct voltage component is applied to the sensor contacts, so that harmful electrolytic effects are avoided.

A particular advantage of the method according to the invention is that the sensor in the proposed circuit reacts with sufficient sensitivity to be able to register only residual moisture present in the surrounding medium at the sensor.

A preferred embodiment of the electronic circuit with four sensor contacts and an LCD with five associated symbols for displaying, for example, a state of "empty" or "non-conductive" as well as four different fill levels of a conductive substance in a container can be realized according to claim 7 with only two commercially available IC components, namely with a 4-way Schmitt trigger - NAND - IC and a 4-way Exclusive - OR - IC. The 4 individual switching elements of the Exclusive - OR - IC are used for measuring at the 4 sensor contacts and for controlling 4 associated symbols of the LCD display (see description of Fig. 1). One switching element of the 4-way NAND - IC is used as a generator of a square wave voltage, one switching element as an inverter and two switching elements (see description of Fig. 1) for the fifth

Symbol for the sensor state "non-conductive" is used.

According to claim 2, a square wave voltage (or alternating voltage) is generated only once in the entire electronic circuit, which is used both for controlling all sensor contacts and switching elements, as well as for the LCD.

In principle, a switching function proposed here can also be implemented with other digital switching elements, for example with NAND switching elements instead of exclusive-OR switching elements. One criterion in this invention for an advantageous embodiment is the smallest possible number of components for the entire circuit, as is shown by way of example in Fig. 1 by the use of an exclusive-OR switching element for the measuring and display function of a sensor contact.

In this description and in the text accompanying the figures, a NAND switching element with Schmitt trigger inputs is preferably meant, even if only the term NAND switching element is used.

The invention is described in detail below with reference to drawings. The following description of an embodiment of the invention is exemplary in nature.

Show it

Fig. 1: Functional diagram of the electronic circuit with an exclusive OR switching element; 5

Fig. 2: Functional diagram of the electronic circuit with NAND gates;

Fig. 3: Functional diagram of the electronic circuit for controlling a

tone generator;

In Figs. 1 and 2, equivalent points in the circuits are shown with the same reference numerals.

Fig. 1 shows a preferred embodiment of the electronic circuit.

The electronic circuit contains a 2-input exclusive

ve-OR circuit 13 for each individual sensor contact 17. 20

The two inputs 14 and 15 of the switching element 13 are continuously supplied with the same alternating voltage, preferably a square wave voltage, at point 19 via the two series resistors 20 and 21.

If there are no other signals at inputs 14 and

15 this means that the voltage level at both inputs of the switching element 13 is the same at all times. In detail, the following happens in this situation:
30

The square wave voltage consists of a temporally alternating sequence of two different voltage values, namely a low level and a high level voltage value. At the two inputs 14 and 15 there is therefore always - in temporally alternating sequence - either the same low level voltage value or the same high level voltage value. According to the logical

Function of the exclusive-OR switching element 13 generates in both cases - with equivalent input signals the voltage value low level at the output 16, corresponding to a constant non-active output signal of the switching element 13.

A fundamentally equivalent behavior also occurs when a different alternating voltage, e.g. a sinusoidal voltage, is fed into point 19. Due to the binary switching behavior of the digital switching element, a low level also appears continuously at the output, and on the other hand a high level also appears in the situation as described below for the preferred case of a square-wave voltage at point 19.

The influence of the sensor contact is taken into account below:

The sensor contact 17 is also connected to an input 14. If the contact surfaces of the sensor 17 are in the non-conductive medium, the contact resistance between the contact surfaces is practically infinite. The sensor contact therefore does not load the input 14, the input 14 still carries the full input signal, i.e. the alternating voltage or square wave voltage that is fed into the point 19. The situation described above applies, with the result of a continuous low level at the output 16.

If, however, the contact surfaces of the sensor 17 are located in a medium with a finite electrical conductivity, the contact resistance between these contact surfaces is correspondingly lower.

A typical resistance value for tap water can be around 50 kOhm. The square wave voltage fed in at point 19 is the voltage

divider consisting of resistor 21 and the contact resistance between the sensor contacts to zero potential.

Since resistor 21 has a high value of, for example, 1 MegOhm, only the small voltage component that corresponds to the contact resistance between the sensor contacts remains at input 14 from the voltage value fed into point 19.

The resulting resistance of the capacitor 18 and the very high input resistance of the switching element 13 can be disregarded here. Furthermore, it is of equal importance for the function of the voltage divider whether resistor 21 is an ohmic or a capacitive resistor.

In detail, the following sequence occurs: During the phase in which the square wave voltage at point 19 is in the low level state, both inputs 14 and 15 receive no voltage, both inputs are at low level, and accordingly output 16 is also at low level.

During the phase in which the square wave voltage at point 19 is in the high level state, input 15 receives the high level voltage value. However, due to the conductive sensor contact, a reduced voltage value is present at input 14, which corresponds to a low level input value. Thus, switching element 13 receives different input signals in this phase and functionally switches output 16 to high level.

In the end, the square wave voltage that is fed in at point 19 appears again at output 16.

The output 16 of the switching element controls an LCD segment/symbol for an associated display via a capacitor 22.

This means that centralized AJf^ab&.de-ir· Ör.Jfin^ung «is realized

The associated symbol on the LCD display is activated when there is a given conductivity between the sensor contacts and is inactive when the non-conductive sensor contacts are "open". The specified value for the resistor 21 results in a sufficiently sensitive threshold value for switching the voltage at the input 14 from the high level to the low level voltage value for practically occurring conductive substances, in particular for water and aqueous solutions. The threshold value can also be set to a lower sensitivity for conductivity detection by reducing the resistance value 21.

In a preferred embodiment, the LCD display has several symbols/segments which correspond, for example, to different fill levels or states. The individual symbols are each statically controlled and thus activated directly, i.e. without a multiplex controller, by the alternating voltage occurring at the output 16 of a switching element. This eliminates the need for a separate voltage source and a controller circuit for the display. According to claim 4, the signal voltage for the LCD is already completely available with the output switching voltage of the switching element 13.

The purely capacitive coupling of an LCD segment via a capacitor 22 at the given low frequency places only an insignificant load on the switching element 13 and at the same time prevents the occurrence of a harmful DC voltage component at the LCD segment.

In a further advantageous embodiment, the sensor located at the lowest position alternatively controls two different LCD symbols, for example the symbols for the two states "dry" and "liquid/moisture present". The control of the first symbol "liquid/moisture present" takes place in the same way as previously described in Fig. 1. The second symbol

"Dry", on the other hand, is controlled, for example, by another exclusive-OR switching element, whose input 14 receives the inverted control voltage 16 assigned to the first symbol instead of a sensor signal.

Through this positive and negative evaluation of the measurement signal of a sensor contact, one of the two symbols mentioned is always activated alternatively, corresponding, for example, to the two alternatively possible states "dry" or "liquid/moisture present".

This has the additional advantage that even when no conductive substance is present, a display is always active and this display also serves as a check for the functionality of the electronics and the battery, for example during longer "dry" or "empty" periods.

An alternating voltage of any shape is suitable for the functioning of the electronics. A preferred form is a square wave voltage. This can be generated in a known manner using a Schmitt trigger NAND component, for example, by adding a charging capacitor to its input and coupling its output to the input via a resistor. The frequency of the square wave voltage is preferably set to a suitable value for controlling the LCD. A suitable frequency is, for example, 80 Hertz.

According to claim 3, the alternating voltage is supplied to the sensor contacts via a capacitor 18. This prevents a direct voltage potential at the sensor contacts 17 and avoids disruptive electrolytic effects at the contacts.

Fig. 2 shows an embodiment of the electronic circuit using NAND gates.

In Fig. 2

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A simple and compact circuit variant is proposed for the case where only a single measuring point is intended. In this case, the circuit can be implemented with a single quadruple NAND component, the standard IC most commonly used in digital electronics and therefore also the cheapest.

Two alternative measuring states of the sensor can also be displayed, as described above for Fig. 1.

The circuit for the measurement requires, as shown in Fig. 2, two NAND switching elements 26 and 27. The first switching element 26 is in the same way as the switching element

13 is wired as shown in Fig. 1. Please refer to the corresponding description for Fig. 1.

In contrast to the operation of the exclusive-OR switching element 13 in Fig. 1, the following voltage values occur at the output 24 of the NAND switching element 26 in Fig. 2:

When the sensor contact 17 is not conductive, the two inputs 14 and 15 of the NAND switching element 2 6 always simultaneously receive the high-level voltage value fed into point 19 or the low-level voltage value. The opposite voltage values then appear at the output 24 of the switching element 2 6, as required.

When the sensor contact 17 is conductive, the input

14 continuously generates the voltage value low level. For the two possible voltage values low level and high level at the input 15, the NAND switching element 2 6 now functionally continuously generates the voltage value high level at the output 24.

The summation of the two possible output signals of point 24 with the control signal of point 19 in the NAND gate 27 produces ^the two signals of point 24 in the output ^{signal of gate} 27.

The desired signal voltage for controlling an LCD segment is now available at the output 16 of the switching element 27:
When the sensor contact 17 is conductive, the square wave voltage (phase-swapped to point 19) activates the associated LCD segment, and in the case of the non-conductive sensor contact 17, a continuous high-level voltage value is blocked by the capacitor 22 so that the LCD segment is not activated.

This corresponds to the initially desired situation, namely the active display when a conductive medium is present at the sensor contact.

An active counter-indication for a lack of conductivity at the sensor contact using a second LCD segment is easily achieved by using the output signal of point 24 to control the second LCD segment.

For the complete function of the circuit, only one additional NAND switching element is required, with which a square-wave voltage is generated in a known manner, as previously described in Fig. 1.

According to the invention, the entire circuit for measuring with one sensor contact and the display of two associated alternative states is realized with three NAND switching elements and a few external components.

Fig. 3: Functional diagram of the electronic circuit for controlling a tone generator.

In addition to an LCD display, an optional sound signal can be generated. In principle, a sound generator can be connected instead of or parallel to an LCD element.

However, f.pfc da*na|i4 d£r·Rpge^L ^^r,jS.iej: a*Lg more essential

The extremely low power consumption of the circuit, which was considered an advantage, is no longer present because a dynamic sound generator in particular consumes considerably more power than an LCD display.

When using a sound signal, it may also be desirable to activate the sound signal only for a limited time. A short-term sound signal means, on average, low power consumption.

In the following, therefore, an advantageous circuit extension is proposed according to claim 5 in order to obtain a short-term active signal voltage from the continuous active signal voltage at the points 16 of Figs. 1 and 2.

This briefly active signal voltage is available at point 40 of the circuit in Fig. 3 in the form of a pulse lasting, for example, 2 seconds. The signal voltage at point 40 can then activate a 2-input NAND switching element via its first input during its duration. The NAND switching element can be switched as a square-wave generator in a known manner via the second input and can then control, for example, a piezo sound generator.

The control pulse at point 40 starts synchronously with the onset of a continuous active signal voltage 16 in the circuits described in Figs. 1 and 2.

For this purpose, the output voltage 16 of the switching element 13 from Fig. 1 is fed to the two NAND switching elements 36 and 37 of Fig. 3 at point 29.
When the sensor contact is conductive, the output voltage 16 is a square wave. This square wave is fed to the

Input 32 of the NAND gate 37 via capacitor 3 0 directly to the ^# E&hg&nrf 33*:dös JÜJSBO'-iSeßaltcjlifedes 3 7

fed inverted via the NAND switching element 36. Therefore, opposite voltage values are present at the two inputs 32 and 3 3 of the NAND switching element 37 in each phase of the square wave voltage and the output 34 of the switching element 3 7 consequently has a continuous high level as per function. A corresponding voltage pulse is derived from this constant positive direct voltage at point 3 4, which occurs depending on the sensor state, via the capacitor 39. The duration of the pulse depends on the size of the capacitor 39 and can therefore be determined by the value of the capacitor 3 9.

When the sensor contact is non-conductive, point 29 receives the low-level voltage value. After inversion via switching element 3 6, this results in a high level at input 33 of switching element 37. Input 32 of switching element 37 now also receives a high level because capacitor 3 0 blocks the low-level voltage value of point 29 and resistor 31 at the positive potential pulls input 32 up to a high-level voltage value. The two identical high-level voltage values at switching element 37 functionally generate the low-level voltage value at output 34, and the tone generator is therefore not activated.

In all circuit examples, optional capacitors are not shown, which may be required to smooth out switching and interference pulses on the signal lines.

The electronic circuit according to the invention is designed for extremely low power consumption during continuous operation. An obvious further power saving can be achieved by connecting another NAND switching element in a known manner as an additional square wave generator, for example with a pulse-pause ratio of one second each. The output of this switching element k^mjjaur S5khrfun^sye|:0© _i rg>Kjigr _# ,4i*lp ^r jüjrijgen switching element

elements are used, which are then switched on and off in the corresponding clock cycle. In this way, the power consumption of the remaining switching elements is halved again.

Claims (8)

1. Circuit for detecting substances with electrical conductivity, in particular water and aqueous solutions, characterized in that the electrical circuit essentially contains a logic function module ( 13 ), all of whose inputs are supplied with a similar square-wave voltage, to at least one input ( 14 ) of which a sensor contact ( 17 ) is connected, and which, when there are different signal levels at its at least two inputs ( 14 , 15 ), provides a specific active output signal ( 16 ) for a display. 2. Circuit according to claim 1, characterized in that a single alternating voltage, preferably a square wave voltage, is generated and continuously used for all measurement and display functions. 3. Circuit according to claim 1, characterized in that an alternating voltage is continuously supplied to the sensor contacts ( 17 ) via a respective capacitor ( 18 ). 4. Circuit according to claim 1, characterized in that the active signal voltage at an output ( 16 ) of the functional module ( 13 ) is continuously available during the duration of a conductivity to be measured and can be used directly to activate a static LCD display signal. 5. Circuit according to claim 1, characterized in that a signal voltage ( 40 ) for controlling a tone generator is derived from the continuous signal voltage ( 16 ) which occurs when the conductivity is measured, which signal voltage is only active during a certain period of time. 6. Circuit according to claim 1, characterized in that with a standard IC, for example a quadruple NAND IC, all necessary functions for measuring on a sensor and for displaying two alternative states can be realized. 7. Circuit according to claim 1, characterized in that with two standard ICs, for example a double NAND IC and a quadruple exclusive OR IC, all necessary functions for measuring four sensors and for displaying five different states can be realized. 8. Electronic circuit according to claim 1, characterized in that an extremely low power consumption is achieved in continuous operation.