DE10159336B4 - Process for self-adjustment of a sensor and self-adjusting sensor - Google Patents

Abstract

Method for the automatic self-adjustment of a sensor, comprising a sensor (1) with an output (1A), which outputs an output voltage (Ua), and a first comparator (31), to which the output voltage (Ua) and a reference voltage (Uref) are applied, the first comparator (31) emitting a switching signal if the output voltage (Ua) is greater than the reference voltage (Uref) and otherwise not emitting a switching signal, or vice versa, characterized in that the reference voltage (Uref) of the output voltage ( Ua) is automatically updated as follows:
(a) If the output voltage (Ua) is both
- Is less than or equal to an upper limit voltage (UGo), which is given by the sum of the reference voltage (Uref) plus a first voltage distance (dU1), as well
- is greater than or equal to a lower limit voltage (UGu), which is given by the difference of the reference voltage (Uref) minus a second voltage distance (dU2), the reference voltage (Uref) is kept constant,
(b) if the output voltage (Ua) is greater than the upper ...

Description

The invention relates to a method for self-adjustment of a sensor and a self-adjusting one Sensor, in particular for capacitive detection of the fill level of a medium in a container as well as for distance monitoring.

Known and widely used capacitive sensors for non-contact level monitoring solid or liquid Media through container walls and the query of various objects at a distance within the Detection range of a sensor field, that is the switching distance.

The principle of operation of such sensors is based on influencing the active field of a capacitive sensor by introducing the dielectrics (Er) of the objects to be detected or media. By introducing these dielectrics, the capacitance becomes one Capacitor, which is due to the capacitively active area of the Sensors on the one hand and earth or those lying at ground potential Sensor parts on the other hand is formed, enlarged. If a certain capacity value is exceeded, solves the Sensor off a switching signal; the sensor is "activated". This is the case, for example, if the level the active surface of a medium of the sensor is sufficiently covered or an object is a certain distance to the active area has fallen below.

The response sensitivity (switching distance on a grounded metal plate) of a capacitive sensor always to the respective measuring or monitoring task (Application) can be adjusted. This results from the fact that the area around the active area is always is "preloaded" by other capacitive influences. This is at capacitive level measurement e.g. the capacity the container wall, through which is measured, or when querying the distance undesirable Objects in the background that are also within the detection range of the sensor, but should not be included. For example, during level detection a container wall through this, the wall already causes a considerable capacitive Preload, the higher can be as the actual capacity of the medium to be detected. The wall thickness also determines the distance to the medium. moreover deliver e.g. Substances such as granules and oil low, water, however high Er values or capacities.

The sensor must therefore, depending on the wall thickness, wall material and the medium to be recorded can be individually adjusted to the level precise to be able to record. A sensor that was set too sensitive would already be due alone the wall of an empty vessel in the actuated Change state, while a sensor that is too insensitive even when the active ones are completely covered area no switching signal triggers. Even when querying the distance of objects, e.g. one immediately behind lying metal wall a too sensitive sensor in the continuously operated state bring, since this only the Would recognize metal wall. The sensor must therefore precise be brought to a sensitivity that is just sufficient in this example when exceeded of the total capacity Object + metal wall to trigger a switching signal. The respective capacitive Preloading thus causes a kind of undesirable "offset" or shift of the "working point", which is caused by a appropriate sensor setting is compensated.

Capacitive sensors rework the state of the art with critically coupled RC oscillators, which is due to small capacity changes with swinging up or swinging down (amplitude evaluation) or stronger Frequency influence (frequency evaluation) react. Furthermore there there are some externally controlled methods, which have a capacity-dependent DC voltage deliver. The sensitivity is usually set by a change the parameter of the capacitive process itself, mostly the change a gain factor in the RC oscillator (Start-up threshold), or by change the threshold of a comparator which, when a certain one is reached adjusting DC voltage triggers the switching signal.

• – Mit Hilfe eines kleinen Schraubendrehers wird ein im Sensor befindliches Potentiometer mit X-Gang Wendel oder 270 Grad Drehwinkel auf die gewünschte Empfindlichkeit justiert. Dieser Vorgang ist meist zeitraubend und erfordert gewisse Übung bei oft kritischen Einstellungen.
• – Mit Hilfe eines kleinen Tasters am Sensor wird in der laufenden Applikation auf Tastendruck die Justage automatisch durchgeführt. Hierzu muß die Applikation in einen gewissen Zustand gebracht werden, z.B. Gefäß leer oder voll. Je nach Zustand sind dann unterschiedliche Tasten in bestimmter Reihenfolge oder eine Taste für bestimmte Zeitdauern zu drücken. Ferner signalisieren Leuchtdioden den Abgleichstatus und müssen ggf. beobachtet und je nach Anzeige weitere Eingaben durchgeführt werden. Der Anwender muß hierzu die Bedienungsanleitung studieren und zum Betätigen der meist wassergeschützten Taste(n) unter Folie oder Gummi ein geeignetes Werkzeug zu Hand haben. Stand der Technik sind auch Sensoren mit Busschnittstellen für PC-Anschluß. Hier erfolgt die Justage über die PC-Tastatur. In jedem Fall erfordert auch diese Methode einige Zeit und Aufwand. Solche "teachbaren" Sensoren arbeiten i.d.R. mit Mikroprozessor und A/D-Wandler. Die kapazitätsabhängige Ausgangsspannung des kapazitiven Aufnehmers wird digitalisiert und der Mikroprozessor erzeugt hieraus mit einem bestimmten Algorithmus einen mehr oder weniger richtigen Schaltpunkt. Hierzu existieren z.B. auch die Offenlegungsschriften DE 195 07094 A1 und DE 19715146 A1 .

The following methods for setting the sensitivity are common and state of the art:

• - With the help of a small screwdriver, a potentiometer in the sensor with X-turn or 270 degrees of rotation is adjusted to the desired sensitivity. This process is usually time-consuming and requires some practice with often critical settings.
• - With the help of a small button on the sensor, the adjustment is carried out automatically at the push of a button in the running application. For this purpose, the application must be brought into a certain state, eg the container is empty or full. Depending on the state, different keys are then to be pressed in a specific order or a key for specific periods of time. Furthermore, LEDs indicate the alignment status and may need to be observed and, depending on the display, further entries made. To do this, the user must study the operating instructions and have a suitable tool to operate the mostly water-protected button (s) under film or rubber. State of the art are also sensors with bus interfaces for PC connection. Here the adjustment is done via the PC keyboard. In any case, this method also takes some time and effort. Such "teachable" sensors usually work with a microprocessor and A / D converter. The capacitance-dependent output voltage of the capacitive transducer is digitized and the microprocessor uses this to generate a algorithm more or less correct switching point. For this purpose there are also the published documents DE 195 07094 A1 and DE 19715146 A1 ,

Through the DE 197 15 146 A1 A method with two separate, independently variable thresholds E1 and E2 has become known. This leads to a complex teach-in process, which has to record all states of an application, eg fill level full or empty, and cannot run independently without operation.

Through the DE 197 07 263 A1 A self-calibrating sensor arrangement with a sensor and a calibration circuit located in the output circuit of the sensor has become known, which adjusts an offset in the output circuit in such a way that the switching points coincide with reference values. An offset D / A converter, which sets the offset in the output circuit, is followed by a detector circuit for determining signal peaks in the output signal of the sensor, which comprises a current divider and a current mirror. Between the offset D / A converter and the detector circuit lies a calibration logic which is controlled by comparators, to which the output signals of the current divider and the current mirror, on the one hand, and the output signal of the sensor, on the other hand, are fed.

Through the DE 196 00 803 A1 Sensor signal processor with an amplifier circuit with an operating limit value and a differential amplification for causing amplification of an alternating sensor output signal from a sensor has become known in order to exceed this operating limit value. The amplifier circuit is used to input the sensor output signal and a comparison voltage to amplify and output a difference between this sensor output signal and this comparison voltage as an output signal. There is a converting circuit which converts the output signal from the amplifier circuit into a signal Vout with a binary value by comparing this output signal with a threshold value. A comparative voltage changing circuit is provided for evaluating whether this output signal from the amplifier circuit is within a predetermined amplitude range and for changing this comparison voltage if this output signal deviates from the predetermined amplitude range so that it is closer to the output signal of the amplifier circuit.

Through the DE 195 40 835 C1 A method for converting ON / OFF analog signals into corresponding ON / OFF digital signals has become known when a specific ON reference threshold value or OFF reference threshold value that can be predetermined by a comparator is reached. A first reference threshold value (EIN-Ref), which detects an ON-analog signal, is assigned to the comparator for the ON-analog signals of a signal generator. For the OFF analog signals of a signal generator, the comparator is assigned a second reference threshold value (AUS Ref), which recognizes an OFF analog signal and is lower in level than the first reference threshold value (On-Ref). The first reference threshold value (EIN-Ref) is set as a function of the amplitude values of the respective ON analog signal. The second reference threshold value (AUS-Ref) is set as a dependency on the absolute amplitude values of the respective OFF analog signal as a dependency on tracking. The first reference threshold value (ON-Ref) is spaced from the second reference threshold value (OFF-Ref) in the sense of a signal-to-noise ratio. The first reference threshold value (ON-Ref) and the second reference threshold value (OFF-Ref) are each within a threshold value range with an upper and a lower range limit (EINmax; EINmin or AUSmax; AUSmin). The range limits of the associated threshold value range are determined in an initialization process on the basis of the maximum and minimum values of previously detected OFF analog signals.

The invention is based on the object a self-adjusting sensor and a method for self-adjustment specify a sensor, with a fully automatic adjustment of the Sensors to a variety of applications without any control element on the sensor and without user intervention.

• (a) Falls die Ausgangsspannung sowohl – kleiner oder gleich einer oberen Grenzspannung ist, welche durch die Summe aus der Referenzspannung plus einem ersten Spannungsabstand gegeben ist, als auch – größer oder gleich einer unteren Grenzspannung ist, welche durch die Differenz der Referenzspannung minus einem zweiten Spannungsabstand) gegeben ist, so wird die Referenzspannung konstant gehalten,
• (b) falls die Ausgangsspannung größer ist als die obere Grenzspannung, so wird die Referenzspannung angehoben, und
• (c) falls die Ausgangsspannung kleiner ist als die untere Grenzspannung, so wird die Referenzspannung abgesenkt.

The object is achieved according to the invention by a method for the automatic self-adjustment of a sensor, comprising a sensor with an output which outputs an output voltage and a first comparator to which the output voltage and a reference voltage are applied, the first comparator outputting a switching signal, if the output voltage is greater than the reference voltage and otherwise does not emit a switching signal, or vice versa, characterized in that the reference voltage is automatically tracked to the output voltage as follows:

• (a) If the output voltage is both - less than or equal to an upper limit voltage, which is given by the sum of the reference voltage plus a first voltage distance, and - greater than or equal to a lower limit voltage, which is given by the difference of the reference voltage minus a second Voltage distance), the reference voltage is kept constant,
• (b) if the output voltage is greater than the upper limit voltage, the reference voltage is raised, and
• (c) if the output voltage is less than that lower limit voltage, the reference voltage is lowered.

• (a) Falls der Ausgangswert sowohl – kleiner oder gleich einem oberen Grenzwert ist, welche durch die Summe aus dem Referenzwert plus einem ersten Abstandswert gegeben ist, als auch – größer oder gleich einem unteren Grenzwert ist, welche durch die Differenz des Referenzwertes minus einem zweiten Abstandswert gegeben ist, so wird der Referenzwert konstant gehalten,
• (b) falls der Ausgangswert größer ist als der obere Grenzwert, so wird der Referenzwert angehoben, und
• (c) falls der Ausgangswert kleiner ist als der untere Grenzwert, so wird der Referenzwert abgesenkt.

The object is further achieved by a method for the automatic self-adjustment of a sensor, comprising a transducer with an output that outputs an output voltage, an analog-digital converter to which the output voltage is applied and to which the latter assigns a digital output value, and a EDP device into which the digital output value is read and which compares the output value with a reference value and emits a switching signal if the output value is greater than the reference value and otherwise does not emit a switching signal, or vice versa, characterized in that the reference value corresponds to the output value is automatically updated as follows:

• (a) If the initial value is both - less than or equal to an upper limit value, which is given by the sum of the reference value plus a first distance value, and - greater than or equal to a lower limit value, which is given by the difference of the reference value minus a second Distance value is given, the reference value is kept constant,
• (b) if the initial value is greater than the upper limit, the reference value is increased, and
• (c) if the output value is less than the lower limit, the reference value is lowered.

• (a) konstant hält, falls die Ausgangsspannung sowohl – kleiner oder gleich einer oberen Grenzspannung ist, welche gegeben ist durch die Summe aus der Referenzspannung plus einem ersten Spannungsabstand, als auch – größer oder gleich einer unteren Grenzspannung ist, welche gegeben ist durch die Differenz der Referenzspannung minus einem zweiten Spannungsabstand,
• s(b) oder anhebt, falls die Ausgangsspannung größer ist als die obere Grenzspannung,
• (c) oder absenkt, falls die der Ausgangsspannung kleiner ist als die untere Grenzspannung.

The object is further achieved by a self-adjusting sensor comprising a transducer with an output that outputs an output voltage, and a first comparator with a signal input to which the output voltage is applied via a first line and a reference input to which one of one Voltage source output reference voltage is applied, wherein the first comparator outputs a switching signal if the output voltage is greater than the reference voltage, and otherwise does not output a switching signal, or vice versa, characterized in that the voltage source is a tracking circuit to which the output voltage is also applied and which is the reference voltage

• (a) holds constant if the output voltage is both - less than or equal to an upper limit voltage, which is given by the sum of the reference voltage plus a first voltage distance, and - is greater than or equal to a lower limit voltage, which is given by the difference the reference voltage minus a second voltage gap,
• s (b) or increases if the output voltage is greater than the upper limit voltage,
• (c) or reduced if the output voltage is less than the lower limit voltage.

• (a) konstant hält, falls der Ausgangswert sowohl – kleiner oder gleich einem oberen Grenzwert ist, welcher gegeben ist durch die Summe aus dem Referenzwert plus einem ersten Abstandswert, als auch – größer oder gleich einem unteren Grenzwert ist, welcher gegeben ist durch die Differenz des Referenzwertes minus einem zweiten Abstandswert,
• (b) oder anhebt, falls der Ausgangswert größer ist als der obere Grenzwert,
• (c) oder absenkt, falls der Ausgangswert kleiner ist als der untere Grenzwert.

The object is further achieved by a self-adjusting sensor comprising a transducer with an output that outputs an output voltage, an analog-digital converter to which the output voltage is applied and to which it assigns a digital output value, and an EDP device , into which the digital output value can be read and which is able to compare the output value with a reference value stored in the EDP device and emits a switching signal if the output value is greater than the reference value and otherwise does not emit a switching signal, or vice versa, characterized .
that the computer equipment the reference value

• (a) holds constant if the output value is both - less than or equal to an upper limit value, which is given by the sum of the reference value plus a first distance value, and - is greater than or equal to a lower limit value, which is given by the difference the reference value minus a second distance value,
• (b) or increases if the initial value is greater than the upper limit,
• (c) or lowered if the output value is less than the lower limit.

According to a variant of the invention the reference voltage is only raised or lowered when the output voltage for a first predeterminable or second predeterminable response time is greater or has remained smaller than the upper or lower limit voltage. In in this case the tracking circuit lifts only then does the reference voltage increase or decrease the reference voltage only when the output voltage for a first specifiable or second predefinable response time remained larger or smaller is the upper or lower limit voltage. That way they can tracking of the invention Reference voltage to higher and / or lower values and thus the self-adjustment of the sensor if necessary with any time delay, in other words, any response time. So that can e.g. advantageously an unwanted response of the tracking e.g. for short disturbances of the Output voltage can be prevented.

Likewise, according to another variant of the invention, the reference value is only raised or lowered when the initial value has remained greater or smaller than the upper or lower limit value for a first predefinable or second predefinable response time period. In this case, the computer equipment only raises the reference value or the computer equipment only lowers the reference value then when the output value has remained greater or smaller than the upper or lower limit value for a first predeterminable or second predefinable response time period.

The first and / or the second response period need not be constant in time. You can e.g. dependent on the time behavior of the output voltage or output value and / or the reference voltage or reference value are changed, i.e. variable his.

The first and / or the second voltage gap or the first and / or the second distance value can be temporal be constant. According to one other variants of the invention are the first and / or the second Voltage distance or the first and / or the second distance value changeable over time. Here you can the first and / or the second voltage spacing or the first and / or the second distance value in particular depending on the behavior over time the output voltage or the output value and / or the reference voltage or the reference value. In a further refinement of this variant, take the first and / or the second voltage spacing or the first and / or the second distance value depending from an average value obtained over time the amount of the slope of the output voltage or the output value and / or the reference voltage or the reference value to or from. The voltage gaps or distance values can in this way e.g. for sensors with non-linear but steady Distance-output voltage characteristic during operation, individually with the level of the output voltage or adjusted from the initial value become.

The first or second voltage gap can the river tension one or a series connection of diodes, which means that these phase clearances hardware on can be provided in a very simple manner.

By connecting further diodes in series, Additional diodes, can the voltage gaps gradually increased become. By bridging individuals Diodes with switches can the voltage gaps further changeable step by step his. Of course can the voltage gaps also continuously changeable his.

The rate of change of the reference voltage over time or the reference value can reach a predeterminable maximum value be limited so that the reference voltage or the reference value e.g. sudden changes in the output voltage or follows the output value only at a limited speed. This can e.g. then be advantageous if the output voltage with high frequency Interference superimposed is. The rate of change over time the reference voltage or the reference value does not need to be constant, but can change over time and e.g. the difference between output and reference voltage or output and depend on the reference value. According to one Variant of the invention starts the rate of change of the reference voltage over time or the reference value after the start of each tracking process with a specific one Value and then decreases asymptotically with time. The maximum can be changed over time will be variable in time.

The tracking circuit can be a pure one Analog circuit without digital components and e.g. a first and comprise a second diode and a charging capacitor, wherein the two diodes antiparallel between the output of the transducer and the reference input of the comparator are switched and the reference input of the comparator the charging capacitor is connected to ground.

The tracking circuit can also be a Hybrid circuit or a digital circuit without a microprocessor his. Furthermore, the tracking circuit comprise an analog / digital converter and a microprocessor, the output voltage being applied to the analog / digital converter is and this digitize the output voltage and in digital Is able to output form to the microprocessor which is the Reference voltage depending from the output voltage to calculate their temporal behavior and over is able to deliver a microprocessor output.

• a) einen zweiten und einen dritten Komparator mit je einem Signaleingang, je einem Referenzeingang sowie je einem Schaltsignal-Ausgang, wobei der zweite bzw. dritte Komparator dann und nur dann ein Schaltsignal über seinen Ausgang abgibt, wenn an seinem Signaleingang eine höhere Spannung anliegt als an seinem Referenzeingang,
• b) eine Serienschaltung aus einem dritten Widerstand, einer dritten Diode D3, einer vierten Diode und einem vierten Widerstand, wobei der dritte Widerstand mit seinem von der dritten Diode abgewandten Anschluß an einen Spannungpol und der vierte Widerstand mit seinem von der vierten Diode abgewandten Anschluß an Masse gelegt ist und die dritte und die vierte Diode in jeweils Durchlaßrichtung geschaltet sind, so daß von dem Spannungspol über diese Serienschaltung ein Strom nach Masse fließt,
• c) eine zweite Leitung, welche zwischen der dritten und der vierten Diode von der Serienschaltung abzweigt und mit dem Ausgang des Aufnehmers verbunden ist, so daß zwischen diesen Dioden die Ausgangsspannung anliegt,
• d) eine dritte Leitung, welche zwischen dem dritten Widerstand (R3) und der dritten Diode von der Serienschaltung abzweigt und an den Referenzeingang des dritten Komparators angelegt ist,
• d) eine vierte Leitung, welche zwischen dem vierten Widerstand und der vierten Diode von der Serienschaltung abzweigt und an den Signaleingang des zweiten Komparators angelegt ist,
• e) einen Binärzähler mit einem Zähleingang, einem Richtungseingang, Ausgängen sowie mit einem an diese Ausgänge angeschlossenen R- oder R2R-Netzwerk mit Widerständen, wobei der Richtungseingang mit dem Schaltsignal-Ausgang des zweiten Komparators verbunden ist und der Binärzähler einen internen Zählerstand inkrementiert, falls an seinem Zähleingang ein Taktpuls ankommt und an seinem Richtungseingang ein High-Signal anliegt, und den internen Zählerstand dekrementiert, falls an seinem Zähleingang ein Taktpuls ankommt und an seinem Richtungseingang ein Low-Signal anliegt, und der Binärzähler über seine Ausgänge und das Widerstandsnetzwerk eine in Stufen veränderliche, dem internen Zählerstand proportionale Spannung an eine fünfte Leitung abzugeben imstande ist, welche an den Signaleingang des dritten Komparators sowie an die Referenzeingänge sowohl des zweiten als auch des ersten Komparators angelegt ist,
• f) ein UND-Gatter mit einem ersten und einem zweiten UND-Eingang und einem logischen UND-Ausgang, welcher an den Zähleingang des Binärzählers angelegt ist,
• g) einen Taktgenerator, welcher über seinen Taktausgang Taktimpulse abgibt, wobei der Taktausgang mit dem ersten UND-Eingang des UND-Gatters verbunden ist, und
• h) ein ODER-Gatter mit einem ersten und einem zweiten ODER-Eingang und einem logischen ODER-Ausgang, welcher an den zweiten UND-Eingang des UND-Gatters angeschlossen ist, wobei der Schaltsignal-Ausgang des dritten Komparators an den ersten ODER-Eingang und der Schaltsignal-Ausgang des zweiten Komparators an den zweiten ODER-Eingang angeschlossen ist.

In one embodiment of the invention, the tracking circuit comprises the following components:

• a) a second and a third comparator, each with a signal input, a reference input and a switching signal output, the second or third comparator emitting a switching signal via its output only when a higher voltage is present at its signal input than at his reference entrance,
• b) a series circuit comprising a third resistor, a third diode D3, a fourth diode and a fourth resistor, the third resistor with its connection facing away from the third diode to a voltage pole and the fourth resistor with its connection facing away from the fourth diode Is connected to ground and the third and fourth diodes are switched in the forward direction, so that a current flows to ground from the voltage pole via this series connection,
• c) a second line which branches off from the series circuit between the third and fourth diodes and is connected to the output of the sensor, so that the output voltage is present between these diodes,
• d) a third line which branches off from the series circuit between the third resistor (R3) and the third diode and is connected to the reference input of the third comparator,
• d) a fourth line which branches off between the fourth resistor and the fourth diode from the series circuit and to the signal input of the second comparator,
• e) a binary counter with a counting input, a direction input, outputs and with an R or R2R network with resistors connected to these outputs, the direction input being connected to the switching signal output of the second comparator and the binary counter incrementing an internal counter reading if A clock pulse arrives at its counter input and a high signal is present at its direction input, and decrements the internal counter reading if a clock pulse arrives at its counter input and a low signal is present at its direction input, and the binary counter receives an in via its outputs and the resistor network Is capable of delivering step-variable voltage proportional to the internal meter reading to a fifth line which is applied to the signal input of the third comparator and to the reference inputs of both the second and the first comparator,
• f) an AND gate with a first and a second AND input and a logic AND output which is applied to the counting input of the binary counter,
• g) a clock generator which emits clock pulses via its clock output, the clock output being connected to the first AND input of the AND gate, and
• h) an OR gate with a first and a second OR input and a logical OR output, which is connected to the second AND input of the AND gate, the switching signal output of the third comparator to the first OR input and the switching signal output of the second comparator is connected to the second OR input.

The first, second and third or fourth diode can to increase the flow voltage at least one first or second or third or fourth additional diode be connected in series, the forward direction with that of first or second or third or fourth diode matches. This allows a gradual increase in the upper or lower Voltage spacing.

The tracking circuit can be an analog / digital converter and comprise a digital circuit, the output voltage being on the analog / digital converter is applied and this digitizes the output voltage and is able to output in digital form to the digital circuit, which is the reference voltage depending on the output voltage or to calculate their temporal behavior and to the reference entrance of the first comparator is able to deliver.

The tracking circuit can be one of a first direct current through which a seventh resistor flows and / or an eighth resistor through which a second direct current flows include, the voltage drop across the seventh and eighth resistor, respectively serves as the first and second voltage spacing.

According to the invention, it is fully automatic Adaptation of the sensor to a variety of applications without any Control element on the sensor and without user intervention. The sensor according to the invention advantageously only needs to be installed and learns independently the correct setting for the application that he "sees" after installation. With a change The sensor automatically adjusts itself to the application: it "teaches" itself.

The automatic tracking of the The reference voltage is largely analogous to the drag pointer principle and can e.g. using normal analog technology, simple digital technology or a microprocessor can be realized. A major advantage across from the conventional Teach technology consists in the elimination of any sensor operation. Further can the correct settings of the sensor with the help of the invention with even higher ones precision be met than with the conventional teach technique. The Depending on the implementation, the invention also allows an adaptation of the sensor sensitivity Real time". This can happen in "dynamic applications" with rapidly changing Requirements of the greatest advantage his.

The tracking according to the invention with rigid "working windows", which depend on the invention of the time course of the output voltage Ua in its entirety be shifted, i.e. the two voltage spacings dU1 and dU2 can after once specified, they remain constant. Of course you can if necessary, e.g. in the case of a strongly curved distance-voltage characteristic of a sensor, individual adjustments of these values e.g. dependent on from the output voltage Ua e.g. done by a microprocessor.

The tracking according to the invention is highly advantageous over the State of the art. A sensor according to the invention can be realize with very little technical or software effort. Another important advantage of the invention is in particular in that one automatic reset of the sensor always takes place when the application is changed, i.e. a Adjustment is possible in real time. The teach-in process is as short as you like, it is only necessary to have one state of an application Example full vessel, for teaching.

A sensor according to the invention can be used in particular for normal standard applications. The sensor can be, for example, a capacitive or an inductive or an acoustic sensor or a sensor for electromagnetic radiation, for example an optoelectronic sensor, or a mechanical touch sensor or a capacitive button. Gegenü The main difference over conventional sensors is that the external adjustment of the sensor, for example by adjusting a potentiometer by means of a screwdriver or control button, is advantageously eliminated due to the self-adjustment according to the invention; this also considerably facilitates the water-tight or airtight encapsulation of the sensor required in many applications, since in the case of a sensor according to the invention, no operating elements need to be guided through the sensor housing or need to be mechanically accessible from the outside. There is also no need to lay any cables for electrical remote adjustment of the sensor. These advantages are particularly advantageous, for example, if the sensor has to be operated in places that are not or not easily accessible or only at risk, such as under water, in radioactive environments Rooms (e.g. within nuclear power plants), in rooms with high toxic loads or in rooms with a risk of explosion.

Furthermore, a sensor according to the invention is the same Shifts in the working point, which may occur during the application e.g. due to contamination, dew formation, moistening of the medium (e.g. outdoors in the rain) or change of medium occur automatically, which significantly reduces the maintenance required to operate the sensor. The invention enables "plug and play" in practically all Applications.

Another advantage of the invention is that a Variety of conventional Sensors easily upgraded with a tracking circuit according to the invention and then be operated using the method according to the invention can.

• – Füllstandsüberwachung (alle Medien die Standardsensor kann, Wasser, Öl, Granulat etc.) bei gängigen Wandstärken,
• - Distanzüberwachung mit Hintergrundausblendung.

A sensor according to the invention can be used for any application for which a conventional sensor can be used and is suitable, for example, for the following applications:

• - Level monitoring (all media the standard sensor can, water, oil, granules etc.) with common wall thicknesses,
• - Distance monitoring with background suppression.

Brief description of the drawing, in which show:

1 a linear distance-output voltage characteristic of a capacitive transducer,

2 1 shows a basic circuit diagram of a conventional capacitive sensor that can be adjusted by external adjustment of a potentiometer,

3 2 shows a basic circuit diagram of another conventional capacitive sensor which can be adjusted by external adjustment of a potentiometer,

4 2 shows a block diagram of a sensor according to the invention with a tracking circuit,

5a an example of a time course of the output voltage of a capacitive transducer and the associated reference voltage, the tracking according to the invention not being activated,

5b the time profile of a sensor switching signal, which leads to the voltage profiles of 5a heard,

5c . d . e Examples of temporal profiles of the output voltage of a capacitive transducer and the associated reference voltages, the tracking according to the invention being activated in each case,

6a . b . c mechanical analogies for tracking according to the invention for different operating states,

7a . b Examples of the process of self-adjustment of a sensor according to the invention after installation in an application, and

8th . 9 . 10 Embodiments of tracking circuits according to the invention.

Ways to Execute the Invention:

To further explain the invention is first of all with reference to 1 a conventional capacitive transducer with a sufficiently linear dependence of its output voltage Ua on the distance of the active surface of the sensor from a grounded metal plate, also called "target", is considered as the starting basis; the sensor therefore has an approximately linear distance-output voltage characteristic, as in 1 is shown using an example. This linear behavior can be achieved very easily, inter alia, with a conventional RC oscillator, which is frequently used in capacitive sensor technology with the prior art, with appropriate dimensioning and adapted rectification of the oscillator output voltage.

In a conventional sensor according to the prior art, 2 , is now via an output 1A output voltage Ua of the transducer 1 in a comparator 31 compared with an adjustable reference voltage Uref. For this purpose, the output voltage Ua is connected to the signal input via a first line L1 31A and the reference voltage Uref via a seventh line L7 to the reference input 31B of the comparator 31 placed. The reference voltage Uref is usually with a potentiometer applied to a voltage Uo 3 generated and adjusted by tapping, which adjusts the sensor sensitivity, so the sensor can be adjusted, what in 2 is shown using an example.

In other conventional sensors is not the reference voltage is set at the comparator - it rather stays on always the same fixed value - but the sensor output voltage Among other things, through change of the gain factor the oscillator or other parameters set in the sensor, i.e. be adjusted.

Exceeds in 2 the one at the signal input 31A applied sensor output voltage Ua from the potentiometer 3 given at the reference entrance 31B If reference voltage Uref is applied, the comparator switches ("tilts") 31 in the "positive" state, ie it generates a switching signal and emits it via a sixth line L6, which corresponds to the switching state "on". Otherwise the comparator is located 31 in the "negative" state, ie it does not emit a switching signal, which corresponds to the switching state "Off". With the help of a first and a second resistor R1, R2 ( 3 ) a small hysteresis is usually generated so that the comparator 31 always clearly and stably tilts into one of the states "positive" or "negative". Since this hysteresis is usually chosen to be very small, it is neglected in the following considerations, whereby the condition applies: R2 >>> Ri.

In contrast, according to the invention, the reference voltage Uref is set automatically. A self-adjusting sensor according to the invention comprises a fully automatic tracking circuit, through which a reference voltage Uref correctly adjusting the sensor is electronically derived from the output voltage Ua. The potentiometer 3 is no longer required. 4 shows a block diagram of a sensor with a tracking circuit according to an embodiment of the invention 10 which below with reference to the 8th and 9 based on exemplary embodiments 10A . 10B the same is explained in more detail. The output voltage Ua is tapped from line L1 and the tracking circuit 10 fed. The tracking circuit 10 acts as a voltage source, which generates the reference voltage Uref and at the reference input 31B emits.

The following will refer to the 5 . 6 and 7 the mode of operation of a preferred variant of a tracking of the reference voltage Uref according to the invention further explained.

To further explain the invention, reference will now be made to 5a Referred. The upper limit voltage UGo is given by the reference voltage Uref plus a first voltage distance dU1, which is also referred to below as the “upper work window”. The lower limit voltage UGu is given by the reference voltage Uref minus a second voltage distance dU2, which in the following also referred to as “lower work window” " is called. An “upper work window” and a “lower work window” are thus generated. The width of these “work windows” is given by the first and second voltage spacing dU1, dU2.

Each of these two working windows is therefore defined by two different voltages, namely by Uref and UGo or by Uref and UGu. The reference voltage Uref is always higher as UGu and smaller than UGo. In a preferred variant of the invention the amount of dU1 and the amount dU2 are constant.

In 5a an example of a time course of the sensor output voltage Ua is also shown. This exceeds in the 5a Example shown after a certain time (time t1) the reference voltage Uref (sensor "actuated") with the result that the comparator 31 ( 4 ) changes to the "positive" switching state and emits a switching signal S ( 5b ). After a further period of time (time t2) in which 5a shown the sensor output voltage Ua again below the reference voltage Uref (sensor "not actuated") with the result that the comparator 31 ( 4 ) changes to the "negative" switching state and no longer outputs a switching signal ( 5b ).

In 5a is the condition that the output voltage Ua is both less than the upper limit voltage UGo and greater than the lower limit voltage UGu. According to the invention, the reference voltage Uref is therefore in 5a kept constant, so that the upper and lower limit voltage UGo, UGu remain constant, so that the position of the two working windows in 5a remains unchanged.

5c a further example of the time profiles of the output voltage Ua, the reference voltage Uref and the two limit voltages UGo, UGu, the output voltage is zero volts up to a point in time t3 and then rises to a certain plateau value Uao, which is reached at a point in time t5. This course of time can correspond, for example, to a level sensor being switched on at time t = 0, the output voltage Ua beginning to rise from time t3, for example because the level of a container to be monitored by the sensor has increased to such an extent that it noticeably influences the output voltage Ua starts.

Accordingly, the reference voltage Uref also initially has the value zero volts. According to the invention, the upper and the lower limit voltage UGo and UGu are given by the sum of the reference voltage Uref plus the first voltage distance dU1 or by the difference of the reference voltage Uref minus a second voltage distance (dU2), which means that the reference voltage Uref, the upper limit voltage UGo and the lower limit voltage UGu always run parallel to each other. The upper and lower limit voltages UGo and UGu therefore initially run horizontally at a distance dU1 and dU2 above and below the zero volt line from 5c ,

According to the invention, the reference voltage does not change until time t4, since the condition is fulfilled that the output voltage Ua is both less than or equal to the upper limit voltage UGo and greater than or equal to the lower limit voltage UGu. At time t4, however, the output voltage Ua exceeds the upper limit voltage UGo. According to the invention, the reference voltage Uref is now raised. In each case the upper and lower limit voltages UGo, UGu also rise in parallel displacement. The position of the “work window” defined above migrates accordingly from time t4 onwards 5c upwards, ie the reference voltage Uref and the “work windows” are tracked from the output voltage Ua from time t4.

At time t5, the output voltage Ua reaches in the example of 5c the plateau value Uao and does not continue to increase, for example because the maximum fill level of the container to be monitored has been reached, but the output voltage Ua is still greater than the upper limit voltage UGo, which is why the reference voltage Uref and thus the two limit voltages UGo, UGu continue to increase according to the invention ,

At time t6, the upper limit voltage UGo has also reached the plateau value Uao, ie the condition that the output voltage Ua is both less than or equal to the upper limit voltage UGo and greater than or equal to the lower limit voltage UGu is fulfilled. According to the invention, the reference voltage Uref and with it also the upper and lower limit voltages UGo, UGu remain constant. The reference voltage Uref and thus the sensor have adjusted themselves according to the invention. The upper limit voltage UGo now coincides with the output voltage Ua; in 5c these two voltages are shown slightly offset from one another merely for reasons of clarity.

According to the referring to 5c In the variant of the invention explained, the reference voltage increases more slowly in the time interval t4 to t6 than the output voltage Ua in the time interval t3 to t5. Such a behavior of the reference voltage Uref can be advantageous for various reasons, for example when the output voltage Ua is superimposed by fast interference pulses (“spikes”) that are scattered in from the outside.

Another variant of the invention is now based on 5d explained in which the output voltage shows the same curve as in 5c , However, the reference voltage Uref and thus also the limit voltages UGo, UGu in grow 5d in the time interval t4 to t6 as quickly as the output voltage Ua in the time interval t3 to t5. The times t5 (reaching the plateau voltage Uao by Ua) and t6 (reaching the plateau voltage Uao by UGo) therefore fall 5d together. Such a behavior of the reference voltage Uref can be advantageous, for example, if the self-adjustment of the sensor is to be carried out very quickly or if the hardware is to be implemented with the least possible hardware outlay, without having to use its own delay elements.The reference voltage Uref was thus tracked to the output voltage Ua in analogy to the drag pointer principle, i.e. the The output voltage Ua has the reference voltage Uref at a certain voltage distance, namely dU1, "pulled behind it". The "working windows" have been "pulled along". In this case, a certain, predeterminable distance dU1 between Ua and Uref is maintained when "pulling".

Uref is tracked by Ua at the distance dU1, so that Ua = Uref + dU1 or Uref = Ua - dU1. Among other things, from time t4 ( 5d ) by dU1 greater than the reference voltage Uref. The comparator 31 ( 4 ) generates a switching signal (high signal) because Ua is greater than Uref, ie the sensor is on from time t4 ( 5d ) operated.

The output voltage Ua now drops, for example due to a falling fill level after the time t6 ( 5c . 5d ) from a time t7 onwards ( 5e ). According to the invention, however, the reference voltage Uref and thus also the two limit voltages UGo, UGu remain constant as long as Ua does not drop below UGu; ie the two “work windows” maintain their position. The reference voltage Uref, ie the working point of the sensor, is thus “fixed”, ie the adjustment of the sensor which is automatically brought about according to the invention remains unchanged as long as Ua does not drop below UGu (or above UGo) increases).

If Ua now drops below the "fixed" value of Uref (time t8 in 5e ), the comparator gives 31 ( 4 ) no more switching signal or a low signal, ie the sensor switches off, which indicates that the level is below a certain level. In the present example, the arbitrarily definable first voltage distance dU1 is a measure of the sensitivity with which the sensor responds to a falling fill level.

Now the output voltage Ua drops even further and falls below the lower limit voltage UGu (t9) 5e ). According to the invention, the reference voltage Uref is now lowered, whereby 5e relates to such a variant of the invention, in which the reference voltage Uref falls from the time t9 at the same speed as the output voltage Ua. The upper and lower limit voltages UGo, UGu also drop parallel to Uref. The position of the “work window” defined above migrates accordingly from time t9 onwards 5e downwards, ie the reference voltage Uref and the “work windows” are tracked from the output voltage Ua from time t9 until Ua no longer drops (time t10 in 5e ). According to the invention, the reference voltage Uref and with it also the upper and lower limit voltages UGo, UGu remain constant. The reference voltage Uref and thus the sensor have adjusted themselves according to the invention. The lower limit voltage UGu now coincides with the output voltage Ua; in 5e these two voltages are shown slightly offset from one another merely for reasons of clarity.

Conversely, if, inter alia, rises again, for example because the level rises again, the reference remains voltage Uref and the position of the "working window""fix" and only change again when Ua exceeds the upper limit voltage UGo. Then the reference voltage and the "working window" are "pulled up" again, ie the output voltage Ua However, Ua exceeds the still "fixed" reference voltage Uref and the sensor switches on again. In the present example, the second voltage spacing dU2, which can be set as desired, is a measure of the sensitivity with which the sensor responds to an increasing fill level.

Of course, is in complete analogy 5c also referring to the 5e explained downward adjustment of the reference voltage, a variant is possible in which the reference voltage drops more slowly than the output voltage. Furthermore, of course, the output voltage Ua does not need, as in 5a . c . d and e shown to be linear in sections; the course can also be curved. According to a variant of the invention, the rate of rise or fall of the reference voltage Uref is not, as in FIG 5a . c . d and e shown, constant, but variable in time, eg progressively increasing in amount with time. Of course, the time dependencies of the rising and falling speed of the reference voltage Uref need not be the same in opposite directions.

According to further variants of the invention with the tracking the reference voltage Uref does not start immediately as soon as the output voltage Ua exceeds the upper limit voltage or, the lower limit voltage UGu falls below. Rather begins the tracking of the reference voltage Uref according to one of these variants then when the output voltage Ua can be predetermined for a specific first Response time T1 remained longer is as the upper limit voltage UGo. According to another of these variants tracking begins the reference voltage Uref down only when the output voltage Ua for a certain second predeterminable response time period T2 has remained smaller is than the lower limit voltage UGu. These variants, of course, too can be combined with each other can e.g. then be advantageous if the self-adjustment according to the invention of the sensor by short, e.g. vibration-related disorders of the Output voltage Ua triggered shall be.

You can use the 5d . 5e Compare the explained tracking process with a mechanical drag pointer principle, which is now based on the 6a . 6b and 6c is explained in more detail. On a main pointer 22 is a driver claw rigidly to this 23 attached so that the main pointer 22 and the driving claw 23 an asymmetrical cross 22 . 23 form, the driving claw 23 the crossbar of the cross 22 . 23 forms and on one side by a distance X1, on the other side by a distance X2 over the main pointer 22 survives. The main pointer 22 is like clock hands around a turning center 24 pivoted and has a drive (not shown), which is the main pointer 22 clockwise and counterclockwise around the turning center 24 is able to swing. Due to the rigid connection to the main pointer 22 follows the driving claw 23 all pivoting movements of the main pointer 22 around the turning center 24 ,

To the turning center 24 is also similar to a clock hand, a drag pointer 21 arranged pivotably, the driving claw 23 the slave pointer 21 crossed without being mechanically connected to it. The drag pointer 21 does not have its own drive.

The driving claw 23 has stops at both ends 23A . 23B for the slave pointer 21 , which is the size of the relative displacement between driving claw 23 and drag pointer 21 and thus also the maximum angular distance between the main pointer 22 and drag pointer 21 limit each to a certain scope; with a movement of the driving claw 23 the trailing pointer is beyond this scope 21 over one of the attacks 23A . 23B from the driving claw 23 pulled and thereby the pivoting movements of the main pointer 22 about the center of rotation 24 tracked with a certain distance. If the lines X1, X2, as in the present example, the 6a-6c , are not the same size, but the cross 22 . 23 regarding the main pointer 22 is asymmetrical, is the maximum angular distance between the main pointer 22 and drag pointer 21 for clockwise movements is different from that for counterclockwise movements.

The maximum angular distance by which the main pointer 22 opposite the drag pointer 21 can be deflected clockwise or counterclockwise by the length of the lines X1 or X2 and by the distance of the crossing points between the driving claw 23 and main pointer 22 from the turning center 24 specified.

The drag pointer 21 is initially in a certain rest position. Now becomes the main pointer 22 due to its drive, for example clockwise, always further towards the drag pointer 21 deflected, the driving claw strikes 23 first with their stop 23A on the slave pointer 21 on. Now becomes the main pointer 22 due to its drive, for example, still clockwise in relation to the drag pointer 21 deflected, the latter is the main pointer 22 over the driving claw 23 dragged clockwise to a new rest position, i.e. adjusted ( 6a ). The main pointer 22 now has opposite the drag pointer 21 about a new asymmetrical scope that is as large on both sides as the previous scope, but clockwise compared to this meaning is shifted.

Now become the main pointer 22 pivoted counterclockwise ( 6b ). Again the drag pointer 21 the movement of the main pointer 22 through the driving claw 23 tracked as soon as the main pointer 22 leaves his scope - this time counterclockwise -; the drag pointer 21 is then again moved to a new rest position, etc. ( 6c ). The drag pointer 21 only comes into action when the main pointer 22 leaves its scope.

This mechanical example is consistently transferred to sensor technology in the invention. The position of the main pointer 22 corresponds to the output voltage Ua, that of the drag pointer 21 the reference voltage Uref. The scope of the main pointer 22 Compared to the drag pointer on both sides, the size of the first or second voltage spacing dU1, dU2 or the width of the "work window" corresponds to the tracking of the drag pointer 21 through the main pointer 22 thus corresponds to that of the reference voltage Uref by the output voltage Ua; In both cases, the tracking becomes active only when a predetermined scope between the tracking and tracking size has been exhausted. The switching point of the sensor is reached when Ua = Uref, which is in the mechanical analogy of 6 the situation (not shown) corresponds to the fact that the main and trailing pointers overlap.

Under the convention that a movement of the hands 21 respectively. 22 clockwise an increase in voltage Uref or Ua and an opposite movement of the hands 21 respectively. 22 corresponds to a decrease in these tensions, corresponds to that in 6a shown situation therefore an actuated sensor (Ua> Uref) and a shift (tracking) of the reference voltage Uref and the working window upwards. The situation of 6b corresponds to an unactuated sensor (Ua <Uref) and a "fixed" position of the reference voltage Uref and working window. The situation of 6c corresponds to an unactuated sensor (Ua <Uref) and a shift (tracking) of the reference voltage Uref and the working window downwards.

In the most common cases in the practice of sensor technology are the "working window" only during assembly or disassembly of the sensor moved into or out of the application. The output voltage Ua then usually varies in the application itself only within the window widths dU1, dU2 around which the reference voltage Uref (= "working point"). This is usually the case remember that the container wall with a fill level application makes such a large contribution to the total capacity that even without Medium the output voltage Ua hardly ever drops to 0 volts, but only to a smaller value than the one who is at full coverage through the medium. The maxima and minima of the output voltage In most applications, for example, only within the Width of the respective "working window". For every application the two "work windows" put themselves through the tracking of the invention Reference voltage Uref to the correct one by the output voltage Ua Value, the operating point is then correct automatically.

• 1. Ua = OV bei Sensor in der Luft (Abstand unendlich), Ua = 7V bei Sensor vollbedämpft, maximale Kapazität bzw. Abstand zu einer geerdeten Meattplatte = 0 erster Spannungsabstand: dU1 = 0,3V zweiter Spannungsabstand: dU2 = 1,2V
• 2. Füllstandsapplikation desselben Sensors mit Medium Wasser und Behälter aus Plexiglas mit 6mm Wandstärke: Ua = 6V bei vollbedecktem Sensor, Ua 4,4V bei leerem Behälter Nun wird der Sensor an einen vollen Behälter montiert. Der Arbeitspunkt wird mit Ua auf Uref = 5,7V (d.h. UGu = 4,5V) verschoben. Der Sensor schaltete ein da Ua über Uref liegt. Der Füllstand sank nun langsam ab. Bei etwa hälftiger Bedeckung der aktiven Sensorfläche unterschritt Ua die auf 5,7V "fixierte" Referenzspannung Uref; der Sensor schaltete aus. Bei leerem Gefäß sank Ua nun auf 4,4 V. Die untere Grenzspannung UGu lag um 100mV höher, nämlich bei UGu = 4,5V. Die Arbeitsfenster und Uref wurden also um 100mV nach unten nachgeführt. Uref war also jetzt erfindungsgemäß automatisch auf 5,6V abgesenkt worden. Beim Wiederansteigen des Flüssigkeitsspiegels schaltete der Sensor daher bei etwa 40% Bedeckung wieder ein. Durch die Fensterverschiebung hat sich der Schaltpunkt (Arbeitspunkt) also nur geringfügig verschoben, die Applikation ist voll erfüllt.
• 3. Füllstandsapplikation desselben Sensors mit Medium Kunststoffgranulatperlen in Behälter mit 2mm Wandstärke aus Plexiglas: Ua= 3,8V bei vollem Behälter, Ua = 2,8V bei leerem Behälter. Der Sensor wurde an ein volles Gefäß montiert. Die Referenzspannung wurde mit Ua auf Uref = 3,5V, die untere Grenzspannung auf UGu = 2,3V verschoben, der Sensor schaltete ein da Ua um 0,3V über der erfindungsgemäß automatisch "fixierten" Referenzspannung von 3,5V lag. Der Füllstand sank nun ab. Bei etwa hälftiger Bedeckung der aktiven Sensorfläche unterschritt Ua den Wert 3,5V und der Sensor schaltete daher aus. Bei weiterem Absinken bis zum Leerzustand erreichte Ua den Tiefstwert von 2,8V. Dieser Wert lag somit über der unteren Grenzspannung UGu. Eine Nachführung erfolgte daher nicht. Beim Wiederanstieg des Füllstandes schaltete der Sensor wieder bei Ua = 3,5V und mittiger Bedeckung ein.

Some numerical values determined or advantageously set in practical operation of a capacitive level sensor are given below:

• 1. Ua = OV with sensor in the air (distance infinite), Ua = 7V with sensor fully damped, maximum capacitance or distance to a grounded plate = 0 first voltage distance: dU1 = 0.3V second voltage distance: dU2 = 1.2V
• 2. Level application of the same sensor with medium water and plexiglass container with 6mm wall thickness: Ua = 6V with fully covered sensor, Ua 4.4V with empty container Now the sensor is mounted on a full container. The working point is shifted with Ua to Uref = 5.7V (ie UGu = 4.5V). The sensor switched on because Ua is above Uref. The fill level now dropped slowly. When the active sensor surface is covered by about half, Ua falls below the reference voltage Uref "fixed" at 5.7V; the sensor switched off. When the vessel was empty, Ua now dropped to 4.4 V. The lower limit voltage UGu was 100mV higher, namely UGu = 4.5V. The working windows and uref were adjusted downwards by 100mV. According to the invention, Uref was now automatically reduced to 5.6V. When the liquid level rose again, the sensor therefore switched on again at about 40% coverage. Due to the window shift, the switching point (working point) has only shifted slightly, the application is fully fulfilled.
• 3. Level application of the same sensor with medium plastic granulate beads in containers with 2mm wall thickness made of plexiglass: Ua = 3.8V with full container, Ua = 2.8V with empty container. The sensor was mounted on a full vessel. The reference voltage was shifted with Ua to Uref = 3.5V, the lower limit voltage to UGu = 2.3V, the sensor switched on since Ua was 0.3V above the automatically fixed 3.5V reference voltage. The fill level now dropped. If the active sensor area is covered by about half, the value falls below 3.5 V and the sensor therefore switches off. With a further decrease to the empty state, Ua reached the lowest value of 2.8V. This value was therefore above the lower limit voltage UGu. There was therefore no tracking. When the level rose again, the sensor switched on again at Ua = 3.5V and central coverage.

The 7a . 7b show for further general NEN illustration of the automatic adjustment process (teach-in process) according to the invention of a sensor using the example of a fill level application, the associated time profiles of the voltages. The sensor is initially in the air (time span t11-t12 in 7a , t18-t19 in 7b ) and then (at time t12 in 7a , at time t19 in 7b ) mounted on a container to be monitored by the sensor for whether it is full or not. In particular, two extreme cases are possible and relevant in practice: The container to be monitored for its fill level can initially be full after the sensor has been installed and commissioned ( 7a ) or be empty ( 7b ).

In which the 7a based on the example, the sensor is mounted on an already full container at time t12. As a result, the output voltage Ua rises to the highest value for Ua occurring in the application, namely Ua _max . The reference voltage Uref and the limit voltages UGo, UGu are tracked according to the invention at time t12. According to the invention, the sensor is actuated correctly (switching signal high, container full) and is automatically correctly adjusted from time t12 without the need for an operation or external adjustment of the sensor. At time t13, the fill level and thus the output voltage Ua begin to drop. At time t14, Ua falls below the value of Uref: the sensor switches off correctly (switching signal low).

At time t15 the container is empty; Ua therefore reaches the minimum possible value in this application, namely Ua _min , which in the present example, however, is still greater than the lower limit voltage UGu, so that the reference voltage Uref and the limit voltages UGu, UGo are not tracked. The container is then refilled in the present example (t15 - tt17). At time t16, the output voltage Ua again reaches the value it had at time t14, namely Uref; the sensor switches on again.

In which the 7b based on the example, the sensor is mounted on an empty container at time t19. Due to the inherent capacity of the container wall and possibly other interference effects, the output voltage Ua does not remain at the value zero, but rather rises to the minimum value for Ua occurring in the application, namely to Ua _min . According to the invention, Uref and the limit voltages UGo, UGu are tracked, but this is still not sufficient to finally adjust the sensor: Ua is larger than Uref between t19 and t21, so that the sensor trips even though the container is empty or not yet full is: First of all, there is a false trigger.

The filling of the container begins at time t20. Therefore, the fill level of the medium and thus Ua continue to increase; Uref and the "work window" are "dragged along", ie tracked according to the invention. At time t21 the container is full; Ua has reached the value Ua _max and does not rise any further, Uref and the "work windows" are "fixed", they "now sit correctly" and the sensor has adjusted itself permanently at this point at the latest. At time t21, the container begins to be emptied; Among other things, begins to fall. At time t22, Ua falls below the "fixed" value of Uref, the sensor switches off correctly (switching signal low). The container is empty in the time interval t23 to t24, and refilling begins at t24. at time t25 - if the permanently "fixed" reference voltage Uref is exceeded - the sensor, which is still correctly adjusted, switches on again (switching signal high).

The voltage spacings dU1, dU2 are advantageously chosen such that the range given by dU1 and dU2 due to the fluctuation of the output voltage Ua between Ua _{m in} and Ua _max (cf. mechanical drag pointer analogy in 6 ) is not exhausted: Uref remains "fixed" for the entire further application of the sensor. The sensor must therefore, so to speak, go through the process once or "see" the medium once in order to adjust itself to it.

8th shows a schematic diagram of a simple technical embodiment of the invention with an embodiment 10A the tracking circuit 10 of 4 with a first and a second diode D1, D2 and a charging capacitor C. The tracking circuit 10A in this simple embodiment does not comprise any further components and acts as a voltage source which generates the reference voltage Uref and at the reference input 31B emits. The two diodes D1, D2 are anti-parallel between the output 1A of the transducer 1 and the reference entrance 31B of the comparator 31 connected. The reference entrance 31B of the comparator 31 is also connected to ground via the capacitor C.

The output voltage Ua can be inside the transducer 1 buffered or low-impedance at the output by a non-inverting voltage follower (not shown) interposed in the signal path there, which has a voltage amplification factor of 1 1A be made available. The exit 1A is via line L1 and the first resistor R1 to the signal input 31A of the comparator 31 placed.

The forward voltages of the diodes D1, D2 generate the widths dU1, dU2 of the "work window" of a total of approximately 1.2V or 0.6V each. Elevated If the voltage Ua increases by more than 0.6V above Uref at C, the first diode Dl conducting and charging C to the value Ua - 0.6V = Uref on. The river tension the diode D1 thus corresponds to the value of the upper voltage gap dU1 in the above Presentation. The "working windows" are now set. If Ua drops again, diode D1 blocks and the voltage value Uref is held by the charging capacitor C1: Uref is "fixed".

If Ua falls below Uref, the sensor switches off (no switching signal or low signal on line 6 ). If Ua rises above Uref, the sensor switches on again. If Ua drops below the value UGu = Uref - 0.6V, the second diode D2 becomes conductive and the voltage at C follows Ua down until Ua remains: Uref is tracked according to the invention. The sensor is now not activated until Ua again exceeds Uref, so it has adjusted itself to a new application.

The width of the "working window" can be added by inserting further diode sections (Additional diodes) varied in series with the diodes D1 and D2 in 0.6V steps become. The advantage of this embodiment is a low switching effort. Using a comparator in C-Mos or FET technology, a few minutes hold time for Uref is achieved. The circuit is therefore ideal for dynamic Applications in which a constant, periodic change the measured variable secured is.

9 shows a further embodiment of the invention 10B a tracking circuit, which is a simple digital binary counter 44 and second and third comparators 32 . 33 having. Each of these comparators 32 . 33 has a signal input 32A respectively. 33A , a reference entrance 32B respectively. 33B and a switching signal output 32C respectively. 33C and emits a switching signal via this then and only when the signal input 32A respectively. 33A applied voltage is greater than that at its reference input 32B respectively. 33B applied voltage.

A positive voltage pole 7 is connected to ground via a series circuit comprising a resistor R3, a third diode D3, a fourth diode D4 and a resistor R4, the two diodes D3, D4 being connected in the forward direction, so that the positive pole 7 A current flows to ground via this series circuit R3, D3, D4, R4. The voltage of the voltage pole 7 is at least 0.6V higher than the maximum output voltage Ua _{max of} the sensor 1 ,

The output voltage Ua can be inside the transducer 1 buffered or low-impedance at the output by a non-inverting voltage follower (not shown) interposed in the signal path there, which has a voltage amplification factor of 1 1A be made available. The exit 1A is, as already in 4 and 8th , via line L1 and resistor R1 to the signal input 31A of the first comparator 31 placed, which also the reference entrance 31B and the switching signal output 31C owns the first comparator 31 emits a switching signal on line L6 when the signal input 31A applied voltage is higher than that at the reference input 31B applied voltage Uref. The tracking circuit 10B acts as a voltage source, which generates the reference voltage Uref and at the reference input 31B emits.

A second line L2 branches off between the two diodes D3, D4, which line leads to line L1 and thus to the output 1A of the transducer 1 is connected so that the output voltage Ua is present between the diodes D3, D4. The signal input 31A is also, as also already in 4 and 8th , through resistor R2 with the output 31C of the comparator 31 connected back, whereby the ohmic value of R2 is much larger than that of R1 (R2 >>> Rl).

A third line L3 branches off between the resistor R3 and the diode D3, which leads to the reference input 33B of the third comparator 33 is created. Furthermore, a fourth line L4 branches off between the resistor R4 and the diode D4, which leads to the signal input 32A of the second comparator 32 is created. Due to the forward voltages of the diodes D3, D4, the line L3 is at a voltage of Ua + 0.6 volts, the line L4 is at a voltage of Ua - 0.6 volts.

The forward voltage of the fourth diode D4 forms the upper voltage gap dU1, i.e. the width of the upper "working window" (0.6V), and the forward voltage the third diode D3 forms the lower voltage gap dU2, i.e. the width of the lower "working window" (also 0.6V). These values can by inserting from further diode sections (additional diodes) in series with the diodes D3 or D4 increased become.

The binary counter 44 has a plurality of, for example, six outputs Q1 to Q6, all of which are separately connected to a resistor 45 on an R or R2R network 45 are connected. Each of the resistors 45 is connected to a fifth line L5, which is connected to the signal input 33A of the comparator 33 as well as at the reference entrance 32B of the comparator 32 as well as at the reference entrance 31B of the comparator 31 connected.

The binary counter 44 is used in conjunction with the R or R2R network used for simple D / A conversion 45 used to generate the reference voltage Uref. Via its outputs Q1 to Q6 and the network 45 the binary counter outputs a voltage on a line L5 which is proportional to an internal counter reading of the binary counter 44 and is therefore gradually variable. 6 bits are sufficient to subdivide this voltage range into 64 steps (the more the better). This voltage is used as the reference voltage Uref and is via line L5 both to the signal input 33A of the third comparator 33 as well as at the reference entrance 32B of the second comparator 32 as well as at the reference entrance 31B of the first comparator 31 created.

The inventive tracking of the binary counter 44 generated reference voltage Uref is in the embodiment of 9 realized as follows.

A clock generator 41 gives about his exit 41A Clock pulses to the one, first AND input 42A an AND gate 42 from, its logical AND output 42C to the counter entrance 44A of the binary counter 44 is created. The binary counter 44 can have a directional entrance 44B toggle between up and down counting modes (ie between incrementing and decrementing the internal counter reading); it is in count up mode when at the direction input 44B a high signal is present, and otherwise in the countdown mode. With every cycle or pulse at the counter input 44A The voltage Uref on the R network (line L5) then increases by 1/64 in the up-counting mode or decreases by 1/64 in the down-counting mode. The counter reading can only vary between the value zero (no voltage is generated) and the value 63 (the highest possible voltage is generated).

The switching signal output 32C of the comparator 32 is at the direction entrance 44B of the binary counter 44 and also to the one OR input 43B an OR gate 43 connected. To the other OR input 43A of the OR gate 43 is the exit 33C of the comparator 33 connected.

The logical OR output 43C of the OR gate 43 is at the other AND input 42B of the AND gate 42 connected. The AND gate 42 outputs via its logical AND output 42C the clock pulses of the clock generator 41 continue to the counter entrance 44A of the binary counter 44 , if at the other, second AND input 42B of the AND gate a switching signal is present.

Now increases that at the resistor R4 (and thus via the line L4 also at the signal input 32A of the comparator 32 ) applied voltage (Ua - 0.6V) above the value of Uref (line L5), which means that Ua is greater than Uref + 0.6V, i.e. Ua exceeds the upper limit voltage UGo = Uref + 0.6V, switches the comparator 32 a: he gives about his exit 32C a switching signal. This passes through the OR gate 43 to the second AND input 42B of the AND gate 42 with the result that the clock pulses of the clock generator 41 to the counter entrance 44A of the binary counter. At the same time, however, as stated above, is the exit 32C of the comparator 32 with the directional entrance 44B of the binary counter 44 connected, which has the consequence that the binary counter 44 through the comparator 32 is put into the up-counting mode, ie the internal counter reading and thus Uref increase until the comparator 32 off. Uref is thus tracked according to the increase in Ua at a distance dU1 = 0.6V.

The reference voltage Uref and the two "work windows" were thus pushed upwards and Uref "fixed". Among other things, it can now move within the scope spanned by dU1, dU2 and via the comparator 31 Depending on the instantaneous size of the output voltage Ua, trigger a switching signal "sensor actuated" or not.

The third comparator 33 is switched off in this state (ie there is no switching signal at its switching signal output 33C ab), since the voltage on line L3, ie at the reference input 33B of the comparator 33 (Ua + 0.6V) is higher than Uref. As long as ua does not leave the above-mentioned scope, both are the second comparator 32 as well as the third comparator 33 switched off; neither of them emits a switching signal. At none of the entrances 43A . 43B of the OR gate 43 there is therefore a high signal, ie also at the second input 42B of the AND gate 42 there is no high signal. The pulses of the clock generator 41 therefore do not reach the counter input 44a of the binary counter, with the result that Uref remains unchanged: Uref remains "fixed".

If the output voltage Ua now drops by more than 0.6V below the reference voltage Uref, ie Ua leaves the "margin", it falls below that at the reference input 33B of the third comparator 33 applied voltage (= Ua + 0.6V) the value of the "fixed" reference voltage Uref. The comparator 33 gives about his exit 33C a switching signal via the OR gate 43 to the second AND input 42B of the AND gate 42 , causing the clock of the clock generator 41 to the counting entrance 44A is unlocked. At the direction entrance 44B there is no switching signal anymore, since the second comparator 32 is switched off. The binary counter 44 counts backwards, the internal counter decrements, the reference voltage Uref drops until it reaches the value at the reference input 33B below; then the third comparator switches 33 off, the meter reading remains, Uref and the "working window" are shifted down and the reference voltage Uref is "fixed" at a new value.

A particular advantage of the embodiment of 9 consists in their ability to store the last generated working point, ie the "fixed" value of Uref, as long as the counter 44 does not change its counter reading as long as, among other things, remains in the "scope". If the supply voltage of the meter is buffered, for example using a C-Mos module with the lowest possible current consumption and storage capacitor, the last value of Uref or meter reading is retained even after the supply voltage has been removed. The last meter reading can also be saved in an EE-Prom and thus be available again after a complete shutdown of the system. The arrangement can be realized with inexpensive components. No microcontroller and no software is required.

10 illustrates an embodiment of the invention with an analog-to-digital converter 50 and an IT facility 51 , which in particular can be a microprocessor. The exit 1A of the transducer 1 outputs the output voltage Ua, which is sent to the analog-digital converter 50 is created. This digitizes the output voltage Ua and assigns it a digital output value Wa, which is via a bus 55 to the IT facility 51 is read. The software compares the output value Wa with that in the EDP device 51 in a store 54 stored reference value Wref and outputs via an output line 52 a switching signal if the output value Wa is greater than the reference value Wref. Furthermore, are in the memory 54 an upper distance value dW1 and a lower distance value dW2 are stored.

• (a) konstant hält, falls der Ausgangswert Wa sowohl – kleiner oder gleich einem oberen Grenzwert WGo ist, welcher gegeben ist durch die Summe aus dem Referenzwert Wref plus dem ersten Abstandswert dW1, als auch – größer oder gleich einem unteren Grenzwert WGu ist, welcher gegeben ist durch die Differenz des Referenzwertes Wref minus dem zweiten Abstandswert dW2,
• (b) oder anhebt, falls der Ausgangswert Wa größer ist als der obere Grenzwert WGo,
• (c) oder absenkt, falls der Ausgangswert Wa kleiner ist als der untere Grenzwert WGu.

The EDP facility 51 is set up to match the reference value Wref

• (a) holds constant if the output value Wa is both - less than or equal to an upper limit value WGo, which is given by the sum of the reference value Wref plus the first distance value dW1, and - greater than or equal to a lower limit value WGu, which is given by the difference of the reference value Wref minus the second distance value dW2,
• (b) or increases if the initial value Wa is greater than the upper limit value WGo,
• (c) or lowered if the output value Wa is less than the lower limit value WGu.

According to a further variant of the Invention includes the tracking circuit a microprocessor and an A / D converter. The voltage Ua des The transducer is digitized using the analog / digital converter. The tracking according to the invention is in the microprocessor e.g. by calculating the reference voltage Uref from Ua - dU1 = Uref and the lower limit voltage UGu simulated. The shifting and comparator function is performed by the microprocessor by comparing Uref and Ua performed with hysteresis. The microprocessor reads in constant Cycles the digitized values of Ua and delivers that directly Switching signal "sensor actuated "(e.g. high signal) or "Sensor not activated" (e.g. low signal).

In this embodiment, all degrees of freedom are given. The widths dU1, dU2 of the "work window" can be specified as desired. Furthermore, a linear characteristic curve of the transducer is not essential 1 needed, but it is sufficient to continuously increase or decrease, for example, the level in a container or the distance to an object to be detected. The microprocessor then adjusts the width of the "work window" depending on the Ua to the respective slope of the characteristic curve. Furthermore, an adaptation to any output voltage range Ua _min to Ua _{max of} any sensors is possible. The last working point Uref is automatically saved in an EE-Prom, for example, when the supply voltage is interrupted. When using a capacitive transducer 1 With a linear characteristic, the software effort is particularly low. With a stroke of Ua from 0 (sensor in the air) to 7V (distance to the metal plate = 0), for example, a value of 0.3V for dUi and a value of 0.6V to 1.2V for dU2 have proven to be particularly favorable proven for a variety of applications.

Industrial applicability:

The method according to the invention is suitable in capacitive sensors, among others For level applications liquid and solid media, automatic readjustment for adhering media, for example when querying glues and varnishes where the Layer thickness on the container wall with the filling increases, with double sheet control with paper query, with capacitive Buttons, distance inquiries with background suppression, label inquiry, for example with a slot sensor, and the like.

Is the leading figure 8th ,

1

pickup

1A

output from 1

1B

active sensor surface

3

potentiometer

7

voltage pole

10,10A, 10B

Nachführschaltungen

21

Peak values

22

main pointer

23

Mitnehmerkralle

23A, 23B

Attacks from 23

24

turning center

31,32,33

First, second, third comparator

31A, 32A, 33A

Signal inputs from 31,32,33

31B, 32B, 33B

Reference inputs from 31,32,33

31C, 32C, 33C

Switching signal outputs from 31,32,33

41

clock generator

42

AND gate

42A, 42B, 42C

first, second AND input of 42 , AND output from 42

43

OR gate

43A, 43B, 43C

first, second OR input of 43 , OR output from 43

44

binary counter

44A, 44B

Counter input, direction input from 44

45

Resistor network

50

Analog to digital converter

51

EDP device

52

Output management from 51

54

Storage

55

bus

Di-D4

diodes

L1-L7

first to seventh line

Ql-Q6

Outputs from 44

Ri-R6

resistors

Claims (29)

Method for automatic self-adjustment of a sensor, comprising a sensor ( 1 ), with one exit ( 1A ), which outputs an output voltage (Ua), and a first comparator ( 31 ) to which the output voltage (Ua) and a reference voltage (Uref) are applied, the first comparator ( 31 ) emits a switching signal if the output voltage (Ua) is greater than the reference voltage (Uref), and otherwise does not emit a switching signal, or vice versa, characterized in that the reference voltage (Uref) automatically tracks the output voltage (Ua) as follows: ( a) If the output voltage (Ua) is both - less than or equal to an upper limit voltage (UGo), which is given by the sum of the reference voltage (Uref) plus a first voltage distance (dU1), and - greater than or equal to a lower limit voltage (UGu), which is given by the difference of the reference voltage (Uref) minus a second voltage distance (dU2), the reference voltage (Uref) is kept constant, (b) if the output voltage (Ua) is greater than the upper limit voltage ( UGo), the reference voltage (Uref) is raised, and (c) if the output voltage (Ua) is lower than the lower limit voltage (UGu), the reference voltage (Uref) is given off lowers. Method for automatic self-adjustment of a sensor, comprising a sensor ( 1 ), with one exit ( 1A ), which outputs an output voltage (Ua), an analog-digital converter ( 50 ), to which the output voltage (Ua) is applied and to which it assigns a digital output value (Wa), and an EDP device ( 51 ) into which the digital output value (Wa) is read and which compares the output value (Wa) with a reference value (Wref) and emits a switching signal if the output value (Wa) is greater than the reference value (Wref), and otherwise no switching signal outputs, or vice versa, characterized in that the reference value (Wref) is automatically tracked to the output value (Wa) as follows: (a) If the output value (Wa) is both - less than or equal to an upper limit value (WGo), which is determined by the Is the sum of the reference value (Wref) plus a first distance value (dW1), as well as - is greater than or equal to a lower limit value (WGu), which is given by the difference of the reference value (Wref) minus a second distance value (dW2), the reference value (Wref) is kept constant, (b) if the output value (Wa) is greater than the upper limit value (WGo), the reference value (Wref) is increased, and (c) if the output value (Wa) is smaller as the lower limit (WGu), the reference value (Wref) is lowered. A method according to claim 1 or 2, characterized in that that the Reference voltage (Uref) is only raised or lowered if the output voltage (Ua) for a first predefinable or second predefinable response time period (dT1, dT2) larger or has remained less than the upper or lower limit voltage (UGo, UGu), or the reference value (Wref) only then raised or lowered if the output value (Wa) for a first predefinable or second predefinable response time (dT1, dT2) remained larger or smaller is as the upper or lower limit (WGo, WGu). Method according to Claim 1 or 2, characterized in that the sensor is a capacitive or an inductive or an acoustic sensor or a Sensor for electromagnetic radiation, for example an optoelectronic sensor, or a mechanical touch sensor or a capacitive button. A method according to claim 1 or 2, characterized in that that the first and / or the second voltage spacing (dU1, dU2) or the first and / or the second distance value (dW1, dW2) can be kept constant over time. A method according to claim 1 or 2, characterized in that that the first and / or the second voltage spacing (dU1, dU2)) or the the first and / or the second distance value (dW1, dW2) can be changed over time A method according to claim 5, characterized in that the first and / or the second voltage spacing (dU1, dU2) or the first and / or the second distance value (dW1, dW2) as a function of temporal behavior of the output voltage (Ua) or the output value (Wa) and / or the reference voltage (Uref) or the reference value (Wref) changed becomes. A method according to claim 7, characterized in that the first and / or the second voltage spacing (dU1, dU2) or the first and / or the second distance value (dW1, dW2) depending on an average value of the Amount of the slope of the output voltage (Ua) or the output value (Wa) and / or the reference voltage (Uref) or the reference value (Wref) enlarged or be made smaller. Method according to one of claims 1 to 7, characterized in that that the rate of change over time the reference voltage (Uref) or the reference value (Wref) to one predeterminable maximum value is limited. A method according to claim 9, characterized in that the maximum value changed over time becomes. Method according to one of claims 1 to 10, characterized in that that the first and / or second response time period (dT1, dT2) depending the time behavior of the output voltage (Ua) or the output value (Wa) and / or the reference voltage (Uref) or the reference value (Wref) changed become. Self-adjusting sensor, comprising a sensor ( 1 ) with one output ( 1A ), which outputs an output voltage (Ua), and a first comparator ( 31 ) with a signal input ( 31A ), to which the output voltage (Ua) is applied via a first line (L1), and a reference input ( 31B ) to which one of a voltage source ( 10 . 10A . 10B ) output reference voltage (Uref) is applied, the first comparator ( 31 ) emits a switching signal if the output voltage (Ua) is greater than the reference voltage (Uref), and otherwise does not emit a switching signal, or vice versa, characterized in that the voltage source ( 10 . 10A . 10B ) a tracking circuit ( 10 . 10A . 10B ) to which the output voltage (Ua) is also applied and which keeps the reference voltage (Uref) (a) constant if the output voltage (Ua) is both - less than or equal to an upper limit voltage (UGo), which is given by the Sum of the reference voltage (Uref) plus a first voltage distance (dU1), as well as - greater than or equal to a lower limit voltage (UGu), which is given by the difference of the reference voltage (Uref) minus a second voltage distance (dU2), (b ) or increases if the output voltage (Ua) is greater than the upper limit voltage (UGo), (c) or decreases if the output voltage (Ua) is less than the lower limit voltage (UGu). Self-adjusting sensor, comprising a sensor ( 1 ), with one exit ( 1A ), which outputs an output voltage (Ua), an analog-digital converter ( 50 ), to which the output voltage (Ua) is applied and to which it assigns a digital output value (Wa), and an EDP device ( 51 ), into which the digital output value (Wa) can be read and which the output value (Wa) with a in the EDP device ( 51 ) is able to compare the stored reference value (Wref) and emits a switching signal if the output value (Wa) is greater than the reference value (Wref), and otherwise does not emit a switching signal, or vice versa, characterized in that the EDP device ( 51 ) keeps the reference value (Wref) (a) constant if the output value (WUa) is both - less than or equal to an upper limit value (WGo), which is given by the sum of the reference value (Wref) plus a first distance value (dW1) , as well - is greater than or equal to a lower limit value (WGu), which is given by the difference of the reference value (Wref) minus a second distance value (dW2), (b) or increases if the initial value (Wa) is greater than that upper limit (WGo), (c) or lowered if the initial value (Wa) is less than the lower limit (WGu). Sensor according to claim 12 or 13, characterized in that the tracking circuit ( 10 . 10A . 10B ) does not raise or lower the reference voltage (Uref) until the output voltage (Ua) has remained larger or smaller than the upper or lower limit voltage (UGo, UGu) for a first predefinable or second predefinable response time period (dT1, dT2), or the EDP device ( 51 ) only increases or decreases the reference value (Wref) when the output value (Wa) has remained greater or smaller than the upper or lower limit value (WGo, WGu) for a first predefinable or second predefinable response time period (dT1, dT2) ). Sensor according to claim 12 or 13, characterized in that the Sensor a capacitive or an inductive or an acoustic Sensor or a sensor for electromagnetic, e.g. optoelectronic sensor, or a mechanical one Push button sensor or a capacitive button. Sensor according to claim 12 or 13, characterized in that the first and / or the second voltage spacing (dU1, dU2) or the first and / or the second distance value (dW1, dW2) are constant over time. Sensor according to claim 12 or 13, characterized in that the first and / or the second voltage spacing (dU1, dU2)) or the the first and / or the second distance value (dW1, dW2) varies over time are. Sensor according to claim 17, characterized in that the first and / or the second voltage spacing (dU1, dU2)) or the first and / or the second distance value (dW1, dW2) as a function of temporal behavior of the output voltage (Ua) or the output value and / or the reference voltage (Uref) or the reference value (Wref) mutable are. Sensor according to claim 18, characterized in that the first and / or the second voltage spacing (dU1, dU2)) or the first and / or the second distance value (dW1, dW2) depending on an average value of the Amount of the slope of the output voltage (Ua) or the output value (Wa) and / or the reference voltage (Uref) or the reference value (Wref) increase or decrease. Sensor according to claim 12 or 13, characterized in that the first and second voltage spacing (dU1, dU2) the forward voltage a diode (D1, D4, D2, D3) or a series connection of diodes is. Sensor according to one of claims 12 to 20, characterized in that that the rate of change over time the reference voltage (Uref) or the reference value (Wref) to one predeterminable maximum value is limited. Sensor according to claim 21, characterized in that the maximum value is variable in time. Sensor according to one of claims 12 to 22, characterized in that the first and / or the second response time period (dT1, dT2) depending on temporal behavior of the output voltage (Ua) or the output value (Wa) and / or the reference voltage (Uref) or the reference value (Wref) mutable are. Sensor according to claim 12, characterized in that the tracking circuit ( 10 . 10A ) an analog circuit ( 10A ) without digital components or a digital circuit without a microprocessor. Sensor according to claim 24, characterized in that the tracking circuit ( 10 . 10B ) comprises a first and a second diode (D1, D2) and a charging capacitor (C), the two diodes (D1, D2) being antiparallel between the output ( 1A ) of the sensor ( 1 ) and the reference input ( 31B ) of the comparator ( 31 ) are switched and the reference input ( 31B ) of the comparator ( 31 ) is connected to ground via the charging capacitor (C). Sensor according to claim 12, characterized in that the tracking circuit ( 10A ) comprises the following components: a) a second and a third comparator ( 32 . 33 ) with one signal input each ( 32A . 33A ), one reference input each ( 32B . 33B ) and one switching signal output ( 32C . 33C ), the second or third comparator ( 32 respectively. 33 ) then and only then a switching signal via its output ( 32C respectively. 33C ) if the signal input ( 32A respectively. 33A ) there is a higher voltage than at its reference input ( 328 respectively. 33B ), b) a series circuit (R3, D3, D4, R4) consisting of a third resistor (R3), a third diode D3, a fourth diode (D4) and a fourth resistor (R4), the third resistor (R3) being connected its connection, facing away from the third diode (D3), to a voltage pole ( 7 ) and the fourth resistor (R4) is connected to ground with its connection facing away from the fourth diode (D4) and the third and fourth diodes (D3, D4) are switched in the forward direction, so that the voltage pole ( 7 ) a current flows to ground via this series circuit (R3, D3, D4, R4), c) a second line (L2) which is connected between the third and fourth diodes (D3, D4) from the series circuit (R3, D3, D4 , R4) branches off and with the output ( 1A ) of the sensor ( 1 ) is connected so that the output voltage (Ua) is present between these diodes (D3, D4), d) a third line (L3) which is connected between the third resistor (R3) and the third diode (D3) from the series circuit (R3 , D3, D4, R4) branches and to the reference input ( 33B ) of the third Kompara tors ( 33 ) is applied, d) a fourth line (L4) which branches between the fourth resistor (R4) and the fourth diode (D4) from the series circuit (R3, D3, D4, R4) and to the signal input ( 32A ) of the second comparator ( 32 ) is created, e) a binary counter ( 44 ) with a counting input ( 44A ), a directional entrance ( 44B ), Outputs (Q1-Q6) and an R or R2R network with resistors connected to these outputs 45 , where the direction input ( 448 ) with the switching signal output ( 32C ) of the second comparator ( 32 ) is connected and the binary counter ( 44 ) increments an internal counter reading, if at its counter input ( 44A ) a clock pulse arrives and at its direction input ( 44B ) there is a high signal and decrement the internal counter reading if at its counter input ( 44A ) a clock pulse arrives and at its direction input ( 44B ) a low signal is present, and the binary counter 44 via its outputs (Q1-Q6) and the resistor network ( 45 ) is able to deliver a voltage (Uref), which is variable in steps and proportional to the internal meter reading, to a fifth line (L5), which is sent to the signal input ( 33A ) of the third comparator ( 33 ) and to the reference inputs ( 32B . 31B ) of both the second and the first comparator ( 32 . 31 ) is created, f) an AND gate ( 42 ) with a first and a second AND input ( 42A . 42B ) and a logical AND output ( 42C ), which at the counter input ( 44A ) of the binary counter ( 44 ) is created, g) a clock generator ( 41 ), which has its clock output ( 41A ) Emits clock pulses, the clock output ( 41A ) with the first AND input. ( 42A ) of the AND gate ( 42 ) is connected, and h) an OR gate ( 43 ) with a first and a second OR input ( 43A . 43B ) and a logical OR output ( 43C ), which is connected to the second AND input ( 42B ) of the AND gate ( 42 ) is connected, whereby the switching signal output ( 33C ) of the third comparator ( 33 ) to the first OR input ( 43A ) and the switching signal output ( 32C ) of the second comparator ( 32 ) to the second OR input ( 43B ) connected. Sensor according to claim 25 or 26, characterized in that too the first or second or third or fourth diode (D1, D2, D3, D4) at least one first or second or third or fourth Additional diode is connected in series, the forward direction with that of the first or second or third or fourth Diode (D1, D2, D3, D4) matches. Sensor according to one of claims 12 to 21, characterized in that the tracking circuit ( 10 ) comprises an analog / digital converter and a digital circuit, the output voltage (Ua) being applied to the analog / digital converter and the latter being able to digitize and output in digital form to the digital circuit which is the reference voltage (Uref) depending on the output voltage (Ua) or its behavior over time and to the reference input ( 31B ) of the first comparator ( 31 ) is able to deliver. Sensor according to claim 12, characterized in that the tracking circuit ( 10 ) comprises a seventh resistor through which a first direct current flows and / or an eighth resistor through which a second direct current flows and the voltage drop across the seventh or eighth resistor is the first or second voltage spacing (dU1, dU2) is used.