WO1997027487A1 - Circuit arrangement for adapting an active sensor to an evaluation circuit - Google Patents

Circuit arrangement for adapting an active sensor to an evaluation circuit Download PDF

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Publication number
WO1997027487A1
WO1997027487A1 PCT/EP1997/000037 EP9700037W WO9727487A1 WO 1997027487 A1 WO1997027487 A1 WO 1997027487A1 EP 9700037 W EP9700037 W EP 9700037W WO 9727487 A1 WO9727487 A1 WO 9727487A1
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WO
WIPO (PCT)
Prior art keywords
comparator
voltage
active sensor
sensor
circuit
Prior art date
Application number
PCT/EP1997/000037
Other languages
German (de)
French (fr)
Inventor
Wolfgang Fey
Michael Zydek
Falk Stricker
Original Assignee
Itt Automotive Europe Gmbh
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Filing date
Publication date
Application filed by Itt Automotive Europe Gmbh filed Critical Itt Automotive Europe Gmbh
Publication of WO1997027487A1 publication Critical patent/WO1997027487A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B60T8/171—Detecting parameters used in the regulation; Measuring values used in the regulation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
    • G01D3/08—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P21/00—Testing or calibrating of apparatus or devices covered by the preceding groups
    • G01P21/02—Testing or calibrating of apparatus or devices covered by the preceding groups of speedometers

Definitions

  • Circuit arrangement for adapting an active sensor to an evaluation circuit
  • the invention relates to a circuit arrangement for adapting an active sensor to an evaluation circuit according to the preamble of claim 1.
  • Active sensors are already known which deliver a binary current signal.
  • Such sensors are based e.g. on the magnetoresistive effect, which consists in the fact that the electrical resistance of a thin ferro-magnetic layer changes due to the action of an external magnetic field in the layer plane.
  • Several such resistors are combined to form a Wheatstone bridge. By evaluating the difference in the voltages at the center taps of the bridge, current sources are switched in such a way that a binary current signal is present at the output of the sensor.
  • Such a sensor can be used, for example, to measure the speed of vehicle wheels, a toothed magnet wheel, which rotates with the vehicle wheel, being guided past the magnetic field-sensitive resistor.
  • the current signal supplied by the sensor is fed to an evaluation circuit which determines the speed.
  • conventional evaluation circuits such as those provided for so-called passive sensors, could be used.
  • An evaluation circuit for a passive sensor is described, for example, in DE 40 33 740 AI. Since a passive sensor supplies voltage signals, the evaluation circuit is based on the evaluation of voltage changes In order to be able to operate such an evaluation circuit with an active sensor, a current / voltage conversion is therefore necessary.
  • the output of the active sensor can be switched to ground via a resistor, so that the sensor current flows through the resistor and the voltage drop across the resistor can be fed to the evaluation circuit.
  • the resistance may only have small values, so that only a correspondingly small voltage signal is available, the fault of which, e.g. due to voltage drifts in the supply voltage may be greater than the voltage difference due to the binary current signal.
  • Such a current mirror circuit is relatively complex.
  • the sensor on the basis of the signal voltage thus obtained, the sensor cannot be checked for its functionality by a window comparator which is present in the usual evaluation circuits. A separate monitoring circuit would therefore have to be provided.
  • the invention is therefore based on the object of providing a simple circuit arrangement which has a voltage provides signal that can be evaluated by an evaluation electronics, wherein the voltage signal can also be checked by means of a window comparator with regard to the functionality of the sensor.
  • the RC element is now designed so that it can follow slow changes in the current or voltage supply to the sensor, so that the comparator detects such slow changes as they e.g. caused by fluctuations in the supply voltage does not respond.
  • the voltage drop across a resistor which is connected in series with the active sensor can be provided as the current / voltage converter.
  • this voltage signal does not enable comparison with a window comparator provided, with which it is to be determined whether the sensor is possibly short-circuited or a short-circuit to the basic potential.
  • a voltage divider is therefore connected in parallel with the active sensor, at the center tap of which the signal voltage, the is fed to the comparator of the evaluation circuit, is removed.
  • the circuit is therefore suitable for connecting an active sensor to an evaluation circuit which has a first comparator, which supplies the actual useful signal, and a window comparator, which monitors the functionality of the sensor.
  • FIG. 1 denotes an active speed sensor, which can be part of a motor vehicle control system, for example an anti-lock braking system, a traction control system, a driving stability control or the like.
  • an active speed sensor which can be part of a motor vehicle control system, for example an anti-lock braking system, a traction control system, a driving stability control or the like.
  • a signal can be obtained, the frequency of which is proportional to the rotational speed of the respective vehicle wheel.
  • the output signal of the active sensor is determined by two current threshold values, namely a low current of 7 mA and a high current of 14 mA. The low current is required in order to maintain the proper functioning of the active sensor 1.
  • the wheel sensor 1 is shown symbolically in FIG. 1 as a current source, which is composed of two individual current sources. One of these individual current sources supplies the low current, which is supplemented to the high current in a high phase of the signal by connecting the second individual current source in parallel or by an additional current component.
  • the second individual current source can be switched, for example, by means of the magnetoresistive effect.
  • the output of the active sensor is connected via a resistor R1 to the ground connection, which is connected to the negative pole of a battery. Since a high voltage has to be applied to the active sensor, the resistance R1 is relatively small. In order to nevertheless obtain a sufficient voltage signal, a voltage divider R3 / R2 is connected in parallel to the active sensor, at its center tap M the actual useful signal is tapped.
  • the voltage U at point M can be calculated using the following formula:
  • the useful signal U " consists of a basic voltage and a component that is proportional to the sensor current I Se " 3or. Since this is switched between two values, there are also two values for the voltage U M , which are between 1.6 and 1.9 V for the low level and between 2.2 and 2.7 V for the high level .
  • the voltage in the center tap M is applied directly to the input 2 of an electronic evaluation circuit 3.
  • the input 2 is connected to the P input (+) of a comparator 4.
  • the center tap M is connected to a second input 5 of the electronic evaluation circuit 3 via a second line, in which a resistor R4 is inserted and which is connected to ground via a capacitor C1, the second input 5 having the N input (-) of the comparator 4 is connected.
  • the electronic evaluation corresponds essentially to the description in the already mentioned DE 40 33 740 AI.
  • the comparator 4 supplies the actual useful signal, which is fed to a further evaluation, which is not shown here, and supplies a value which corresponds to the speed.
  • the useful signal at the output of the comparator 4 is preferably in the form of an alternating signal or a pulse sequence, the frequency of which contains the speed information.
  • input 2 is still connected to a window comparator 6, 7, which consists of two comparators 6 and 7, which are linked by means of a voltage divider or a voltage chain 8.
  • the input 2 is at the P input of the first comparator 6 and at the N input of the second comparator 7.
  • the other input is connected to different voltage stages of the voltage chain 8. In this way it can be determined whether the voltage signal at input 2 lies between two limit values which are predetermined by the division of voltage chain 8. If the voltage value is too high, the comparator 6 delivers a corresponding output signal which indicates that the active sensor may be short-circuited.
  • the comparator 7 supplies a corresponding value which indicates that there is a short circuit to ground.
  • the corresponding signals of the window comparator 6, 7 can subsequently be evaluated and, depending on the interpretation, lead to the system being switched off.
  • the voltage divider R2 / R3 is matched to the specified voltage chain 8.
  • the voltage in the center tap M is fed to the input 2 of the electronic evaluation unit 3, while a time-delayed signal is applied to the input 5. lies.
  • a change in the switching process of the active sensor leads to an increased or decreased voltage at the center tap M. This results in a recharging or discharging of the capacitor C1, so that the voltage at input 5 always lags behind the voltage at input 2.
  • the reference voltage at the N input of the comparator is tracked in the event of slow changes in the center tap M, which result, for example, from changes in the supply voltage.
  • the comparator 4 therefore only responds to changes in point M which are due to a change in the switching state of the active sensor.
  • the time constant of the RC element should only be slightly less than half the pulse duration of the expected maximum transmitter frequency of the current signal of the sensor.
  • the circuit arrangement shown thus makes it possible to connect an active sensor to an electronic evaluation circuit 3, which was originally designed for so-called passive sensors.

Abstract

A circuit arrangement is disclosed which permits connection of an active sensor (1) in the form of a binary current source to an electronic evaluation circuit (3) designed for use with a passive sensor. The electronic evaluation circuit (3) comprises a comparator (4) which produces a signal proportional to the speed (revs.) and a window comparator (6, 7) with which the functioning of the sensor (1) can be monitored. The voltage signal applied to the comparator (4) is produced by a resistor (R1) connected in series with the active sensor (1) and with a voltage divider (R2, R3) which is connected in parallel with the active sensor. The voltage signal is led to the N input of the comparator (4) via an RC element (R4, C1) and to the P input of the comparator (4) directly, thus ensuring that the comparator responds to fluctuations at the central tap (M) of the voltage divider. This circuit is not sensitive to fluctuations in the intensity or voltage of the supply current or to drift in the active sensor.

Description

Schaltungsanordnung zur Anpassung eines aktiven Sensors an eine Auswerteschaltung Circuit arrangement for adapting an active sensor to an evaluation circuit
Die Erfindung bezieht sich auf eine Schaltungsanordnung zur Anpassung eines aktiven Sensors an eine Auswerteschaltung gemäß Oberbegriff des Anspruchs 1.The invention relates to a circuit arrangement for adapting an active sensor to an evaluation circuit according to the preamble of claim 1.
Es sind bereits aktive Sensoren bekannt, die ein binäres Stromsignal liefern. Solche Sensoren basieren z.B. auf dem magnetoresistiven Effekt, der darin besteht, daß sich der elektrische Widerstand einer dünnen ferro-magnetischen Schicht durch die Einwirkung eines äußeren Magnetfeldes in der Schichtebene verändert. Mehrere solcher Widerstände wer¬ den dabei zu einer Wheatston'sehen Brücke zusammengefaßt. Durch Auswertung der Differenz der Spannungen an den Mitten¬ abgriffen der Brücke werden Stromquellen derart geschaltet, daß am Ausgang des Sensors ein binäres Stromsignal vorliegt.Active sensors are already known which deliver a binary current signal. Such sensors are based e.g. on the magnetoresistive effect, which consists in the fact that the electrical resistance of a thin ferro-magnetic layer changes due to the action of an external magnetic field in the layer plane. Several such resistors are combined to form a Wheatstone bridge. By evaluating the difference in the voltages at the center taps of the bridge, current sources are switched in such a way that a binary current signal is present at the output of the sensor.
Ein solcher Sensor kann z.B. zur Drehzahlmessung an Fahr¬ zeugrädern eingesetzt werden, wobei am magnetfeldempfindli¬ chen Widerstand ein gezahntes Polrad, das sich mit dem Fahr¬ zeugrad dreht, vorbeigeführt wird. Das vom Sensor gelieferte Stromsignal wird einer Auswerteschaltung zugeführt, die die Drehzahl ermittelt. Von Vorteil wäre es, wenn übliche Aus¬ werteschaltungen, wie sie z.B. für sog. passive Sensoren vorgesehen sind, eingesetzt werden könnten. Eine Auswerte¬ schaltung für einen passiven Sensor ist z.B. der DE 40 33 740 AI beschrieben. Da ein passiver Sensor Spannungssignale liefert, beruht die Auswerteschaltung auf der Auswertung von Spannungsänderungen Um eine solche Auswerteschaltung mit einem aktiven Sensor betreiben zu können, ist daher eine Strom/Spannungswandlung notwendig.Such a sensor can be used, for example, to measure the speed of vehicle wheels, a toothed magnet wheel, which rotates with the vehicle wheel, being guided past the magnetic field-sensitive resistor. The current signal supplied by the sensor is fed to an evaluation circuit which determines the speed. It would be advantageous if conventional evaluation circuits, such as those provided for so-called passive sensors, could be used. An evaluation circuit for a passive sensor is described, for example, in DE 40 33 740 AI. Since a passive sensor supplies voltage signals, the evaluation circuit is based on the evaluation of voltage changes In order to be able to operate such an evaluation circuit with an active sensor, a current / voltage conversion is therefore necessary.
Im Prinzip kann der Ausgang des aktiven Sensors über einen Widerstand gegen Masse geschaltet werden, so daß der Sensor¬ strom über den Widerstand abfließt und der Spannungsabfall am Widerstand der Auswerteschaltung zugeführt werden kann.In principle, the output of the active sensor can be switched to ground via a resistor, so that the sensor current flows through the resistor and the voltage drop across the resistor can be fed to the evaluation circuit.
Da der aktive Sensor zum Betrieb aber eine sehr hohe Min¬ destspannung benötigt, darf der Widerstand nur kleine Werte aufweisen, so daß nur ein entsprechend kleines Spannungs¬ signal zur Verfügung steht, dessen Störung z.B. durch Span- nungsdrifte der Versorgungsspannung möglicherweise größer sein kann, als die Spannungsdifferenz aufgrund des binären Stromsignals.However, since the active sensor requires a very high minimum voltage for operation, the resistance may only have small values, so that only a correspondingly small voltage signal is available, the fault of which, e.g. due to voltage drifts in the supply voltage may be greater than the voltage difference due to the binary current signal.
In der nicht vorveröffentlichten deutschen Patentanmeldung P 44 34 180.6 (DE 44 34 180 AI) wurde daher schon vorge¬ schlagen, den Sensorstrom einem Stromspiegel zuzuführen, der einen gespiegelten Strom liefert, welcher kleiner ist als der Sensorstrom. Der gespiegelte Strom ruft über einem Wi¬ derstand einen Spannungsabfall hervor, der elektronisch ausgewertet wird.In the unpublished German patent application P 44 34 180.6 (DE 44 34 180 AI) it has therefore already been proposed to supply the sensor current to a current mirror which delivers a mirrored current which is smaller than the sensor current. The mirrored current causes a voltage drop across a resistor, which is evaluated electronically.
Eine derartige Stromspiegelschaltung ist relativ aufwendig. Außerdem kann auf Basis der so gewonnenen Signalspannung keine Überprüfung des Sensors hinsichtlich seiner Funktions¬ tüchtigkeit durch einen Fensterkomparator vorgenommen wer¬ den, der in den üblichen Auswerteschaltungen vorhanden ist. Es müßte daher eine gesonderte Überwachungsschaltung vor¬ gesehen werden.Such a current mirror circuit is relatively complex. In addition, on the basis of the signal voltage thus obtained, the sensor cannot be checked for its functionality by a window comparator which is present in the usual evaluation circuits. A separate monitoring circuit would therefore have to be provided.
Der Erfindung liegt daher die Aufgabe zugrunde, eine ein¬ fache Schaltungsanordnung zu schaffen, die ein Spannungs- signal liefert, das von einer Auswerteelektronik ausgewertet werden kann, wobei das Spannungssignal darüber hinaus mit¬ tels eines Fensterkomparators auch im Hinblick auf die Funk¬ tionstüchtigkeit des Sensors überprüft werden kann.The invention is therefore based on the object of providing a simple circuit arrangement which has a voltage provides signal that can be evaluated by an evaluation electronics, wherein the voltage signal can also be checked by means of a window comparator with regard to the functionality of the sensor.
Zur Lösung dieser Aufgabe wird erfindungsgemäß vorgeschla¬ gen, das Ausgangssignal eines Strom/Spannungngswandlers direkt dem P-Eingang eines Komparators der Auswerteschal¬ tung und zeitlich verzögert dem N-Eingang des Komparators zuzuführen.To achieve this object, it is proposed according to the invention to feed the output signal of a current / voltage converter directly to the P input of a comparator of the evaluation circuit and with a time delay to the N input of the comparator.
Dies hat zur Folge, daß vom Komparator nicht das Spannungs¬ signal selbst, sondern die Änderung des Signals detektiert wird.The result of this is that the comparator does not detect the voltage signal itself, but rather the change in the signal.
Am einfachsten läßt sich eine Verzögerung durch ein RC-Glied realisieren, wobei am N-Eingang des Komparators ein Konden¬ sator, der über einen Widerstand geladen wird, gegen Grund¬ potential liegt.The easiest way to implement a delay is by means of an RC element, a capacitor at the N input of the comparator, which is charged via a resistor, being connected to ground potential.
Das RC-Glied wird nun so ausgelegt, daß es langsamen Ände¬ rungen in der Strom- bzw. Spannungsversorgung des Sensors folgen kann, so daß der Komparator auf solch langsamen Ände¬ rungen, wie sie z.B. durch Schwankungen der Versorgungsspan¬ nung hervorgerufen werden, nicht anspricht.The RC element is now designed so that it can follow slow changes in the current or voltage supply to the sensor, so that the comparator detects such slow changes as they e.g. caused by fluctuations in the supply voltage does not respond.
Wie schon erläutert, kann als Strom/Spannungswandler im Prinzip der Spannungsabfall an einem Widerstand, der in Rei¬ he mit dem aktiven Sensor geschaltet ist, vorgesehen wer¬ den. Dieses Spannungssignal ermöglicht aber nicht den Ab¬ gleich mit einem vorgesehenen Fensterkomparator, mit dem festgestellt werden soll, ob der Sensor ggf. kurzgeschlossen ist oder ein Kurzschluß zum Grundpotential vorliegt. Es wird daher zum aktiven Sensor ein Spannungsteiler parallel¬ geschaltet, an dessen Mittenabgriff die Signalspannung, die dem Komparator der Auswerteschaltung zugeführt wird, abge¬ nommen wird.As already explained, in principle the voltage drop across a resistor which is connected in series with the active sensor can be provided as the current / voltage converter. However, this voltage signal does not enable comparison with a window comparator provided, with which it is to be determined whether the sensor is possibly short-circuited or a short-circuit to the basic potential. A voltage divider is therefore connected in parallel with the active sensor, at the center tap of which the signal voltage, the is fed to the comparator of the evaluation circuit, is removed.
Die Schaltung ist daher geeignet, einen aktiven Sensor an eine Auswerteschaltung anzuschließen, die über einen ersten Komparator, der das eigentliche Nutzsignal liefert, und über einen Fensterkomparator verfügt, der den Sensor hinsichtlich seiner Funktionstauglichkeit überwacht.The circuit is therefore suitable for connecting an active sensor to an evaluation circuit which has a first comparator, which supplies the actual useful signal, and a window comparator, which monitors the functionality of the sensor.
Ein Ausführungsbeispiel der Erfindung wird im folgenden an¬ hand einer Schaltung, die in der Fig. 1 dargestellt ist, näher erläutert. Mit 1 ist ein aktiver Drehzahlsensor be¬ zeichnet, der Bestandteil eines Kraftfahrzeugregelungssy¬ stems sein kann, beispielsweise eines Antiblockiersystems, eines Antriebsschlupfregelungssystems, einer Fahrstabili- tätsregelung oder dergleichen. Mit Hilfe solcher Sensoren bzw. Radsensoren läßt sich ein Signal gewinnen, dessen Fre¬ quenz der Drehgeschwindigkeit des jeweiligen Fahrzeugrades proportional ist. Das Ausgangssignal des aktiven Sensors ist durch zwei Stromschwellenwerte bestimmt, nämlich einem Low- Strom von 7 mA und einem High- Strom von 14 mA. Der Low- Strom ist erforderlich, um die ordnungsgemäße Funktion des aktiven Sensors 1 aufrechtzuerhalten.An exemplary embodiment of the invention is explained in more detail below with reference to a circuit which is shown in FIG. 1. 1 denotes an active speed sensor, which can be part of a motor vehicle control system, for example an anti-lock braking system, a traction control system, a driving stability control or the like. With the help of such sensors or wheel sensors, a signal can be obtained, the frequency of which is proportional to the rotational speed of the respective vehicle wheel. The output signal of the active sensor is determined by two current threshold values, namely a low current of 7 mA and a high current of 14 mA. The low current is required in order to maintain the proper functioning of the active sensor 1.
Der Radsensor 1 ist in der Fig. 1 als Stromquelle, die sich aus zwei Einzelstromquellen zusammensetzt, symbolisch dar¬ gestellt. Eine dieser Einzelstromquellen liefert den Low- Strom, der in einer Highphase des Signals durch Parallel¬ schalten der zweiten Einzelstromquelle bzw. durch eine zu¬ sätzliche Stromkomponente zum High-Strom ergänzt wird.The wheel sensor 1 is shown symbolically in FIG. 1 as a current source, which is composed of two individual current sources. One of these individual current sources supplies the low current, which is supplemented to the high current in a high phase of the signal by connecting the second individual current source in parallel or by an additional current component.
Die zweite Einzelstromquelle kann z.B. mittels des magneto- resistiven Effektes geschaltet werden. Der Ausgang des aktiven Sensors wird über einen Widerstand Rl an den Masseanschluß, der mit dem negativen Pol einer Batterie verbunden ist, geschaltet. Da am aktiven Sensor eine hohe Spannung anliegen muß, ist der Widerstand Rl rela¬ tiv klein.Um trotzdem ein ausreichendes Spannungssignal zu erhalten, ist parallel zum aktiven Sensor ein Spannungstei¬ ler R3/R2 geschaltet, an dessen Mittenabgriff M das eigent¬ liche Nutzsignal abgegriffen wird. Die Spannung U im Punkt M läßt sich nach der folgenden Formel berechnen:The second individual current source can be switched, for example, by means of the magnetoresistive effect. The output of the active sensor is connected via a resistor R1 to the ground connection, which is connected to the negative pole of a battery. Since a high voltage has to be applied to the active sensor, the resistance R1 is relatively small. In order to nevertheless obtain a sufficient voltage signal, a voltage divider R3 / R2 is connected in parallel to the active sensor, at its center tap M the actual useful signal is tapped. The voltage U at point M can be calculated using the following formula:
VCCU ♦ (Rl * R2) " " Rl ♦ R2 ♦ R3 + Semor VCCU ♦ (Rl * R2) "" Rl ♦ R2 ♦ R3 + Semor
Man erkennt, daß das Nutzsignal U„ aus einer Grundspannung und einem Anteil besteht, der proportional ist zum Sensor¬ strom ISe„3or. Da dieser zwischen zwei Werten geschaltet wird, ergeben sich auch für die Spannung UM zwei Werte, die für das Low-Niveau zwischen 1,6 und 1,9 V und für das High-Niveau zwischen 2,2 und 2,7 V liegt.It can be seen that the useful signal U "consists of a basic voltage and a component that is proportional to the sensor current I Se " 3or. Since this is switched between two values, there are also two values for the voltage U M , which are between 1.6 and 1.9 V for the low level and between 2.2 and 2.7 V for the high level .
Die Spannung im Mittenabgriff M wird unmittelbar auf den Eingang 2 einer elektronischen Auswerteschaltung 3 gelegt. Der Eingang 2 ist mit dem P-Eingang (+) eines Komparators 4 verbunden.The voltage in the center tap M is applied directly to the input 2 of an electronic evaluation circuit 3. The input 2 is connected to the P input (+) of a comparator 4.
Der Mittenabgriff M wird über eine zweite Leitung, in der ein Widerstand R4 eingefügt ist und die über einen Kondensa¬ tor Cl an Masse geschaltet ist, an einen zweiten Eingang 5 der elektronischen Auswerteschaltung 3 gelegt, wobei der zweite Eingang 5 mit dem N-Eingang (-) des Komparators 4 verbunden ist. Die elektronische Auswertung entspricht im wesentlichen der Beschreibung in der schon erwähnten DE 40 33 740 AI. Der Komparator 4 liefert dabei das eigentliche Nutzsignal, daß einer weiteren Auswertung, die hier nicht dargestellt ist, zugeführt wird, und einen Wert liefert, der der Drehzahl entspricht. Das Nutzsignal am Ausgang des Komparators 4 liegt vorzugsweise in Form eines Wechselsignals oder einer Pulsfolge vor, deren Frequenz die Drehzahlinformation ent¬ hält.The center tap M is connected to a second input 5 of the electronic evaluation circuit 3 via a second line, in which a resistor R4 is inserted and which is connected to ground via a capacitor C1, the second input 5 having the N input (-) of the comparator 4 is connected. The electronic evaluation corresponds essentially to the description in the already mentioned DE 40 33 740 AI. The comparator 4 supplies the actual useful signal, which is fed to a further evaluation, which is not shown here, and supplies a value which corresponds to the speed. The useful signal at the output of the comparator 4 is preferably in the form of an alternating signal or a pulse sequence, the frequency of which contains the speed information.
Der Eingang 2 liegt aber weiterhin an einem Fensterkompara¬ tor 6,7, der aus zwei Komparatoren 6 und 7 besteht, die mit Hilfe eines Spannungsteilers bzw. einer Spannungskette 8 verknüpft sind. Der Eingang 2 liegt dabei am P-Eingang des ersten Komparators 6 und am N-Eingang des zweiten Kompara¬ tors 7. Der jeweils andere Eingang ist mit verschiedenen Spannungsstufen der Spannungskette 8 verbunden. Auf diese Weise kann festgestellt werden, ob das Spannungssignal am Eingang 2 zwischen zwei Grenzwerten liegt, die durch die Aufteilung der Spannungskette 8 vorgegeben sind. Liegt ein zu hoher Spannungswert vor, liefert der Komparator 6 einen entsprechendes Ausgangssignal, das darauf hinweist, daß der aktive Sensor möglicherweise kurzgeschlossen ist.However, input 2 is still connected to a window comparator 6, 7, which consists of two comparators 6 and 7, which are linked by means of a voltage divider or a voltage chain 8. The input 2 is at the P input of the first comparator 6 and at the N input of the second comparator 7. The other input is connected to different voltage stages of the voltage chain 8. In this way it can be determined whether the voltage signal at input 2 lies between two limit values which are predetermined by the division of voltage chain 8. If the voltage value is too high, the comparator 6 delivers a corresponding output signal which indicates that the active sensor may be short-circuited.
Liegt ein zu tiefer Spannungswert vor, so liefert der Kompa¬ rator 7 einen entsprechenden Wert, der darauf hinweist, daß ein Kurzschluß gegen Masse vorliegt. In weiterer Folge kön¬ nen die entsprechenden Signale des Fensterkomparators 6,7 ausgewertet werden, und je nach Interpretation zur Abschal¬ tung des Systems führen. Der Spannungsteiler R2/R3 wird da¬ bei auf die vorgegebene Spannungskette 8 abgestimmt.If the voltage value is too low, the comparator 7 supplies a corresponding value which indicates that there is a short circuit to ground. The corresponding signals of the window comparator 6, 7 can subsequently be evaluated and, depending on the interpretation, lead to the system being switched off. The voltage divider R2 / R3 is matched to the specified voltage chain 8.
Wie schon erläutert, wird die Spannung im Mittenabgriff M auf den Eingang 2 der elektronischen Auswerteeinheit 3 ge¬ führt, während am Eingang 5 ein zeitverzögertes Signal an- liegt. Eine Änderung des Schaltvorgangs des aktiven Sensors führt zu einer erhöhten oder erniedrigten Spannung am Mit¬ tenabgriff M. Dies hat eine Nachladung oder Entladung des Kondensators Cl zur Folge, so daß die Spannung am Eingang 5 der Spannung am Eingang 2 stets zeitlich nachläuft. Ent¬ scheidend ist aber, daß damit die Referenzspannung am N-Ein¬ gang des Komparators bei langsamen Änderungen im Mittenab¬ griff M, die z.B. von Änderungen in der Versorgungsspannung herrühren, nachgeführt wird. Der Komparator 4 spricht daher nur auf Änderungen im Punkt M an, die auf eine Änderung des Schaltzustandes des aktiven Sensors zurückzuführen sind. Zwar wird nach einer Änderung des Schaltzustandes der La¬ dungszustand des Kondensators Cl und damit die Spannung am Eingang 5 entsprechend nachgeführt. Dies erfolgt aber zeitversetzt, so daß am Komparator 4 für eine kurzen Moment (Ladezeit des Kondesators Cl) eine Spannungsdifferenz an¬ liegt, die ein Ausgansignal hervorruft, welches in einem dem Komparator 4 nachgeschalteten (nicht dargestellten) Zähler registriert wird. Jede kurzzeitige Änderung im Mittenabgriff M führt daher zu einem Zählimpuls in der Auswerteschaltung. In der Praxis wird mit der erfindungsgemäßen Schaltungsan¬ ordnung ein Nutzsignal (Nutzpegel am Ausgang des Komparators 4) gewonnen, das gegenüber dem Nutzsignal, das sich mit ei¬ ner konventionellen Schaltung erzielen ließe, nahezu verdop¬ pelt ist.As already explained, the voltage in the center tap M is fed to the input 2 of the electronic evaluation unit 3, while a time-delayed signal is applied to the input 5. lies. A change in the switching process of the active sensor leads to an increased or decreased voltage at the center tap M. This results in a recharging or discharging of the capacitor C1, so that the voltage at input 5 always lags behind the voltage at input 2. It is crucial, however, that the reference voltage at the N input of the comparator is tracked in the event of slow changes in the center tap M, which result, for example, from changes in the supply voltage. The comparator 4 therefore only responds to changes in point M which are due to a change in the switching state of the active sensor. After a change in the switching state, the charge state of the capacitor C1 and thus the voltage at the input 5 are correspondingly tracked. However, this takes place with a time delay, so that a voltage difference is present at the comparator 4 for a brief moment (charging time of the capacitor C1), which produces an output signal which is registered in a counter (not shown) connected downstream of the comparator 4. Every brief change in the center tap M therefore leads to a counting pulse in the evaluation circuit. In practice, with the circuit arrangement according to the invention, a useful signal (useful level at the output of the comparator 4) is obtained, which is almost doubled compared to the useful signal that could be achieved with a conventional circuit.
Die Zeitkonstante des RC-Gliedes sollte nur geringfügig kleiner sein als die halbe Pulsdauer der zu erwartenden ma¬ ximalen Geberfrequenz des Stromsignals des Sensors.The time constant of the RC element should only be slightly less than half the pulse duration of the expected maximum transmitter frequency of the current signal of the sensor.
Die dargestellte Schaltungsanordnung ermöglicht es also, einen aktiven Sensor an eine elektronische Auswerteschaltung 3 anzuschließen, die ursprünglich für sog. passive Sensoren konzipiert worden ist. The circuit arrangement shown thus makes it possible to connect an active sensor to an electronic evaluation circuit 3, which was originally designed for so-called passive sensors.

Claims

Patentansprüche claims
1. Schaltungsanordnung zum Anpassen eines aktiven Sensors an eine Auswerteschaltung (3), die einen ersten Kompara¬ tor (4) aufweist, wobei die Schaltungsanordnung einen Strom/Spannungswandler (R1,R2, R3) aufweist, dessen Aus¬ gang (M) an den P-Eingang des Komparators (4) gelegt ist, dadurch gekennzeichnet, daß der Ausgang (M) des Strom/Spannungswandlers über ein Verzögerungsglied (R4,C1) an den N-Eingang des Komparators (4) gelegt ist.1. Circuit arrangement for adapting an active sensor to an evaluation circuit (3) which has a first comparator (4), the circuit arrangement having a current / voltage converter (R1, R2, R3), the output (M) of which the P input of the comparator (4) is connected, characterized in that the output (M) of the current / voltage converter is connected to the N input of the comparator (4) via a delay element (R4, C1).
2. Schaltungsanordnung nach Anspruch 1, dadurch gekenn¬ zeichnet, daß das Verzögerungsglied aus einem Kondensa¬ tor (Cl), der gegen Masse geschaltet ist, und einem Wi¬ derstand (R4) besteht.2. Circuit arrangement according to claim 1, characterized gekenn¬ characterized in that the delay element consists of a capacitor (Cl), which is connected to ground, and a resistor (R4).
3. Schaltungsanordnung nach Anspruch 1, dadurch gekenn¬ zeichnet, daß die Auswerteschaltung einen Fensterkompa¬ rator (6,7,8) aufweist und daß der Ausgang des Strom/Spannungswandlers dem Fensterkomparator zugeführt ist.3. Circuit arrangement according to claim 1, characterized gekenn¬ characterized in that the evaluation circuit has a window comparator (6,7,8) and that the output of the current / voltage converter is fed to the window comparator.
4. Schaltungsanordnung nach Anspruch 1, dadurch gekenn¬ zeichnet, daß der Strom/Spannungswandler aus einem er¬ sten Widerstand (Rl) besteht, der in Serie mit dem akti¬ ven Sensor gegen Masse geschaltet ist und einem Span¬ nungsteiler (R2, R3), der parallel zum aktiven Sensor (1) geschaltet ist, wobei der Mittenabgriff (M) des Spannungsteilers (R2,R3) den Ausgang des Strom/Spannungswandlers bildet. 4. Circuit arrangement according to claim 1, characterized in that the current / voltage converter consists of a first resistor (Rl) which is connected in series with the active sensor to ground and a voltage divider (R2, R3 ), which is connected in parallel to the active sensor (1), the center tap (M) of the voltage divider (R2, R3) forming the output of the current / voltage converter.
PCT/EP1997/000037 1996-01-23 1997-01-08 Circuit arrangement for adapting an active sensor to an evaluation circuit WO1997027487A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19602243.6 1996-01-23
DE1996102243 DE19602243A1 (en) 1996-01-23 1996-01-23 Circuit arrangement for adapting an active sensor to an evaluation circuit

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