DE3516162A1 - Evaluating electronics for differential capacitors for use in sensors - Google Patents

Evaluating electronics for differential capacitors for use in sensors

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Publication number
DE3516162A1
DE3516162A1 DE19853516162 DE3516162A DE3516162A1 DE 3516162 A1 DE3516162 A1 DE 3516162A1 DE 19853516162 DE19853516162 DE 19853516162 DE 3516162 A DE3516162 A DE 3516162A DE 3516162 A1 DE3516162 A1 DE 3516162A1
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Germany
Prior art keywords
capacitor
capacitors
charging
charging resistor
resistors
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
DE19853516162
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German (de)
Inventor
Rüdiger Prof. Dr.-Ing. Haberland
Berthold Dipl.-Ing. 6750 Kaiserslautern Vogt
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Priority to DE19853516162 priority Critical patent/DE3516162A1/en
Publication of DE3516162A1 publication Critical patent/DE3516162A1/en
Priority to DE19853542030 priority patent/DE3542030A1/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
    • G01D5/241—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes
    • G01D5/2412—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes by varying overlap
    • 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
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
    • G01D5/241—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes
    • G01D5/2417—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes by varying separation

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Transmission And Conversion Of Sensor Element Output (AREA)

Abstract

The stability of the measurement value of evaluating electronics for differential capacitors with a pulse-width-modulated squarewave output voltage, in which the individual capacitors are alternately loaded via 2 independent resistors, the capacitor not loaded in each case being connected to earth potential, depends, on the one hand, on a stable squarewave voltage amplitude and, on the other hand, especially on the equality and the drift characteristics of the two charging resistors. This instability caused by the resistors can be prevented in this invention by using only one charging resistor which is connected to the capacitor to be charged in each case by means of a change-over switch. It is also found that the stability of the circuit does not depend on the quality of the charging resistor.

Description

Beschreibung Xuswerteelektronik für Differentialkondensatoren zur Verwendung in Sensoren Die Erfindung betrifft eine Auswerteelektronik für Dif--fe-rentialkondensatoren mit einer pulsbreiten modulierten Ausgangsspannung bei der die einzelnen Kondensatoren wechselseitig geladen werden und der jeweils nicht geladene Kondensator auf definiertem Potential (meist Masse) liegt. Description Xuswerteelektronik for differential capacitors for Use in sensors The invention relates to evaluation electronics for differential capacitors with a pulse-width modulated output voltage for the individual capacitors are charged alternately and the respective uncharged capacitor on a defined Potential (mostly ground).

Die Differentialkondensatoren werden hauptsächlich als Meßwertaufnehmer eingesetzt, wobei sich der Kapazitätswert bei dieser Anordnung entweder infolge einer Abstandsänderung der Mittelelektrode nach Fig. la oder durch eine Uberdeckungsänderung der Kondensatorplatten nach Fig. 1b verändern läßt.The differential capacitors are mainly used as transducers used, the capacitance value in this arrangement either as a result a change in the distance of the center electrode according to FIG. la or by a change in overlap the capacitor plates can change according to Fig. 1b.

Die Auswerteelektronik soll folgende Aufgaben erfüllen: Ausgangsspannung streng linear zur Meßgröße, d.h.The evaluation electronics should fulfill the following tasks: Output voltage strictly linear to the measurand, i.e.

zur Plattenverschiebung - einstellbarer Nullpunkt - werinre Drift Für die Auswertung von Differentialkondensator-Aufnehmern eist das Umladeverfahren aufgrund der geringen Bauelementeanzahl und der Proportionalität der Ausgangsspannung zur Meßgröße klare Vorteile gegenüber anderen Schaltungen auf. for plate displacement - adjustable zero point - werinre drift The reloading process is used to evaluate differential capacitor sensors due to the small number of components and the proportionality of the output voltage to the measurable variable has clear advantages over other circuits.

Zunächst werden an Hand des Standes der Technik einige wesentliche Eigenschaften bekannter Auswerteelektroniken für Differentialkondensatoren erläutert, um anschließend die dann offensichtlichen Vorteile der erfindungsgemäßen Form daraus abzuleiten. Bei der im U.S. P. 3518536 beschriebenen Schaltung (Fig. 2), wird einer der beiden Kondensatoren des Differentialkondensators über je einen der zwei Ladewiderstände bis zur Referenzspannung Uref aufgeladen, wobei der jeweils nicht geladene Kondensator auf Massepotential liegt.First, a few essentials will be presented on the basis of the state of the art Properties of known evaluation electronics for differential capacitors explained, to subsequently the then obvious advantages of the invention Derive form from it. In the U.S. P. 3518536 described circuit (Fig. 2), one of the two capacitors of the differential capacitor will have one each of the two charging resistors are charged up to the reference voltage Uref, each of which uncharged capacitor is at ground potential.

Nachdem die Kondensatorspannung Uc des zu ladenden Kondensators die Referenzspannung ref erreicht hat, ändert der Komparator seine Ausgangsspannung und läßt das nachfolgende Schaltwerk umspringen. Der im vorhergehenden Ladezyklus auf Massepotential liegende Kondensator wird nun aufgeladen und der geladene Kondensator entladen. Während der entsprechenden Ladezeittt steht am Ausgang der Aufnehmerelektronik die stabilisierte Spannung U1 bzw. -U1 an (Fig. 3), wobei sich die einzelnen Ladezeiten nach ti = RLi#Ci#ln#UL/UL-Uref# (1) mit i = 1,2 berechnen.After the capacitor voltage Uc of the capacitor to be charged has reached the reference voltage ref, the comparator changes its output voltage and causes the following switching mechanism to jump. The capacitor which was at ground potential in the previous charging cycle is now charged and the charged capacitor is discharged. During the corresponding charging time, the stabilized voltage U1 or -U1 is present at the output of the sensor electronics (FIG. 3), with the individual charging times following each other ti = RLi # Ci # ln # UL / UL-Uref # (1) calculate with i = 1.2.

Der Gleichspannungsanteil des pulsbreiten modulierten Recht- ecksignals beträgt tl Um t1+1 t ( jU1 d t + 4( ~ U1 ) dz tl t1-t2 = # U1 (2) t1 + t2 erden in Gleichung (2) die einzelnen Ladezeiten durch Gleichung (1) ersetzt, so ergibt sich Um RL1#C1-RL2#C2 = (3) U1 RL1#C1+RL2#C2 Unter der Voraussetzung, daß RL1 = RL2 ist, läßt sich Gleichung (3) in Um = C1 - C2 (4) U1 C1 + C2 umformen.The DC voltage component of the pulse-width modulated right ecksignal is tl At t1 + 1 t (jU1 dt + 4 (~ U1) dz tl t1-t2 = # U1 (2) t1 + t2 ground the individual charging times in equation (2) and replace them with equation (1), so Um RL1 # C1-RL2 # C2 = (3) U1 RL1 # C1 + RL2 # C2 Assuming that RL1 = RL2, equation (3) can be converted into Um = C1 - C2 (4) U1 C1 + C2.

Für die in Fig. la gezeigte Anordnung ist Um = x U1 xo mit xo = Mittelstellung der Mittelelektrode X = Auslenkung von Mittelstellung Für die in Fig. 1b gezeigte Anordnung ist Um xv#k = U1 Co mit Co = Grundkapazität in Mittelstellung XV = Verschiebung von Mittelstellung k = Empfindlichkeitskonstante Hier wird deutlich, daß die Ausgangsspannung der dargestellten Schaltung sowohl. für die in Fig. la als auch Fig. 1b @ezeigte Anordnung streng linear mit der Verschiebung Xv bzw. der Auslenkung X ist.For the arrangement shown in FIG. La, Um = x U1 xo with xo = middle position of the center electrode X = deflection from center position For the one shown in FIG. 1b The arrangement is Um xv # k = U1 Co with Co = basic capacitance in the middle position XV = displacement from middle position k = sensitivity constant Here it becomes clear that the output voltage the circuit shown both. for that shown in Fig. la as well as Fig. 1b The arrangement is strictly linear with the displacement Xv or the deflection X.

Die Stabilität der Ausgangsspannung hängt hier jedoch neben einer stabilen Rechteckspannungsamplitude Uf bzw. -U1 hauptsächlich von der Gleichheit und dem Driftverhalten der beiden Ladewiderstände RL1 bzw. RL2 ab.However, the stability of the output voltage depends here next to one stable square wave voltage amplitude Uf or -U1 mainly from equality and the drift behavior of the two charging resistors RL1 and RL2.

Aufgrund von Bauteiletoleranzen kann nicht davon ausgeganen werden, daß die Forderung für eine hochstabile Schaltung erfüllt -sind und auch Schaltungen mittlerer Qualität benötigen hinsichtlich Gleichheit und Gleichlauf mit Temperatur und Zeit hochwertige Ladewiderstände.Due to component tolerances, it cannot be assumed that that the requirement for a highly stable circuit is met and also circuits need medium quality in terms of equality and synchronization with temperature and time high quality charging resistors.

Der Erfindung liegt die Aufgabe zugrunde, diese Instabilität aufgrund unterschiedlicher Ladewiderstandstoleranzen zu beseitigen.The invention is based on the object of this instability to eliminate different load resistance tolerances.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß nur noch ein Ladewiderstand eingesetzt wird (Fig. 4), der durch einen Umschalter mit dem jeweils zu ladenden Kondensator verbunden wird. Hierdurch wird erreicht, daß die Voraussetzung für Gleichung (4), d.h. RL = R immer voll erfüllt ist.This object is achieved in that only one Charging resistor is used (Fig. 4), which is controlled by a switch with the respectively capacitor to be charged is connected. This achieves that the requirement for equation (4), i.e. RL = R is always fully fulfilled.

Eventuelle Toleranzen des Ladewiderstandes RL spielen hier überhaupt keine Rolle mehr, da jeder Teil des Differentialkondensators über den gleichen widerstand geladen wird, so daß auch für Präzisionsanwendungen ein einfacher Ladewiderstand eingesetzt werden kann.Any tolerances of the charging resistor RL play a role here no longer matters as each part of the differential capacitor has the same resistance is charged, so that a simple charging resistor is also used for precision applications can be used.

Der Nullpunktsabgleich der Schaltung erfolgt durch eine Parallelkapazität in einem Zweig des Differentialkondensators oder eine Veränderung des Komparatoroffsets.The zero point adjustment of the circuit is carried out by a parallel capacitance in a branch of the differential capacitor or a change in the comparator offset.

Weiterhin läßt sich das pulsbreiten-modulierte Ausgangssignal direkt von den Anschlüssen Q bzw. Q des Flip-Flop?s 12 in Fig. 6 abnehmen, allerdings mit gewissen Qualitätseinbußen.Furthermore, the pulse-width-modulated output signal can be sent directly from the connections Q and Q, respectively, of the flip-flop 12 in FIG. 6, but with certain loss of quality.

Die mit der Erfindung erzielten Vorteile bestehen insbesondere darin, daß trotz der Verwendung eines - preisgünstigen - Ladewiderstandes eine verbesserte Stabilität der Schaltung erreicht wird und zwar sowohl hinsichtlich der Temperatur als auch hinsichtlich des Alterungsverhaltens.The advantages achieved with the invention are in particular: that despite the use of a - inexpensive - charging resistor an improved Stability of the circuit is achieved both in terms of temperature as well as in terms of aging behavior.

Weiterhin wird zusätzlich ein Bauteil einyespart, was zu einer Verkleinerung der Schaltung beiträgt.Furthermore, a component is also saved, resulting in a reduction in size contributes to the circuit.

Ein Ausführungsbeispiel der Erfindung ist in Fig. 4, 5 und @ dargestellt und wird im folgenden näher beschrieben.An embodiment of the invention is shown in FIGS. 4, 5 and @ and is described in more detail below.

In Fig. 4 ist die Auswerteelektronik für einen Differentialkondensator mit den Einzelkondensatoren 1 und 2 dargestellt.In Fig. 4 is the evaluation electronics for a differential capacitor shown with the individual capacitors 1 and 2.

[it dem Spannungsteiler, bestehend aus den Widerständen @ und 6 wird aus der Ladespannung UL die Referenzspannung Uref gebildet. In der gezeigten Schaltung wird über den Schalter 9a und den Ladewiderstand 5 der Kondensator 1 geladen. Die Komparatoren 3 und 4 vergleichen die Sondensatorspannung Uc mit der Referenzspannung Uref und ändern ihren Ausgangswert sprungartig von -Uv auf Uv sobald Uc nur geringfügig größer als ref ist. Das Flip-Flop 7 ändert daraufhin seinen Zustand, was wiederum die Schalter 9 und 10 beeinflußt. Der Kondensator 2 wird nun über Schalter 9b und Ladewiderstand 3 geladen und Kondensator 1 über Schalter 9a entladen. Die Ausgangsspannung Ua springt im leichen Zeitpunkt von U1 auf -U1.[it is the voltage divider, consisting of the resistors @ and 6 the reference voltage Uref is formed from the charging voltage UL. In the circuit shown the capacitor 1 is charged via the switch 9a and the charging resistor 5. the Comparators 3 and 4 compare the probe voltage Uc with the reference voltage Uref and change their initial value abruptly from -Uv to Uv as soon as Uc is only slightly is greater than ref. The flip-flop 7 then changes its state, which in turn the switches 9 and 10 influenced. The capacitor 2 is now via switches 9b and Charging resistor 3 charged and capacitor 1 discharged via switch 9a. The output voltage Among other things, it jumps from U1 to -U1 at the same point in time.

In Fig. 5 ist die Möglichkeit einer Nullpunktseinstellung dargestellt, indem parallel zu dem Kondensator 1 bzw. 2 des Differentialkondensators ein Abgleichkondensator 11 geschaltet wird.In Fig. 5 the possibility of a zero point setting is shown, by parallel to the capacitor 1 or 2 of the differential capacitor a balancing capacitor 11 is switched.

Wird, wie in Fig. 6 gezeigt, die Versorgungsspannung des Flip-Flop's 12 auf U1 bzw. -U1 stabilisiert, so läßt sich die pulsbreiten-modulierte Ausgangsspannung direkt an den Ausgängen Q bzw. Q abnehmen. Hierdurch läßt sich der Schalter 10 in Fig. 4 einsparen.As shown in Fig. 6, the supply voltage of the flip-flop 12 stabilized at U1 or -U1, the pulse-width-modulated output voltage Pick up directly at the Q or Q outputs. This allows the switch 10 in Save Fig. 4.

- L e e r s e i t e -- L e r s e i t e -

Claims (3)

patentansprüche 1. Auswerteelektronik für einen Differentialkondensator mit wechselseitigem Laden der beiden kondensatoren und pulsbreiter modulierter Ausgangsspannung ist dadurch gekennzeichnet, daß für den Ladevorgang der Kondensatoren nur ein Ladewiderstand für beide Kondensatoren eingesetzt wird, wobei der jeweils zu ladende Kondensator durch einen Umschalter mit dem Ladewiderstand verbunden wird. Claims 1. Evaluation electronics for a differential capacitor with alternating charging of the two capacitors and pulse-width modulated output voltage is characterized in that only one charging resistor is used to charge the capacitors is used for both capacitors, the capacitor to be charged is connected to the charging resistor by a switch. 2. Auswerteelektronik nach Anspruch 1 dadurch gekennzeichnet, daß die Stabilität des Meßwertes infolge Verbindung nur eines Ladewiderstandes, unabhängig von der Temperatur - und Langzeitdrift des Ladewiderstandes RL ist, so daß ein Widerstand mit minderer Qualität eingesetzt werden kann.2. Evaluation electronics according to claim 1, characterized in that the stability of the measured value due to the connection of only one charging resistor, independent on the temperature and long-term drift of the charging resistor RL, so that a resistance can be used with inferior quality. 3. Auswerteelektronik nach Aunspruch 1 und 2, dadurch gekennzeichnet, daß das pulsbreite modulierte Ausgangssibnal direkt von den Anschlüssen (' bzw. Q des Flip-Flopts 19 in Fig. 6 abgenommen werden kann3. Evaluation electronics according to Aunspruch 1 and 2, characterized in that that the pulse-width modulated output signal comes directly from the connections ('resp. Q of the flip-flop 19 in FIG. 6 can be removed
DE19853516162 1985-05-06 1985-05-06 Evaluating electronics for differential capacitors for use in sensors Withdrawn DE3516162A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
DE19853516162 DE3516162A1 (en) 1985-05-06 1985-05-06 Evaluating electronics for differential capacitors for use in sensors
DE19853542030 DE3542030A1 (en) 1985-05-06 1985-11-28 Evaluating electronics for differential capacitors

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3528416A1 (en) * 1985-08-08 1987-03-05 Philips Patentverwaltung Evaluating circuit for a capacitive sensor
EP0250028A2 (en) * 1986-06-18 1987-12-23 Philips Patentverwaltung GmbH Circuit device for compensation of temperature dependent and temperature independent drifts of a capacitive sensor
DE3740544A1 (en) * 1987-11-30 1989-06-08 Neutron Mikroelektronik Gmbh Device for converting a length or angle quantity into an electric incremental or digital quantity
AT391913B (en) * 1988-03-18 1990-12-27 Setec Messgeraete Gmbh PINCH PROTECTION FOR WINDOWS AND DOORS
DE4103200A1 (en) * 1991-02-02 1992-08-06 Vdo Schindling Measurement transducer for physical parameters - has two sensors e.g. capacitive, inductive or resistor sensors, and changeover switch selecting on sensor at time for connection to evaluation circuit
DE9107467U1 (en) * 1991-06-18 1992-10-22 Mesacon Gesellschaft für Meßtechnik mbH, 4600 Dortmund Arrangement for hardness measurement
DE4423907A1 (en) * 1994-07-11 1996-01-18 Ifm Electronic Gmbh Capacitive sensor esp. pressure sensor with measurement capacitor
DE10006534B4 (en) * 2000-02-15 2013-12-19 Continental Automotive Gmbh Method and sensor element for deformation measurement

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3528416A1 (en) * 1985-08-08 1987-03-05 Philips Patentverwaltung Evaluating circuit for a capacitive sensor
EP0250028A2 (en) * 1986-06-18 1987-12-23 Philips Patentverwaltung GmbH Circuit device for compensation of temperature dependent and temperature independent drifts of a capacitive sensor
EP0250028A3 (en) * 1986-06-18 1989-05-31 Philips Patentverwaltung Gmbh Circuit device for compensation of temperature dependent and temperature independent drifts of a capacitive sensor
DE3740544A1 (en) * 1987-11-30 1989-06-08 Neutron Mikroelektronik Gmbh Device for converting a length or angle quantity into an electric incremental or digital quantity
DE3740544C2 (en) * 1987-11-30 1999-08-12 Neutron Mikroelektronik Gmbh Device for converting a path or angle variable into an electrical incremental or digital variable
AT391913B (en) * 1988-03-18 1990-12-27 Setec Messgeraete Gmbh PINCH PROTECTION FOR WINDOWS AND DOORS
DE4103200A1 (en) * 1991-02-02 1992-08-06 Vdo Schindling Measurement transducer for physical parameters - has two sensors e.g. capacitive, inductive or resistor sensors, and changeover switch selecting on sensor at time for connection to evaluation circuit
DE9107467U1 (en) * 1991-06-18 1992-10-22 Mesacon Gesellschaft für Meßtechnik mbH, 4600 Dortmund Arrangement for hardness measurement
DE4423907A1 (en) * 1994-07-11 1996-01-18 Ifm Electronic Gmbh Capacitive sensor esp. pressure sensor with measurement capacitor
DE4423907C2 (en) * 1994-07-11 2000-05-18 Ifm Electronic Gmbh Capacitive sensor
DE10006534B4 (en) * 2000-02-15 2013-12-19 Continental Automotive Gmbh Method and sensor element for deformation measurement

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