EP0343403A1 - Circuit pour l'auto-excitation d'un oscillateur mécanique jusqu'à sa fréquence de résonance propre - Google Patents

Circuit pour l'auto-excitation d'un oscillateur mécanique jusqu'à sa fréquence de résonance propre Download PDF

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Publication number
EP0343403A1
EP0343403A1 EP89107994A EP89107994A EP0343403A1 EP 0343403 A1 EP0343403 A1 EP 0343403A1 EP 89107994 A EP89107994 A EP 89107994A EP 89107994 A EP89107994 A EP 89107994A EP 0343403 A1 EP0343403 A1 EP 0343403A1
Authority
EP
European Patent Office
Prior art keywords
circuit
amplifier
voltage
input
vibrations
Prior art date
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.)
Granted
Application number
EP89107994A
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German (de)
English (en)
Other versions
EP0343403B1 (fr
Inventor
Martin Pfändler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Endress and Hauser SE and Co KG
Original Assignee
Endress and Hauser SE and Co KG
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Publication date
Application filed by Endress and Hauser SE and Co KG filed Critical Endress and Hauser SE and Co KG
Publication of EP0343403A1 publication Critical patent/EP0343403A1/fr
Application granted granted Critical
Publication of EP0343403B1 publication Critical patent/EP0343403B1/fr
Anticipated expiration legal-status Critical
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/0207—Driving circuits
    • B06B1/0223—Driving circuits for generating signals continuous in time
    • B06B1/0238—Driving circuits for generating signals continuous in time of a single frequency, e.g. a sine-wave
    • B06B1/0246—Driving circuits for generating signals continuous in time of a single frequency, e.g. a sine-wave with a feedback signal
    • B06B1/0261—Driving circuits for generating signals continuous in time of a single frequency, e.g. a sine-wave with a feedback signal taken from a transducer or electrode connected to the driving transducer

Definitions

  • the invention relates to a circuit arrangement for self-excitation of a mechanical vibration system for natural resonance vibrations with an electromechanical transducer system which is arranged in the feedback circuit of an electronic amplifier circuit, so that it is excited by the output AC voltage of the amplifier circuit to mechanical vibrations and an AC voltage with the frequency of the input of the amplifier circuit mechanical vibrations.
  • the object of the invention is to provide a circuit arrangement for self-excitation of a mechanical vibration system which, with little circuit complexity, ensures reliable starting even under unfavorable operating conditions and reduces the risk of incorrect displays of the vibration state.
  • this object is achieved in that the amplifier circuit has a non-linear gain characteristic which gives a greater gain for small values of the input signal than for larger values of the input signal.
  • the circuit arrangement embodied according to the invention has a high sensitivity with small values of the input signal of the amplifier circuit, so that even weak ones Interfering effects, for example slight external vibrations, thermal noise or similar interfering effects, an oscillation is triggered which quickly builds up. In contrast, the input sensitivity is reduced for larger values of the input signal, so that good insensitivity to external vibrations is achieved. If the circuit arrangement is used, for example, in a fill level sensor of the type described above, it has a very good start-up behavior in a large temperature range and a very high starting tolerance, while at the same time being insensitive to external vibrations.
  • the required nonlinear gain characteristic can be achieved with little circuit complexity, since a two-stage gain is sufficient, which changes from a large value to a smaller value if the size of the input signal exceeds a predetermined threshold value.
  • FIG. 1 shows, as an example of a mechanical vibration system that is to be excited to vibrate at the natural resonance frequency, a fill level sensor 10 with two vibrating bars 12, 14.
  • the vibrating bars are set into flexural-phase bending vibrations, which are so strongly damped when the bars are immersed in the product that the vibrations cease, whereby it can be determined that the filling material has reached a predetermined filling level, while conversely the re-insertion of the vibrations indicates that the filling level has again fallen below the level to be monitored.
  • the vibrating rods 12, 14 are each fastened at one end to a membrane 16 which is clamped at the edge in a holder 18.
  • an electromechanical transducer system 20 is connected to the membrane i6, which has a transmitter transducer 22 and a receiver transducer 24.
  • the transmitter converter 22 is connected to the output of an amplifier circuit 30 and is designed such that it converts an electrical alternating voltage (or an electrical alternating current) supplied by the amplifier circuit 30 into a mechanical oscillation which acts on the membrane 16 and on the oscillating rods 12, 14 is transmitted.
  • the reception converter 24 is connected to the input of the amplifier circuit 30 and is designed such that it converts the mechanical oscillation of the oscillation system 10 into an electrical alternating voltage of the same frequency.
  • This AC input voltage is amplified by the amplifier circuit, and the amplified AC output voltage of the same frequency thus obtained is applied to the transmitter converter 22.
  • the electromechanical transducers 22, 24 can be of any type known per se, for example electromagnetic or electrodynamic transducers with coils, magnetostrictive transducers, piezoelectric transducers or the like. In the described embodiment, it is assumed that it is a piezoelectric transducer which contains, in a known manner, a piezo crystal arranged between two electrodes, which undergoes a change in shape when an electrical voltage is applied to the two electrodes, and vice versa in the case of a mechanically forced one Shape change creates an electrical voltage between the two electrodes.
  • the transmitter converter 22 and the receiver converter 24 can therefore be of the same type.
  • the amplifier circuit 30 contains an input amplifier 32, the input terminals of which are connected to the two electrodes of the receiving transducer 24, a bandpass filter 34 connected to the output of the input amplifier 32, and a power amplifier 36, the output electrodes of which are connected to the two electrodes of the transmitter transducer 22.
  • the bandpass filter 34 is tuned to the natural resonance frequency of the electromechanical oscillation system 10 to be excited, so that the electrical AC voltage is selectively amplified with this frequency. This can be the frequency of the fundamental oscillation or the frequency of a harmonic of the natural resonance of the mechanical oscillation system 10.
  • the peculiarity of the amplifier circuit 30 is that its gain characteristic, depending on the size of the input signal, is so non-linear that the amplification is greater for small amplitudes of the input signal than for large amplitudes.
  • this non-linear gain characteristic of the amplifier circuit 30 is achieved in that the input amplifier 32 is designed with a non-linear gain.
  • Fig. 2 shows an embodiment of the input amplifier 32, which gives the desired non-linear gain characteristic with particularly simple means.
  • the input amplifier 32 is designed as a differential amplifier with an operational amplifier 40.
  • the two inputs of the operational amplifier 40 are connected via identical resistors 41, 42 of the resistance value R 1 to the two electrodes of the receiving transducer 24, so that the voltage between these electrodes forms the input voltage U e of the differential amplifier.
  • In the leading from the output to the inverting input feedback branch of the operational amplifier 40 are two resistors 43, 44 with the resistance values R2 and R3 in series, and two further resistors 45, 46 with the same resistance values R2 and R3 are in series between the non-inverting input of the operational amplifier 40 and ground connected.
  • Two semiconductor diodes 47, 48 are connected in parallel in opposite directions to resistor 44, and in a corresponding manner two further semiconductor diodes 49, 50 are connected in parallel in opposite directions to resistor 46.
  • the differential amplifier shown in FIG. 2 has the following mode of operation:
  • the receiving transducer 24 initially only emits very small voltages which are caused by slight external vibrations, thermal noise and similar interference effects. These small voltages are amplified by the differential input amplifier 32. As long as the resulting output voltage U a of the differential input amplifier is so small that the voltage drops across the resistors 44 and 46 are smaller than the forward voltage of the semiconductor diodes 47, 48, 49, 50 (which is about 0.6 V for silicon diodes ), the semiconductor diodes block in both directions and the resistors 44 and 46 are fully effective. For such small input signals, the gain factor V of the differential input amplifier is 32
  • the diagram A in FIG. 3 shows this dependence of the gain factor V on the voltage
  • the diagram B in FIG. 3 shows the relationship between the input voltage U e and the output voltage U a of the input differential amplifier 32 that is achieved.
  • the output voltage U a is determined by the constant gain factor V 1, so that it with a relatively high steepness of the input voltage U e pro is portional.
  • the amplifier circuit 30 has a high input sensitivity, so that a reliable start-up is ensured even with weak interference effects and with temperature-related changes in the transmission factor and with build-ups on the oscillating rods 12, 14.
  • the output voltage U a reaches a value U a1 due to the amplification with the amplification factor V1, which is equal to the forward voltage of the semiconductor diodes 47, 48, 49, 50.
  • the gain factor V therefore has the smaller value V2, so that the output voltage U a rises less steeply as a function of the input voltage U e .
  • the input sensitivity of the amplifier circuit is therefore reduced, so that voltages which are generated by interference vibrations cannot reach values which simulate a resonant vibration of the mechanical vibration system 10.
  • Fig. 4 shows another embodiment of the input amplifier 32, which also gives the desired non-linear gain characteristic.
  • the Input amplifier 32 from two amplifier stages.
  • the first amplifier stage corresponds to the input amplifier of FIG. 2 with the only difference that the resistors 44 and 46 with the semiconductor diodes 47, 48 and 49, 50 connected in parallel in opposite directions are omitted.
  • the remaining components of this amplifier stage which correspond to those of the input amplifier of FIG. 2, are designated by the same reference numerals as in FIG. 2.
  • the two electrodes of the receiving transducer 24 are connected via the same resistors 41, 42 of the resistance value R 1 to the two inputs of the operational amplifier 40, so that the voltage between these electrodes forms the input voltage U e of the differential amplifier.
  • this amplifier stage has the constant gain factor
  • the second amplifier stage contains an operational amplifier 60, the non-inverting input of which is connected to the output of the first amplifier stage, so that the output voltage U a 'of the first amplifier stage forms the input voltage of the second amplifier stage, the output voltage U a of which also represents the output voltage of the input amplifier 32.
  • a resistor 61 with the resistance value R4.
  • the resistance R FET of the field effect transistor 63 depends on the control voltage applied to its gate electrode.
  • This control voltage is obtained from the output voltage U a by rectification by means of a rectifier circuit which contains two semiconductor diodes 64, 65 and a smoothing circuit with a capacitor 66 in parallel with a resistor 67.
  • the current path resistance R FET of the field effect transistor 63 is dependent on the amplitude of the output voltage U a .
  • U a U eV G (8)
  • the diagram A shows the voltage-dependent course of the gain factor V I and the diagram B shows the relationship between the input voltage U e and the output voltage U a 'of the first amplifier stage.
  • the gain factor V 1 is constant, so that the voltage U a ' is proportional to the input voltage U e .
  • the diagrams C and D show the conditions for the second amplifier stage in a corresponding manner. Up to a value U a1 'of the voltage U a' has the amplification factor V II a relatively large constant value V II1, so that the output voltage U a of the voltage U a 'with a relatively large slope is proportional.
  • diagram E shows the total amplification factor V G of the input amplifier 32, which results from the product of the two amplification factors V I and V II
  • diagram F shows the corresponding relationship between the Input voltage U e and the output voltage U a .
  • diagram F of FIG. 5 is very similar to diagram B of FIG. 3.
  • the input amplifier has a large amplification factor and therefore a high input sensitivity for small values of the input voltage U e , while the amplification factor is smaller for higher values of the input voltage and consequently the input sensitivity is reduced.
  • the embodiment of FIG. 4 therefore gives the same advantageous effects as were previously explained for the embodiment of FIG. 2.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Amplifiers (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
  • Inductance-Capacitance Distribution Constants And Capacitance-Resistance Oscillators (AREA)
  • Oscillators With Electromechanical Resonators (AREA)
EP89107994A 1988-05-03 1989-05-03 Circuit pour l'auto-excitation d'un oscillateur mécanique jusqu'à sa fréquence de résonance propre Expired - Lifetime EP0343403B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3815007 1988-05-03
DE3815007 1988-05-03

Publications (2)

Publication Number Publication Date
EP0343403A1 true EP0343403A1 (fr) 1989-11-29
EP0343403B1 EP0343403B1 (fr) 1993-09-08

Family

ID=6353496

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89107994A Expired - Lifetime EP0343403B1 (fr) 1988-05-03 1989-05-03 Circuit pour l'auto-excitation d'un oscillateur mécanique jusqu'à sa fréquence de résonance propre

Country Status (6)

Country Link
US (1) US5029268A (fr)
EP (1) EP0343403B1 (fr)
JP (1) JPH0775700B2 (fr)
DE (1) DE58905505D1 (fr)
ES (1) ES2042865T3 (fr)
WO (1) WO1989010802A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4327167A1 (de) * 1993-08-13 1995-02-16 Vega Grieshaber Gmbh & Co Verfahren und Vorrichtung zum Feststellen eines vorbestimmten Füllstandes in einem Behältnis
DE4429236A1 (de) * 1994-08-18 1996-03-14 Grieshaber Vega Kg Verfahren und Vorrichtung zur Füllstandauswertung

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5446420A (en) * 1993-08-25 1995-08-29 Motorola, Inc. Method and apparatus for reducing jitter and improving testability of an oscillator
DE112012005578B4 (de) * 2012-01-05 2019-11-07 Tdk Corporation Differenzielles Mikrofon und Verfahren zum Ansteuern eines differenziellen Mikrofons
US9934902B2 (en) * 2012-12-05 2018-04-03 Samsung Electronics Co., Ltd. Apparatus and method for transceiving wireless power

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB845267A (en) * 1955-10-20 1960-08-17 Vickers Electrical Co Ltd Improvements relating to electronic circuits
US3469211A (en) * 1967-10-16 1969-09-23 Branson Instr Oscillatory circuit for electro-acoustic converter with starting means
EP0240360A2 (fr) * 1986-04-03 1987-10-07 Tonen Corporation Oscillateur ultrasonore

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4393373A (en) * 1981-03-16 1983-07-12 Fuji Electrochemical Co., Ltd. Piezoelectric audible sound generator
JPS57158687A (en) * 1981-03-27 1982-09-30 Oki Electric Ind Co Ltd Hangul character display unit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB845267A (en) * 1955-10-20 1960-08-17 Vickers Electrical Co Ltd Improvements relating to electronic circuits
US3469211A (en) * 1967-10-16 1969-09-23 Branson Instr Oscillatory circuit for electro-acoustic converter with starting means
EP0240360A2 (fr) * 1986-04-03 1987-10-07 Tonen Corporation Oscillateur ultrasonore

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, Band 8, Nr. 163 (P-290)[1600], 27. Juli 1984; & JP-A-59 58 581 (MATSUSHITA DENKI SANGYO K.K.) 04-04-1984 *
WIRELESS WORLD, Band 73, Nr. 12, Dezember 1967, Seiten 594-598, Sussex, GB; A.E. CRUMP: "Diode function generators" *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4327167A1 (de) * 1993-08-13 1995-02-16 Vega Grieshaber Gmbh & Co Verfahren und Vorrichtung zum Feststellen eines vorbestimmten Füllstandes in einem Behältnis
DE4429236A1 (de) * 1994-08-18 1996-03-14 Grieshaber Vega Kg Verfahren und Vorrichtung zur Füllstandauswertung
DE4429236C2 (de) * 1994-08-18 1998-06-18 Grieshaber Vega Kg Messung des Füllstandes in einem Behälter

Also Published As

Publication number Publication date
JPH0775700B2 (ja) 1995-08-16
US5029268A (en) 1991-07-02
EP0343403B1 (fr) 1993-09-08
ES2042865T3 (es) 1993-12-16
JPH02502267A (ja) 1990-07-26
DE58905505D1 (de) 1993-10-14
WO1989010802A1 (fr) 1989-11-16

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