Circuit for the detection of an asymmetry in the magnetization current of a magnetic modulator

• US 4,912,396 A
• Filed: 10/17/1988
• Issued: 03/27/1990
• Est. Priority Date: 10/15/1987
• Status: Expired due to Fees

• Current Assignee: Holec Systemen En Componenten B.V. (Eaton Corporation PLC.)
• Original Assignee: Holec Systemen En Componenten B.V. (Eaton Corporation PLC.)
• Inventors: Groenenboom, Maarten
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US07/258,500
• Time in Patent Office: 526 Days
• Field of Search: 324/117 R, 324/127, 363/26, 363/56, 323/246, 323/357, 323/358
• US Class Current: 324/117.00R
• CPC Class Codes: G01R 15/185 with compensation or feedback windings or interacting coils, e.g. 0-flux sensors using galvano-magnetic field sensors G01R15/20; conversion of DC into AC using transductors G01R19/20

Abstract

Circuit for detection of an asymmetry in the magnetization current, generated by a reference alternating voltage, in a magnetic modulator, in particular a magnetic modulator for zero-flux detection. This magnetic modulator comprises two virtually identical, wound magnet cores (T2, T3), each with a primary winding (W1) to be fed with a modulating current (i₁) and a series circuit of an auxiliary winding (W3) and an impedance (Z2, Z3) across which a voltage proportional to the magnetization current arises during operation. The reference alternating voltage (U_m) is fed to the respective series circuits (W3, Z2; W3, Z3) such that no resultant induction current is induced in the modulating current (i₁). The voltages over the impedances (Z2, Z3) form input signals for two peak value detectors (PD1, PD2), the strength of the output signal of which represents the degree of asymmetry of magnetization current. For processing the output signals of the two peak value detectors (PD1, PD2), devices (D) are provided which produce a virtually ripple-free output signal in the case of a symmetrical magnetization current. The invention also relates to a measurement circuit for the accurate measurement of direct and alternating currents.

Claims

1. Circuit for the detection of an asymmetry in the magnetization current of a magnetic modulator caused by a modulating current in a magnetic modulator for zero flux detection comprising first and second substantially identical wound magnetic cores, each at least provided with a primary winding and a series circuit of an auxiliary winding and an impedance voltage proportional to the magnetization current is generated during operation, it being necessary to supply the reference alternating voltage to the respective series circuits, each of said series circuits having first and second connecting terminals to which a common reference voltage source is connected, for providing each of said first and second magnet cores with said magnetization current, such that substantially no resultant induction current is induced in the modulating current, said modulating current being applied to a series connection of the primary windings of said first and second magnet cores, and further comprising a bipolar peak value detector having input and output connecting terminals, said input connecting terminals being connected across the impedance of one of said series circuits, the voltage across said impedance being proportional to the magnetization current of said one series circuit, the amplitude of the signal at the output connecting terminals of said bipolar peak value detector representing the degree of asymmetry of said magnetization current, a further bipolar peak value detector having input and output connecting terminals, said input connecting terminals being connected across the impedance of the other of said series circuits, and processing means having input and output connecting terminals, the output connecting terminals of said bipolar peak value detectors being connected to the input connecting terminals of said processing means, and the output signal at the output connecting terminals of said processing means being substantially ripple-free for symmetrical magnetization currents.

2. Circuit according to claim 1, in which at least one of said bipolar peak value detectors is a peak rectifier, comprising first and second devices having a diode which, respectively, are connected to first and second elements having a capacitive function such that a portion of the positive half period of the voltage across the impedance of one of said series circuits, which is proportional to said magnetization current, is stored in said first element and a portion of the negative half period of said voltage is stored in said second element, further comprising summation devices for the summation of the voltages stored in said first and second elements, the output of said summation devices constituting the output of one of said bipolar peak value detectors, and further comprising third and fourth devices having a diode function which, respectively, are connected to said third and fourth elements having a capacitive function such that a portion of the positive half period of the voltage across the impedance of the other series circuit, which is proportional to the magnetization current, is stored in the said third element and a portion of the negative half period of said voltage is stored in said fourth element, and further comprising summation devices for the summation of the voltages over said third and fourth elements, the output of said further summation devices constituting the output of the said further bipolar peak value detector.

3. Circuit according to claim 2, in which the anode connection of said first devices is connected to the cathode connection of said second devices and their connection point constitutes one input connection point of one of said bipolar peak value detectors, the first and second elements being formed by first and second capacitors connected to one another by one of their electrodes and their connection point forming the other input connection point of said one of said bipolar peak value detectors, and the other electrode of said first capacitor being connected to the cathode connection of said first devices and to one electrode of a first resistance, and the other electrode of the second capacitor being connected to the anode connection of the second devices and to one electrode of a second resistance, said resistances are connected to one another by their other electrodes and their connection point constitutes the output of one bipolar peak value detector, and wherein the anode connection of said third devices is connected to the cathode connection of said fourth devices and their connection point constitutes one input connection point of said further bipolar peak value detector, said third and fourth elements being formed by third and fourth capacitors connected to one another by one of their electrodes and their connection point constitutes the other input connection point of said further bipolar peak value detector, and the other electrode of said third capacitor is connected to the cathode connection of said third devices and to one electrode of a third resistance, and the other electrode of said fourth capacitor is connected to the anode connection of said fourth devices and to one electrode of a fourth resistance, said resistances being connected to one another by their other electrodes and their connection point constitutes the output of said further bipolar peak value detector.

4. Circuit according to claim 3, wherein said first, second, third and fourth devices are semiconductor diodes having substantially identical electrical characteristics and are located in the same substrate of semiconductor material.

5. Circuit according to claim 3, wherein said first, second, third and fourth devices each consist of a differential amplifier, the output of which is connected to the inverting input thereof via a series circuit of a resistance and a semiconductor diode and further comprising a further semiconductor diode connected anti-parallel to said series circuit, the forward direction of the device having a diode action corresponding to the forward direction of the semiconductor diode in said series circuit, and the anode and cathode connections corresponding therewith being formed by the connection point of said resistance and said semiconductor diode and by the free electrode of a further resistance connected to the inverting input of said differential amplifier.

6. Circuit according to claim 1, wherein said means for processing the output signals of the two bipolar peak value detectors comprise devices for the summation of said output signals.

7. Circuit according to claim 6, wherein said devices for the summation of the output signals of the two bipolar peak value detectors comprise a differential amplifier, the outputs of said bipolar peak value detectors being connected to the differential inputs of said differential amplifier and the output thereof constituting the output of the circuit.

8. Measurement circuit for the accurate measurement of direct and alternating current, comprising substantially first, second and third transformer, having primary windings, connected in series with one another, to be fed with the current to be measured, and having secondary windings, connected in series with one another, and connected to the output of an amplifier circuit, and having auxiliary windings, wherein the auxiliary winding of the first transformer being connected to the input of the amplifier circuit and the auxiliary winding of the second and third transformer each constituting a series circuit of an impedance and reference voltage source, which impedances are each connected to the inputs of a first and second bipolar peak value detector, respectively, the outputs of said first and second bipolar peak value detectors being connected to the inputs of signal summation means, the output of which is connected to the input of the amplifier circuit.