DD299091A5 - DEVICE FOR DETECTING A MAGNETIC FIELD OR WHICH CHANGE - Google Patents

Abstract

The present invention describes a device for detecting a magnetic field or its change. The invention can be used as a sensor or switching element in connection with mesz-, control and control equipment. The essence of the invention consists in the fact that a bistable magnetic element known per se is used, which generates periodically alternating pulses when controlled by a sufficiently large alternating magnetic field whose amplitude is a field intensity of the field of the excitatory field or the field strength of a field superimposed DC field, wherein the pulse amplitude is evaluated by a signal processing unit {magnetic field sensor; bistable magnetic element; Impulsdraehte; magnetic field strength; Frequency measurement}

Description

For this 7 pages drawings

Field of application of the invention

The invention can be used as a sensor or switching element in connection with measuring, control and regulating devices. With it, the field strength or the period of magnetic alternating fields can be determined. A determination of the strength of DC magnetic fields is possible.

Characteristic of the known state of the art

As an alternative to the induction coil, the torque probe or the Hall probe, the robust, environmentally stable, bistable magnetic elements whose production and mode of operation are described in the patent specifications DE-OS 21 43326 and DE-OS 281919305 provide high voltage signals.

The BME consists of a wire with coil winding or for signal power increase of a number of parallel connected windings with wire core as shown in DE 3406871.

The wire with a length I of about 20mm and a diameter d of about 0.2 mm is made of a Ni-Fe-Co or Co-Fe-V alloy. By special thermal and mechanical treatment, an axial preferred direction of the magnetization is set in the wire, which precondition for a jerky remagnetization when a critical field strength of the external magnetic field (Hs = 15ACnT ¹ KiSt.

This change in the magnetic flux taking place in a time range τ <100 ps produces a voltage pulse dependent on the number of turns and the load in a coil comprising the wire.

In DE 3008562, based on the BME, a proximity switch is described which, when the critical field strength is exceeded (eg, by decreasing the distance of a permanent magnet from the BME), not only a single, d. H.

Volatile pulse, but for the duration of exceeding the critical field strength, a periodic pulse train, d. H.

generates a non-volatile output signal, which is achieved by a BME exciting alternating field with a superimposed DC field.

This known solution has the disadvantages that for excitation a DC magnetic field and a magnetic alternating field are required, that practical technical solutions e.g. With regard to the evaluation of the phase position of the pulses or the amplitude of the output signal is missing that temporal fluctuations of the pulse (jitter), which can affect the measurement result, are not taken into account and that this device only as a switch, but not for metrological purposes (eg. the field and frequency measurement) can be used.

Object of the invention

The aim of the invention is to provide a device for detecting a magnetic field or its change, which eliminates the disadvantages resulting from the characteristic of the known technical solution.

Using the BME and low specific component cost, a technical solution variant is proposed, which can be used both as a switching element and for the continuous measurement of magnetic field quantities.

Explanation of the essence of the invention

According to the invention, the object, detection of a magnetic field or its change, is solved by the following technical means:

- bistable magnetic element (BME) consisting of wire and coil;

- Device for generating an alternating magnetic field consisting of generator and exciter coil;

- Signal processing unit.

As a signal processing unit, a peak value rectifier circuit is suitable, which generates a DC voltage which is proportional to the information parameter and which can be evaluated with different measuring means.

Comparators or analog-to-digital converters in conjunction with digital information processing means are still conceivable for evaluation purposes.

If a BME is located in a sufficiently large alternating magnetic field, an alternating pulse pair is generated in the coil in each period whose amplitude value is directly related to the time change and the strength of the exciter field.

Taking advantage of this dynamic property, the BME can be used to measure period duration or effective magnetic field strength.

If a constant field H = is superimposed on the alternating field under constant excitation conditions (eg f = ¹ kHz, H ₆ = 8OA cm ^-1 ), the signal amplitude also changes significantly, which enables determination of the magnetic field strength.

embodiment

The possible technical realization of the device according to the invention will be described with reference to Figures 1 to 8. Show it

Fig. 1: principle arrangement of the bistable magnetic element and AC voltage generator with exciting coil. A superimposed constant field is symbolized by the permanent magnet.

Fig. 2: Course of the magnetic field strength h _o and idealized signal curve Ui with alternating field excitation Fig.3: Dependence of the pulse amplitude U, the rms value of the magnetic exciter field H _e at two constant frequencies

Fig. 4: Dependence of the pulse amplitude Uj on the frequency f at a constant rms value of the magnetic exciter field Fig. 5: Course of the magnetic field strength h _e and idealized signal course U ₁ with alternating field excitation and superimposed

Gleichfeld Fig. 6: Dependence of the pulse amplitude UjFrom field strength of the magnetic DC field H = at constant

Excitation conditions FIG. 7: block diagram of the device FIG. 8: circuit diagram of the signal processing unit (peak value rectifier circuit).

If a BME 2 is controlled by the alternating field of an excitation coil 3 according to FIG. 1, the typical signal curve u is produced when the critical field strength H ₅ or -H _{s of} the excitation field is exceeded or undershot _. on the coil of the BME (Figure 2). For the measurement of a magnetic field or its change is used as an information parameter, the pulse amplitude Ü, which in a simple alternating field excitation in a characteristic manner of the effective field strength H _e at a constant frequency f (Figure 3) or the frequency f at a constant field strength H _e (Figure 4) is dependent.

A bias of the BME by a DC magnetic field, symbolized in Figure 1 by the permanent magnet, causes a change in the signal voltage u; in accordance with FIG. 5. FIG. 6 shows the dependence of the pulse amplitude U- on the uniform field strength H ₌ under constant excitation conditions, ie f = const. and H _e = const.

For measuring the parameters H _e orf of an alternating magnetic field, the device 1 consists of a BME 2 and the signal processing unit 4, wherein the BME can be introduced into any excitation field whose frequency f or its effective field strength H _e is known in each case.

To measure DC magnetic fields H =, the device 1 is composed of the BME 2, the device for generating the magnetic exciter field with H _e = const. And f = const., 3 and the signal processing unit 4 (FIG. 7).

For signal processing, a peak value rectifier circuit is used which has one of the pulse amplitudes Ü; generates sufficiently proportional DC voltage U _s , which can be erased eg by successive measurements by a switch S (Figure 8).

An indicator 5 allows the further processing of the voltage U ₃ for controlling an actuator 6 (Figure 7).

In the following table experimentally determined characteristics are summarized with respect to an alternating and dc field measurement.

N = 3000, d / l = ΙΟ "" ²

Fc-Co-Mn-V

Measuring range sensitivity Change field measure 20Acm ^ <He <10 ² Acm " aU, _ _ni V AHe ~ ^{U> 1} Acm "" (f = 1kHz) GIcichfeldmcssung 10 ² Hz <f <3-10 ³ IT " ^T0 · Hz. (He = ^ ACrTT" ¹ ) Ю ^л Аст ^л < H = <10 ² Acm " ^{1 А} І = 0.05 _Л ^Ѵ . 4H- 'Acrrr (He = 80Acm ^ f = 1kHz)

Measuring range and sensitivity of the device are essentially determined by the respectively constant selected parameter. An advantage of this evaluation method is that random temporal fluctuations of the pulse have no influence on the

Have measurement result.

Claims (4)

1. A device for detecting a magnetic field or its change using a bistable magnetic element (hereinafter referred to as BME) whose core is a ferromagnetic wire with a sufficiently rectangular hysteresis loop, the jerky by reversal magnetization upon reaching a critical field strength in a coil an electric Pulse, characterized in that the BME or that the BME coupled with a periodic magnetic excitation field, which is so high that the critical field strength for the jerky remagnetization of the wire is achieved in the two axial magnetic preferred directions, in conjunction with a pulse amplitude evaluating means for determining the strength and frequency of an alternating magnetic field or for measuring the strength of the exciting field superimposed magnetic DC field can be used. 2. Apparatus according to claim 1, characterized in that the signal processing unit for pulse evaluation is a peak rectifier circuit, which converts the pulse amplitude into a sufficiently proportional DC voltage. 3. Apparatus according to claim 1 and 2, characterized in that the measuring sensitivity can be increased by evaluating the difference of the output voltages of two peak value rectifiers, each of which converts the positive and negative pulse amplitudes. 4. Apparatus according to claim 1 to 3, characterized in that the measuring sensitivity for determining the magnetic field strength or the frequency can be varied by changing the frequency or the effective field strength of the excitation field.