DE2547254A1 - MAGNETOMETER - Google Patents

Description

MISHIMA KOSAN CO., LTD., 1-15, 2-chome, Edamitsu, Yawatahigashi-ku,

Kitakyushu City, Fukuoka Prefecture, Japan

Magnetometer

The invention relates to a magnetometer for measuring an external Magnetic field.

The object of the invention is to provide a magnetometer of the type mentioned at the beginning Art to be designed so that an external magnetic field can be measured as precisely as possible with the simplest possible means.

The invention is characterized in that an oscillating circuit operated by a DC voltage source is provided with an oscillation-determining inductance which is electromagnetically assigned to a magnetic core serving as a magnetic field probe, which oscillating circuit is overdriven so that a provided transistor becomes conductive and non-conductive with each oscillation and that the time ratio for the duration of the conductive and the non-conductive state is dependent on the external magnetic field and influences an output voltage that can be tapped off via an output resistor.

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According to the invention, an oscillating circuit is constructed which works like a multivibrator and in which the essential, frequency-determining element is one or more inductances. The pulse-to-meke ratio of the generated deformed square-wave voltage is determined by the action of the external magnetic field via the magnetic core on these inductances and is therefore a measure of the external magnetic field * In addition to the pulse-gap ratio, the frequency of the deformed voltage also changes Square wave voltage as a function of the external magnetic field *

The invention will now be described in more detail with reference to the accompanying drawing explained

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In the drawing shows:

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6 Figure 7 Figure 8

Figure 9

Figure 1o

at a to d four different embodiments of the circuit of a magnetometer according to the invention with a single transistor,

at a and b two voltage diagrams to explain the function of the exemplary embodiments according to Figure 1,

a characteristic curve for the exemplary embodiments according to FIG. 1,

another embodiment with a playback device and a zero point compensation,

under a, b and c three further examples, which are equipped with two transistors to linearize the characteristic curve,

under a and b voltage diagrams for Figure 5, the characteristic curve for Figure 5,

an embodiment with the circuit from Figure 5 a and the playback device from Figure 4,

the structural design of an exemplary embodiment with U-shaped bent magnetic core,

the arrangement of linear magnetic cores to measure a three-dimensional magnetic field vector, and

Figure 11

in the block diagram an arrangement for measuring an external alternating magnetic field.

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In Figure T a to d, the circuits of magnetometers are shown, which are each equipped with a single transistor and have two windings and a DC voltage source. According to Figure 1a, an NPN transistor is used, which is designated by Q ₁ . 1 with an elongated, rectilinear magnetic core is referred to, on which the coils 2 and 3 are wound. The coil 2 is connected to the negative pole of the DC voltage source Bd via the resistor R. The other end of the coil 2 is connected to the base electrode of the transistor Q ₁ and via the resistor R ₂ to the positive pole of the voltage source Ed. The coil 3 is connected between the collector electrode and the positive pole of the voltage source Ed. _{A resistor R Q is} connected between the emitter electrode and the negative pole of the voltage source Ed, via which an output _{AC voltage e Q1 is} tapped, on which a DC voltage is superimposed. This DC voltage can be tapped off as the output voltage E _Q alone if a capacitance C _{Q is connected in} parallel with the resistor R _Q.

The mode of operation is described below using an oscillation mode. The magnetic flux level in the magnetic core 1 ■ is caused by an external magnetic field H. When voltage from the voltage source Sd reaches the transistor Q., a current flows through the switching elements Sd + - R ₂ - Q ₁ - S ₀ - Sd -. The collector current of the transistor Q- flows as a function of this current and a voltage is induced in the coil 2 as a result of the increase in the base current in the transistor Q-. The collector current of the transistor Q ₁ thus rises rapidly ^ due to the positive feedback "and the transistor is conductive. The magnetic core 1 has a non-linear saturation characteristic so that with increasing collector current of the value of the magnetic flux change a $ / AT becomes smaller, whereby the voltage induced in the coil 2 also becomes smaller and smaller and the collector current becomes smaller until the transistor finally becomes non-conductive.

When the transistor Q _{1 is} non-conductive, no collector current flows and the flux level in the magnetic core 1 reaches the original level again and the cycle repeats itself, causing a magnetic oscillation. The flux level in the magnetic core 1 of the

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external magnetic field H, determines the ratio between the duration of the conductivity period and the non-conductivity period of the transistor Q-, as will be explained in more detail with reference to FIG Diagrams of Figure 2 will be explained below.

In FIGS. 1b and 1c, modified circuits are shown compared to the circuit from FIG. 1a. Corresponding parts are denoted by the same reference numerals in FIGS. The magnetic oscillation is caused according to FIGS. 1b and 1c, just as in FIG. 1a, by an interaction between the transistor and the magnetic core. According to FIG. 1d, a PNP transistor Q _{2 is} used. In this case there is _{no resistance corresponding to the resistance R 2} , because the circuit according to FIG. 1d oscillates even without this resistance. The magnetic oscillation otherwise corresponds to that explained for FIG. 1a.

_{The diagrams from FIGS.} 2a and 2b are actually measured voltages e Q1f tapped across the resistor R _Q from FIG. 1a, specifically when there is no capacitance C _Q. FIG. 2a shows the output voltage with an external magnetic field H _ex = 0. In this case, the ratio between the conductivity period T _{QN of} the transistor Q ₁ and the non-conductivity period T _{Opp is} namely T _ON / T _opp = 3.13.

FIG. 2b shows the voltage profile for the same circuit, but with an external magnetic field EL _V = 1 Gauss, which acts on the magnetic core 1. Now the ratio Tqn ^ OFF ⁼ ^ »44, from which it can be seen that this ratio is ^t on / ^T OFF of the external magnetic field H acting on it. Accordingly, the direct voltage _{component of the alternating voltage tapped across the resistor R Q} is also dependent on the size of the external magnetic field H_ ". _{Finally, by comparing FIGS} . 2a and 2b, it can also be determined that the frequency of the magnetic oscillation, _i.e. 1 / (Τ ΟΝ + Τ _ορρ ), is dependent on the external magnetic field Η βχ.

Figure 3 illustrates graphically the dependence of the capacitance C with inserted ₀ above this can be tapped DC component E _Q of the external magnetic field H for the circuit of Figure 1a with an inserted capacitance C _n ^ 3 it can be seen that this

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The periodicity T _QN + Τ _ορρ is also different in FIG. 6b compared to FIG. 6a.

As in FIG. 3, FIG. 7 shows the dependency of the direct voltage _{component ^ 02} , tapped when the capacitance C _{Q is used} , in a circuit according to FIG. 5a. It can be seen from FIG. 7 that the characteristic is more linear compared to FIG.

Figure 8 shows the circuit of Figure 5a in combination with a reproducing circuit DSP corresponding to Figure 4 »As shown in FIG 6 is connected to the amplifier A ₂ is a low-pass filter combination, consisting of the resistors R ^, R ~, Rg and the capacitances CL and C _2» This low-pass filter serves -unterdrücken the AC component of the magnetic oscillation au * the output of the amplifier a ₂ is applied to an as regards the degree of amplification · adjustable amplifier a _3, and the output signal of the amplifier a ₃ is displayed in the reproducing circuit DSP · the adjustable resistor Hg serves to Compensation and can also be replaced by an adjustable resistor R ^. The output signal of the amplifier A "reaches _{the coil 4 via the negative feedback sensor R nf} and serves to compensate for the external magnetic field H." to be able to make the display with zero compensation.

Figure 9 shows an embodiment with a U-shaped bent magnetic core 1 »

The wound around this curved magnetic core 1 correspond with the coil bobbin shown in Figures la to 1d "5a and 5b _f 4 xaid. 8 The coil 1o, which consists of several parts, is wound around the legs and the transverse web of the U-shaped bent magnetic core "Keep away unwanted external magnetic fields. In the head area 60 -» the housing 5o has an opening in which the two ends of the magnetic core 1 face each other and enclose a narrow air gap.

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refers to a sticky element that is magnetized for the purpose of testing. The magnetic lines of force 4o of this magnetization are deformed at the fault location 3o. If the faulty element Zo is moved past the air gap, the fault location 3o can be identified by a sudden change in the measured external magnetic field.

According to FIG. Ίο, the three components of a magnetic field with three straight cores ix, 1y, Iz arranged according to these components x, y and ζ are measured. In this exemplary embodiment, only the absolute value of the assigned external magnetic field component is measured with the individual cores. A circuit, as shown, for example, in FIGS. 1a to 1d, 5a and 5b, 4 and 8, can be assigned to each of the individual cores. At the output terminals of these three circuits can then the voltages ^E _{xout "V} out ^e ^ ¹¹¹ ^ ^e zout be tapped, which are assigned to magnetic field components in the respective coordinate directions. These output voltages can then be squared in squaring circuits

2 2 2

become the voltages e _xout »e _yout and e _zout · These squared voltages are then added in an addition circuit, so that an output signal corresponding to the voltage 2 2 2

xout ⁺ vout ^{+ e} zout ^results · This square sum signal is then processed in a square root circuit and an output signal corresponding to the value is produced

e ² Ve ^ Ve ¹
xout yout zout

This output signal corresponds to the absolute value of the measured external magnetic field. One can therefore adjust the size of the external Measure the magnetic field with such a circuit and also display it in a playback circuit DSP.

FIG. 11 shows an exemplary embodiment for measuring an external magnetic alternating field H which reaches the magnetic core 1. This alternating magnetic field is measured with high accuracy by a phase measurement of the output signal 6 _out "that is taken from amplifier A- or A" from FIG. 4 or 8.

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DC voltage component E _Q1 is dependent on the size of the external magnetic field H _{Q ".}

FIG. 4 shows the circuit from FIG. 1a with a playback circuit DSP. According to FIG. 4, A ₁ denotes an amplifier which integrates and amplifies _{the tapped voltage e Q.} R ^ and Rp are gain adjusters, SW is a bias switch, and Cr. a capacity for integration * The integrated and amplified signal at the output of the amplifier A ₁ is reproduced in the playback circuit DSP * The playback circuit can be a known measuring device, a device for converting an electrical input signal into an acoustic sound, for example a Loudspeaker, or an optical display device act * Sin adjustable resistance S, is used to adjust the reproduction or display of the reproduction circuit DSP on KuIl e to whom the external magnetic field H_ "= 0 · To expand the measuring range» Jcann a negative one Feedback current to compensate for the external magnetic field E _av via the Kompensaticnsspule 4 and the resistor E _n p for negative feedback to the magnetic core 1 -be fed back »The magnetometer according to the invention is very simple, constructed and has only a single transistor. You can meet even measures such magnetometers to the nonlinearity and the Temperaturabhäiig "" ^one counter -it the display, which is illustrated in the following. For example, figures * *

According to FIG. 5a and 5b, circuits for magnetometers each with 2 'transistors, four coils and a GleicBspaiinungsquelle Ed are shown · According to FIG. 5a, two NPN transistors Q ₃ and Q, are used and the oscillation operation is as follows.

First, voltage from the DC voltage source Sd reaches the transistor Q ₃ and current flows as follows from the plus pole of the DC voltage source Sd via the resistor R ₅ , via the transistor Q " and via the resistor S _Q to the minus pole of the DC voltage source Sd . The collector current of the transistor Q ₃ begins to flow and that through the resistor S ₀ to the coil 6, mj is induced by voltage in the coil 5 * This induced voltage causes

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a collector current of the transistor Q ^ i which is connected with its base electrode via the resistor R _{5 to} the positive pole of the direct voltage source Ed and with its emitter electrode connected to the negative pole of the direct voltage source Ed _{via the resistor R 0.} The transistor Q ₃ therefore becomes conductive. On the other hand, the voltage induced in the coil 8 makes the transistor Q. non-conductive, because the voltage induced in the coil 8 by the aforementioned collector current is negative at the base electrode and positive _{at the emitter electrode of the transistor Q 4.} During this state, as a result of the non-linear characteristic of the magnetic core 1, the value αφ / dt in the magnetic core 1 becomes smaller and smaller and finally zero, as described in detail in the text relating to FIG. 1a. When the voltage induced in the coil 5 becomes zero and as a result the collector current of the transistor Q ₃ becomes smaller and smaller, the original flux value, which is determined by the external magnetic field H, is set in the magnetic core 1 again, so that now the induced voltage in the coil 8 has opposite polarity and a _{positive voltage is applied to the base electrode of the transistor Q 4} and a negative voltage to the emitter electrode, whereby the transistor Q ₄ becomes conductive and collector current flows through the coil 7 _{via the resistor R 0.} Voltage is now induced in coil 5, which makes transistor Q_ non-conductive. The game repeats itself and a magnetic oscillation occurs. The circuits according to FIGS. 5b and 5c are modified compared to FIG. 5a. According to Figure 5b, two PNP transistors are used and according to Figure 5c, as in Figure 5a, two NPN transistors. Otherwise, the same reference numerals are used in FIGS. 5 for the same or corresponding parts.

FIGS. 6a and 6b show voltage diagrams as they were actually _{tapped as alternating voltage e O2} , that is to say when there was no capacitance C ₀ , on a circuit according to FIG. 5a. Figure 6a shows the output voltage e _Q2 with an external magnetic field H _ex = O with a time _ratio between conductivity period T QN and non-conductivity period T _opF based on the conductivity state of transistor Q ₃ in the value of T _ON / T _opp = 1.2. Figure 6b shows the corresponding diagram for an external magnetic field H _ex β 1 Gauss and a corresponding ratio ^t on / ^t off ~ ^{1f36 #}

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and is compared with a reference signal. In figure 11 is provided with 7o a differential amplifier designated with which the GIeichspannungsSignalkomponente from the in the circuit of Figure 11 fed in at the output of amplifier A or A ₃ off 'gripped output signal e _out is suppressed and the AC component is amplified alone. A tuned amplifier is denoted by 71, which amplifies only the frequency component which corresponds to the frequency of the external magnetic alternating field to be measured. The off passage signal of the amplifier 71 is applied to a phase detector 72 and to an amplifier 73 which serves to cause the reference signal for the phase comparison, the amplifier ¹ J3 controls a J? Echteckformer 74 on, in which the off passage signal of the amplifier in A hexagonal clamping is converted.This signal is used to control an abs tiismver 75, which is matched to the alternating frequency of the external magnetic field controls the phase detector 72 » The signal-to-noise ratio of the electrical signal, which corresponds to the external magnetic alternating field, is improved and in this way the field measurement is possible with high accuracy. 78 is an integrating amplifier which suppresses the noise component in the output signal of the phase detector 72. The amplified signal is displayed in the playback device DSF (a digital display, a loudspeaker or the like). In this embodiment it is assumed that a reference signal is derived from the output signal of the tuning amplifier 71 in the branch beginning with the amplifier 72. Of course, the reference signal can also be fed into the amplifier 73 from the outside and the connection between the output of the amplifier must then be established 71 "at the input of the amplifier 73

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Claims (6)

P 30 919 EXPECTATIONS Magnetometer for measuring an external magnetic field, characterized in that an oscillating circuit operated with a DC voltage source is provided with a Vibration-determining inductance (2, 3), which is electromagnetically assigned to a magnetic core serving as a magnetic field probe is, which resonant circuit is overdriven so that a provided transistor conducts once with each oscillation and once becomes non-conductive and that the time ratio for the duration of the conductive and the non-conductive state depends on the external magnetic field and influences an output voltage that can be tapped off via an output resistor. 2. Magnetometer according to claim 1, characterized in that two inductors are wound onto the magnetic core (1), one of which is connected in the collector circuit and the other in the base circuit of _{the transistor (Q 1).} 3. Magnetometer according to claim 1, characterized in that two transistors (Q ₁ - and Q ₆ ) operated in push-pull are provided, each of which is assigned two of a total of four inductances wound on a common magnetic core (1), 609819/0343 l - P 3o 919 by switching one of these into the base circuit and the other into the collector circuit of the associated transistor is. 4. Magnetometer according to one of the preceding claims, characterized by means of a zero point compensation with one of the amplified and filtered direct voltage components of the Output signal controlled, on the common magnetic core (1) wound compensation coil (4). 5. Magnetometer according to one of the preceding claims, characterized in that a display device with the output signal (DSP) is controlled. 6. Magnetometer according to one of the preceding claims, characterized in that for measuring an external magnetic Alternating field, the frequency component of the output signal that corresponds to the frequency of this alternating field is filtered out and is compared in a phase detector with a reference signal of the same frequency with regard to their phase position. 7 »Magnetometer according to one of the preceding claims, characterized in that a U-shaped bent magnetic core is provided in order to find faults in jaagnetized workpieces or similar magnetic field defects, which, together with the vibration-stabilizing inductances, is housed in a magnetically shielding housing, which for some air gap therebetween enclosing Po lspitzen of the magnetic core one opening aufwe is where the% is passed u examined workpiece " 8 «Magnetometer according to one of the preceding claims», characterized in that for measuring a three-dimensional external magnetic field, three linearly acting probes each having a straight magnetic core {ι) are arranged in sighting of the three orthogonal axes * with which the three components of the Magnetic field yes. and that the absolute value of the vector quantity is calculated from the determined Ifeß voltages by squaring, adding and ratifying the square suns, 609819/0343