RU2154280C2 - Gear measuring intensity of magnetic field - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: gear measuring intensity of magnetic field includes first generator of rectangular pulses, ferrosonde with core made of permalloy with hysteresis loop having squareness ratio near one, integrator connected to output winding of ferrosonde and linked with output to input of amplifier whose output is connected to input of threshold unit and logic AND gate, pulse counter, digital-to- analog converter, controlled current source, key and excitation winding of ferrosonde connected in series. First input of logic AND gate is connected to output of generator. Novelty of gear lies in insertion of RS flip-flop and second generator of rectangular pulses. Output of second generator of rectangular pulses is connected to first input of RS flip-flop and second input of pulse counter. Output of threshold unit is connected to second input of RS flip-flop and output of RS flip-flop is linked to second inputs of key and logic AND gate. EFFECT: increased measurement speed thanks to achievement of value of compensating field with use of single pulse. 2 dwg

Description

 The invention relates to magnetic measurements and is intended to measure magnetic field strength.

 A known magnetometer comprising a generator, a nuclear magnetic resonance sensor, an amplifier, a frequency controller, a code-voltage converter, an error signal receiver, a level discriminator, a reversible counter, a recording device / ed. St. USSR 580536, class G 01 R 33/08, 1977 /. However, due to the large size of the nuclear magnetic resonance sensor, the device does not allow measuring magnetic fields in small volumes and at a small distance from the surface of ferromagnetic bodies, i.e. This device cannot be used to test samples of ferromagnetic materials.

 A device containing a flux-gate is also known, in the magnetizing winding of which is included a square-wave generator and series-connected variable and reference resistors, in parallel with which a measuring device is connected, and a series-connected amplifier, integrator, threshold unit, and indicator device are connected in series to the output winding of the flux-gate. The device allows you to measure large fields near the surface of ferromagnetic bodies by the compensation method / auth. USSR 525902, class G 01 R 33/02, 1976 /. The disadvantage of this device is the long measurement process due to manual adjustment of the amplitude of the compensating field.

 The closest in technical essence to the claimed device is selected as a prototype device for measuring magnetic field strength / ed. St. USSR 815690, class G 01 R 33/02, 1981 /, containing a square-wave generator, a flux gate with a core made of permalloy with a hysteresis loop with a square factor close to unity, to the output winding of which an integrator is connected, with an output connected to the input of the amplifier, the output of which is connected to the threshold block input, and the measuring device, as well as the AND-NOT element connected in series, a reversible pulse counter, a digital-to-analog converter, a controlled current source and a key, the second input of a reversing counter and pulses and a first input of a logical AND-NO element are connected to the output of the threshold unit, a second input of the AND gate is coupled to the output of the generator of rectangular pulses, the output DAC AND-NO element is connected to the input of the measuring device. The second key input is connected to the output of the rectangular pulse generator, and the key output is connected to the magnetizing winding of the flux gate.

где H_max - предел измерения устройства; n - разрядность реверсивного счетчика импульсов.A disadvantage of the known device is the following. The amplitude of the compensating pulses H _k at a constant duration of t _and increases in the prototype device from zero to the measured value of the voltage H _ISM discretely in N steps:

where H _max is the measurement limit of the device; n is the width of the reversible pulse counter.

The duration t _and compensating pulses H _k should be greater than or equal to the magnetization reversal time of the flux-gate core along the limit hysteresis loop. In the general case, the magnetization reversal time of the core of the flux gate is determined by the value of the intensity of the external magnetization field, its rate of change, the shape and dimensions of the core, as well as the type of material from which it is made. The magnetization reversal process is often considered as the process of rotation of domains with "inertia" or magnetic viscosity. The rotation speed of domains is greater, the greater the external magnetic field affects them. Another factor that slows down magnetization reversal is eddy currents, arising, they create their own magnetic field directed opposite to magnetization reversal. For the same core of the listed factors, the magnetization reversal time is affected by the value of the external field strength and its rate of change. Moreover, an increase in the first leads to a decrease in the magnetization reversal time, and an increase in the second (due to an increase in eddy currents) leads to an increase. The rectangular shape of the compensating impulse H _k does not allow one to choose its amplitude equal to H _ISM . This makes it possible to make a sawtooth shape of the compensating pulse H _k , in addition, such a pulse shape is more advantageous from the point of view of eddy currents (they are smaller) than rectangular, although worse from the point of view of overcoming the magnetic viscosity of the domains. In this regard, the magnetization reversal time by a rectangular pulse is comparable to the time of magnetization reversal by a sawtooth pulse. Therefore, if the compensating impulse H _k will have a sawtooth shape with an amplitude equal to H _max and a duration close to t _and compensation of the intensity H _{meas of the} measured field will be achieved in a time commensurate with t _and .

An object of the invention is to increase the measurement performance by achieving the value of the compensating field with a single pulse of duration comparable with t _and .

 The problem is solved using a device for measuring the magnetic field strength, containing the first rectangular pulse generator, a flux gate with a core made of permalloy with a hysteresis loop with a square coefficient close to unity, to the output winding of which an integrator is connected, with an output connected to the amplifier input, an output which is connected to the input of the threshold block, the logic element AND, the pulse counter, a digital-to-analog converter, a controlled source current ir, key and excitation coil of a flux gate, the first input of the AND gate connected to the output of the first rectangular pulse generator, additionally equipped with an RS-trigger and a second rectangular pulse generator. Moreover, the output of the second rectangular pulse generator is connected to the first input of the RS-trigger and the second input of the pulse counter, the output of the threshold block is connected to the second input of the RS-trigger, and the output of the RS-trigger with the second inputs of the key and logic element I.

 Comparative analysis with the prototype shows that the inventive device is characterized by the presence of new units: RS-flip-flop, the second generator of rectangular pulses and their relationships with other elements of the circuit.

 Thus, the claimed device meets the criteria of the invention of "novelty."

 A comparison of the proposed solutions with other technical solutions shows that the RS-trigger and the square-wave pulse generator are widely known.

However, when they are introduced in this connection with the other elements of the circuit into the inventive device for measuring the magnetic field strength, the above blocks exhibit new properties, which leads to increased measurement performance by achieving the value of the compensating field with a single pulse of duration comparable with t _and .

 This allows us to conclude that the technical solution meets the criterion of "significant differences".

 In FIG. 1 shows a block diagram of a device for measuring magnetic field strength; in FIG. 2 - time diagrams of the operation of the device.

 A device for measuring the magnetic field strength (Fig. 1) contains a first rectangular pulse generator 1, a flux gate 2 with a core made of permalloy with a hysteresis loop with a square coefficient close to unity, to the output winding of which 3 an integrator 4 is connected, with an output connected to the input amplifier 5, the output of which is connected to the input of the threshold block 6, the logic element And 7 is connected in series, a pulse counter 8, a digital-to-analog converter 9, a controlled current source 10, a key 11, and a winding in excitation of the flux gate 12, and the first input of the logic element And 7 is connected to the output of the first rectangular pulse generator 1, in addition, the RS-trigger 13 and the second rectangular pulse generator 14. Moreover, the output of the second rectangular pulse generator 14 is connected to the first input of the RS-trigger 13 and the second input of the pulse counter 8, the output of the threshold unit 6 is connected to the second input of the RS-trigger 13, and the output of the RS-trigger 13 with the second inputs of the key 11 and the logical element And 7.

 The device operates as follows. In the initial state, at the output of the RS-trigger 13, the voltage level is prohibiting: the passage of current from the output of the controlled current source 10 through the key 11 to the excitation winding 12 of the flux-gate 2 and pulses from the output of the first rectangular pulse generator 1 to the first input of the pulse counter 8 through the And 7 logic element .

The flux gate 2 is placed in a constant or time-varying measured field H _ISM (Fig. 2). The state of the core of the flux gate 2 is determined by the magnitude of the field H _ISM , as well as the value of the compensating field H _k in the case of a current flowing in the excitation winding 12 of the flux gate 2. The magnitude of the compensating field is proportional to the current of the controlled current source 10, switched by key 11. For normal operation of the device, the measured and compensating fields directed counter.

At the beginning of each measurement cycle, a short trigger pulse from the output of the second rectangular pulse generator 14 is fed to the second input of the pulse counter 8, bringing it to zero, and to the first input of the RS trigger 13, as a result of which the voltage level is set at the output of the RS trigger 13 allowing the flow of current from the output of the current source 10 through the key 11 to the excitation winding 12 of the flux gate 2 and the passage through the logic element And 7 pulses from the output of the first generator of rectangular pulses 1 to the first input of the pulse counter 8. The output code in the pulse counter 8 progressively increases, which leads to an increase in the voltage at the output of the digital to analog converter 9 and, as a consequence, a current controlled current source 10. There is a ramp pulse shaping compensating field H _k. The EMF induced in the output winding 3 of the flux gate 2 during the magnetization reversal of its core (U3 in Fig. 2) is integrated by the integrator 4, amplified by the amplifier 5, and the voltage at the output of the amplifier 5 is proportional to the change in the induction in the core of the flux gate 2. From the output of the amplifier 5, this the voltage (U5 in Fig. 2) is applied to the input of the threshold unit 6, which is configured so that it is triggered if the change in the induction in the core of the flux-gate 2 exceeds a value equal to the maximum induction of the hysteresis loop of the core material (U _then Fig. 2). The core of the flux-gate 2 is made of permaloy with a hysteresis loop with a rectangular coefficient close to unity, i.e., the maximum induction of the core material is practically independent of the magnetic field strength and is equal to the value of the residual induction B _r (Fig. 2). Thus, if the measured field H _ISM becomes equal to the amplitude of the compensating field H _k , a pulse appears at the output of threshold block 6 (U6 in Fig. 2), which acts on the second input of the RS-trigger 13 and returns it to its original state. As a result: the current supply from the output of the controlled current source 10 through the key 11 to the excitation winding 12 of the flux-gate 2 is stopped, the pulses from the output of the first pulse generator 1 through the AND 7 logic element are stopped to the input of the pulse counter 8, and the digital counter 8 is installed at the output of the pulse counter 8 the code is directly proportional to the magnitude of the compensating, and therefore the measured field H _meas .

The blocks included in the device for measuring the magnetic field can be performed, for example:
first and second rectangular pulse generator, integrator, amplifier, threshold block, logic element And, pulse counter, digital-to-analog converter, key, RS-trigger / Yakubovsky SV, Barkanov N.A., Kudryashov B.P. Analog and digital integrated circuits. - M .: Owls. Radio 1979, 336 pp. /;
a flux gate as two windings on a core made of permalloy with a hysteresis loop with a rectangular coefficient close to unity;
controlled current source as an amplifier with current feedback / Falkenberry L. Application of operational amplifiers and linear ICs: Transl. from English. - M.: Mir, 1985, 572 p. /.

Experimental studies of the layout of the inventive device for measuring magnetic field strength showed that, compared with a device of a similar purpose (prototype), the inventive device provides improved measurement performance by achieving the value of the compensating field with a single pulse of duration comparable with t _and .

Claims (1)

 A device for measuring the magnetic field strength, containing the first generator of rectangular pulses, a flux gate with a core made of permalloy with a hysteresis loop with a rectangular coefficient close to unity, to the output winding of which an integrator is connected, with an output connected to an amplifier input, the output of which is connected to a threshold input block, series-connected logic element And, pulse counter, digital-to-analog converter, controlled current source, key and excitation winding ferro a probe, the first input of the AND gate being connected to the output of the generator, characterized in that it is equipped with an RS trigger and a second rectangular pulse generator, the output of the second rectangular pulse generator being connected to the first input of the RS trigger and the second input of the pulse counter, output of the threshold block connected to the second input of the RS-trigger, and the output of the RS-trigger with the second inputs of the key and logical element I.

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