RU2147752C1 - Quick-acting device for measurement of magnetic field strength - Google Patents

Abstract

FIELD: magnetic measurements. SUBSTANCE: quick-acting device for measurement of magnetic field strength has the first square-wave generator, ferroprobe with a core made of permalloy with a hysteresis loop with a squareness ratio close to unity. Connected to the ferroprobe output winding is an integrator, whose output is connected to the input of the first threshold unit, series-connected AND gate, pulse counter, digital-to analog converter, controlled current source, key and ferroprobe exciting winding. The first input of the AND gate is connected to the output of the first square-wave generator. Novelty in the invention is provision of RS-flip-flop, second square-wave generator and threshold unit. The output of the second square-wave generator is connected to the first input of the RS-flip-flop and second input of the pulse counter, the output of the first threshold unit is connected to the second input of the RS-flip-flop, the output of the RS-flip-flop is connected to the second inputs of the key and AND gate, the input of the second threshold unit is connected to the ferroprobe output winding, and the output - to the third input of the AND gate. EFFECT: enhanced speed of response due to attaining of the value of compensating field with the aid of one pulse whose duration is commensurable with t_i. 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 N 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 compensation method / ed. St. USSR N 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 N 815690, class G 01 R 33/02, 1981 /, containing a rectangular pulse 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 amplifier input, the output of which is connected to the input of the threshold unit, and the measuring device, as well as series-connected AND-NOT elements, a reversible pulse counter, a digital-to-analog converter, a controlled current source and a key, the second input of a reversing counter mpulsov 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, output digital to analog converter coupled 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. Это происходит потому, что прямоугольная форма компенсирующего импульса H_к не позволяет за один шаг подобрать его амплитуду равной H_изм. Длительность t_и компенсирующих импульсов H_к должна быть больше или равна времени перемагничивания сердечника феррозонда по предельной петле гистерезиса. В общем случае время перемагничивания сердечника феррозонда определяется: значением напряженности внешнего перемагничивающего поля, скоростью его изменения, формой и размерами сердечника, а также типом материала, из которого он изготовлен. Процесс перемагничивания часто рассматривают как процесс вращения доменов, обладающих "инерционностью" или магнитной вязкостью. Скорость вращения доменов тем больше, чем большее внешнее магнитное поле на них воздействует. Другим фактором, замедляющим перемагничивание, являются вихревые токи, возникая, они создают собственное магнитное поле, направленное встречно перемагничивающему. Для одного и того же сердечника из перечисленных факторов на время перемагничивания оказывает влияние значение напряженности внешнего поля и скорость его изменения. Причем увеличение первого - приводит к уменьшению времени перемагничивання, а увеличение второго (за счет возрастания вихревых токов) - к увеличению.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 device of the prototype from zero to the measured value of tension 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. This is because the rectangular shape of the compensating impulse H _k does not allow one to select its amplitude equal to H _meas . 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 flux-gate core is determined by: the value of the external magnetizing field strength, 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.

Until the amplitude of the compensating field
H _to <(H _ISM - H _t ),
where H _t is the starting field, the magnetic state of the core of the fluxgate does not change (it is in saturation). This means that eddy currents in the core are not induced, therefore, it can be affected by an external field with a high rate of change. As soon as the amplitude of the compensating field H _k becomes comparable with H _meas , magnetization reversal of the core of the flux gate will occur, and as a result eddy currents will occur to counteract this. To reduce them, it is preferable to limit the magnetization reversal rate in this region by choosing another form of a compensating pulse, for example, exponential, with an amplitude equal to H _meas . Moreover, the duration of this pulse, by virtue of the foregoing, will be commensurate with t _and .

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

 The problem is solved using a high-speed 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 square factor close to unity, to the output winding of which an integrator is connected, with an output connected to the input of the first threshold block, series-connected logical element And, pulse counter, digital-to-analog converter, controlled current source, key and a flux-gate excitation coil, the first input of the AND gate being connected to the output of the first rectangular pulse generator, additionally equipped with an RS-trigger, the second rectangular pulse generator and the threshold block. 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 first threshold block is connected to the second input of the RS-trigger, the output of the RS-trigger is connected to the second inputs of the key and logic element And, the input of the second threshold block is connected with the output winding of the flux gate, and the output with the third input of the logical 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 the threshold block, 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 solution with other technical solutions shows that the RS-trigger, the square-wave pulse generator and the threshold block 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 high-speed device for measuring magnetic field strength; in FIG. 2 - time diagrams of the operation of the device.

 A high-speed device for measuring the magnetic field strength (Fig. 1) contains the 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 is connected an integrator 4, the output connected to the input of the first threshold block 5, a logical element And 6 connected in series, a pulse counter 7, a digital-to-analog converter 8, a controlled current source 9, a key 10 and an excitation winding 11 ferros onda 2, and the first input of the logic element And 6 is connected to the output of the first rectangular pulse generator 1, as well as the RS-trigger 12, the second rectangular pulse generator 13 and the threshold block 14. Moreover, the output of the second rectangular pulse generator 13 is connected to the first input of the RS-trigger 12 and the second input of the pulse counter 7, the output of the first threshold block 5 is connected to the second input of the RS-trigger 12, the output of the RS-trigger 12 is connected to the second inputs of the key 10 and logic element 6, the input of the second threshold block 14 is connected to the output winding 3 of the fer probe 2, and an output to the third input of the AND gate 6.

 The device operates as follows. In the initial state, at the output of the RS-flip-flop 12, the voltage level is forbidding: the passage of current from the output of the controlled current source 9 through the key 10 to the excitation winding 11 of the flux-gate 2 and pulses from the output of the first generator of rectangular pulses 1 to the input of the pulse counter 7 through the logical element And 6. The output level of the second threshold block 14 does not impede the passage of pulses from the output of the first rectangular pulse generator 1 to the input of the pulse counter 7 through the AND 6 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 and the value of the compensating pulsed field H _k created by the current in the excitation winding 11 of the flux gate 2. The magnitude of the compensating field is proportional to the current of the controlled current source 9, switched by key 10. For normal operation of the device, the measured and compensating fields are directed opposite .

At the beginning of each measurement cycle, a short trigger pulse from the output of the second rectangular pulse generator 12 is supplied to the second input of the pulse counter 7, bringing it to zero and to the first input of the RS-trigger 12, as a result of which the voltage level is set at the output of the RS-trigger 12 : the flow of current from the output of the current source 9 into the excitation winding 11 of the flux gate 2 and the passage through the logic element And 6 pulses from the output of the first rectangular pulse generator 1 to the input of the pulse counter 7. The output code is 7 etchika pulses increases, which leads to an increase in the voltage at the output of the digital to analogue converter 8 and as a consequence the current controlled current source 9. Starting pulse generation compensating field H _k. EMF induced in the output winding 3 of the flux-gate 2 during the magnetization reversal of its core is proportional to the rate of change of induction in the core of the flux-gate 2 (U3 in Fig. 2). In the interval t0 - t1, it is equal to zero, because induction does not change. The second threshold unit 14 has a zero setting, so its output signal does not change and the digital code of the counter increases with the frequency of the first pulse generator 1. In the region t1 - t2, magnetization reversal of the core of the flux gate 2 occurs, which causes the appearance of an EMF at the output of the output winding 3 of the flux gate 2, and means to trigger the second threshold block 14 (U14 in Fig. 2). The changed output signal of the second threshold block 14, acting on the third input of the And 6 logic element, prevents the passage of pulses from the output of the first rectangular pulse generator 1 to the input of the pulse counter 7. The change of the output code of the pulse counter 7 stops until the core remagnetization process is completed flux-gate 2. With the completion of this process, the output signal of the second threshold block 14 goes to its initial state and the process continues. Thus, in the interval t1 - t2, the rate of rise of the pulse of the compensating field will decrease and, on the whole, the shape of this pulse will be close to exponential. The EMF from the output of the output winding 3 of the fluxgate 2 is integrated by the integrator 4, the voltage at the output of the integrator 4 is proportional to the change in the induction in the core of the fluxgate 2. From the output of the integrator 4 this voltage (U4 in Fig. 2) is supplied to the input of the first threshold block 5 configured in this way that it is triggered if the change in 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 in Fig. 2). The core of the flux-gate 2 is made of permalloy with a hysteresis loop with a rectangular coefficient close to unity, i.e. the value of 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 _meas becomes equal to the amplitude of the compensating field H _k , a voltage level appears at the output of the first threshold block 5 (U5 in Fig. 2), which acts on the second input of the RS trigger 12 and causes the RS trigger 12 to return to initial condition. As a result: the current supply from the output of the controlled current source 9 through the key 10 to the excitation winding 11 of the flux-gate 2 is stopped, the pulses from the output of the first pulse generator 1 through the And 6 logic element are stopped to the input of the pulse counter 7, and the digital counter is installed at the output of the pulse counter 7 the code is directly proportional to the magnitude of the compensating, and therefore the measured field H _meas .

The blocks that make up the high-speed device for measuring magnetic field strength can be performed, for example:
first and second rectangular pulse generator, integrator, amplifier, threshold blocks, logic element And, pulse counter, digital-to-analog converter, key, RS-trigger, as described in / Yakubovsky SV, Barkanov NA, Kudryashov B. P. Analog and digital integrated circuits. - M .: Owls. radio, 1979, 336 p. /;
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 according to / Falkenberry L. Application of operational amplifiers and linear ICs: Transl. from English. - M.- Mir, 1985.572 s./.

Experimental studies of the layout of the inventive high-speed 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 high-speed 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 square coefficient close to unity, to the output winding of which an integrator is connected, with an output connected to the input of the first threshold block, logic connected in series element And, pulse counter, digital-to-analog converter, controlled current source, key and excitation coil of a flux gate, the first the first input of the AND gate is connected to the output of the first rectangular pulse generator, characterized in that it is equipped with an RS trigger, a second rectangular pulse generator and a threshold block, the output of the second rectangular pulse generator connected to the first input of the RS trigger and the second input of the pulse counter, the output of the first threshold block is with the second input of the RS-trigger, the output of the RS-trigger is with the second inputs of the key and logic element And, the input of the second threshold block is with the output winding of the flux gate, and the output is from the third m input logic element I.

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