SU789923A1 - Method of measuring field intensity of constant and low frequency magnetic fields - Google Patents

Description

The invention relates to magnetic measurements and can be used to measure weak constant and low frequency magnetic fields with enhanced accuracy for purposes of geology, geophysics, and other fields of science and technology. The known method of measuring the intensity of weak constant and low-frequency magnetic fields, based on the periodic modulation of the permeability of the ferromagnetic cores of the magnetic modulation converter by alternating excitation current. According to this method, the converter cores are periodically brought to saturation and according to the level of the even (for example, second) harmonics of the output EMF, the strength of the measured field ijf is judged. However, the described method has insufficient measurement accuracy due to instability of the transmissivity of the converter cores, and is characterized by a considerable power consumption over the excitation circuit due to large hysteresis losses during cyclic magnetic reversal of the cores by alternating current. The closest to the proposed technical essence and the achieved result is a method of measuring the strength of weak constant and low-frequency magnetic fields, based on the periodic modulation of the permeability of ferromagnetic cores of a magnetic-modulating converter with a pulsating excitation current. According to this method, in the excitation circuit of the transducer, not only alternating, but also direct current is created, which displaces the operating point of the transducer cores to the region of the maximum steepness of the effective permeability. The intensity of the measured field is judged by the level of the odd (usually the first) harmonic of the output emf of the L2J transducer. The disadvantage of this method is the low measurement accuracy due to instability of the magnetic permeability of the core material of the transducer caused by temperature changes, mechanical effects and natural aging. .

The purpose of the invention is to improve the accuracy of measurements.

This goal is achieved by the fact that in the method of measuring the strength of permanent and low-frequency magnetic fields, which consists in modulating the permeability of ferromagnetic cores of an induction converter with a pulsing excitation current, the converter is affected by an auxiliary variable magnetic field whose frequency is at least more than the frequency excitation current, allocate a correction current proportional to the envelope of the signal generated by the auxiliary field at the output of the converter, and then excitaton) kdeni formed by summing the corrective currents and pulsating.

FIG. 1 shows a block diagram of a device implementing the proposed method in FIGS. 2, 3, and 4 are timing diagrams explaining the processes in the device.

The method is implemented as follows.

Magnetic modulation transducer 1 is placed in a measurable magnetic field and periodic permeability of its cores is carried out by pulsating excitation current from reference generator 2 through adder 3. Transmitter output is connected to measurement one. unit 4, which contains a selective amplifier, tuned to the first harmonic of the output EDC, according to the level of which judges the intensity of the measured field.

To eliminate the effect of core permeability instability on measurement accuracy, the converter is impacted by an alternating magnetic field created by generator 5 and covers the converter with a correction circuit consisting of a series-connected selective amplifier b and an amplitude detector 7, the output of which is connected to the second input of the adder 3 The frequency of the auxiliary field is chosen an order of magnitude higher than the frequency of the excitation.

Under the action of the auxiliary field, an amplitude-modulated signal appears at the output of the converter, the carrier of which has the frequency of the auxiliary field, and the shape of the envelope corresponds to the law of change in the effective permeability of the cores with time (Figures 2 and 3). Amplitude modulated signal

amplified and filtered by a selective amplifier 6, detected by an amplitude detector 7, and a correction current proportional to the change in the envelope of the amplitude-modulated signal is selected in the detector load (Fig. 4). In this case, the polarity of the direct current, the magnetizing converter cores, is chosen so that the correction current is inverted relative to the reference excitation current by 180. The resulting excitation current of the converter cores is formed by summing the reference pulsating and correction currents from

using the adder. By introducing a correction current into the drive circuit of the converter, the measurement error caused by instability of the permeability of its cores is compensated.

This is explained as follows. Suppose, under the action of destabilizing factors, the permeability of the cores has changed in such a way that its steepness in the work area has become greater than the original. This will increase the signal emf.

in the measuring path and, consequently, to the appearance of measurement error. However, the amplitude of the amplitude-modulated signal envelope will simultaneously increase, t: o3 given by the auxiliary field at the output of the converter, the correction current will increase accordingly, and the resulting excitation current will decrease as the correction current is inverted relative to the reference current by 180. A decrease in the resultant excitation current will reduce the change EMF signal in the measuring path and, consequently, to a decrease in measurement error.

Claims (2)

1. Afanasyev Yu. V. Ferrozondy, L., Energie, 1966, pp.28-30. 2. Afanasyev Yu. V. Ferrozondy, L., Energie, 1966, p. 25-26. / ./. ./X