SU1659912A1 - Method for calibrating meter of magnetic field strength - Google Patents

Abstract

The invention relates to radio measurement methods and can be used to calibrate a magnetic field strength meter both in air and in a conductive medium. The purpose of the invention is to expand the calibration frequency range. The method allows calibration of the magnetic field intensity meter in the entire frequency range due to additional measurement of the signal voltage directly at the output of the probe. To determine the calibration factor K (co), choose the frequency of the Sho calibration range in the low-frequency part of the measurement range in which the calibration field is known or not dependent on the conductivity of the medium (when conducting calibration in a conducting medium). At this frequency, the most accurate absolute value of the calibration field intensity is calculated. The field value selected in this way is used to calculate the calibration factor using the above formula. 1 il.

Description

The invention relates to radio measurements and can be used to calibrate a magnetic field strength meter.

The purpose of the invention is to expand the calibration frequency range.

The drawing shows a structural electrical circuit of a device implementing the proposed method.

The device contains Helmholtz rings 1, connected to the output of the signal generator 2 via a balancing transformer 3, probe 4 under investigation, the output of which is connected via key 5 to the input of preamplifier 6 and placed in the center of the Helmholtz rings 1 in the induction zone of the calibration field. The output of the preamplifier 6 is connected to the input of the microvoltmeter 7. The output of the probe 4 is through

the key 8 is connected to the input of the microvoltmeter 9. The voltmeter 10 through the matching transformer 11 is connected to a resistor connected in the secondary circuit of the balancing transformer 3.

The calibration method of the magnetic field meter is implemented as follows.

Measuring the voltage UK (.W) directly at the probe output, together with measuring the voltage of the signal IR (w) at the output of the measuring device at the same frequency, makes it possible to determine from their ratio the total transmission coefficient of the probe-output device of the measuring device and thereby exclude the need to determine the absolute value of the intensity of the calibration field Hk (s) for all frequencies.

ON (L O Yu

GO

Measuring the voltage U c (o) o) directly at the output of the probe at any frequency () of the range allows us to determine the value of the constant of the probe, determined by its geometric dimensions and the number of turns.

The combination of these measurements in the calibration field allows, when the quasistationarity condition determining the electrically small probes is fulfilled:

2 l RCp "A, (1)

where Rep is the average radius of the coil of the probe;

A-wavelength,

to determine the calibration coefficient of the measuring probe using the Farade electromagnetic induction law.

The electromagnetic Farad's law, under the condition of quasi-stationarity (1), allows to determine the signal voltage at the output of the field intensity meter, which, taking into account the transmission coefficient of the probe-output system, the field intensity meter P / b is written as follows:

UK (w) P ((o) o) / h05MN, (w). (2)

Index k corresponds to the placement of the probe in the calibration field. The calibration factor according to (2) is determined by

as

K (s)

Hk (ft

one

(3)

w) P (uJ) ftJ / M0SN- Add to equation (2) equations describing additional measurements, separate the equation describing measuring the voltage of the signal directly at the output of the probe at the frequency Ho, at which the value of Hk (cr 0 of the calibration field is known:

and | to (a) w / o5MNA (su)

U K (ftfe) UJbjWoSNH, ()

(4) (5)

Equations (2), (4) and (5) form a system of equations, which, if solved, can determine the unknown value of the measuring probe. From equations (2) and (4), excluding the unknown value H | / y of the 1-gauge field at the frequency w of the required research range, we express P (w and, having substituted into equation (3), we get

K (ffl) f) (6)

Express the probe constant from equation (5) and, substituting in (6), we get

K (",) uU) (aJo). (7)

five

0

five

0

five

0

five

0

Using the proposed method allows to take into account not only the transmission coefficient of the probe-measuring device, but also take into account the effect of changes in the quality of the formed circuit (inductance of the probe is the input capacitance of the measuring device) when conducting research in a conductive environment, since the change in the quality of the output impedance depending on the frequency, they are automatically taken into account by conducting calibration measurements at the same frequencies of the research range with the same external conductivity redy.

The device works as follows.

The gauge magnetic field is excited by a current flowing in the Helmholz rings 1 whose planes are at a distance r equal to their radius. The rings are switched in phase with the output of the signal generator 2 via transformer 3. Probe 4, the output of which via key 5 is loaded on amplifier 6, is placed in the center of the Helmholtz rings 1 in the induction zone of the calibration field. Supply from the generator 2 signal to the Helmholtz 1 rings, measure the voltage of the signal 11k (w) at the output of the amplifier 6 with a microvoltmeter 7. In this case, the key 5 is in the on state, and the key 8 is in the off state. Changing the state of the keys 5 and 8 to the opposite, at the same frequency, the voltage of the signal and k (y) directly at the output of probe 4 is measured by a microvoltmeter 9 with a high-resistance stroke. Changing the frequency of the oscillator 2 signal is done similarly to measuring at all frequencies of the required calibration range.

The determination of the absolute value of the voltage of the calibration field is carried out on the basis of the value of the voltage drop across the resistor (soy), measured by the voltmeter 10 through the transformer 11 with the transformation ratio n 1, the primary winding of which is loaded on the resistor R, according to the expression

H, (ЈY) 01716 U14. (0625g, oa) 2.

(eight)

To determine the calibration coefficient КЈи), it is necessary to select the frequency of the calibration range, od, at which the dependence on the conductivity of the medium and in expression (8) can be neglected, and the transformation ratio n 1. At this frequency, the voltage drop of the signal UR at the resistor R is measured with a voltmeter

10 and calculate the absolute value of the intensity of the calibration field

Hk (GJb) 0.716 MЈJ

rR

The value of H selected in this way (fAe is used to calculate the calibration factor using formula (7).

The proposed method, in comparison with the known ones, provides a significant expansion of the calibration frequency range and the possibility of calibrating a meter in the range of 1–30 MHz in a conducting medium.

Claims (1)

Invention Formula A method for calibrating a magnetic field meter, including irradiating a probe with a calibrating magnetic field, measuring the voltage of a signal at the output of the meter, and calculating a calibration factor, characterized in that, in order to expand the frequency range of the calibration, the voltage of the signal directly at the output of the probe is also measured in the required frequency range uVa)), including at the OA frequency at which the magnitude of the voltage is known calibration magnetic field. and calculate the calibration coefficient of the magnetic field intensity meter using the formula kg)  (a) where UK is the signal voltage at the output of the meter at the frequency w.