SU119600A1 - A method of measuring weak constant magnetic fields and indicating a magnetic field zero - Google Patents

Description

A known method of measuring weak constant magnetic fields and zero magnetic field indication using a system of two magnetically saturated probes, one of which is placed in the measured field, and the other is shielded from it.

A significant disadvantage of this method is the need to completely demagnetize the ferromagnetic core of the probe, since otherwise it is impossible to determine the zero field with an accuracy higher than the value of the coercive force of the core material used. This circumstance limits the accuracy of determining the zero field by values of ± 0.05 byst using high-quality permalloys.

In order to increase the sensitivity of the probes, it is suggested that their magnetic field should be excited by a variable magnetic field, which is much larger than the measured fields, and to determine the magnitude of the probes measured by the phase angle between the pulses induced in the secondary windings of both probes.

This phase shift can be measured by applying the compared pulses after amplifying them and forming them on a coincidence circuit or using a phase-pulse detector made up of three triggers to charge the storage capacitor to a voltage proportional to the length of time between the compared pulses.

FIG. 1 shows a block diagram of an apparatus for carrying out the proposed method using a coincidence circuit, where the letters / Mi and MZ denote magnetic probes whose primary windings feed on the same 50 Hz alternating current exciting an alternating field acting on the cores. Partial stabilization of this current in amplitude without affecting its shape can be accomplished with the help of thermistors.

No. 119600-2 -

The pulses coming from the secondary windings of the probes are amplified and formed in the amplifying-forming cascades of the Y and Ug-C cascades of the Y and Y2 pulses are fed to the coincidence circuit of the CC. Cases of coincidence of pulses in time are marked by a pointer device installed after recorder P.

In order to be able to determine the sign or direction of small constant fields, it is necessary to translate relative temporal shifts of one pulse relative to another into a change in voltage.

The impulse under study coming from the probe placed in the measured field may lag behind the reference impulse taken from the shielded probe or be ahead of it depending on the sign of the magnetic field. When the field passes through a zero value, a coincidence of the reference and studied pulses will be observed.

To determine the sign of the field, it is necessary that the lag and lead of the pulse under investigation relative to the reference pulse correspond to the voltage of one sign or another at the device output. The latter can be achieved by using a phase-pulse detector instead of a coincidence circuit (see Fig. 2).

On the block diagram (fig. 2) it is indicated: A sd B - the inputs of the reference and, accordingly, of the investigated pulses; TI is a trigger controlling the charger of the charger; T2 - trigger controlling the discharge device RU; Gz - trigger return; 3 - delay lines; C - capacitor capacitor.

In the event of an advance of the reference pulse, the trigger TI is triggered, controlling the charger of the charger, and the return trigger P. After that, the charging of the storage capacitor C begins, continuing until the moment of the pulse being investigated, which triggers the trigger of the RU. This triggers the Gz return trigger, which returns to its initial state and simultaneously returns to the initial state the remaining two triggers. Since in this case the trigger T2, acting on the discharge device RU, remains out of its original state for a very short time determined by the delay circuit 3, during this time the capacitor C ne has time to completely discharge and there remains some charge on it, proportional to largest pause between pulses, and the sign corresponding to the advance of the reference pulse.

 In the case of a delay of the reference pulse relative to the test circuit, the operation of the circuit occurs in a similar way with the only difference being that the discharge device acts first. In this case, the charge on the storage capacitor also turns out to be proportional in magnitude to the pause between pulses, and in sign, the opposite of the first case.

Thus, the voltage at the output of the phase-pulse detector will be proportional to the relative shift between pulses and will change its sign when the temporal relationship between them, the pulses is changed.

A method of measuring weak constant magnetic fields and indications, a magnetic field zero using a system of two magnetically saturated probes, one of which is placed in the measured field, and the other is shielded from it, in order to increase the sensitivity of the probes, the magnetic cores excite a variable magnetic field, much larger than the measured fields, and determine the magnitude of the latter by measuring the phase shift between the pulses induced in the secondary windings of both probes, for example, by comparing Mykh pulses after amplifying them and generating a coincidence circuit either pomopdyu phase pulse detector composed of three flip-flops, providing the charge storage capacitor to a voltage proportional to the magnitude of the time interval between the compared pulses.

No. 119600

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