SU750407A1 - Magnetometer - Google Patents

Description

(54) MAGNETOMETER

The invention relates to magnetic measurements and can be used in apparatus for measuring magnetic fields based on the nuclear magnetic resonance method.

A magnetometer is known for measuring the intensity of a magnetic field. The magnetometer contains a threshold generator, which is coupled to a nuclear magnetic resonance signal (NMR) sensor and a synchronous detector, which generates an error signal to control the frequency of the threshold generator in such a way that the resonance conditions 1 are maintained.

The disadvantage of this device is the relatively low accuracy of measurements of the intensity of the magnetic field, which is determined, besides its own width of the NMR line, also by the stability of the oscillation frequency of the threshold generator and the uniformity of the measured magnetic field. 25

Of the known devices for measuring the strength of the magnetic field, the closest to the technical essence, and the achieved result is a device that contains JQ

NMR sensor, high frequency generator, high frequency amplifier, detector, low frequency amplifier. A key, an automatic frequency control system that includes a low-frequency synchronous detector, a precise search generator and a selective amplifier 2.

The device works as follows.

In the absence of an NMR signal, an accurate search generator is turned on, the voltage from which is supplied to the reactive element of the high-frequency generator and changes the generator frequency until the NMR signal with a double modulation frequency appears, which will correspond to the fulfillment of exact resonance conditions. This signal is extracted by a selective amplifier, which, through the key, turns off the generator of the exact search and closes the tracking system. A constant voltage appears at the output of the synchronous detector, under the influence of which the frequency of the high frequency generator exactly adjusts to the resonance value. The disadvantage of the known device is the low resolution and accuracy of the magnetic field intensity measurements due to the low frequency stability of the high frequency generator. The aim of the invention is to improve the measurement accuracy and resolution. The goal is achieved by including a magnetometer containing a series-connected high-frequency threshold generator, a detector and a synchronous detector, a modulator, the output of which is connected to the second input of the synchronous detector, a magnetic nuclear resonance sensor and a recording device, a sensor displacement mechanism, kinematically connected with a high frequency threshold generator and said sensor, is introduced, and electrically with an input meters of the recording device, as well as serially connected integrator, mode switch, controlled frequency standard and high-frequency phase detector, the second input of which is connected to the second output of the threshold generator, and the output of the high-frequency phase detector is connected to the control input of which. The integrator input is connected to the EVE of the synchronous detector, and its output is connected with the second input of the recording device. Functional diagram of the device shown in the drawing. The device consists of an NMR sensor 1 placed in the measured magnetic system 2, a high-frequency threshold generator 3, a detector 4 of a low-frequency synchronous detector 5, a modulator b, a controlled frequency reference 7, a high-frequency phase detector 8, an integrator 9 of a switch 10 modes operation, the mechanism of movement 11 of the NMR sensor of the two-coordinate recorder 12, the modulation coils 13. The magnetic system 2 is placed yes. NMR 1 of the high-frequency threshold generator 3. The signal from generator 3 is fed to detector 4, the output of which is fed to one of the inputs i.h. synchronous detector I, to the second input of which the flow from the reference signal from modulator 6. In turn} the low-frequency synchronous detector signal is fed to the input of the integrator 9, whose output is connected through switch 10, in position A with a controlled input of the threshold generator 3, in position B - with the input of the controlled frequency standard 7, the output of which is fed to the input of the high-frequency phase detector 8, the second input of which receives the signal from the high-frequency output of the threshold generator 3, the output signal of the high-frequency phase detector 8 is fed to a controllable oscillator input threshold 3. The apparatus operates as follows. The magnetometer operates in tracking mode. The NMR signal of the threshold generator 3, detected by detector 4, is fed to a low-frequency synchronous detector 5, the voltage from which is fed to the input of integrator 9, the output voltage from which is fed to the input of a controlled frequency standard 7, adjusting its frequency to coincide with the frequency of the resonant NMR absorption fp. The high frequency voltage frequency fp from reference 7 is compared in h.ch. phase detector 8 with a high-frequency signal coming from the threshold generator 3 and an error signal with h.ch. the phase detector 8 controls the reactive element of the threshold generator 3, adjusting its frequency to match the frequency of the reference 7, which in turn adjusts to equal the frequency of the resonance NMR. fp. Measure the frequency of the threshold oscillator 3 and use the well-known equation f --S- U t R27G N where fp is the resonant absorption NMR frequency; y is the gyromagnetic ratio of the nucleus spin-containing substance of the NMR signal sensor; H is the intensity of the measured. The magnetic field is essentially measured by the magnitude of the magnetic field of the measured magnetic system. The introduction of an integrator into a phase locked loop (FLPC) system provides astatism of the PLL system, which allows improving the accuracy of the PLL system and, consequently, increasing the accuracy of measuring the magnetic field strength by reducing the static error in the PLL system. A magnetometer with a switch of 10 operation modes introduced into it works as follows; In position A of switch 10, the NMR signal of the threshold generator 3 is fed to detector 4, the output of which is fed to the input of a low-frequency synchronous detector 5, the output voltage of which through the integrator 9 and switch 10 controls the frequency of the threshold generator 3 so that its frequency field for equality (1). In the position B of the switch 10, the voltage of the low-frequency synchronous detector 5 through the integrator 9 and the switch 10 controls the frequency

Claims (1)

Claim A magnetometer comprising a threshold high-frequency oscillator connected in series, a detector and a synchronous detector, a modulator, the output of which is connected to the second input of the synchronous detector, a nuclear magnetic resonance sensor and a recording device, characterized in that, in order to increase the accuracy of measurements and resolution, it introduced a mechanism for moving the sensor, kinematically connected with a threshold high-frequency generator and the aforementioned sensor, and electrically - with the input of the recording device, as well as integrally connected integrator, an operating mode switch, a controlled frequency standard and a high-frequency phase detector, the second input of which is connected to the second output of the threshold generator, to the controlled input of which a high-frequency phase detector output is connected via the operating mode switch, the integrator input is connected to the output of a synchronous detector, and its output is with the second input of the recording device.