Fig. 4-5- 1 CZM-2 proton precession magnetometer
(1) principle
The CZM-2 proton precession magnetometer consists of three parts: the instrument body (Figure 4-5-2), the probe (Figure 4-5-3) and the power supply (Figure 4-5-4). The part that feels the external magnetic field is called the probe, which consists of a cylinder filled with hydrogen-containing solution (water, kerosene, alcohol, etc.). ) and a coil wound on the cylinder. The magnetic moment of hydrogen proton in hydrogen-containing solution is paramagnetic under the action of external magnetic field. When a strong artificial magnetic field (generated by 1 ~ 2A DC in the coil) is applied to the horizontal probe in the direction perpendicular to the geomagnetic field T, hydrogen protons will form a strong macroscopic magnetic moment in the direction perpendicular to T (this process is called polarization). When the current is suddenly cut off, due to the spin of hydrogen protons, the macroscopic magnetic moment does not immediately fall in the direction of geomagnetic field, but precesses (or precession) around the direction of geomagnetic field T. The precession angular frequency is proportional to the magnitude of geomagnetic field;
Figure 4-5-2 CZM-2 Proton precession magnetometer host panel
Practical guidance of applied geophysics teaching
Where: γp is the magnetic rotation ratio of protons and is a stable constant (0.2675 13Hz/nT).
It can also be written in frequency form, that is
Practical guidance of applied geophysics teaching
rule
Practical guidance of applied geophysics teaching
Because the macro magnetic moment precession cuts the coil in the probe, the induced voltage with the same precession frequency is generated in the coil. Obviously, the absolute value of the total intensity of geomagnetic field is determined by measuring the frequency of this induced voltage signal.
Figure 4-5-3 czm-2 proton precession magnetometer probe
Figure 4-5-4 CZM-2 Proton Spinning into the Magnetometer Battery Box
(II) Operation method of CZM-2 proton precession magnetometer
CZM-2 proton precession magnetometer consists of three parts: instrument host, probe and battery box. The host panel is shown in Figure 4-5-2, and the magnetometer probe is shown in Figure 4-5-3.
(1) After connecting the wiring of the battery box (Figure 4-5-4) with the power socket of the host, turn on the power switch.
(2) After connecting the power supply (don't connect the probe wire first), conduct self-calibration inspection. The method is to turn the switch to the "self-calibration" position, and then press the polarization switch (microswitch). After about 4s, the display screen shows the number 49 152 1 (that is, the self-calibration is normal), indicating the frequency multiplier and the counting display system.
(3) After self-calibration, connect the probe wire to the probe socket of the host computer and place the probe shaft in the east-west direction. Refer to the distance distribution table (Table 4-5- 1) to select the normal harmonic gear in the measurement area, and press the polarization switch. After about 4s, the absolute value of the total intensity of geomagnetic field will be displayed on the display screen, and the polarization switch will be pressed several times continuously. If the displayed numbers are repeated, magnetic measurement can be started. If the repeatability is poor, magnetic measurement should be started.
Table 4-5- 1 Range Distribution Table
sequential
(4) Each observation point shall be continuously read for 2 ~ 3 times. If you repeat it twice, there is no need to read it a third time. Calculate the average of the two readings, that is, the absolute value of the total geomagnetic field intensity at this point.
(5) Field work requires two people, one holding the probe and the other operating and recording. The probe frame should be free of all magnetic objects on the body, and the distance from the operator should be more than 4 meters, and the probe axis should be in the east-west direction.
(6) During the field observation, some measuring points may be in abnormal areas, and their magnetic fields may be quite different from the normal magnetic fields at the base points. At this time, the position of the harmonic switch should change according to the changing law of the magnetic field. At a certain measuring point, in general, the readings of three adjacent gears may be correct, but there must be a gear with better repeatability, and this gear should be selected. It should be noted that the repeatability of readings should not be excessively required at points with large abnormal gradients. If the gradient is too large, the repeatability of the reading will become worse, and even the correct reading cannot be obtained.
(7) Unplug the power plug (cut off the power supply) immediately after a day's work.
Note: the probe distance of demagnetizer is 5 ~ 10m, the probe direction is east-west, and the repeated reading is 1nT.
(3) Instrument performance, advantages and disadvantages
The repeated measurement error is 2.0nT, the mean square error is 1.5nT, and the measurement range is 3.2× 104 ~ 7× 104 nt.
The instrument is easy to operate and can directly read nt.
The measured slope shall not be greater than150nt/m/m.