Magnetograph

magnetograph [mag′ned·ə‚graf]

(electromagnetism)

A set of three variometers attached to a suitable recording unit, which records the components of the magnetic field vector in each of three perpendicular directions.

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Magnetograph 

an instrument for continuous recording of variations of the geomagnetic field over time (magnetic variations). It consists of magnetic variometers and a recording system. The simplest magnetograph contains a photographic recorder, a light source, and three opticomechanical variometers in which the sensing elements are magnetic needles (with mirrors) suspended on elastic fibers. Such a magnetograph records on a chart (photographic film or paper) the variations of the three orthogonal elements of the earth’s magnetic field with periods of several seconds to several months and an accuracy of the order of 10^-5 oersted. The magnetogram thus produced carries information regarding the time, amplitude, and period of the magnetic variations. Magnetometers can be equipped with opticomechanical variometers and photoelectric converters of the angle of rotation of the magnetic needle or with fluxgate, induction, proton, quantum, and superconducting transducers whose electric output signal frequency or amplitude is proportional to the amplitude of the magnetic variation (see Table 1).

Table 1. Characteristics of various types of magnetographs
*1 oersted = 79.6 A/m
Type of variometer	Sensitivity (oersteds)*	Period of recorded variations (sec)
Opticomechanical	10-5	1-∞
Opticomechanical with photoelectric transducer	10-7	2 × 10-1-∞
Fluxgate	10-7	2 × 10-1-∞
Induction	10-7	3 × 10-1-∞
Proton	10-6	1-∞
Quantum	10-7	10-1-∞
Superconducting	10-8	10-1-∞

The recording devices for such magnetographs may be frequency meters, digital voltmeters with a digital printout device, electric pen recorders, tape recorders, or perforators. The readings of a magnetograph are encoded and processed on electronic computers. The sensitivity of magnetographs depends to a great extent on the technical potential of the variometers used.

REFERENCE

lanovskii, B. M. Zemnoi magnetizm [3rd ed.], vol. 1. Leningrad, 1964.

IU. A. BURTSEV