RU2098844C1 - Acceleration seismic receiver - Google Patents

Abstract

FIELD: geophysical investigations, vibration instruments. SUBSTANCE: device has magnetic system which has permanent magnet which diameter is D, length l, magnetic intensity H, magnetic inductance B in point corresponding to maximal magnetic power of specific magnetic flux which is output by permanent magnet into air spaces. In addition device has two pole pieces which are mounted on permanent magnet, magnetic circuit, two coaxial pole pieces which are located in magnetic circuit and have equal length with pole pieces which are mounted on permanent magnet. Said pole pieces provide two ring air spaces. In addition device has mechanical oscillating member which has two coils with windings which are located on conducting rings. Characteristics of members of device conform to condition

, where μ_o = 1,256•10^-6 H/m is magnetic permeability of air, t is thickness of pole piece wall, C is thickness of conducting ring of coil, Δ is ring air space, σ is factor for averaging magnetic inductance which is distributed in air space along length of coil winding, f_o is characteristic frequency of mechanic oscillating member, δ is coil density which is calculated as ratio of coil weight by volume which is occupied by coil in air space along length of windings, F is ratio of square of upper frequency of bandwidth by square of f_o, a = (a₁+a₂)/2, where a₁ is space between inner cylindrical surface of coil and cylindrical surface of pole pieces of magnetic circuit, a₂ is space between external cylindrical surface of coil and cylindrical surface of pole pieces of magnetic circuit, α is factor which takes into account linear dissipation of magnetic flux in air space; ε is factor which takes into account non-linear dissipation of magnetic flux. EFFECT: increased functional capabilities. 2 dwg

Description

 The invention relates to geophysical instrumentation, and can also be used in vibroengineering.

 Known geophone / 1 / with an output signal proportional to the acceleration of the movements of its body. The inertial element of the geophone is a conductive ring located in two air gaps of the differential magnetic system. Eddy currents arising in the conductive ring during the relative movement of the magnetic system and the conductive ring induce in the windings of the EMF, proportional to the acceleration of the relative displacement. The disadvantage of the geophone is that the signal at its output is proportional to the acceleration of movement, starting from the natural frequency of the geophone and to the natural frequency, the output signal is proportional to the fourth degree of relative movement. In addition, the conversion rate of a geophone is an order of magnitude smaller than the conversion rates of known geophone.

 Known low-frequency seismometer / 2 / with an output signal proportional to the acceleration of the movement of its body. A seismometer contains a magnetic system, an inertial element made in the form of a coil with a conductive ring and a winding, and two springs connecting the coil to the magnetic system. An annular air gap of the magnetic system is located between the pole piece mounted on the permanent magnet and the pole piece installed in the magnetic circuit. The coil is located in the annular air gap symmetrically with respect to the length of the pole pieces.

 The disadvantage of the seismometer is that it is not protected from external electromagnetic fields and, in addition, its mass is more than an order of magnitude greater than the mass of geophones used in seismic surveys.

 The closest in technical solution is the electrodynamic transducer block of the acceleration seismic receiver / 3 /, containing a magnetic system consisting of a permanent magnet with a selected diameter and length, as well as intensity and magnetic induction at a point corresponding to the maximum specific magnetic energy on the curve of the specific magnetic flux given a permanent magnet into the air gaps, from two pole pieces mounted on a permanent magnet, from a magnetic circuit with two pole pieces, made in it concentrically and coinciding in length with pole pieces mounted on a permanent magnet, and forming two ring air gaps with them, a mechanical oscillating link consisting of a coil with a winding located in one ring air gap and occupying its entire used volume, and with a conductive ring located in the other annular and air gap symmetrically on both sides of the length of the pole pieces and occupying its entire used volume, of two springs connecting the coil to magnetic system.

 The disadvantage of / 3 / is that its conversion coefficient at medium frequencies is less than the conversion coefficient of known electrodynamic velocity geophones and, moreover, it is not protected from the influence of external electromagnetic fields.

 The purpose of the invention is to increase the conversion coefficient of the acceleration seismic receiver at medium frequencies, expand the frequency range towards low frequencies and protect it from the influence of external electromagnetic fields.

где Δ длина кольцевого воздушного зазора;
m_o 1,256•10^-6 Гнм^-1 магнитная проницаемость воздуха;
t толщина стенки полюсного наконечника, установленного на постоянном магните;
c толщина проводящего кольца катушки;
σ коэффициент усреднения магнитной индукции, распределенной в воздушном зазоре по длине обмотки катушки;
f₀ собственная частота механического колебательного звена;
d плотность катушки, определяемая отношением массы катушки к объему, занимаемому катушкой в воздушных зазорах на длине обмоток;
F отношение квадрата верхней частоты частотного диапазона к квадрату f₀;
a (а₁+ а₂)/2, где a₁ зазор между внутренней цилиндрической поверхностью катушки и цилиндрической поверхностью полюсных наконечников магнитопровода, a₂ зазор между наружней цилиндрической поверхностью катушки и цилиндрической поверхностью полюсных наконечников магнитопровода;
a коэффициент, учитывающий линейное рассеивание магнитного потока в воздушном зазоре;
e коэффициент, учитывающий нелинейное рассеяние магнитного поля.The goals are achieved by the fact that in an acceleration seismic receiver containing a magnetic system consisting of a permanent magnet with a selected diameter D, length l, strength H and magnetic induction B at a point corresponding to the maximum specific magnetic energy on the curve of the specific magnetic flux given off by a constant magnet in air gaps, from two pole pieces mounted on a permanent magnet, from a magnetic circuit, from two pole pieces made in a magnetic circuit concentrically and coinciding in length not with pole pieces mounted on a permanent magnet, and forming two ring air gaps with it, a mechanical oscillating link consisting of a coil with a winding and a conductive ring installed in ring air gaps, of two springs connecting the coil with a magnetic system, characterized in that the second winding and the second conductive ring are introduced into it, and the windings are located on the conductive rings and are installed in each annular air gap, while the design parameters of the geophone accelerations are related by the ratio:

where Δ is the length of the annular air gap;
m _o 1,256 • 10 ^-6 GNM ^-1 magnetic permeability of air;
t wall thickness of the pole piece mounted on a permanent magnet;
c is the thickness of the conductive ring of the coil;
σ is the averaging coefficient of magnetic induction distributed in the air gap along the length of the coil winding;
f _{0 is the} natural frequency of the mechanical vibrational link;
d the density of the coil, determined by the ratio of the mass of the coil to the volume occupied by the coil in the air gaps along the length of the windings;
F is the ratio of the square of the upper frequency of the frequency range to the square f ₀ ;
a (a ₁ + a ₂ ) / 2, where a _{1 the} gap between the inner cylindrical surface of the coil and the cylindrical surface of the pole pieces of the magnetic circuit, a _{2 the} gap between the outer cylindrical surface of the coil and the cylindrical surface of the pole pieces of the magnetic circuit;
a coefficient taking into account the linear dispersion of the magnetic flux in the air gap;
e coefficient taking into account nonlinear scattering of the magnetic field.

 In FIG. 1 shows an acceleration seismic receiver and a graph of the distribution of magnetic induction in an annular air gap; in FIG. 2 amplitude frequency characteristics (AFC) of geophones.

 The magnetic system of the acceleration seismic receiver (see Fig. 1) consists of a permanent magnet 1, two pole tips 2, a magnetic circuit 3 with two pole tips 4. The flange 5 is connected by pole tips 2 to the magnetic circuit 3. The mechanical vibrational link of the acceleration geophysic receiver consists of an inertial element of the coil 6, two springs 7, connecting the coil with the magnetic system, and electromagnetic damping-conducting rings 8 of the coil, located in the annular air gaps of the magnetic system. The coil windings 9 located in the annular air gaps of the magnetic system are an electrodynamic transducer. The distribution of magnetic induction in the annular air gap is shown in graph 10.

The design parameters of the acceleration seismic receiver are designated as follows: D and l are the diameter and length of the permanent magnet; D is the length of the annular air gap; b pole length; l _k is the length of the coil of the coil; t wall thickness of the pole piece; a ₁ and a ₂ gaps between the pole pieces and the coil.

The maximum value of magnetic induction in the annular air gap is indicated by B _m . Ha FIG. Figure 2 shows the frequency response of the GS-20DX velocity electrodynamic receiver (with a natural frequency of 10 Hz), graph II, the frequency response of the acceleration electrodynamic converter unit of acceleration graph 12 and the frequency response of the acceleration seismic receiver 13.

 The acceleration seismic receiver operates as follows.

 A mechanical vibrational link converts the vibrational displacements of the magnetic system connected through the body of the seismic receiver to the object under study into the oscillatory displacements of the magnetic system relative to the inertial element of the coil. The electrodynamic transducer of the coil winding, located in the annular air gaps of the magnetic system, converts the relative oscillatory movements of the magnetic system and the coil into voltage.

где K_п коэффициент преобразования сейсмоприемника ускорений по скорости перемещения;
m масса катушки;
ω_o собственная круговая частота механического колебательного звена, равная 2πf_o
β степень затухания;
L индуктивность катушки.The source / 3 / shows that the inductive coupling existing between the conductive ring and the winding wound on it reduces the frequency range of the acceleration seismic receiver from above to the frequency w by the expressed formula

where K _{p the} coefficient of conversion of the geophones accelerations in speed;
m is the mass of the coil;
ω _o natural circular frequency of the mechanical vibrational link, equal to 2πf _o
β degree of attenuation;
L inductance coils.

Подставив эти выражения в формулу, после преобразования получим

Выразим K_п, m и L через заданные и конструктивные параметры сейсмоприемника ускорений.Large values of w _o and β can reduce the frequency ω to values lower than the upper frequency of the desired frequency range of the geophone. We assume that the frequency w must not be less than the frequency equal to 2ω _in where ω _{is the} upper frequency of the frequency range of the acceleration geosensor. From the source / 3 / it is known that

Substituting these expressions in the formula, after the conversion, we obtain

We express K _p , m and L in terms of the given and design parameters of the acceleration geophone.

In a seismic receiver with a differential magnetic system and two windings
K _n 2K _{n 1} 2B _cf l ₀ W ₁ ,
Where
B _cf - the average value of the magnetic induction in the annular air gap;
l _{0 the} average length of one coil of the winding;
W _{1 the} number of turns of the winding in one annular air gap.

B _cf we find from the expression
B _cp = B _m • σ,
Where
σ is the averaging coefficient of magnetic induction.

Для рассматриваемого сейсмоприемника ускорений 0,91 < σ < 0,95.The averaging coefficient is determined from FIG. one

For the acceleration seismic receiver under consideration, 0.91 <σ <0.95.

Средняя длина одного витка обмотки равна

Подставив найденные выражения для B_ср и l₀ в формуле для определения K_п, получим

Массу катушки найдем из выражения

Индуктивность катушки будет складываться из индуктивности двух обмоток
L = 2L₁= 2gW $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$
где
g проводимость кольцевого воздушного зазора, в направлении, перпендикулярному потоку.From the source / 3 / it is known that

The average length of one winding is equal to

Substituting the found expressions for B _cf and l ₀ in the formula for determining K _p , we obtain

We find the mass of the coil from the expression

The inductance of the coil will be the sum of the inductance of the two windings
L = 2L ₁ = 2gW $\genfrac{}{}{0ex}{}{\text{2}}{\text{one}}$
Where
g conductivity of the annular air gap in a direction perpendicular to the flow.

Тогда

Найденные выражения для K_п, m и L подставим в формулу для определения f₀ и после преобразования получим

Из источника /3/ известно то, что

Подставив выражение l_k в предыдущее уравнение и, решив его относительно Δ получим

Значение Δ по этой формуле просто получить способом последовательного приближения. Задавшись начальным значением D равным, например, 2 мм, и подставив это значение D в правую часть формулы, вычислим D Вычисленное значение D вновь подставим в правую часть формулы и вычислим новое значение D Такой способ решения быстро, через два-три шага, приводим к точному значению D Этот способ решения проще прямого способа, заключающегося в том, что правую и левую часть формулы возводят в четвертую степень, и получив уравнение четвертой степени, находят его корни.This conductivity is equal to half the conductivity of the annular air gap along the magnetic flux.

Then

The found expressions for K _p , m and L substitute in the formula for determining f ₀ and after the conversion we get

From the source / 3 / it is known that

Substituting the expression l _k in the previous equation and solving it with respect to Δ we obtain

The value of Δ by this formula is simply obtained by the successive approximation method. Given the initial value of D equal to, for example, 2 mm, and substituting this value of D in the right side of the formula, we calculate D The calculated value of D is again substituted in the right side of the formula and we will calculate the new value of D This solution method quickly, in two or three steps, leads to the exact value of D This solution method is simpler than the direct method, namely, that the right and left sides of the formula are raised to the fourth power, and having received the fourth-degree equation, find its roots.

 After calculating the size of the annular air gap, then, according to the formulas given in the source / 3 /, the remaining design parameters of the acceleration geophone are determined.

 The proposed technical solution will allow you to create an acceleration seismic receiver, protected from external electromagnetic interference with increased compared to the prototype conversion coefficient and with a reduced coefficient of non-linear distortion. The acceleration seismic receiver will find application in seismic surveys using the high-resolution seismic survey method and can be used as a control device in vibroseismic sources of oscillations.

Claims (1)

An acceleration seismic receiver containing a magnetic system consisting of a permanent magnet with a selected diameter D, length L, intensity H and magnetic induction B at a point corresponding to the maximum specific magnetic energy on the specific magnetic flux curve given by a permanent magnet to the air gaps, two pole pieces, mounted on a permanent magnet, magnetic circuit, two pole pieces made concentrically in the magnetic circuit and coinciding in length with pole pieces mounted on stationary magnet, and two ring air gaps forming with them, a mechanical oscillating link consisting of a coil with a winding and a conductive ring installed in the ring air gaps, and two springs connecting the coil to the magnetic system, characterized in that a second winding is inserted into it and a second conductive ring, the windings being located on the rings and installed in each annular air gap, while the design parameters of the acceleration seismic receiver are related by the relation

where Δ is the length of the annular air gap;
μ _o - 1,256 • 10 ^{- 6} GNM ^{- 1} magnetic permeability of air;
t wall thickness of the pole piece mounted on a permanent magnet;
c is the thickness of the conductive ring of the coil;
σ is the averaging coefficient of magnetic induction distributed in the air gap along the length of the coil winding;
f _{0 is the} natural frequency of the mechanical vibrational link;
δ is the density of the coil, determined by the ratio of the mass of the coil to the volume occupied by the coil in the air gaps along the length of the windings;
F is the ratio of the square of the upper frequency of the frequency range to the square f ₀ ;
a (a ₁ + a ₂ ) / 2, where a _{1 is the} gap between the inner cylindrical surface of the coil and the cylindrical surface of the pole pieces of the magnetic circuit, and _{2 is the} gap between the outer cylindrical surface of the coil and the cylindrical surface of the pole pieces of the magnetic circuit;
α - coefficient taking into account the linear dispersion of the magnetic flux in the air gap;
ε is the coefficient taking into account the nonlinear scattering of the magnetic field.

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