RU2167436C1 - Vibration bed to examine and calibrate seismic prospecting equipment - Google Patents

Abstract

FIELD: calibration of seismic prospecting equipment. SUBSTANCE: vibration bed includes springy member in the form of bellows forming closed volume jointly with table and base that houses piezoelectric exciter of mechanical vibrations coupled to table and base, control acceleration transducer put on table and additional control acoustic transducer mounted on base. Hole communicating closed volume with atmosphere is made in table. Effective section of hole is chosen from specified condition. Location member made of elastic material and ensuring interaction with sensitive element of control acoustic transducer is positioned on outside of table, on hole. EFFECT: expanded application field, range of operational frequencies and diminished effect of external noises. 1 dwg

Description

 The invention relates to a research tool for inertial and acoustic sensors and can be used to calibrate seismic equipment.

 Known systems for the study of acoustic sensors (microphones and hydrophones) containing a sealed chamber in which the studied devices are placed, and where the changing pressure is created by a piston connected to an electrodynamic vibrator, for example, a microphone (1).

 The disadvantage of such a system is its limited capabilities, as it is not a means for studying inertial sensors, as well as for research in the frequency range below 40-60 Hz.

 A vibrostand is known for research and standardization of seismic equipment containing a base on which a piezoelectric exciter of mechanical vibrations assembled on a centering element is mounted, a table, a control sensor connected to the base, pistons connected to the centering element and forming a closed volume filled with its axial channel liquid (2).

 The disadvantage of this device is the inability to calibrate acoustic sensors.

 The closest set of common features to the proposed one is a vibration stand for research and calibration of geophones, containing a base on which a piezoelectric exciter of mechanical vibrations is mounted, a table and a control sensor mounted on the base, interconnected by a centering element (3).

 The disadvantage of the prototype is also the lack of calibration of acoustic sensors. In addition, this device has an uneven amplitude-frequency characteristic, which complicates the work with him when conducting research.

 An object of the invention is to expand the scope, range of operating frequencies and reduce the influence of external interference.

 The problem is solved as follows.

(1)
где S_эф - эффективная площадь стола;
L - длина отверстия в столе;
ν - кинематическая вязкость воздуха;
f_рез. - резонансная частота колебаний вибростенда;
A_рез. - амплитуда колебаний на резонансной частоте;
r - радиус стола;
Δ - высота столба воздуха от основания до стола;
а с внешней стороны стола, на отверстии, расположен установочный элемент, выполненный из эластичного материала.In the vibration stand for research and calibration of seismic equipment containing a piezoelectric exciter of mechanical vibrations connected with the table and base, a control sensor, an elastic element is introduced in the form of a bellows, forming a closed volume with a table and base, in which the exciter of mechanical vibrations, a control sensor, mounted on the table and, additional, a control acoustic sensor mounted on the base, while a hole is made in the table connecting the closed volume m with the atmosphere, the effective cross section of which is selected from the condition:

(1)
where S _eff is the effective area of the table;
L is the length of the hole in the table;
ν is the kinematic viscosity of air;
f _res. - resonant vibration frequency of the vibrating stand;
A _res. - the amplitude of the oscillations at the resonant frequency;
r is the radius of the table;
Δ is the height of the air column from the base to the table;
and on the outside of the table, at the hole, is a mounting element made of elastic material.

Distinctive features in the claimed device are:
- a closed volume formed by an elastic element-bellows with a table and a base, allows you to place in it a control sensor and a causative agent of mechanical vibrations, to shield them from the influence of external electromagnetic fields;
- the hole made in the table of the vibrating stand, connecting the closed volume with the atmosphere, expands the possibilities of using the device, namely for the study of acoustic sensors and provides pneumatic damping in the system;
- the effective cross section selected from the condition in accordance with expression (1) is such that it does not interfere with the flow of air through it, with vibrations of the vibrostand table in the frequency range from the lower cut-off frequency f _n to the upper cut-off frequency f _in and begins to prevent the flow of air with increasing it to a resonant frequency f _res. vibration stand, i.e. performs the function of a pneumatic damper, which reduces the "ejection" at the resonant frequency, which allows you to adjust the amplitude-frequency characteristic of the vibration bench, to expand the working frequency range;
- the installation element located on the outside of the table at the hole, for the formation of an air gap provides interaction with the sensitive element of the controlled acoustic sensor;
- an additional control acoustic sensor with predetermined output parameters, installed on the base, provides the study of controlled acoustic sensors.

 The sources of scientific and patent-technical information known to the authors do not describe a device with the listed set of features aimed at solving the technical problem posed, this made it possible to conclude that the claimed technical solution has the invention criterion of "inventive step".

 In practice, the choice of the effective cross section of the hole in the table of the vibrating stand is made from the following considerations.

The resistance force acting in the hole during vibrations of the table of the vibrating stand is such that it does not interfere with the flow of air in the operating frequency range (f _n - f _in ) and prevents at frequencies adjacent to the frequency of the first electromechanical resonance - f _res. , wherein
f _cut > f _in
F _c = H • X ' ₁ (2)
where H is the attenuation index;
X ' ₁ - air velocity in the hole.

(3)
где μ - динамическая вязкость воздуха;
L - длина отверстия в столе;
S_эф, S_эф.отв. - эффективные площади стола и отверстия.It is known that

(3)
where μ is the dynamic viscosity of air;
L is the length of the hole in the table;
S _eff. , S _eff. - effective area of the table and holes.

(4)
где X' - скорость воздуха в замкнутом объеме, равная
X′= 2•πfA (5)
где A - амплитудное значение колебания стола;
f - текущая частота.Wherein

(4)
where X 'is the air velocity in a closed volume equal to
X ′ = 2 • πfA (5)
where A is the amplitude value of the table;
f is the current frequency.

(6)
Сила давления, возникающая в замкнутом объеме при колебаниях стола вибростенда, заставляющая перетекать воздух из области избыточного давления в атмосферу и обратно в замкнутый объем:
F_y= ΔP•S_эф (7)
ΔP - избыточное давление в замкнутом объеме, равное

(8)
где λ - коэффициент сопротивления;
Δ - высота столба воздуха от основания до стола;
r - радиус стола;
ρ - плотность воздуха.Thus

(6)
The pressure force arising in a closed volume during vibrations of the table of the vibrating stand, forcing air to flow from the overpressure region to the atmosphere and back to the closed volume:
F _y = ΔP • S _eff (7)
ΔP - overpressure in a closed volume equal to

(8)
where λ is the resistance coefficient;
Δ is the height of the air column from the base to the table;
r is the radius of the table;
ρ is the density of air.

(9)
где R - Рейнольдсово число ≈2000 с учетом приведенного:

(10)
По условию необходимо выполнить неравенство:
F_c > F_q (11),
т.е.It is known that

(9)
where R is the Reynolds number ≈2000, taking into account the above:

(10)
By condition, it is necessary to fulfill the inequality:
F _c > F _q (11),
those.

(12)
где ν = μρ - кинематическая вязкость воздуха.

(12)
where ν = μρ is the kinematic viscosity of air.

(14)
На чертеже представлен общий вид предлагаемого устройства. Вибростенд содержит упругий элемент в виде сильфона 1, образующий со столом 2 и основанием 3 замкнутый объем, в котором расположены пьезоэлектрический возбудитель механических колебаний 4, связанный со столом 2 и основанием 3, контрольный датчик ускорения 5, установленный на столе и, дополнительный, контрольный акустический датчик 6, установленный на основании. В столе вибростенда выполнено отверстие 7, связывающее замкнутый объем с атмосферой, на котором с внешней стороны стола, расположен установочный элемент 8.Considering that the amplitude of the vibration of the table of the vibrostand at the resonant frequency should be approximately the same as on a flat section of the amplitude-frequency characteristic, i.e. 40 dB less (100 times) then
F _c = 100 F _g (13)
or

(14)
The drawing shows a General view of the proposed device. The vibrostand contains an elastic element in the form of a bellows 1, forming a closed volume with a table 2 and a base 3, in which a piezoelectric exciter of mechanical vibrations 4 is connected, connected with a table 2 and a base 3, a control acceleration sensor 5 mounted on the table and, additionally, an acoustic control sensor 6 mounted on the base. A hole 7 is made in the table of the vibrating stand, connecting the closed volume with the atmosphere, on which the mounting element 8 is located on the outside of the table.

 The device operates as follows.

 When an electric signal is supplied from the generator, the piezoelectric elements of the mechanical vibration exciter 4 are deformed, causing the bellows 1, table 2, the acceleration control sensor 5 and the test objects to move: the acoustic sensor 9 and the seismic sensor 10. The value of the closed volume changes, which leads to a change in the overpressure it and this pressure is fixed by the control acoustic pressure sensor 6. Air flowing through the hole 7 into the air gap formed by the installation element 8, made on an example, in the form of a rubber ring or sleeve, between the table 2 and the sensing element of the tested acoustic sensor 9, leads to the appearance, in this gap, of excessive pressure, which acts on the sensitive element of the transducer of the tested sensor 9. A proportional change in pressure in the closed volume and the air gap, acting on the sensitive elements of the control and test acoustic pressure sensors, leads to the appearance of electrical signals, comparing which, they judge the main characteristics line providers investigated acoustic sensors. Comparing the output electrical signals of the control acceleration sensor 5 and the test seismic sensor 10, determine the characteristics of the investigated object. The design of the vibrating stand provides protection against electromagnetic interference and interference, which significantly increases the accuracy of the study equipment especially in the low frequency region.

Literature
1. "Devices and systems for the study of vibration, noise and shock." Handbook, vol. 2, edited by V.V. Klyueva. Moscow, "Engineering", 1978, p. 235-236.

 2. "Vibration stand for research and standardization of seismic equipment." A.S. 1762285, publ. 09/15/92, BI N 34.

 3. "Vibration stand for the study and calibration of vertical geophones". A.S. N 700849, publ. 11/30/79, BI N 44 (prototype).

Claims (1)

Vibration stand for research and calibration of seismic equipment, containing a piezoelectric exciter of mechanical vibrations connected with the table and base, a control sensor, characterized in that an elastic element is introduced in the form of a bellows, forming a closed volume with the table and base, in which the exciter of mechanical oscillations, a control sensor mounted on the table, and an additional control acoustic sensor mounted on the base, while a hole is made in the table, with knitting closed volume with the atmosphere, the effective cross section of which is selected from the condition

where S _eff is the effective area of the table;
L is the length of the hole in the table;
ν is the kinematic viscosity of air;
f _res - the resonant frequency of vibration of the vibrating stand;
A _res - the amplitude of the oscillations at the resonant frequency;
r is the radius of the table;
Δ is the height of the air column from the base to the table,
and on the outside of the table on the hole is a mounting element, which is made of elastic material.