CN103728657B - Method for the detection of geophone alias - Google Patents

Abstract

The method for false frequency detection of geophones includes: fixing the standard acceleration sensor and the geophone under test on the vibration table at the same time, and making the axes of the two sensors perpendicular to the main vibration direction of the vibration table; The output voltage waveform of the geophone under test, and calculate the output voltage waveform of the geophone caused by the lateral vibration of the shaking table; subtract the output voltage waveform caused by the lateral vibration of the shaking table from the actual output voltage waveform of the geophone under test, After calculating its amplitude, divide it by the velocity amplitude in the main vibration direction of the shaking table at the current moment, and the obtained quotient is the lateral sensitivity of the measured geophone; excite the geophone point by point from low frequency to high frequency, and obtain the lateral amplitude frequency The characteristic curve, the frequency point corresponding to the peak value of the curve is the alias frequency of the geophone under test. The invention has the advantage that the alias frequency of the geophone can be accurately measured by using a common vibrating table.

Description

Method for false frequency detection of geophones

technical field

The invention relates to a method for detecting aliasing of a geophone.

technical background

The geophone is a vibration sensor widely used in seismic exploration, among which the moving coil induction velocity sensor is the most widely used, and its function is to convert the ground vibration caused by the earthquake into an electrical analog quantity. With the development of digital signal processing methods and seismic exploration technology, the quality requirements for the output signal of the geophone are getting higher and higher. For the moving coil inductive speed sensor, it is assumed that the normal movement direction of the internal coil-spring leaf system is the axial direction, and the direction perpendicular to this direction is the transverse direction. Since there is a transverse resonance in the coil-spring system, which is coupled to the axial vibration of the coil and superimposed on the output of the geophone, the transverse resonance will affect the output accuracy of the geophone. We call this transverse resonance frequency false frequency. In order for the geophone to work normally, there must be no aliasing in its application frequency range. The aliasing has been used as an important technical index to measure the quality of the geophone, so it is very important to detect the aliasing of the geophone.

Chongqing University’s method for false frequency detection of geophones is: install the geophone to be tested on the vibration table perpendicular to the main vibration direction of the vibration table, and the vibration table excites the geophone laterally, measures its output, and obtains the transverse amplitude of the geophone Frequency characteristic curve, the frequency corresponding to its peak value is the alias frequency of the detector. Since the lateral sensitivity of the geophone is much smaller than the axial sensitivity, when the geophone is laterally excited, the axial vibration amplitude is required to be less than 1% of the lateral vibration amplitude. However, ordinary vibrating tables often have a lateral vibration ratio greater than 1% at high frequencies. At this time, the lateral vibration of the vibrating table will excite the geophone to generate axial output, which is superimposed on the output signal of the geophone’s transverse excitation, especially At the transverse resonance point of the vibrating table, it will cause a large output value of the geophone, thereby covering or confusing the aliasing frequency point of the geophone, making it impossible to accurately measure the aliasing frequency of the geophone with an ordinary vibrating table.

Contents of the invention

In order to overcome the disadvantage that the conventional vibration table cannot accurately detect the false frequency of the geophone, the present invention proposes a compensation method, which can accurately detect the false frequency of the geophone by using the common vibration table.

The method for false frequency detection of a geophone mainly includes the following steps:

1) Select a standard acceleration sensor with high natural frequency and low lateral sensitivity, fix it and the geophone under test on the vibration table at the same time, and make the axial direction of the two sensors perpendicular to the main vibration direction of the vibration table, vibrate When the table is in steady sinusoidal vibration, the two sensors are laterally excited;

2) Collect the output waveforms of the standard acceleration sensor and the geophone under test. Considering that the amplitude-frequency characteristic of the standard acceleration sensor is constant within the operating frequency range and the phase-frequency characteristic is approximately 0°, the lateral vibration of the shaking table can be calculated. Acceleration waveform, the velocity waveform is obtained after integration, combined with the known axial amplitude-frequency and phase-frequency characteristics of the geophone under test, the output voltage of the geophone under test due to the lateral vibration of the vibration table is obtained by calculating the velocity waveform of the lateral vibration of the vibration table waveform;

3) Subtract the output voltage waveform calculated in step 2) from the actual output voltage waveform of the geophone under test. The result is the output voltage waveform completely generated by the transverse excitation of the geophone. After calculating its amplitude, then Divided by the velocity amplitude in the main vibration direction of the shaking table at the current moment, the obtained quotient is the lateral sensitivity of the geophone under test;

4) According to steps 2) and 3), excite the geophone point by point from low frequency to high frequency to obtain the transverse amplitude-frequency characteristic curve, and the frequency point corresponding to the peak value of the curve is the alias frequency of the geophone under test.

The invention has the advantage that the alias frequency of the geophone can be accurately measured by using a common vibrating table.

Description of drawings

Fig. 1 is a flowchart of the present invention.

Figure 2 is a schematic diagram of the installation of vertical geophones and standard acceleration sensors.

Figure 3 is a structural diagram of the vertical geophone.

Fig. 4 is a model of a horizontal seismic table excited vertically to the geophone.

Figure 5 is the coil motion state at non-aliasing frequency.

Figure 6 is the mechanical equivalent model of the non-horizontal state of the spring leaf.

Figure 7 shows the coil motion state at the false frequency point.

detailed description

Fig. 1 is a flowchart of a false frequency detection method for a geophone, and the geophone can be divided into two types: vertical and horizontal. Taking the vertical detector as an example, the detection method of the present invention includes the following steps:

1) As shown in Figure 2, select a standard acceleration sensor 3 with high natural frequency and low lateral sensitivity, and fix it and the vertical geophone 2 to be tested on the horizontal vibration table 1 at the same time, and make the two sensors The axial direction is perpendicular to the main vibration direction of the horizontal vibrating table 1, and when the horizontal vibrating table 1 is vibrating in a steady state sinusoidally, the two sensors are laterally excited;

2) Collect the output waveforms of the standard acceleration sensor 3 and the measured vertical geophone 2. Considering that the amplitude-frequency characteristic of the standard acceleration sensor 3 within the operating frequency range is constant and the phase-frequency characteristic is approximately 0°, it can be calculated as The acceleration waveform of the lateral vibration of the horizontal vibrating table 1 is integrated to obtain the velocity waveform, combined with the known axial amplitude-frequency and phase-frequency characteristics of the measured detector 2, the measured detection wave is obtained by calculating the velocity waveform of the lateral vibration of the horizontal vibrating table 1 The output voltage waveform of the device 2 due to the lateral vibration of the horizontal vibrating table 1;

3) Subtract the output voltage waveform calculated in step 2 from the actual output voltage waveform of the measured vertical geophone 2, and the result obtained is completely the output voltage waveform generated by the transverse excitation of the geophone, after calculating its amplitude , and then divided by the velocity amplitude in the main vibration direction of the horizontal shaking table 1 at the current moment, the obtained quotient is the lateral sensitivity of the measured vertical geophone 2;

4) Follow steps 2) and 3) to excite the vertical geophone 2 point by point from low frequency to high frequency to obtain the transverse amplitude-frequency characteristic curve, and the frequency point corresponding to the peak value of the curve is the measured vertical geophone 2 aliasing.

In order to illustrate the feasibility of the method described in the above steps, the concrete principle of the present invention is set forth as follows:

The structure of the vertical geophone 2 is shown in FIG. 3 , which mainly consists of an upper cover 4 , a spring piece 5 , a yoke 6 , a coil 7 , a magnetic steel 8 , a coil frame 9 , a casing 10 and a lower cover 11 . The upper cover 4 and the lower cover 11 are connected with the shell 10 , the coil 7 is wound on the bobbin 9 , the spring leaf 5 is between the upper and lower end covers and the yoke 6 , and the yoke 6 is used for positioning the magnetic steel 8 . The coil 7 and the coil frame 9 are supported in the magnetic circuit gap of the magnet steel 8 by a spring system to form a vibrating system.

FIG. 4 is a model of the horizontal vibration table 1 laterally exciting the vertical geophone 2 , and 7 is the coil of the vertical geophone 2 . The axial movement of the coil 7 cuts the lines of magnetic force and generates the output signal of the detector. When the vibrating table 1 laterally excites the geophone 2 at different frequencies, considering that the spring plate 5 cannot be completely horizontal when installed, the coil 7 produces an axial displacement at the same time , lateral displacement and swing , especially at the alias frequency point, the coil 7 will produce a relatively severe axial displacement under the condition of transverse excitation, that is, transverse resonance occurs, which will cause a larger sensor output at this time. In addition, since the lateral vibration ratio of the vibrating table 1 cannot be zero, the coil 7 is not only subjected to the lateral ( In addition to the excitation, it is also subject to the axial ( To) incentives. The following analysis will focus on the two motion situations of the coil 7 at the non-alias frequency point and the alias frequency point.

1. At non-false frequency points

At frequencies other than aliasing, since the lateral stiffness of the spring sheet 5 is much larger than the axial stiffness, as long as the excitation is within the allowable range, the coil 7 moves smoothly and the swing is negligible. The motion state of the coil 7 is shown in FIG. 5 . The axial movement of the coil 7, that is, the output of the geophone, is mainly caused by the fact that the spring sheet 5 is not in a horizontal state during installation and the lateral vibration of the vibrating table.

(1) Spring leaf 5 is not in a horizontal state. FIG. 6 is a mechanical equivalent model when the leaf spring 5 is not in a horizontal state. Let the angle between the spring leaf 5 and the horizontal direction be , Indicates the displacement excitation of the main vibration of the vibration table to the geophone, which can be decomposed into and , The direction is perpendicular to the axial direction of the geophone, and will not excite the geophone to produce an axial output. The direction is the same as the axis of the geophone

, (Equation 1.1)

The differential equation of motion can be obtained as

, (Equation 1.2)

In the formula, Indicates the mass of the coil 7, Indicates the axial displacement of the coil 7 relative to the detector housing caused by the spring leaf 5 not being in a horizontal state, Indicates the axial stiffness of the spring sheet 5, and it can be solved that the axial velocity of the coil 7 relative to the detector shell at this time is

, (Equation 1.3)

in, is the excitation frequency output by the vibrating table, Indicates the velocity excitation of the main vibration of the vibrating table to the geophone.

(2) The vibration table vibrates laterally. suppose Indicates the displacement excitation of the geophone by the lateral vibration of the shaking table, for Component on the geophone axis. As mentioned in (1), it can be solved that the axial velocity of the coil 7 relative to the detector shell at this time is

, (Equation 1.4)

in, Indicates the velocity excitation of the geophone by the lateral vibration of the shaking table.

Considering that the geophone is a speed sensor, the output voltage of the geophone is proportional to the speed of the coil 7 axially relative to the geophone shell, assuming that the proportional coefficient is a constant value , so the detector output voltage can be expressed as

. (Equation 1.5)

The output voltage of the detector caused by the lateral vibration of the shaking table measured by the acceleration sensor can be expressed as

, (Equation 1.6)

in, is the frequency response function of the axial velocity of the geophone. The transverse vibration of the shaking table excites the geophone to generate axial output. According to the derivation method above (Equation 1.4), it can be obtained .

Subtract the output voltage of the geophone from the measured output voltage of the geophone caused by the lateral vibration of the shaking table to get

, (Equation 1.7)

considering value is small, so , can be solved

, (Equation 1.8)

The obtained output voltage of the geophone only includes the part generated due to the incomplete installation of the spring plate 5, which realizes the purpose of eliminating the output of the geophone caused by the lateral vibration of the vibrating table from the output signal of the geophone.

2. At the false frequency point

When the output signal frequency of the vibrating table is the alias frequency of the detector, the motion state of the coil 7 is shown in FIG. 7 . The main vibration of the vibrating table causes the detector coil-spring system to resonate transversely, causing the spring to lose stability, twist and deform, and generate a strong axial displacement, resulting in a large voltage output. Therefore, the spring is negligible here. 5Geophone output produced by not being completely level. Considering that the output of the geophone is still caused by the lateral resonance of the geophone and the lateral vibration of the shaking table, the following two cases are discussed:

(1) Transverse resonance of the geophone. suppose is the displacement excitation of the main vibration of the vibration table to the geophone. When the spring leaf 5 loses stability, according to the dynamic stability theory of the elastic system, the system is simplified to a rigid frame model for analysis, and it can be obtained

, (Equation 1.9)

in, Indicates the speed excitation of the main vibration of the shaking table to the geophone; Indicates the velocity of the coil 7 axially relative to the housing of the geophone when the main vibration of the vibration table excites the geophone to generate transverse resonance; is the correction factor; is the lateral stiffness of spring leaf 5.

(2) The vibration table vibrates laterally. suppose Indicates that the lateral vibration of the vibrating table excites the displacement of the geophone, which is the same as that described for the non-alias frequency point, and the velocity of the coil 7 axially relative to the geophone shell caused by the lateral vibration of the vibrating table can be obtained as

, (Equation 1.10)

in, Indicates the velocity excitation of the geophone by the lateral vibration of the shaking table.

The detector output voltage can be expressed as

.(Formula 1.11)

The output voltage of the detector caused by the lateral vibration of the shaking table measured by the acceleration sensor can be expressed as

, (Equation 1.12)

in, .

Subtract the output voltage of the geophone from the measured output voltage of the geophone caused by the lateral vibration of the shaking table to get

. (Equation 1.13)

As described for the non-aliased frequency point, it can be solved

, (Equation 1.14)

The obtained output voltage of the geophone only includes the part generated by the transverse resonance, and the purpose of eliminating the output of the geophone caused by the lateral vibration of the vibrating table from the output signal of the geophone is realized.

Based on the above analysis, the amplitude-frequency characteristic curve of the geophone compensated according to the method of the present invention is obtained, and the frequency point corresponding to the peak value is the alias frequency of the vertical geophone under test.

The method proposed by the invention can accurately test the alias frequency of the vertical geophone by using the horizontal vibrating table. In the same way, this method is also suitable for accurately testing the aliasing frequency of the horizontal geophone by using the vertical shaking table.

The content described in the embodiments of this specification is only an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms stated in the embodiments. Equivalent technical means that a person can think of based on the concept of the present invention.

Claims (1)

1. The method for false frequency detection of geophone mainly comprises the following steps: 1) Select a standard acceleration sensor with high natural frequency and low lateral sensitivity, fix it and the geophone under test on the vibration table at the same time, and make the axial direction of the two sensors perpendicular to the main vibration direction of the vibration table, vibrate When the table is in steady sinusoidal vibration, the two sensors are laterally excited; 2) Collect the output waveforms of the standard acceleration sensor and the geophone under test, calculate the acceleration waveform of the lateral vibration of the shaking table, and obtain the velocity waveform after integration; calculate the vibration of the geophone under test through the calculation of the velocity waveform of the lateral vibration of the shaking table The output voltage waveform caused by the lateral vibration of the table: at the non-alias frequency point, the output voltage waveform of the tested detector due to the lateral vibration of the vibration table The relationship with the acceleration waveform of the lateral vibration of the shaking table is: ,in: is the axial velocity frequency response function of the geophone, ; Indicates the velocity excitation of the geophone by the lateral vibration of the shaking table; in step 3), for the output voltage waveform generated by the lateral excitation of the measured geophone, the output voltage of the geophone is subtracted from the measured output of the geophone caused by the lateral vibration of the shaking table The voltage is: ,in, is the output voltage of the detector under test, Indicates the mass of the detector coil under test, Indicates the axial stiffness of the spring leaf of the geophone under test, is a proportional coefficient and is a fixed value; Indicates the velocity excitation of the main vibration of the shaking table to the geophone, Indicates the velocity excitation of the geophone by the lateral vibration of the shaking table, yes derivative of Indicates the speed of the coil axial relative to the housing of the geophone caused by the spring piece of the geophone under test not being in a horizontal state; At the false frequency point, the output voltage of the detected detector can be expressed as: ; The output voltage of the geophone caused by the lateral vibration of the shaking table measured by the standard acceleration sensor can be expressed as: ,in, , is a proportional coefficient and is a fixed value; Indicates the speed excitation of the main vibration of the shaking table to the geophone; is the transverse stiffness of the spring leaf of the tested detector; is the correction factor; Indicates the axial stiffness of the spring leaf of the tested detector; is the excitation frequency output by the vibrating table; Indicates the quality of the coil of the detector under test; Indicates the velocity excitation of the geophone by the lateral vibration of the vibrating table; in step 3), the output voltage of the geophone caused by the lateral vibration of the vibrating table obtained by subtracting the output voltage of the measured geophone is: , yes derivative of Indicates the speed of the coil axial relative to the housing of the geophone caused by the spring piece of the geophone under test not being in a horizontal state; 3) Subtract the output voltage waveform calculated in step 2) from the actual output voltage waveform of the geophone under test. The result is the output voltage waveform completely generated by the transverse excitation of the geophone. After calculating its amplitude, then Divided by the velocity amplitude in the main vibration direction of the shaking table at the current moment, the obtained quotient is the lateral sensitivity of the geophone under test; 4) According to steps 2) and 3), excite the geophone point by point from low frequency to high frequency to obtain the transverse amplitude-frequency characteristic curve, and the frequency point corresponding to the peak value of the curve is the alias frequency of the geophone under test.