CN114814366B

CN114814366B - Device and method for testing characteristic impedance of seismic exploration cable

Info

Publication number: CN114814366B
Application number: CN202210415227.7A
Authority: CN
Inventors: 阎志武; 李广辉; 吴学兵; 高翀; 瞿婉洁; 付淼星
Original assignee: Material And Equipment Center Of Sinopec Petroleum Engineering Geophysics Co ltd; Sinopec Oilfield Service Corp; Sinopec Petroleum Engineering Geophysics Co Ltd; Sinopec Petroleum Engineering Geophysics Co Ltd Equipment Management Center
Current assignee: Material And Equipment Center Of Sinopec Petroleum Engineering Geophysics Co ltd; Sinopec Oilfield Service Corp; Sinopec Petroleum Engineering Geophysics Co Ltd
Priority date: 2022-04-20
Filing date: 2022-04-20
Publication date: 2025-08-08
Anticipated expiration: 2042-04-20
Also published as: CN114814366A

Abstract

The present invention discloses a device for testing the characteristic impedance of seismic exploration cables. The device is characterized by connecting the cable to be tested to a directional coupler, connecting a signal source to the input of a power divider, connecting one output of the power divider to a phase detection module to obtain phase difference information, and connecting the other output to an amplitude detection module via a directional coupler to obtain amplitude difference information. The signal source is a high-frequency sine function generator. The device and algorithm are specifically designed for testing the impedance of seismic exploration cables, including total frequency, different connection schemes, and post-data calculation algorithms. This differs from conventional cable testing and enables rapid, high-precision, and automated geophysical cable impedance testing.

Description

Device and method for testing characteristic impedance of seismic exploration cable

Technical Field

The invention belongs to the field of seismic exploration, and particularly relates to a device and a method for testing characteristic impedance of a seismic exploration cable.

Background

The characteristic impedance is also called "characteristic impedance", which is not a direct current resistance, and belongs to the concept of long-line transmission. In the high frequency range, in the process of signal transmission, an instantaneous current is generated between the signal line and the reference plane (power supply or ground plane) due to the establishment of an electric field, if the transmission line is isotropic, a current I always exists as long as the signal is transmitted, and if the output level of the signal is V, the transmission line is equivalent to a resistor with the size of V/I in the process of signal transmission, and the equivalent resistor is called the characteristic impedance Z of the transmission line. During transmission of the signal, if the characteristic impedance of the transmission path changes, the signal will reflect at the junction where the impedance is discontinuous. Factors affecting the characteristic impedance include dielectric constant, dielectric thickness, line width, and copper foil thickness. The characteristic impedance is an electrical parameter that measures the quality of the match between the seismic data cable and the acquisition station. Good impedance matching is beneficial to improving the transmission quality of data signals, eliminating reflection noise, improving the reliability of a system and reducing the transmission error rate.

Abrupt changes in the characteristic impedance, called discontinuities in the characteristic impedance or anomalies in the characteristic impedance, can cause reflections of the signal, thereby causing distortion of the transmitted signal in the cable and resulting in data transmission errors. Typically the impedance of the cable changes at the connection and termination of the cable, and hard turns or kinks of the cable also change the characteristic impedance of the cable. In cases where the impedance discontinuity is not severe, data transmission is sometimes still possible because the reflected signal is weak and has been attenuated by the cable, but a more severe impedance discontinuity will interfere with the data transmission. Serious impedance discontinuities are caused by poor electrical connection, incorrect cable end ties, mismatched cables, and twisted pair twist pattern errors in the cable. Therefore, the shorter and better the non-twisted part of the joint is in the maintenance process of the cable, the cable is not bent or knotted in the use process of the cable, the minimum bending radius of the cable is not too small, and the cable is not rolled or bound too tightly.

The data transmission cable is a channel for various commands and data between the instrument host and the field arrangement, and in practical production application, the stability of the central control unit of the earthquake acquisition system and the field electronic unit is good, and the quality of the data transmission cable becomes a key factor for influencing the construction quality and progress. The performance of the cable is critical to the accurate, stable and undistorted transmission of digital signals, and the field construction efficiency and quality are determined, wherein the essence of the performance of the cable is whether the performance parameters of the cable are matched with the field part of the whole instrument system. If the performance parameters of the data transmission cable change, cable transmission faults can be caused, the transmission quality of the seismic data is affected, and the production efficiency is reduced.

1. Related industries and state of the art in China, development trend

Domestic data transmission cable manufacturers use an HP network analyzer to detect secondary parameters of the cable. The working principle is that the network analyzer generates 2MHz-12MHz scanning sine signal, and the phase and amplitude changes applied on the data transmission cable are picked up by the directional coupler to convert the average value of different frequency points.

The testing principle of the current field-used data transmission cable tester is that the tester generates a cosine single pulse with a high frequency of 1/4 period and applies the cosine single pulse to the data transmission line. And the other end of the data transmission line is connected with a potentiometer (or a digital potentiometer) serving as a matching resistor. A reflection pulse is generated except for 1/4 period single pulse at the signal applying end, and the matching resistance is adjusted to be free of reflection, so that the reading matching resistance value is the characteristic impedance value of the cable.

The FLUKE network cable analyzer can test, analyze and diagnose faults of the local area network twisted pair cable. The tester uses a new testing technology, combines pulse signals and digital signals, and provides quick and accurate testing results. The test result can be displayed in a digital form or a graphical form, and the test frequency is 0-300 MHz. Meanwhile, the tester can also be directly connected with a computer through a serial port, and the computer is used for analyzing the test result and testing and analyzing the electrical characteristic index of the data transmission cable.

2. State of the art and industry

HP4395A of Hewlett-packard tests secondary parameters of the cable and can test cable impedance, attenuation, near-end crosstalk and other parameters. The geophysical prospecting cable testing industry recognizes its testing methods and testing accuracy. The secondary parameter testing device has the characteristics of high secondary parameter testing precision, stability, incapability of testing primary parameters of the cable by the instrument, high requirement on professional knowledge of operators, and high price of the instrument, accessories, fixtures and testing software.

The TDR tester technology uses a time domain reflectometry method, the model TCA-1 has poorer testing precision, and the adaptability to the geophysical prospecting cable needs to be improved. The use amount in the market is very small.

At present, no special instrument for testing impedance of a geophysical prospecting cable exists in the geophysical prospecting market, other instruments are complex to operate and high in price, and accuracy and efficiency are low.

Disclosure of Invention

Aiming at the problems in the background technology, the invention designs an impedance measuring device with high sensitivity and high precision, which is suitable for various common geophysical prospecting cable tests and is used for production, manufacture, maintenance and detection.

The invention firstly discloses a testing device for characteristic impedance of a seismic exploration cable, wherein a cable to be tested is connected with a directional coupler, a signal source is connected with the input end of a power distributor, one output end of the power distributor is connected with a phase detection module to obtain phase difference information, the other output end of the power distributor is connected with a amplitude detection module through the directional coupler to obtain amplitude difference information, and the signal source is a high-frequency sine function generator.

The signal source comprises a function generator, wherein the output end of the function generator is connected with a frequency synthesizer, the control module is connected with the frequency synthesizer through a bus to send out PC1-PC14 digital codes, the output of the frequency synthesizer is amplified through a current and then is input into the function generator, the control module is connected with a D/A converter through the bus to send out PC1-PC12 digital codes, on one hand, the D/A converter outputs reference voltage V _ref, and the output reference voltage V _ref is input into the function generator through a voltage/current conversion amplifying circuit, and on the other hand, the output current Iout is output to the function generator.

The amplitude detection module comprises a diode, a filter circuit and an amplifier which are connected in series, and the amplitude of the amplitude detection module is picked up by changing a high-frequency signal into a direct-current potential.

The phase detection module comprises a phase detector, wherein the output end of the phase detector is connected with a filter circuit, the output end of the filter circuit is connected with a sampling resistor, and the analog quantity of the phase is represented by digital quantity.

The power divider comprises a first power divider 1, a second power divider 2 and a third power divider 3, wherein an input signal is connected with the input end of the first power divider 1, the first output end of the first power divider 1 is connected with the input end of the third power divider 3, and the second output end is connected with the first input ends of the directional coupler and the comparator;

the directional coupler is also connected with a cable and a first fixed amplifying circuit, the first fixed amplifying circuit is sequentially connected with the program-controlled amplifying circuit, a second fixed amplifying circuit and a second power divider 2, the output end of the second power divider 2 is connected with the second input end of the comparator through a filter circuit, and the output end of the comparator outputs a control signal to the program-controlled amplifying circuit.

The invention also discloses a testing method of the characteristic impedance of the seismic exploration cable, which is based on the device provided by the invention and is characterized in that the device collects the values of the phase difference phi and the amplitude difference A so as to calculate the characteristic impedance of the cable.

It comprises the following steps:

S1, inputting a start frequency f _a, a final frequency f _b, and a frequency step f _s, then nf= (f _b-f_a)-f_s+1、f_i＝f_a+(i-1)f_s, i=1, 2,) nf;

S2, connecting a signal source with a voltage value V _CO and a frequency f _i to a calibration circuit;

S3, i=1, reading the value A _i0 of the phase detection module and the amplitude detection module,

S4, i=1+1, reading the values A _i0 of the phase detection module and the amplitude detection module,

S5, judging whether i is greater than nf, otherwise returning to S4, and entering S5 if yes;

S6, connecting a signal source with a voltage value V _CO and a frequency f _i with a cable to be tested;

S7, i=1, reading the value A _ix of the phase detection module and the amplitude detection module,

S8, i=1+1, reading the values A _ix of the phase detection module and the amplitude detection module,

S9, judging whether i is greater than nf, otherwise returning to S8, and entering S9 if yes;

S10, calculating i=1, 2,.., R represents the corresponding impedance measured by different counters;

S11、 Z _{Total (S)}＝(Z₁+Z₂+...+Z_nf)÷n,Z_i1 is open circuit impedance, Z _i2 is short circuit impedance, and Z _{Total (S)} is cable characteristic impedance.

The calibration circuit is a pass-through or an open circuit.

The open circuit calibration includes the steps of:

S2A-1, an impedance test channel is established by the analog board AB, a channel IN4 is selected by the multiplexer, the gain of the amplifier is 0dB, and the sampling frequency of the system is 32Khz;

S2A-2, an input/output module, wherein the input/output module receives an instruction of a control module, and the functional relay and the channel relay establish an open circuit calibration relay channel according to a preset instruction;

S2A-3, a high frequency signal source board HFB receives an instruction from a control module, sets a starting frequency and a finishing frequency, and starts a function generator in a starting frequency state to wait for the control module to start the instruction;

S2A-4, the control module starts open circuit calibration, writes open circuit calibration data into the RAM of the tester, inquires an AB state signal of the analog board, reads the RAM data of the tester under the control of a software control reading instruction when the state signal is enabled, and calculates and stores the calibration data.

The short circuit calibration includes the steps of:

S2B-1, an impedance test channel is established by the analog board AB, a channel IN8 is selected by the multiplexer, the gain of the amplifier is 0dB, and the sampling frequency of the system is 32Khz;

S2B-2, an input/output module, wherein the input/output module receives the instruction of the control module, and the functional relay and the channel relay establish a short circuit calibration relay channel according to the preset instruction;

S2B-3, the HFB receives an instruction from the control module, the starting frequency and the ending frequency are set, and the starting function generator is in a starting frequency state and waits for the control module to start the instruction;

S2B-4, the control module starts short circuit calibration, writes short circuit calibration data into the RAM of the tester, inquires an AB state signal of the analog board, reads the RAM data of the tester under the control of a software control reading instruction when the state signal is enabled, and calculates and stores the calibration data.

The beneficial effects of the invention are that

Specifically designed devices and algorithms for seismic cable impedance testing, including total frequency times, different connection schemes, and post-data operation algorithms, are different from the testing of a typical cable. The impedance test of the geophysical prospecting cable can be realized rapidly, the precision is high, and the degree of automation is high.

Drawings

FIG. 1 is a block diagram of a testing apparatus according to the present invention

FIG. 2 is a block diagram of a signal source in a test apparatus

FIG. 3 is a block diagram showing the structure of an amplitude detection module in the test apparatus

FIG. 4 is a block diagram showing a phase detection module in the test apparatus

FIG. 5 is a block diagram of a power divider in a test apparatus

FIG. 6 is a flow chart of the testing method of the present invention

Detailed Description

The invention is further illustrated below with reference to examples, but the scope of the invention is not limited thereto:

the invention discloses a testing device for characteristic impedance of a seismic exploration cable, which is combined with fig. 1, wherein a cable to be tested is connected with a directional coupler, a signal source is connected with the input end of a power distributor, one output end of the power distributor is connected with a phase detection module to obtain phase difference information, the other output end of the power distributor is connected with a amplitude detection module through the directional coupler to obtain amplitude difference information, and the signal source is a high-frequency sine function generator.

Referring to fig. 2, the signal source includes a function generator, an output end of the function generator is connected with a frequency synthesizer, digital codes PC1-PC14 are input to the frequency synthesizer through a bus, an output of the frequency synthesizer is amplified by a current and then is input to the function generator, the digital codes PC1-PC12 are input to a D/a converter through the bus, on one hand, an output reference voltage V _ref is input to the function generator through a voltage/current conversion amplifying circuit, and on the other hand, a current Iout is output to the function generator. During frequency calibration, the D/A digital-to-analog converter outputs an analog direct current signal to control the function generator and thus the frequency synthesizer.

The digital codes PC1-PC14 come from a control module, 8-bit data PD0 from a PC computer and PD7378H parallel port data are respectively written into the 8-bit data PD0 from the PC computer for 2 times under the control of write signals WR5 and WR6 to form PC1-PC14 data streams, wherein a data latch latches the PC1-PC12 data streams as the digital input of a 12-bit D/A digital-to-analog converter, a function generator outputs a voltage signal with precision VREF=2.5V, the digital-to-analog converter is connected with an Iout end to form a digital multiplier, the D/A digital-to-analog converter outputs a voltage/current conversion signal, an amplifier further amplifies and improves the signal-to-noise ratio, a frequency end IIN of the function generator is controlled by current, the output frequency of the function generator is increased when the input current is increased, and preliminary adjustment (coarse adjustment) of the frequency is performed by the function generator.

The data latches latched PC1-PC14 data streams are used as digital input signals for a 14 bit frequency synthesizer, which is actually a frequency phase locked loop PLL core circuit, using a MOTOROLA MC145151 device, with a crystal of 8.192Mhz, to detect SYNC synchronization signals from the function generator output signals, generate differential current frequency adjustment signals, and amplify the current signals as frequency calibration control signals.

Specifically, the 12-bit D/A digital-to-analog converter for PC1-PC12 data stream control generates a main frequency signal, which is a coarse tuning frequency. The main frequency signals may be different, and the data streams of the PCs 1-14 are used as digital input signals of the 14-bit frequency synthesizer, and the circuit uses the frequency phase-locked loop (PLL) technology and is a fine tuning signal of the output frequency, and can generally control (change or increase or decrease) the main frequency signals by about 15%.

Referring to fig. 3, the amplitude detection module includes a diode, a filter circuit and an amplifier connected in series, and converts the high-frequency signal into a dc potential pickup amplitude.

Referring to fig. 4, the phase detection module includes a phase detector, an output end of the phase detector is connected with a filter circuit, an output end of the filter circuit is connected with a sampling resistor, and an analog quantity of the phase is represented by a digital quantity.

Referring to fig. 5, the power divider includes a first power divider 1, a second power divider 2, and a third power divider 3, where an input signal is connected to an input end of the first power divider 1, a first output end of the first power divider 1 is connected to an input end of the third power divider 3, and a second output end is connected to a first input end of the directional coupler and the comparator, and the first output end of the third power divider 3 is connected to the filter circuit and then outputs a reference voltage vbase, and the second output end is used as a reference voltage and is output to the phase detection module;

The invention also discloses a testing method of the characteristic impedance of the seismic exploration cable, which collects the values of the phase difference phi and the amplitude difference A so as to calculate the characteristic impedance of the cable.

With reference to fig. 6, it comprises the following steps:

S1, inputting a start frequency f _a, a final frequency f _b (1 MHZ-40 MHZ), a frequency step f _s, then nf= (f _b-f_a)-f_s+1、f_i＝f_a+(i-1)f_s, i=1, 2,) nf;

The calibration circuit is a pass-through or an open circuit.

The calibration circuit is respectively 50 ohm standard load calibration, open circuit calibration and short circuit calibration. The network analyzer tests the geophysical prospecting cable to perform open circuit calibration and short circuit calibration generally.

The PC computer controls the module under the control of the system software, the control module generates corresponding control signals and data flow signals, receives the state signals of the function generator from the high-frequency signal source board HFB, and detects the state signals from the analog board AB. When the tester performs open circuit calibration or short circuit calibration, the analog board AB, the high-frequency signal source board HFB and the control board CB work cooperatively and orderly under the control of the PC computer.

The open circuit calibration includes the steps of:

The short circuit calibration includes the steps of:

The specific embodiments described herein are offered by way of example only to illustrate the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.

Claims

1. A testing device for the characteristic impedance of a seismic exploration cable is characterized in that the cable to be tested is connected with a directional coupler, a signal source is connected with the input end of a power distributor, one output end of the power distributor is connected with a phase detection module to obtain phase difference information, and the other output end of the power distributor is connected with a amplitude detection module through the directional coupler to obtain amplitude difference information;

The signal source comprises a function generator, wherein the output end of the function generator is connected with a frequency synthesizer, the control module is connected with the frequency synthesizer through a bus to send out PC1-PC14 digital codes, the output of the frequency synthesizer is amplified through a current and then is input into the function generator;

The power divider comprises a first power divider, a second power divider and a third power divider, wherein an input signal is connected with the input end of the first power divider, the first output end of the first power divider is connected with the input end of the third power divider, and the second output end of the first power divider is connected with the first input ends of the directional coupler and the comparator;

the directional coupler is also connected with a cable and a first fixed amplifying circuit, the first fixed amplifying circuit is sequentially connected with the program-controlled amplifying circuit, a second fixed amplifying circuit and a second power divider, the output end of the second power divider is connected with the second input end of the comparator through a filter circuit, and the output end of the comparator outputs a control signal to the program-controlled amplifying circuit.

2. The apparatus of claim 1, wherein the amplitude detection module comprises a diode, a filter circuit, and an amplifier in series.

3. The apparatus of claim 1, wherein the phase detection module comprises a phase detector, an output terminal of the phase detector is connected with a filter circuit, and an output terminal of the filter circuit is connected with a sampling resistor.

4. A method of testing the characteristic impedance of a seismic cable, based on the apparatus of any one of claims 1-3, characterized in that it collects values of phase difference phi and amplitude difference a to calculate the characteristic impedance of the cable;

it comprises the following steps:

S5, judging whether i is greater than nf, otherwise returning to S4, and entering S6 if yes;

S9, judging whether i is greater than nf, otherwise returning to S8, and entering S10 if yes;

5. The method of claim 4, wherein the calibration circuit is a pass-through or an open circuit.

6. The method of claim 5, wherein the open circuit calibration comprises the steps of:

7. The method of claim 5, wherein the short circuit calibration comprises the steps of: