Device and method for testing characteristic impedance of seismic exploration cable

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

Technical Field

[0001] The present invention belongs to the field of seismic exploration, and in particular relates to a device and method for testing the characteristic impedance of a seismic exploration cable. Background Art

[0002] Characteristic impedance, also known as "characteristic impedance," is not DC resistance but a concept used in long-distance transmission. In the high-frequency range, during signal transmission, the electric field established between the signal line and the reference plane (power supply or ground plane) generates a transient current at the point where the signal reaches the transmission line. If the transmission line is isotropic, a current I will always exist as long as the signal is transmitting. However, if the signal output level is V, the transmission line will be equivalent to a resistance with a magnitude of V / I during signal transmission. This equivalent resistance is called the characteristic impedance Z of the transmission line. If the characteristic impedance of the transmission path changes during signal transmission, the signal will be reflected at the node where the impedance is discontinuous. Factors affecting characteristic impedance include dielectric constant, dielectric thickness, line width, and copper foil thickness. Characteristic impedance is an electrical parameter that measures the matching quality between seismic data transmission cables and acquisition stations. Good impedance matching improves data signal transmission quality, eliminates reflection noise, enhances system reliability, and reduces bit error rates.

[0003] A sudden change in characteristic impedance is called a characteristic impedance discontinuity or anomaly. This can cause signal reflections, which can distort the signal transmitted through the cable and lead to data transmission errors. Generally, cable impedance changes at the connection and termination points. Hard bends or kinks in the cable can also change the characteristic impedance. In the case of a mild impedance discontinuity, data transmission can still proceed because the reflected signal is weak and attenuated by the cable. However, more severe impedance discontinuities can interfere with data transmission. Severe impedance discontinuities are caused by poor electrical connections, improper cable terminations, mismatched cables, and incorrect twisting of the twisted pairs within the cable. Therefore, when repairing cables, it is best to keep untwisted sections at the connection as short as possible. During use, avoid bending or tying cables, keep the minimum bend radius small, and avoid rolling over or over-tightening the cables.

[0004] The data transmission cable is the conduit for various commands and data between the instrument mainframe and the field array. In actual production applications, the stability of the central control unit and field electronics unit of the seismic acquisition system is very important. The quality of the data transmission cable is a key factor affecting the quality and progress of construction. Its performance is crucial for the accurate, stable, and distortion-free transmission of digital signals, and also determines the efficiency and quality of field operations. Its performance essentially refers to whether the performance parameters of the cable match the field portion of the entire instrument system. If the performance parameters of the data transmission cable vary, it will cause cable transmission failure, affecting the quality of seismic data transmission and reducing production efficiency.

[0005] 1. Current status and development trends of related domestic industries and technologies

[0006] Domestic data cable manufacturers use HP network analyzers to test cable secondary parameters. The operating principle is that the network analyzer generates a swept sinusoidal signal between 2MHz and 12MHz, picks up the phase and amplitude changes applied to the data cable through a directional coupler, and converts the average value at different frequency points.

[0007] The testing principle of current field-tested data cable testers is to generate a high-frequency, quarter-cycle cosine pulse and apply it to the data transmission line. A potentiometer (or digital potentiometer) is connected to the other end of the data transmission line as a matching resistor. In addition to the quarter-cycle pulse, a reflected pulse is generated at the applied signal end. By adjusting the matching resistor to eliminate reflection, the matching resistor value is read as the cable's characteristic impedance.

[0008] The Fluke Network Cable Analyzer can test, analyze, and troubleshoot LAN twisted-pair cables. This tester utilizes cutting-edge testing technology, combining pulse and digital signals to provide fast and accurate test results. Test results can be displayed digitally or graphically, with a test frequency range of 0 to 300 MHz. The tester can also be connected directly to a computer via a serial port, allowing analysis of test results and the electrical characteristics of digital cables.

[0009] 2. Current status of related domestic industries and technologies

[0010] HP's HP4395A tests cable secondary parameters, including impedance, attenuation, and near-end crosstalk. Its testing methods and accuracy are recognized within the geophysical cable testing industry. Features include high accuracy and stability for secondary parameter testing. However, the instrument cannot test cable primary parameters, requiring high operator expertise and resulting in high costs for the instrument, accessories, fixtures, and testing software.

[0011] The TDR tester, model TCA-1, uses time domain reflectometry. Its accuracy is poor and its suitability for geophysical cables needs improvement. It is rarely used in the market.

[0012] Currently, there is no instrument specifically used for testing impedance of geophysical cables in the geophysical prospecting market. Other instruments are complicated to operate, expensive, and have low accuracy and efficiency. Summary of the Invention

[0013] In view of the problems existing in the background technology, the present invention designs an impedance measuring device with high sensitivity and high precision, which is suitable for a variety of commonly used geophysical cable tests and can be used for production, manufacturing, maintenance and detection.

[0014] The present invention first discloses a device for testing the characteristic impedance of a seismic exploration cable. The cable to be tested is connected to a directional coupler, a signal source is connected to the input end of a power divider, one output end of the power divider is connected to a phase detection module to obtain phase difference information, and the other output end is connected to an amplitude detection module through a directional coupler to obtain amplitude difference information; the signal source is a high-frequency sine function generator.

[0015] The signal source includes a function generator, the output end of the function generator is connected to the frequency synthesizer, the control module is connected to the frequency synthesizer through a bus to send the PC1-PC14 digital code to it, the output of the frequency synthesizer is input to the function generator after current amplification; the control module is connected to the D / A converter through a bus to send the PC1-PC12 digital code to it, and the D / A converter outputs a reference voltage V ref After passing through the voltage / current conversion amplifier circuit, it is input to the function generator, and on the other hand, the output current Iout is sent to the function generator.

[0016] The amplitude detection module includes a diode, a filter circuit and an amplifier connected in series, which converts the high-frequency signal into a DC potential to pick up the amplitude.

[0017] The phase detection module includes a phase detector, an output end of the phase detector is connected to a filter circuit, an output end of the filter circuit is connected to a sampling resistor, and an analog quantity of the phase is expressed in a digital quantity.

[0018] The power divider includes a first power divider 1, a second power divider 2, and a third power divider 3. The input signal is connected to the input end of the first power divider 1, the first output end of the first power divider 1 is connected to the input end of the third power divider 3, and the second output end is connected to the first input end of the directional coupler and the comparator; the first output end of the third power divider 3 is connected to the filter circuit and then outputs the reference voltage Vreference, and the second output end is output as the reference voltage to the phase detection module;

[0019] The directional coupler is also connected to the cable and the first fixed amplifier circuit, the first fixed amplifier circuit is sequentially connected to the programmable amplifier circuit, the second fixed amplifier circuit and the second power divider 2, the output end of the second power divider 2 is connected to the second input end of the comparator through the filter circuit; the output end of the comparator outputs a control signal to the programmable amplifier circuit.

[0020] The present invention also discloses a method for testing the characteristic impedance of a seismic exploration cable. The method is based on the device of the present invention and is characterized in that it collects the values of the phase difference φ and the amplitude difference A to calculate the characteristic impedance of the cable.

[0021] It includes the following steps:

[0022] S1, input starting frequency f a , end frequency f b , 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;

[0023] S2, set the voltage value V CO Frequency f i The signal source is connected to the calibration circuit;

[0024] S3, i=1, read the phase detection module and amplitude detection module value A i0 ,

[0025] S4, i=1+1, read the phase detection module and amplitude detection module value A i0 ,

[0026] S5, determine whether i is greater than nf, otherwise return to S4, if yes, enter S5;

[0027] S6, set the voltage value V CO Frequency f i Connect the signal source to the cable under test;

[0028] S7, i=1, read the phase detection module and amplitude detection module value A ix ,

[0029] S8, i=1+1, read the phase detection module and amplitude detection module value A ix ,

[0030] S9, determine whether i is greater than nf, otherwise return to S8, if yes, go to S9;

[0031] S10, calculate i=1,2,...,nf, r represents the corresponding impedance measured by different counters;

[0032] S11, Z 总 =(Z1+Z2+...+Z nf )÷n,Z i1 is the open circuit impedance, Z i2 is the short-circuit impedance, Z 总 is the characteristic impedance of the cable.

[0033] The calibration circuit is a through circuit or an open circuit.

[0034] Open circuit calibration consists of the following steps:

[0035] S2A-1. Set up impedance test channel on analog board AB. Select channel IN4 on the multiplexer. Set amplifier gain to 0dB and system sampling frequency to 32Khz.

[0036] S2A-2, input / output module: accepts the control module instruction, and the function relay and channel relay establish the open circuit calibration relay channel according to the preset instruction;

[0037] S2A-3, the high frequency signal source board HFB receives the instruction from the control module, sets the starting frequency and the ending frequency, starts the function generator at the starting frequency state, and waits for the start instruction from the control module;

[0038] S2A-4, the control module starts the open circuit calibration, writes the open circuit calibration data into the tester RAM, queries the analog board AB status signal, and when the status signal is enabled, reads the tester RAM data under the control of the software control read instruction, calculates and stores the calibration data.

[0039] Short circuit calibration consists of the following steps:

[0040] S2B-1. Set up impedance test channel on analog board AB. Select channel IN8 on the multiplexer. Set amplifier gain to 0dB and system sampling frequency to 32Khz.

[0041] S2B-2, input / output module: accepts the control module instruction, and the function relay and channel relay establish the short-circuit calibration relay channel according to the preset instruction;

[0042] S2B-3, the high frequency signal source board HFB receives the instruction from the control module, sets the starting frequency and the ending frequency, starts the function generator at the starting frequency state, and waits for the start instruction from the control module;

[0043] S2B-4. The control module starts short-circuit calibration, writes short-circuit calibration data into the tester RAM, queries the analog board AB status signal, and when the status signal is enabled, reads the tester RAM data under the control of the software control read instruction, calculates and stores the calibration data.

[0044] Beneficial effects of the present invention

[0045] The device and algorithm are specifically designed for seismic cable impedance testing, including frequency totaling, different connection schemes, and post-data calculation algorithms. Unlike general cable testing, this device can quickly perform geophysical cable impedance testing with high accuracy and a high degree of automation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a structural diagram of the test device of the present invention.

[0047] Figure 2 This is the structural block diagram of the signal source in the test device

[0048] Figure 3 This is the structural diagram of the amplitude detection module in the test device

[0049] Figure 4 This is the structural block diagram of the phase detection module in the test device

[0050] Figure 5 This is the structural block diagram of the power divider in the test device.

[0051] Figure 6 Schematic diagram of the test method of the present invention DETAILED DESCRIPTION

[0052] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto:

[0053] The present invention discloses a device for testing the characteristic impedance of a seismic exploration cable. Figure 1 The cable to be tested is connected to a directional coupler, the signal source is connected to the input end of the power divider, one output end of the power divider is connected to the phase detection module to obtain phase difference information, and the other output end is connected to the amplitude detection module through a directional coupler to obtain amplitude difference information; the signal source is a high-frequency sine function generator.

[0054] Combine Figure 2 The signal source includes a function generator, the output of the function generator is connected to the frequency synthesizer, the digital code PC1-PC14 is input to the frequency synthesizer through the bus, the output of the frequency synthesizer is input to the function generator after current amplification; the digital code PC1-PC12 is input to the D / A converter through the bus, and the reference voltage V is output. refAfter passing through the voltage / current conversion amplifier circuit, the signal is input to the function generator, while the output current Iout is sent to the function generator. During frequency calibration, the analog DC signal output by the D / A converter controls the function generator and thus the frequency synthesizer.

[0055] Digital codes PC1-PC14 come from the control module. The 8-bit data PD0:PD7378H parallel port data from the PC computer is written twice under the control of write signals WR5 and WR6 to form the PC1-PC14 data stream. The data latch latches the PC1-PC12 data stream as the digital input of the 12-bit D / A digital-to-analog converter. The function generator outputs a precise VREF=2.5V voltage signal, which is connected to the Iout terminal of the D / A digital-to-analog converter to form a digital multiplier. The D / A digital-to-analog converter outputs a voltage / current conversion signal. The amplifier further amplifies it to improve the signal-to-noise ratio and control the frequency terminal IIN of the function generator. The IIN terminal of the function generator is the current control terminal. As the input current increases, the output frequency of the function generator increases. This is the initial adjustment (coarse adjustment) of the frequency.

[0056] The PC1-PC14 data stream latched by the data latch serves as the digital input signal of the 14-bit frequency synthesizer. The frequency synthesizer is actually a frequency phase-locked loop (PLL) core circuit. It uses the MC145151 device from Motorola and has an 8.192Mhz crystal. It detects the SYNC synchronization signal from the function generator output signal, generates a differential current frequency adjustment signal, and amplifies the current signal as a frequency calibration control signal.

[0057] Specifically, the PC1-PC12 data stream controls the 12-bit D / A converter to generate the main frequency signal, which serves as a coarse frequency adjustment. The main frequency signal may vary. The PC1-PC14 data stream serves as the digital input signal to the 14-bit frequency synthesizer. This circuit uses phase-locked loop (PLL) technology to fine-tune the output frequency, typically controlling (changing, increasing, or decreasing) the main frequency signal by approximately 15%.

[0058] Combine Figure 3 The amplitude detection module includes a diode, a filter circuit and an amplifier connected in series, which converts the high-frequency signal into a DC potential to pick up the amplitude.

[0059] Combine Figure 4 The phase detection module includes a phase detector, the output end of the phase detector is connected to the filter circuit, the output end of the filter circuit is connected to the sampling resistor, and the analog value of the phase is reflected in a digital value.

[0060] Combine Figure 5The power divider includes a first power divider 1, a second power divider 2, and a third power divider 3. The input signal is connected to the input end of the first power divider 1, the first output end of the first power divider 1 is connected to the input end of the third power divider 3, and the second output end is connected to the first input end of the directional coupler and the comparator; the first output end of the third power divider 3 is connected to the filter circuit and then outputs the reference voltage Vreference, and the second output end is output as the reference voltage to the phase detection module;

[0061] The directional coupler is also connected to the cable and the first fixed amplifier circuit, the first fixed amplifier circuit is sequentially connected to the programmable amplifier circuit, the second fixed amplifier circuit and the second power divider 2, the output end of the second power divider 2 is connected to the second input end of the comparator through the filter circuit; the output end of the comparator outputs a control signal to the programmable amplifier circuit.

[0062] The invention also discloses a method for testing the characteristic impedance of a seismic exploration cable, which collects the values of the phase difference φ and the amplitude difference A to calculate the characteristic impedance of the cable.

[0063] Combine Figure 6 , which includes the following steps:

[0064] S1, input starting frequency f a , end frequency f b (1MHZ-40MHZ), 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;

[0065] S2, set the voltage value V CO Frequency f i The signal source is connected to the calibration circuit;

[0066] S3, i=1, read the phase detection module and amplitude detection module value A i0 ,

[0067] S4, i=1+1, read the phase detection module and amplitude detection module value A i0 ,

[0068] S5, determine whether i is greater than nf, otherwise return to S4, if yes, enter S5;

[0069] S6, set the voltage value V CO Frequency f i Connect the signal source to the cable under test;

[0070] S7, i=1, read the phase detection module and amplitude detection module value A ix ,

[0071] S8, i=1+1, read the phase detection module and amplitude detection module value A ix ,

[0072] S9, determine whether i is greater than nf, otherwise return to S8, if yes, go to S9;

[0073] S10, calculate i=1,2,...,nf, r represents the corresponding impedance measured by different counters;

[0074] S11, Z 总 =(Z1+Z2+...+Z nf )÷n,Z i1 is the open circuit impedance, Z i2 is the short-circuit impedance, Z 总 is the characteristic impedance of the cable.

[0075] The calibration circuit is a through circuit or an open circuit.

[0076] The calibration circuits include 50 ohm standard load calibration, open circuit calibration, and short circuit calibration. Network analyzers testing geophysical cables generally perform open circuit calibration and short circuit calibration.

[0077] Specific form: The PC controls the module under the control of the system software. The control module generates corresponding control signals and data stream signals, receives function generator status signals from the high-frequency signal source board HFB, and simultaneously detects status 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 in a coordinated and orderly manner under the control of the PC.

[0078] Open circuit calibration consists of the following steps:

[0079] S2A-1. Set up impedance test channel on analog board AB. Select channel IN4 on the multiplexer. Set amplifier gain to 0dB and system sampling frequency to 32Khz.

[0080] S2A-2, input / output module: accepts the control module instruction, and the function relay and channel relay establish the open circuit calibration relay channel according to the preset instruction;

[0081] S2A-3, the high frequency signal source board HFB receives the instruction from the control module, sets the starting frequency and the ending frequency, starts the function generator at the starting frequency state, and waits for the start instruction from the control module;

[0082] S2A-4, the control module starts the open circuit calibration, writes the open circuit calibration data into the tester RAM, queries the analog board AB status signal, and when the status signal is enabled, reads the tester RAM data under the control of the software control read instruction, calculates and stores the calibration data.

[0083] Short circuit calibration consists of the following steps:

[0084] S2B-1. Set up impedance test channel on analog board AB. Select channel IN8 on the multiplexer. Set amplifier gain to 0dB and system sampling frequency to 32Khz.

[0085] S2B-2, input / output module: accepts the control module instruction, and the function relay and channel relay establish the short-circuit calibration relay channel according to the preset instruction;

[0086] S2B-3, the high frequency signal source board HFB receives the instruction from the control module, sets the starting frequency and the ending frequency, starts the function generator at the starting frequency state, and waits for the start instruction from the control module;

[0087] S2B-4. The control module starts short-circuit calibration, writes short-circuit calibration data into the tester RAM, queries the analog board AB status signal, and when the status signal is enabled, reads the tester RAM data under the control of the software control read instruction, calculates and stores the calibration data.

[0088] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A device for testing the characteristic impedance of a seismic exploration cable, characterized in that: The cable to be tested is connected to a directional coupler, and a signal source is connected to the input of a power divider. One output of the power divider is connected to a phase detection module to obtain phase difference information, and the other output is connected to an amplitude detection module through a directional coupler to obtain amplitude difference information. The signal source is a high-frequency sine function generator. The signal source includes a function generator, the output end of the function generator is connected to the frequency synthesizer, the control module is connected to the frequency synthesizer through a bus to send the PC1-PC14 digital code to it, the output of the frequency synthesizer is input to the function generator after current amplification; the control module is connected to the D / A converter through a bus to send the PC1-PC12 digital code to it, and the D / A converter outputs a reference voltage V ref After passing through the voltage / current conversion amplifier circuit, it is input to the function generator, and on the other hand, the output current Iout is sent to the function generator; The power divider includes a first power divider, a second power divider, and a third power divider. The input signal is connected to the input end of the first power divider, the first output end of the first power divider is connected to the input end of the third power divider, and the second output end is connected to the directional coupler and the first input end of the comparator; the first output end of the third power divider is connected to the filter circuit and then outputs a reference voltage Vreference, and the second output end is output as a reference voltage to the phase detection module; The directional coupler is also connected to the cable and the first fixed amplifier circuit, the first fixed amplifier circuit is sequentially connected to the programmable amplifier circuit, the second fixed amplifier circuit and the second power divider, the output end of the second power divider is connected to the second input end of the comparator through the filter circuit; the output end of the comparator outputs a control signal to the programmable amplifier circuit.

2. The device according to claim 1, characterized in that: The amplitude detection module includes a diode, a filter circuit and an amplifier connected in series.

3. The device according to claim 1, characterized in that: The phase detection module includes a phase detector, an output end of the phase detector is connected to a filter circuit, and an output end of the filter circuit is connected to a sampling resistor.

4. A method for testing the characteristic impedance of a seismic exploration cable, based on the device according to any one of claims 1 to 3, characterized in that It collects the values of phase difference φ and amplitude difference A to calculate the characteristic impedance of the cable; It includes the following steps: S1, input starting frequency f a , end frequency f b , 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, set the voltage value V CO Frequency f i The signal source is connected to the calibration circuit; S3, i=1, read the phase detection module and amplitude detection module value A i0 , S4, i=1+1, read the phase detection module and amplitude detection module value A i0 , S5. Determine whether i is greater than nf. If not, return to S4. If yes, go to S6. S6, set the voltage value V CO Frequency f i Connect the signal source to the cable under test; S7, i=1, read the phase detection module and amplitude detection module value A ix , S8, i=1+1, read the phase detection module and amplitude detection module value A ix , S9, determine whether i is greater than nf, otherwise return to S8, if yes, go to S10; S10, calculate i=1,2,...,nf, r represents the corresponding impedance measured by different counters; S11, Z 总 =(Z1+Z2+...+Z nf )÷n,Z i1 is the open circuit impedance, Z i2 is the short-circuit impedance, Z 总 is the characteristic impedance of the cable.

5. The method according to claim 4, characterized in that The calibration circuit is a through circuit or an open circuit.

6. The method according to claim 5, characterized in that Open circuit calibration consists of the following steps: S2A-1. Set up impedance test channel on analog board AB. Select channel IN4 on the multiplexer. Set amplifier gain to 0dB and system sampling frequency to 32Khz. S2A-2, input / output module: accepts the control module instruction, and the function relay and channel relay establish the open circuit calibration relay channel according to the preset instruction; S2A-3, the high frequency signal source board HFB receives the instruction from the control module, sets the starting frequency and the ending frequency, starts the function generator at the starting frequency state, and waits for the start instruction from the control module; S2A-4, the control module starts the open circuit calibration, writes the open circuit calibration data into the tester RAM, queries the analog board AB status signal, and when the status signal is enabled, reads the tester RAM data under the control of the software control read instruction, calculates and stores the calibration data.

7. The method according to claim 5, characterized in that Short circuit calibration consists of the following steps: S2B-1. Set up impedance test channel on analog board AB. Select channel IN8 on the multiplexer. Set amplifier gain to 0dB and system sampling frequency to 32Khz. S2B-2, input / output module: accepts the control module instruction, and the function relay and channel relay establish the short-circuit calibration relay channel according to the preset instruction; S2B-3, the high frequency signal source board HFB receives the instruction from the control module, sets the starting frequency and the ending frequency, starts the function generator at the starting frequency state, and waits for the start instruction from the control module; S2B-4. The control module starts short-circuit calibration, writes short-circuit calibration data into the tester RAM, queries the analog board AB status signal, and when the status signal is enabled, reads the tester RAM data under the control of the software control read instruction, calculates and stores the calibration data.

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