CN102012518B - Intrinsically-safe 24-bit seismic data acquisition circuit board - Google Patents

Abstract

The present invention is an intrinsically safe 24-bit seismic data acquisition circuit board, which consists of hardware and software. The hardware part mainly includes: a power conversion circuit, an acquisition control circuit, a signal conditioning circuit, an analog/digital conversion circuit and an auxiliary circuit. The software part mainly includes: communication module, acquisition control module, low power consumption management module and drift calibration module; Performance, low power consumption devices and circuit optimization design, low power consumption management, realized the intrinsically safe explosion-proof circuit, with the characteristics of small size, low power consumption, high precision, dustproof, waterproof, explosion-proof, the acquisition circuit board can be It is packaged in the same housing with the seismic signal sensor to form a 24-bit digital three-component geophone, and can be packaged separately to form a 24-bit three-channel seismic data acquisition station, which is suitable for seismic data acquisition at engineering sites and underground coal mines.

Description

Intrinsically safe 24-bit seismic data acquisition circuit board

technical field

The invention belongs to the technical field of geophysical exploration, is a seismic data acquisition device for high-resolution seismic exploration, and is suitable for distributed seismic data acquisition systems on engineering sites and underground coal mines.

technical background

Due to its outstanding technical advantages such as non-destructive, simple, advanced, fast, efficient, and low-cost, geophysical detection technology has gradually become a necessary new technology to solve many mine (engineering) geological problems. Existing mine geophysical prospecting technologies mainly include seismic wave method, direct current method, electromagnetic wave and channel wave and other exploration methods. These methods have achieved certain results in practical application, but existing mine geophysical prospecting instruments generally have low precision, poor stability and single function. Or lack of portability and other issues, can not keep up with the rapid development of today's geophysical exploration technology and equipment, thus restricting their application in mines.

Seismic exploration has the characteristics of long seismic wave propagation distance, rich wave field information and multi-attribute parameter inversion. Its newly developed multi-wave and multi-component seismic exploration is a kind of seismic exploration used to solve high-precision detection and engineering geological problems in complex areas. The new technology of exploration, the use of three-component acquisition of rich seismic wave information of the seismic wave field, provides a prerequisite for seismic exploration to move towards accurate exploration. At present, the equipment used in ground three-dimensional three-component seismic Exploration is still rarely used in the engineering field, especially in coal mine engineering, because of its environmental conditions and special requirements (explosion-proof), there is no geophysical equipment suitable for underground development of this technology.

At present, most of the seismographs used in the engineering field are centralized single-component acquisitions, and the AD conversion accuracy is generally less than 24 bits, mainly 12 bits and 16 bits. Because the large line of the centralized control system is heavy and cannot be split, its receiving The number of channels is generally small, mostly 12 or 24. However, the geological tasks of engineering seismic exploration are varied, ranging from large-scale exploration to a certain area to local small-area detection. Therefore, centralized seismometers are often difficult to meet the requirements of engineering exploration. At the same time, due to Centralized control and analog signal transmission are prone to channel crosstalk, external telecommunication interference, etc. The difference in the transmission distance of the analog signal of each channel will also lead to different signal attenuation, which makes the use of seismic data for AVO and other attribute analysis to form systematic errors; because mine seismic exploration Portable and flexible equipment is required during work, and the equipment used in coal mines must have explosion-proof performance, so the mine seismic data acquisition should be designed as an intrinsically safe portable instrument to have applicability. The present invention requires high precision, weak signal pick-up and To meet the requirements of strong anti-interference performance, flexibility and portability, a high-performance seismic data acquisition circuit is designed. By selecting a new programmable instrument amplifier and 24-bit, multi-channel synchronous analog-to-digital converter, a high-performance seismic data acquisition circuit is formed. The acquisition The circuit board can be packaged in the same shell with the seismic signal sensor (detector core) to form a high-performance 24-bit digital three-component geophone, and can also be packaged separately to form a high-performance three-channel seismic data acquisition station, using intrinsically safe portable The mine seismic recorder (patented, patent number ZL200610165382.9) is controlled to form a distributed seismic data acquisition system to improve the overall performance of the acquisition system.

The working principle of the present invention is: the seismic wave generated by the excitation of the seismic source, after propagating through the underground medium, returns to the ground with the structural information inside the medium, and is received by the core body of the geophone at each measuring point, and the core body of the geophone will be measured The vibration signal is converted into an electrical signal, which is sent to the input end of the anti-aliasing filter circuit through the signal input interface, and the filtered signal is sent to the input end of the variable gain operational amplifier, and the amplified analog signal is sent to the 24-bit high-performance The analog/digital converter performs data conversion. The converted digital signal is first stored in the data memory, and then transmitted to the external host through the serial interface. The host displays and records the collected data. The recorded data can be processed and analyzed to obtain relevant geological results.

Contents of the invention

In order to meet the application needs of high-precision seismic data acquisition, a 24-bit seismic data acquisition circuit board was designed and developed. It is mainly composed of hardware and software. The hardware is mainly composed of power conversion circuit, acquisition control circuit, signal conditioning circuit, analog It is composed of digital/digital conversion circuit and auxiliary circuit, and the software is mainly composed of communication module, acquisition control module, low power consumption management module and drift calibration module. Among them, the power conversion circuit adopts the way of separate power supply of digital power supply and analog power supply, and is composed of corresponding digital power conversion circuit and analog power conversion circuit respectively; the acquisition control circuit part is mainly composed of a microcontroller and a trigger circuit for starting acquisition; signal conditioning The circuit is mainly composed of an anti-aliasing filter circuit and a variable gain operational amplifier; the analog/digital conversion circuit is mainly composed of a reference source circuit, an analog/digital converter and a data memory; the auxiliary circuit is mainly composed of a reset circuit, a status indication circuit, a signal Input interface and serial communication interface. In order to achieve low power consumption, small size, high precision, and high resolution in the design, the signal amplifier selects a new, low-noise programmable instrumentation amplifier AD8253, and the analog-to-digital converter selects a high-performance 24-bit, 4-channel synchronous acquisition analog/ The digital converter is ADS1274, and the microcontroller (Micro-Controller Unit referred to as MCU) uses high-performance, micro-power consumption, 16-bit RISC microcontroller MSP430F2232. In addition, in order to meet the application of large data collection, two 32Kb×8 The low-power data memory FM26L256, the selected devices and wiring methods of the acquisition circuit meet the requirements of intrinsically safe design, and the circuit board is uniformly sprayed with three anti-corrosion paints after debugging. The acquisition circuit board can realize 1-3 channel adjustable seismic signals Acquisition, storage and digital signal transmission functions, through the selection of high-performance, low-power devices and circuit optimization design, low-power management, to achieve circuit intrinsically safe explosion-proof, with small size, low power consumption, high precision, dustproof, Waterproof and explosion-proof, the acquisition circuit board can be packaged in the same shell with the seismic signal sensor (detector core) to form a high-performance 24-bit digital detector, and can be separately packaged to form a high-performance three-channel acquisition station. It is suitable for seismic data acquisition at engineering sites and underground coal mines. The main technical indicators of the seismic data acquisition circuit board are as follows:

Number of channels: 3

Sampling interval: 100us～2ms increment optional

Sampling points: 512, 1024, 2048 optional

Allowable dynamic range: >110dB

Common mode rejection ratio: >100dB (G=10)

Preamplifier noise: <1.0uV

Working voltage: ±12V

Non-linearity: <0.05%

Dimensions: π×50 ² mm ²

Description of drawings

Fig. 1 Block diagram of hardware composition of seismic data acquisition circuit board

Figure 2 Design of signal conditioning circuit

Figure 3 Interface between MCU and ADS1274

Figure 4 Interface between MCU and FM25L256

Figure 5 Design process of acquisition control module

Figure 6 Design process of communication module

Figure 7 Design process of the low-power management module

Detailed ways

1 hardware design

Figure 1 is a block diagram of the hardware composition of the seismic data acquisition circuit board. In the design, the analog circuit and the digital circuit are powered separately. The analog power supply is only for the signal conditioning circuit, the analog/digital converter and the reference source circuit, and the digital power supply is for the MCU, memory, Power supply for digital circuits such as communication interface. The output signal of the seismic signal sensor is first sent to the acquisition circuit board through the signal input interface, and then sent to the analog/digital converter after filtering and amplifying. The communication interface is sent to the host, and the trigger circuit is used to realize the synchronization of the start time of acquisition and the external seismic source during distributed seismic data acquisition.

(1) Signal conditioning circuit design

The function of the signal conditioning circuit is to properly adjust and process the analog signal picked up by the sensor, so as to provide corresponding measurements for the physical characteristics. The structure and performance of the conditioning circuit depend on the electrical characteristics and output of the sensor. Based on the two factors of simplifying the structure and preventing signal distortion, the analog low-cut filter is removed in the design of the acquisition system, and only a first-stage anti-aliasing filter is added at the data input end. The filter circuit is shown in Figure 2. In the figure, +IN and -IN represent the differential input signal from the analog seismic sensor respectively. The low-pass filter composed of R, _CD and C _C is filtered and then sent to the input of the instrumentation amplifier. The capacitor _CD and C _C can be connected in parallel. Effectively reduce the AC CMR error caused by C _C mismatch at the two input terminals. When _CD is 10 times larger than C _C , the CMR error caused by C _C mismatch can be reduced by 20 times.

The A/D converter selected in this design is a high-speed, 24-bit Δ-Σ type A/D converter. Its main feature is that it has excellent AC and DC characteristics, and the sampling rate can reach up to 128KSPS. When working in high-precision mode, the signal The noise ratio (SNR) can reach 111dB, and the offset drift is 0.8μV/℃. Considering that the performance of each device that makes up the system will affect the overall performance of the acquisition system, and the input signal is a quantity that changes with the use conditions, the amplifier drive circuit in this design system is a programmable instrument with high performance indicators. amplifier.

In the seismic data acquisition system, the preamplifier circuit has the greatest influence on the whole system, and its performance is directly related to the anti-interference ability of the system to the input signal and the output sensitivity of the detector (that is, the output efficiency). Since the differential amplifier is used as the input circuit, it has the characteristics of high input impedance, strong anti-common-mode interference ability, etc., and will not cause phase distortion of the composite signal, so the single-chip integrated three-op-amp instrumentation amplifier AD8253 is selected as the pre-amplifier in the design. It has the characteristics of small size, low noise, and short settling time, so it is very suitable for the design needs of broadband and high-resolution signal acquisition. Since the amplitudes of the seismic wave signals from the three channels are somewhat different, three preamplifiers are used in the design to condition the three input signals separately to balance the amplitude of each channel. Figure 2 shows the application circuit of AD8253. In order to match with ADS1274 in the design, it adopts differential output, and at the same time shifts the potential by 2.5V to meet the level requirements of ADS1274.

(2) Design of data acquisition circuit

In the design of data acquisition circuit, the performance of analog/digital converter (abbreviated as ADC) is directly related to the quality of signal acquisition. The main performance indicators of ADC are sampling rate and sampling accuracy. The sampling rate determines the effective input signal. The frequency range, that is, the bandwidth of the input signal, and the sampling accuracy determine the dynamic range of the input signal.

The selection of ADC in the design of this acquisition circuit is mainly based on the following factors: First, the frequency band of the acquired signal: it is mainly used to acquire medium and shallow seismic wave reflection signals, and the effective signal frequency band is mostly tens of Hz to hundreds of Hz , when it is used for ground engineering exploration, the maximum can reach more than 1000Hz; the second is the sampling accuracy: the seismic wave signals excited by conventional seismic sources can range from uV level to hundreds of mV, in order to record seismic wave signals from different depths (signal strength gradually increases with depth Weakness), the dynamic range of the ADC is required to be greater than 110dB; the third is the power consumption and volume of the acquisition system: the circuit board of the acquisition system is required to be embedded in the conventional three-component analog detector shell, and it is powered by a battery, so it requires small size and low power consumption. Low. In the design of this system, 24-bit, high-speed, delta-sigma ADC is selected from the analysis of power consumption, integration, sampling rate, precision and other requirements.

In the specific model selection, by consulting the relevant new components and parts, the new 24-bit high-speed analog-to-digital converters AD7760 and AD7764 of ADI Company and the new 24-bit high-speed analog-to-digital converters ADS1271 and ADS1274 of TI Company were selected for performance analysis and comparison , by comprehensively considering the indicators of the current new ADC, it is decided to choose a single-channel, single-AD solution. In order to save space, the ADS127, which integrates four ADCs on a single chip, is selected. The interface circuit between ADS1274 and the microcontroller MCU is shown in Figure 3. Show.

In order to flexibly adjust the power consumption and precision in the design, the working mode of ADS1274 is set to adjustable mode, and the sampling frequency is set to be adjustable according to the needs of practical applications. The data output rate of ADS1274 is the same as the clock frequency CLK Related, in practical application, the output of ACLK of MCU is used as CLK, and the frequency can be set by the program; the data output adopts SPI interface, and the converted data adopts TDM mode shift output, and the FORMAT[2:0] is set to 000 in the design, The serial data output adopts the SPI interface protocol, the data collected by all channels is output through the DOUT1 pin, and the output data positions of each channel are dynamically allocated. In the figure, VREFP and VREFN are the reference power supply for A/D conversion, and the reference voltage signal of 2.5V is connected in the design.

(3) Memory and interface design

In the design of the acquisition circuit, the collected data needs to be stored in the memory, and the new ferroelectric memory FM25L256 is used in the design to store the collected data. The FM25L256 is a 256Kb low-power ferroelectric memory produced by RAMTRON (hereinafter referred to as FRAM), which not only has the fast read and write characteristics of SRAM and DRAM, but also has the non-volatile characteristics of EEPROM and Flash. The system formed has the characteristics of simple interface, less system resources, non-volatile, and no read and write delay. In the design, FM25L256 is used to realize the data acquisition buffer storage function. Figure 4 is the interface circuit between FM25L256 and MSP430F2232. In this design, the standard SPI bus is used to transmit data.

(4) Auxiliary circuit and its description

The auxiliary circuit is mainly composed of a reset circuit, a status indication circuit, a signal input interface and a serial communication interface. The reset circuit includes a power-on reset and a manual reset. The manual reset is realized by an external reset button; the status indication circuit is used to indicate the current state of the acquisition circuit. In the design, the two color changes of the two-color light-emitting diode are used as the status indication; the signal input interface is used to send the output signal of the seismic signal sensor to the input port of the acquisition circuit, and the three-channel differential signal can be sent in the design; the serial The communication interface is used for information transmission with the external host, and the RS-485 communication interface is used in the design.

2 software design

(1) Program design of acquisition control module

The software part of the seismic data acquisition circuit board mainly includes: a communication module, an acquisition control module, a low-power management module, and a drift calibration module. Store the collected data in random access memory; before data collection, firstly carry out the initialization setting of collection parameters, and then wait for the trigger signal from the start of the external seismic source. Figure 5 shows the program design process of the seismic data collection control module. During data collection, The system shields all interrupts and enters the state to be triggered. Once the acquisition trigger signal is detected, the system starts the analog/digital converter for data acquisition. The converted multi-channel data is first sent to the register of the MCU, and then written into the random access memory (FRAM) At last, according to the data transmission command given by the host, the collected data is sent to the host through the serial port.

(2) Program design of communication module

The function of the communication module is to complete the command transmission and data exchange between the host computer and the acquisition circuit board. Each communication between the host and the acquisition circuit board is initiated by the host and ends with the correct response from the acquisition circuit board (referred to as the slave). Real-time inspection is performed on each field according to the agreement when receiving, so as to improve the reliability of communication. There are two forms of commands sent by the master, one is the commands executed by each slave separately, such as handshake command, parameter setting command, which requires each slave to respond separately, at this time, the communication between the master and each slave is based on the address of the slave The other command is a broadcast command, which is a command that each slave needs to execute at the same time, such as a collection command and a background check command. At this time, all slaves perform corresponding operations at the same time after receiving the command, but only One of the slaves designated by the master sends back a reply message. In order to ensure the reliability of the communication, when the master sends a command frame to the slave, it sets the timeout detection and retransmission function (the number of retransmissions allowed is three times), and the programming flow of the communication module is shown in Figure 6.

(3) Program design of drift calibration module

Zero drift is the value by which the measured output value deviates from zero when the input signal is zero. The size of the zero drift and whether the zero is stable are one of the main sources of measurement errors. To eliminate this effect, on the one hand, amplifiers and A/D converters with low drift and high temperature stability should be selected on the hardware to make the drift as much as possible. Small; on the other hand, it takes advantage of the microprocessor and adjusts it through software. The implementation process of the drift calibration of this acquisition circuit is: firstly, set the acquisition parameters according to the parameter setting command sent by the host computer, then the microprocessor controls the multiplexer to switch to the ground input terminal, starts the back check operation, collects a set of data, and then Obtain an average value for this set of data, and store this average value in an internal RAM unit of the MCU. In subsequent data collection, subtract the collected data from the previously measured average value each time to obtain the corrected value. The data. In the subsequent acquisition process, if you need to modify the acquisition parameters, you can re-measure the drift value and store it in the original unit according to the above steps. The mathematical model of the operation is:

$\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}$

In the formula, D = drift value; I = each sample point value; n = sample point sequence number; N = total sample point number.

(4) Program design of low power consumption management module

In order to realize the low power consumption operation and management of the acquisition system, on the one hand, it is necessary to provide corresponding low power consumption control signals in the hardware design, and on the other hand, it is necessary to cooperate with the corresponding management instructions in the software. Figure 7 is the acquisition circuit system low power management process. After starting up, the system initializes and waits to receive the control command from the host. At this time, except the communication circuit should maintain normal operation to ensure that the host command can be received at any time, the rest of the circuits are in an invalid operating state. At this time, they should be put into a low-power standby state ( The analog-to-digital conversion module and the storage module are placed in the idle mode), and when the acquisition system receives the command sent by the host, the corresponding circuit module enters the normal working state. In order to prevent the communication circuit and MCU from being in a blind waiting state, a timeout detection circuit is set in the design. If the waiting time is overtime, the MCU enters the standby mode and the serial port interrupt is enabled. Only when the serial port interruption is detected, the MCU returns to the normal working state.

Claims (4)

1. 24 earthquake data acquisition circuit boards of an intrinsic safety type, constituted by hardware and software two parts, hardware components mainly comprises: power converting circuit, acquisition control circuit, signal conditioning circuit, mould/number conversion circuit and auxiliary circuit, and software section mainly comprises: communication module, acquisition control module, low-power consumption administration module and drift calibration module; Wherein power converting circuit adopts the separately mode of power supply of digital power and analog power, is made of corresponding digital power translation circuit and analog power translation circuit respectively; The acquisition control circuit part mainly is made up of the trigger circuit that microcontroller, startup are gathered; Signal conditioning circuit mainly is made up of anti-confusion filtering circuit and variable gain operational amplifier; Mould/number conversion circuit mainly is made up of reference source circuit, 24 high-performance A/D converters and data-carrier store; Auxiliary circuit mainly is made up of reset circuit, condition indication circuit, signal input interface and serial communication interface; The annexation of each several part is: signal input interface is used for inserting the output signal of outside triple channel seismic sensor, the signal that inserts directly with three independently the input end of anti-confusion filtering circuit be connected, the output terminal of filtering circuit is connected to three independently input ends of variable gain amplifier, the output signal line of amplifier is connected with three pairs of differential input ends of A/D converter respectively, the data output signal line of A/D converter is connected with the data input pin of microprocessor, the signal wire of data-carrier store is connected with the corresponding port of microcontroller respectively, serial communication interface chip one end is connected with microcontroller, the other end is connected with the interface of external transmission lines, analog power output and modulate circuit, the power input of A/D converter and reference source circuit is connected, the output of digital power and data-carrier store, microcontroller, the power input of reset circuit digital device connects; This collecting circuit board can be realized collection, storage and the digital data transmission function of the seismic signal that 1～3 passage is adjustable; The output signal of outside earthquake signal transducer is sent into the input end of anti-confusion filtering circuit by signal input interface, send into the input end of variable gain operational amplifier again through filtered signal, send into 24 high-performance A/D converters through amplified analog signal and carry out mould/number conversion, digital signal after the conversion at first deposits in the data-carrier store, is sent to external host by serial line interface then; This collecting circuit board can cooperate with main frame, form distributed earthquake data acquisition system (DAS), this collecting circuit board can and main frame between realize transmission and the data exchanging function of order, acquisition parameter, background inspection, data acquisition, data transmission can be set according to the command execution that main frame sends, be data exchange operation, wherein acquisition parameter comprises port number, sampling interval, sampling number; The acquisition channel number can be set to 3 passages, 2 passages or 1 passage by software, and it is optional that sampling interval is that 100us～2ms increases progressively, sampling number be 512,1024,2048 optional; By selecting high-performance, low energy-consumption electronic device and circuit optimization design, low-power consumption management for use, realized the circuit inbeing safe explosion prevention, have that volume is little, low in energy consumption, precision is high, dustproof, waterproof, explosion-proof characteristics, this collecting circuit board both can with the seismic signal sensor, be that detector core body is packaged in formation high-performance 24 bit digital three-component seismometers in the same housing, can encapsulate simultaneously 24 triple channel earthquake data acquisitions of formation high-performance station again separately, be applicable to the distributed earthquake data acquisition system (DAS) under engineering site and the coal mine.

2. earthquake data acquisition circuit board according to claim 1, it is characterized in that: the hardware and software that is integrated with the seismic signal collection, storage and the digital data transmission that realize that 1～3 passage is adjustable on the collecting circuit board, the device that each channel selecting is identical constitutes independently anti-confusion filtering circuit and amplifying circuit respectively, by selecting high-performance, low energy-consumption electronic device and circuit optimization design, low-power consumption management for use, realized the circuit inbeing safe explosion prevention; Wherein amplifier is selected high performance programmable instrument amplifier AD8253 for use, analog to digital converter is selected for use is 24 of the TI company high-performance of producing, 4 passages are gathered analog to digital converter ADS1274 synchronously, can realize the synchronous acquisition function of four-way at most, that the microcontroller reason device that realization collection is controlled is selected for use is super low-power consumption type microcontroller MSP430F2232, select the data of novel ferroelectric storer FM25L256 storage of collected for use, the selected device of Acquisition Circuit and wire laying mode all satisfy the design of essence safety requirement, it is little that circuit board even three times three anti-lacquers of spraying after debugging is finished, collecting circuit board have a volume, low in energy consumption, the precision height, dustproof, waterproof, explosion-proof characteristics.

3. earthquake data acquisition circuit board according to claim 1, it is characterized in that: this collecting circuit board can cooperate with main frame, form distributed earthquake data acquisition system (DAS), this collecting circuit board can and main frame between realize transmission and the data exchanging function of order, acquisition parameter, background inspection, data acquisition, data transmission can be set according to the command execution that main frame sends, be data exchange operation, wherein acquisition parameter comprises port number, sampling interval, sampling number; The acquisition channel number can be set to 3 passages, 2 passages or 1 passage by software, and sampling number is 512,1024,2048 optional, and it is optional that sampling interval is that 100us～2ms increases progressively.

4. earthquake data acquisition circuit board according to claim 1, it is characterized in that: this Acquisition Circuit plate bulk is little, and its physical dimension only is π * 50 ²Mm ²Both can with the seismic signal sensor, be that detector core body is packaged in 24 three-component digital geophones of formation high-performance in the same housing, can encapsulate separately again simultaneously and constitute 24 triple channel earthquake data acquisitions of high-performance station, leave on the collecting circuit board triple channel seismic signal input interface, with the RS-485 serial communication interface of main-machine communication, be applicable to the earthquake data acquisition under engineering site and the coal mine.

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