CN111211856B - Wired seismograph time synchronization system and method based on WR protocol - Google Patents
Wired seismograph time synchronization system and method based on WR protocol Download PDFInfo
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Abstract
The application relates to a wired seismograph time synchronization system and method based on WR protocol, the system includes seismograph, cross station and host computer, the host computer is WR master clock, receive the external clock reference source and regard it as time reference to carry on the time synchronization; the cross station is a WR switch, the host is used as a reference point for time synchronization, the seismograph is a WR node, the cross station is used as a reference time point for time synchronization, and the secondary seismograph uses the clock of the primary seismograph as a reference. The time synchronization in the WR technology comprises two layers of meanings, the synchronous Ethernet technology is utilized to finish the release of the clock source frequency, the clocks of all nodes in the network run on the same frequency, and the PTP technology and the DDMTD technology are combined to realize sub-nanosecond time synchronization. The WR clock synchronization technology is a novel distributed clock synchronization scheme provided by CERN and GSI based on synchronous Ethernet, precise timing protocol, full-digital double-mixing phase discriminator and other technologies, so as to realize high clock synchronization precision of master-slave nodes in a large range.
Description
Technical Field
The application belongs to the technical field of urban underground space detection, in particular to an anti-interference high-precision time synchronization system and method for a shallow three-dimensional seismograph, and particularly relates to a time synchronization system and method for a wired seismograph based on a WR protocol.
Background
At present, the wider synchronization technology put into seismometer application mainly comprises the following steps: GPS, NTP, IEEE1588, the technology is widely applied to the fields of national defense construction and national economy related fields such as telecom, power systems, transportation, finance and the like. Meanwhile, new synchronization technologies such AS White Rabbit abbreviated WR and SAE AS6802 protocols have also been rapidly developed. SAE AS6802 defines a high-precision and fault-tolerant synchronization technique that can establish and maintain a low-delay, low-jitter, high-precision global synchronization clock for the TTE, improving the quality of the TTE's service. The WR technology can be applied to a large-scale physical experiment device with higher precision requirements and a multi-node time synchronization system for long-time efficient continuous acquisition.
When the seismic prospecting system performs long-time efficient continuous acquisition, the problems of clock drift, communication delay and the like exist among nodes of the existing synchronous system. The data transmission of the whole system of the wired synchronous IEEE1588V2 protocol applied by the wired telemetry seismograph GEIST438 is based on 10/100M Ethernet. According to the characteristic that the system is more in moving in the actual seismic exploration construction, a relay type network topology structure is adopted, and a multi-acquisition-station synchronous data uploading strategy is provided according to the data transmission characteristic in the seismic exploration, so that the relay type network data transmission efficiency is improved. The IEEE1588V2 standard defines a precision time protocol PTPV2. However, the PTPV2 protocol has certain limitations: the frequency of the master clock and the slave clock has deviation, high synchronous precision requires synchronous messages with high frequency, and the network occupancy rate is high; the synchronization process is implemented based on calculating the difference of the time stamps of the messages, and the minimum interval of the time stamps of the messages is limited (e.g. 8ns for gigabit ethernet); the low jitter clock recovery requires that each slave has a very stable oscillator, or a high frequency synchronization message; the asymmetry of the transmission medium is not taken into account, and the transceiving links are assumed to be exactly equal.
Disclosure of Invention
The application aims to provide an anti-interference high-precision shallow three-dimensional wired seismograph time synchronization system and method based on a WR protocol, which are used for overcoming the defects of clock drift, communication delay and the like among nodes when a seismic exploration system is continuously collected for a long time with high efficiency, and avoiding the use of synchronous messages and additional communication links.
The application aims at realizing the following technical scheme:
a wired seismograph time synchronization system based on WR protocol comprises a plurality of seismographs, a plurality of cross stations and a host; the seismographs are connected through cables, the cross stations are connected through optical cables, and the seismographs connected in series on each cable line are connected with the host through the cross stations and the optical fibers;
the system comprises a plurality of seismometer acquisition stations, a plurality of data transmission stations and a plurality of data transmission stations, wherein the seismometer acquisition stations are distributed by adopting a relay Ethernet structure, each seismometer acquisition station is connected with eight high-resolution single-channel seismometers, data collected from the seismometer acquisition stations at two ends are integrated into a cross station, and the cross station transmits the data back to a host computer at a high speed through optical fibers; the host acquires connection information of the acquisition station from the cross station, starts IP forwarding of the cross station and the acquisition station, and performs data transmission based on a TCP/IP protocol;
the host is a WR master clock, receives an external clock reference source and performs time synchronization by taking the external clock reference source as a time reference; the cross station is a WR switch, and a host is used as a reference point for time synchronization; the seismograph is a shallow three-dimensional seismograph and is a WR node, a cross station is used as a reference time point for time synchronization, the secondary seismograph uses the clock of the primary seismograph as a reference, all the nodes form a clock network topological structure, and a sub-node or a sub-switch recovers the clock from a data link by using clock recovery;
the seismograph comprises an ARM embedded module, a collecting unit, an SDRAM, a MINI-WR module and an Ethernet card, wherein the seismograph can receive eight-channel data and reset and start a chip of the collecting board, the two Ethernet interfaces are used for relay transmission of instructions and data, and the MINI-WR module is used for clock synchronization and data transmission.
The MINI-WR module is integrated with an electronic device and a chip for realizing an all-digital double-mixing phase discriminator, an IEEE1588V2 protocol and regulating master-slave clock bias.
The synchronization method of the wired seismograph time synchronization system based on the WR protocol comprises the following steps:
A. establishing a global clock reference source, and externally connecting a host with the clock reference source; performing acquisition station arrangement, distributing IP addresses for each station according to a connection sequence, building a corresponding routing table, then returning own state information to a host by each station, if the state information is a tail station, setting a tail information flag bit in the state information, informing the host that the arrangement process is finished, and obtaining a logic connection relation of each station by a host end according to the IP address information;
B. the cross station is connected with the host computer through an optical fiber link, and time synchronization is carried out by taking the host computer as a reference point, so that a network node can recover a clock with uniform frequency from an Ethernet physical link, and the clock has long-term stability of +/-10 PPT;
C. the clocks of the shallow three-dimensional seismometers are compared by taking the clocks of the cross stations as reference sources, and the clocks of the shallow three-dimensional seismometers are recovered from the data links by using a clock recovery technology; the secondary seismograph adjusts by taking the clock of the superior seismograph as a reference source, and circularly operates until reaching the tail station;
D. clocks are recovered from the data links by shallow three-dimensional seismometers and cross-stations using clock recovery techniques so that the clock frequencies of all nodes of the entire network are precisely synchronized with the master node clock frequency (±10ppt long-term accuracy).
Further, in the step A, the reference source is a GPS or an atomic clock.
Compared with the prior art, the application has the beneficial effects that:
according to the wired seismograph time synchronization method based on the WR protocol, the clock system can distribute clocks within a range of 10km by utilizing the WR protocol, and meanwhile, the clock synchronization precision of hundreds of picoseconds can be still achieved; the method is established on the synchronous Ethernet, and the Ethernet is a quite mature mainstream data transmission technology, and a plurality of network equipment interfaces can be used commonly, so that the method has good expandability; the combination of the synchronous Ethernet and the PTP protocol enables the master node and the slave node to acquire clocks with consistent frequency, so that the requirement of the PTP protocol on high-frequency synchronous messages is greatly reduced; the full-digital double-mixing phase discriminator is provided, the time stamp precision of PTP is improved to the picosecond level, in addition, the White Rabbit establishes an accurate network link delay model, and the asymmetry of a master-slave back-and-forth link is accurately calculated; the combination of various technologies ensures that White Rabbit realizes sub-nanosecond synchronization precision, can realize the transmission rate of kilomega bandwidth, and meets the requirements of time synchronization precision and transmission rate of a large-scale distributed seismograph.
Drawings
Fig. 1 PTPv2 synchronous message exchange process;
fig. 2 WR is a comparison of a conventional ethernet with a time synchronized ethernet;
fig. 3 is a schematic diagram of the operation of an all-digital double mixing phase detector;
FIG. 4 White Rabbit synchronous link and partial clock relationships;
FIG. 5 slave node clock bias adjustment process;
FIG. 6 White Rabbit synchronous network topology;
FIG. 7 is a six-time network synchronization accuracy comparison of a single seismograph acquisition node;
FIG. 8 is a plot of synchronization time accuracy versus the number of seismograph acquisition nodes;
FIG. 9 distributed seismograph time synchronization system
FIG. 10 is a block diagram of a control panel of a seismometer system
Detailed Description
The application is further illustrated by the following examples:
as shown in FIG. 9, the wired seismograph time synchronization system based on White Rabbit protocol of the application is composed of a shallow three-dimensional seismograph, a cross station, a power supply, an electric cable, an optical cable and a host computer. Fig. 6 is a White Rabbit synchronous network topology. The shallow three-dimensional seismometers are connected through cables; the seismographs connected in series on each cable line are connected with the host computer through the cross station and the optical fiber; the plurality of cross stations are connected through optical cables. The host is a WR master clock, receives an external clock reference source and performs time synchronization by taking the external clock reference source as a time reference; the cross station is a WR switch, and takes a host as a reference point to perform time synchronization; the shallow three-dimensional seismograph is a WR node, time synchronization is carried out by taking a cross station as a reference time point, and the clock of the secondary shallow three-dimensional seismograph above the primary seismograph is taken as a reference; all nodes form a clock network topology, and the sub-nodes or sub-switches recover clocks from the data links using clock recovery.
The seismograph adopts relay Ethernet structure distribution, carries out data transmission by carrying out route arrangement on dynamic IP, each seismograph has eight-channel data acquisition capacity, is connected with eight high-resolution single-channel seismometers, data collected from the seismograph at two ends are integrated into a cross station, and the cross station transmits data back to a host computer at a high speed through optical fibers due to poor reliability of cable transmission of a large amount of data. Generally, in field engineering operation, a UDP protocol is adopted to perform interaction of control commands, and an FTP protocol is adopted to acquire collected seismic data from a collection station. The host firstly establishes and arranges with the cross stations, the host distributes IP addresses for each cross station according to the sequence, establishes a corresponding routing table, can know the position of the seismograph after the routing table is established, and can rapidly maintain or replace the power supply after the seismograph fails or the power supply is not powered. The biggest innovation point of the application is that by utilizing WR technology and through the cooperation of each module, the time synchronization precision of the system is greatly improved compared with the use of IEEE1588V2 protocol.
The seismograph consists of an ARM embedded module, an acquisition unit, SDRAM, a MINI-WR module, an Ethernet card and the like. The seismometer system control board structure diagram is shown in figure 10. The system uses an ARM core controller STM32F429VG as a core processor, 256M SDRAM is used for a system memory, MAX-10 is used for expanding an interface of the STM32F429VG to receive eight-channel data and controlling the reset, the starting and the like of a chip of an acquisition board, two Ethernet interfaces are used for relay transmission of instructions and data, and a MINI-WR module is used for clock synchronization and data transmission.
The MINI-WR module is a key module for realizing the WR protocol, and an electronic device and a chip for realizing the full-digital double-mixing phase discriminator, the IEEE1588V2 protocol and regulating master-slave clock deviation are integrated in the MINI-WR module.
The time synchronization in the WR technology comprises two layers of meanings, namely, the synchronous Ethernet technology is utilized to finish the release of the clock source frequency, so that clocks of all nodes in the network run on the same frequency, and the PTP technology and the DDMTD technology are combined to realize sub-nanosecond time synchronization.
The White Rabbi clock synchronization technology is a novel distributed clock synchronization scheme provided by CERN and GSI based on synchronous Ethernet, precision timing protocol (IEEE 1588V 2), full digital double mixing phase discriminator and other technologies, so as to realize high clock synchronization precision of master-slave nodes in a large range.
The synchronization mechanism of the IEEE1588V2 precision clock protocol PTPV2 is specifically as follows:
unlike dedicated clock synchronization systems, the PTPv2 timing link is multiplexed with the data link of the system, avoiding the overhead of adding additional communication links for the timing function. PTPv2 defines a clock synchronization network of master-slave structure, i.e. the local clocks of all slave nodes need to be synchronized with the master node clock to which they refer. This point-to-point clock synchronization is achieved by exchanging time-stamped network packets, as shown in fig. 1:
(1) At the time t1, the master node sends a Sync message to the slave node, and the slave node receives the Sync message at the time t2;
(2) The master node embeds a time stamp t1 into a Follow_Up message and sends the Follow_Up message to the slave node;
(3) The slave node sends a delay_req message to the slave node, and records the sending time t3;
(4) The master node records the time t4 when the delay_req message is received, embeds the delay_req message in the delay_resp message, and then sends the delay_req message to the slave node.
And after the slave node calculates the deviation of the link transmission delay and the master-slave clock according to the four time stamps, the slave node correspondingly compensates the local clock. If the master-slave round-trip links are completely symmetrical, the transmission delay from the master node to the slave node is:
the deviation of the master clock and the slave clock is as follows:
the applicability of synchronous ethernet is as follows:
the synchronous ethernet technology plays a role in WR technology in publishing the frequency of the clock source to the entire WR network. The use of sophisticated synchronous ethernet technology to transmit clock and data over low cost cables or optical fibers is a big feature of WR technology. Unlike conventional Ethernet, the clock of each node in synchronous Ethernet is the clock of the main endpoint recovered after the jitter is eliminated by the PLL inside the node, and the node clock in the network has + -10 -11 Long-term stability of (c). The WR technology has the advantage that it builds on synchronous ethernet, which is a well established mainstream data transmission technology, and many network device interfaces are universal and therefore have good scalability. Fig. 2 illustrates the difference between the conventional ethernet and the synchronous ethernet.
The full-digital double-frequency phase discriminator has the following functions:
the White Rabbit adopts an all-digital double-mixing phase discriminator, and the working principle is shown in figure 3: an auxiliary clock signal is generated with an external phase-locked loop, the frequency of which differs slightly from the frequency of the signals under test (clkA and clkB) (fpll=n/(n+1) fclk). The clkA and clkB are sampled separately inside the FPGA using the auxiliary clock signal. Since the sampling frequency is very close to the frequency of the signal under test, the D flip-flop will output a very low frequency signal. The phase difference of the measured signal is amplified after mixing, so the phase difference of the original signal can be calculated by measuring the phase difference of the output signal of the trigger:
wherein phase is DMTD Is the phase difference of the mixed signal. From the above equation, the time resolution of the measured phase difference is improved by n+1 times. In White Rabbit, N is 16384, phase DMTD Is measured by a 125MHz clock driven counter, so the DDMTD time resolution is 0.5ps (8 ns/16384). As jitter exists between the detected signal and the sampling signal, and the probability of metastable state in the sampling process is increased when the N Value is larger, burrs exist on the edge of the output signal of the D trigger, and the White Rabbit finds the optimal clock edge by adopting the Bit Value media algorithm.
The synchronization method of the wired seismograph time synchronization system based on the White Rabbit protocol comprises the following steps:
a global clock reference source is established and the host is externally connected with clock reference sources, such as GPS and atomic clocks. And (3) establishing the acquisition station, distributing IP addresses for each station according to the connection sequence, establishing a corresponding routing table, returning the state information of each station to the host, if the station is the tail station, setting a tail information flag bit in the state information, informing the host that the establishment and arrangement process is finished, and obtaining the logic connection relation of each station by the host end according to the IP address information.
The cross station is connected with the host computer through an optical fiber link, and the cross station uses the host computer as a reference point for time synchronization, so that the network node can recover a clock with uniform frequency from the Ethernet physical link, and the clock has long-term stability of +/-10 PPT. The clocks of the shallow three-dimensional seismometers are compared by taking the clocks of the cross stations as reference sources, and the clocks of the shallow three-dimensional seismometers are recovered from the data links by using a clock recovery technology. The secondary seismograph is adjusted by taking the clock of the superior seismograph as a reference source, and the secondary seismograph is circularly operated until the tail station.
Clocks are recovered from the data links by shallow three-dimensional seismometers and cross-stations using clock recovery techniques so that the clock frequencies of all nodes of the entire network are precisely synchronized with the master node clock frequency (±10ppt long-term accuracy).
The synchronous link of White Rabbit master-slave node is shown in fig. 1, and the total delay of the round-trip link is composed of three parts, specifically:
hardware delay (delta) of master-slave node transceiver circuit TXM ，Δ RXM ，Δ TXS ，Δ RXS ) The method comprises the steps of determining the delay of internal logic of the FPGA, the delay of internal wiring of the FPGA, the delay of PCB wiring, the delay of a high-speed serial transceiver and the delay of an optical fiber transceiver, wherein the delay can be considered to be relatively fixed;
bit sliding delay (epsilon) M ，ε S ) The Bit sliding caused by the serial-parallel conversion circuit when the word alignment operation is carried out is caused, the delay remains unchanged after the connection of the optical fiber link is established, and the delay can be automatically acquired through a Bit Slide state machine after each link is established;
fiber link propagation delay (delta) MS ，δ SM ) This part of the delay is very sensitive to temperature fluctuations, requiring real-time calibration and compensation.
The total latency of the White Rabbit round-trip link can be expressed as:
dealy MM ＝δ MS +δ SM +Δ+ε M +ε S
where Δ=Δ TXM +Δ RXS +Δ TXS +Δ RXM
White Rabbit scales the link transmission delay variation in real time using the packet switching mechanism of PTPv2, the relationship of the partial clocks in the process is shown in FIG. 4. The master node encodes data by a reference clock (1) and transmits the data to the slave node, and records a transmission time stamp t1; after the slave node recovers the clock (2) from the data stream, phase locking (frequency synchronization) of the local clock (3) and the recovered clock is completed by using a phase-locked loop technology, and a receiving time stamp t2 is recorded; the slave node uses the local clock (3 codes the data and sends to the master node, records the sending time stamp t3; the master node recovers the clock (4) from the data stream, records the receiving time stamp t 4).
The time stamps t1, t4, t2 and t3 are respectively from a timer driven by the local clocks of the master node and the slave node, the clock frequency is 125MHz, and the time stamp resolution is 8ns.
The arrival time of the received packet is synchronous with the clock recovered from the received data stream, but asynchronous with respect to the local clock of the receiver, and therefore requires correction of the reception time stamps t2 and t4, with the t2 correction value being phase S The t4 correction value is phase M ,phase M And phase S And respectively recovering phase differences of clocks and local clocks for data of the master node and the slave node. Thanks to the physical layer clock distribution technique, the receiving clock and the local clock have the same frequency, so phase M And phase S The measurement of (2) can be completed by phase detectors at the two ends of the master and slave, and the accuracy is far better than that of the time interval measurement technology.
The corrected time is:
t 2p ＝t 2 -phase S
t 4p ＝t 4 -phase M
the total round trip link delay is:
dealy MM ＝dealy MS +dealy SM ＝t 4p -t 3 +t 2p -t 1
the delay of the round-trip optical fiber link is as follows:
δ MS +δ SM ＝dealy MM -(ε M +ε S +Δ)
in order to accurately calculate the one-way delay of the optical fiber link, the asymmetry of the optical fiber link needs to be considered. The White Rabbit uses a single-mode fiber to connect the master node and the slave node, adopts the wavelength division multiplexing technology to realize full duplex communication, the wavelength of light emitted by the master node is 1490nm, and the wavelength of light emitted by the slave node is 1310nm. The use of wavelength division multiplexing can save cost, but more importantly, the round-trip link length in a single fiber is completely consistent, and the delay asymmetry is completely determined by the refractive index of light with different wavelengths in the fiber.
White Rabbit defines the fiber asymmetry coefficient α, expressed as:
n 1490 and n 1310 For the refractive indexes of the optical fibers with two wavelengths, the alpha value calculated by the formula is inaccurate due to slight difference of the refractive indexes of the optical fibers produced by different factories, and the asymmetric coefficients of the optical fibers need to be calibrated in advance in a laboratory. The asymmetry of the optical fiber can calculate the unidirectional total delay of the master-slave link as follows:
dealy MS ＝δ MS +Δ TXM +Δ RXS +ε S
＝(1+α)(dealy MM -(ε M +ε S +Δ))/(2+α)+Δ TXM +Δ RXS +ε S
the deviation of the master clock and the slave clock can be known by combining the formula:
offset MS ＝t 1 -t 2p +(1+α)(dealy MM -(ε M +ε S +Δ))/(2+α)+Δ TXM +Δ RXS +ε S
the adjustment of the slave node clock bias can be divided into three steps as shown in fig. 5.
TAI time correction: offset (offset) MS The deviation of the whole second is completed by correcting the international atomic time timer;
corr TAI ＝[offset MS /1s]
clock cycle counter correction: adjusting a counter to compensate for deviation of an integer multiple period (8 ns);
corr cnt ＝[(offset MS -corr TAI )/8ns]
and (3) phase adjustment: deviations of less than one period are phase adjusted by the phase locked loop of the slave node.
corr phase ＝offset MS -[offset MS ]
Thus, sub-nanosecond synchronization of master clock and slave clock is completed, and offset is realized due to the influence of environmental factors such as temperature MS Changes over time and therefore it is necessary to periodically measure the change in time offset of the master and slave nodes and compensate for this to the current phase.
corr phase ＝offset MS -offset MS_previous
After a seismometer node (WR node) is opened, the seismometer node picks up and collects seismic signals through eight single-component detectors, collected data is transmitted back to a host computer at high speed through a plurality of cascaded cross stations, wired multi-jump can be carried out in the plurality of cross stations, the problem that a common serial wired seismometer fails in data transmission due to line breakage is avoided, and the efficiency of field construction is greatly improved.
And finally, collecting the data to a host, namely a data supervision center. The system consists of an infrastructure layer, an information resource layer, an application supporting layer, an application layer and a supporting system, wherein the infrastructure layer can support the bottom layer of the whole system and comprises a machine room, a host, a storage, a network communication environment, various hardware and system software; the information resource layer comprises all data and databases of the data center, is responsible for storing and planning data information of the whole data center, covers the planning of the information resource layer and the definition of a data flow, and provides a unified data exchange platform for the data center; the application supporting layer builds various components required by the application layer, is proposed and designed based on the modular design thought and the reuse requirement, and also comprises purchased third party components; the application layer is an application system custom developed and developed for a data center and comprises an earthquake acquisition node call, earthquake data real-time processing, a data service application and a network management operation and maintenance application; the support system comprises a standard specification system, an operation and maintenance management system, a safety guarantee system and a disaster recovery backup system. The safety guarantee system focuses on the three-dimensional safety protection of the data center, and the disaster recovery backup system focuses on the data and disaster recovery of the data center. The data center supervision system can work uninterruptedly under the UPS provided on site, so that the normal operation of system equipment when the mains supply is powered off is ensured, and the system paralysis caused by the power off is avoided; the dual-computer redundancy design mechanism is adopted, two servers with the same configuration are erected in the site center, and when the main server fails, the backup server can automatically take over all the work of the main server without interruption; the system also adopts an advanced multithreading polling technology, automatically distributes threads according to the number of monitored devices, realizes load balancing, and adopts a real-time database technology, so that data returned by the station nodes can be processed and collected in real time.
Compared with the IEEE1588V2 protocol, the WR protocol has high bandwidth and ultra-high time synchronization precision, avoids the use of synchronous messages and additional communication links, and effectively solves the problems of clock drift, communication delay and the like among nodes caused by long-time efficient continuous acquisition of a seismic exploration system. Different simulation scenes are adopted on the basis of comparing the WR protocol with the IEEE1588V2 protocol. And respectively carrying out comparison analysis on one seismic acquisition node and a plurality of seismic acquisitions to compare the performance of the improved protocol.
And (3) establishing a test environment of IEEE1588V2 through GEI438, and operating an upper computer program to realize system arrangement after the seismometer system is powered on. In order to realize bidirectional data transmission between all seismographs in the survey network and a host, a routing table of an experimental seismograph is manually added through a terminal in an experiment. After the network of the seismograph is established successfully, the network synchronous test of the seismograph can be realized.
The seismometer is connected with the WR switch through the 2m optical fiber, and the WR switch is connected with the host by the 2m optical fiber synchronously. Cascading White Rabbit switches can reduce synchronization accuracy.
For the first experiment, the host measured the WR node by connecting the WR switch. The host computer measures time accuracy by connecting two seismometers in series. The specific results are shown in FIG. 7.
In the second experiment, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 seismometer nodes are respectively connected for comparison and analysis.
By comparing simulation experiment results, the WR protocol can be obtained, compared with the IEEE1588V2 protocol, the synchronization precision of the wired network is greatly improved, and the problem that the time synchronization precision is greatly reduced due to clock drift and communication delay among nodes caused by long-time efficient continuous acquisition of a seismic exploration system is solved.
The application has the following advantages:
1. the application of WR technology to shallow three-dimensional seismometers has the great advantage of long distance (< 10 km), multiple nodes (> 1000) and high accuracy (< 1 ns).
2. The White Rabbit adopts a synchronous Ethernet technology to realize the frequency distribution of a multi-seismometer, utilizes an IEEE1588v2 precise timing protocol to realize the time synchronization, and utilizes a full-digital double-mixing phase discriminator to further improve the synchronization precision to subnanosecond level.
3. In synchronous Ethernet, all nodes form a clock network topology, and the sub-nodes or sub-switches recover the clock from the data link using clock recovery techniques so that the clock frequencies of all nodes of the entire network are exactly synchronized to the master node clock frequency (long-term accuracy of 10 ppt)
4. In IEEE1588V2, the timing link of PTPv2 is multiplexed with the data link of the system, avoiding the overhead of adding additional communication links for the timing function. PTPv2 defines a clock synchronization network of master-slave structure, i.e. the local clocks of all slave nodes need to be synchronized with the master node clock to which they refer. .
5. The accuracy is limited due to the inherent limitations of the PTPV2 technology in gigabit Ethernet, i.e., the minimum interval of message timestamps of 8ns. The WR technology introduces an all-digital double-mixing phase discrimination technology, so that the synchronization precision is improved to the picosecond level. The full-digital double-mixing phase discrimination module can linearly amplify the clock phase difference of the master end and the slave end, so that the measurement precision is improved.
Claims (3)
1. A wired seismograph time synchronization system based on WR protocol is characterized in that: comprises a plurality of seismometers, a plurality of cross stations and a host; the seismometers are connected through cables, the cross stations are connected through optical cables, and the seismometers connected in series on each cable line are connected with the host through the cross stations and the optical fibers;
the seismograph acquisition stations are distributed by adopting a relay Ethernet structure, data transmission is carried out through dynamic IP routing, each seismograph acquisition station is connected with eight high-resolution single-channel seismometers, data collected from the seismograph acquisition stations at two ends are integrated into a cross station, and the cross station transmits the data back to a host computer at a high speed through optical fibers; the host acquires connection information of the acquisition station from the cross station, starts IP forwarding of the cross station and the acquisition station, and performs data transmission based on a TCP/IP protocol;
the host is a WR master clock, receives an external clock reference source and performs time synchronization by taking the external clock reference source as a time reference; the cross station is a WR switch, and a host is used as a reference point for time synchronization; the seismograph is a WR node, time synchronization is carried out by taking a cross station as a reference time point, the secondary seismograph takes the clock of the primary seismograph as a reference, all the nodes form a clock network topological structure, and the sub-nodes or sub-switches recover the clock from the data link by using clock recovery;
the seismograph comprises an ARM embedded module, a collecting unit, an SDRAM, a MINI-WR module and an Ethernet card, wherein the MINI-WR module can receive eight-channel data and reset and start a chip of the collecting board, the two Ethernet interfaces are used for relay transmission of instructions and data, and the MINI-WR module is used for clock synchronization and data transmission; the MINI-WR module is integrated with an all-digital double-mixing phase discriminator, an IEEE1588V2 protocol, and an electronic device and a chip for regulating master-slave clock deviation;
the seismograph is a shallow three-dimensional seismograph.
2. The synchronization method of a wired seismometer time synchronization system based on WR protocol according to claim 1, characterized by comprising the steps of:
A. establishing a global clock reference source, and externally connecting a host with the clock reference source; performing acquisition station arrangement, distributing IP addresses for each station according to a connection sequence, building a corresponding routing table, then returning own state information to a host by each station, if the state information is a tail station, setting a tail information flag bit in the state information, informing the host that the arrangement process is finished, and obtaining a logic connection relation of each station by a host end according to the IP address information;
B. the cross station is connected with the host computer through an optical fiber link, and time synchronization is carried out by taking the host computer as a reference point, so that a network node can recover a clock with uniform frequency from an Ethernet physical link, and the clock has long-term stability of +/-10 PPT;
C. comparing clocks of the seismographs by taking clocks of the cross stations as reference sources, and recovering the clocks from the data link by the seismographs by using a clock recovery technology; the secondary seismograph adjusts by taking the clock of the superior seismograph as a reference source, and circularly operates until reaching the tail station;
D. clock recovery techniques are used to recover the clock from the data links by the seismometers and cross-over stations so that the clock frequency of all nodes of the entire network are precisely synchronized with the master node clock frequency.
3. The synchronization method of the wired seismograph time synchronization system based on the WR protocol as claimed in claim 2, wherein: and step A, the reference source is a GPS or atomic clock.
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| CN113098650B (en) * | 2021-03-29 | 2023-07-25 | 大连市共进科技有限公司 | Time deviation measuring method, apparatus, communication device and readable storage medium |
| CN114205045B (en) * | 2021-11-16 | 2023-10-03 | 西安云维智联科技有限公司 | TTE network clock calibration method and system |
| CN114124342B (en) * | 2021-11-25 | 2024-07-30 | 广东大普通信技术股份有限公司 | Clock frequency maintaining system |
| CN115426068B (en) * | 2022-09-20 | 2023-10-27 | 北京智芯微电子科技有限公司 | TSN clock synchronization system and method, computer storage medium and chip |
| CN115903436B (en) * | 2022-10-14 | 2024-06-25 | 鹏城实验室 | Time calibration method for submarine seismograph array system and related device |
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