CN108768605B - Online synchronization method for detecting magnetic flux leakage and inertial navigation subsystem data in pipeline - Google Patents
Online synchronization method for detecting magnetic flux leakage and inertial navigation subsystem data in pipeline Download PDFInfo
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Abstract
The invention discloses an online synchronization method for detecting magnetic flux leakage and inertial navigation subsystem data in a pipeline based on PIG magnetic flux leakage and inertial navigation subsystem output data in real time, which comprises the following steps that firstly, a PIG main control computer collects inertial navigation data in real time; step two, the PIG main control computer collects magnetic flux leakage data in real time; and step three, synchronizing online real-time magnetic flux leakage and inertial navigation data. The synchronization method of the invention makes full use of the characteristic that the delay of the online communication system is far less than the requirement of synchronization precision, and directly uses the real-time data fusion of online data to solve the problem of time synchronization. Compared with an offline processing method using all mileage data as a synchronization reference, the method can greatly improve the synchronization precision and effectively solve the problem of synchronization failure caused by failure of the odometer or later-stage mileage data correction in the PIG motion process.
Description
Technical Field
The invention relates to the field of pipeline detection, in particular to a method for synchronizing output data of an internal subsystem of a pipeline internal detection device (PIG), and specifically relates to a magnetic flux leakage subsystem and an inertial navigation subsystem in the pipeline internal detection device.
Background
1. In-pipeline inspection
The pipeline internal detection device (PIG) can measure the defect or deformation of the pipeline in the motion process of the pipeline. The PIG may carry multiple detection subsystems, typically depending on the current task needs. Because each detection subsystem needs to be flexibly combined according to different tasks, each subsystem generally has independent data acquisition and storage capacity. Because the magnetic leakage device occupies a relatively large PIG space, the magnetic leakage device and the inertial navigation device cannot be installed in a cavity of the PIG, cannot be viewed as a whole in space, and cannot share one mileage datum.
Synchronization problem between PIG internal subsystems
When multiple detection subsystems need to be used together, the synchronous relation among data is very important. For example, when two subsystems of magnetic flux leakage detection and inertial navigation positioning detection are mounted on the same PIG platform and online detection is performed simultaneously, theoretically, downloaded data should be highly synchronous, that is, when the detection work is finished, objects of inertial navigation positioning and magnetic flux leakage detection must keep the same scale in time and space according to the detected data. The problem of the space scale is easy to solve, the relative positions of the inertial navigation system and the magnetic leakage system are fixed, and the relative positions of an object measured by the inertial navigation system and an object measured by the magnetic leakage system are also fixed at the same time.
For example, when the magnetic flux leakage system and the inertial navigation system are respectively installed in two cabin bodies, and the magnetic flux leakage system is in front, the distance between the measurement centers of the two systems is 3 meters, and if a certain pipe wall defect is detected by the magnetic flux leakage detector, the inertial navigation positioning device should give a corresponding geographic coordinate at the position 3 meters behind the defect along the pipeline at the same time.
However, the detection principle of the sensor is different, the electrical structures of the corresponding detection devices are also different, and the sampling rate, the signal format, the system clock and even the format of the output data are completely different. Therefore, it is difficult to determine the one-to-one correspondence relationship of the output data of the inertial navigation subsystem and the magnetic flux leakage subsystem in time.
This requires synchronizing the data output by the two subsystems. The essence is to ensure that the two batches of output data use the same time scale on their respective time axes.
3. Limitations of existing synchronization methods
A previous approach to this problem is a method of directly using mileage data as a synchronization reference. This is an off-line data processing method.
After the detection is finished, the data of each subsystem (such as the odometer, the magnetic leakage and the inertial navigation) are respectively downloaded, and the same path of odometer signals are respectively introduced into different detection subsystems to be used as a column of an output data matrix. The output data matrix means that each row of data comprises a plurality of data items (one of which is mileage), and is called a sampling point; all data of sampling points are from sampling of the detection subsystem at the same moment; by introducing parameters such as the sampling frequency and the signal format of the subsystem, the sampling time of the row sampling point under the subsystem clock can be calculated. Since each sampling point contains a mileage data item, the mileage data can be taken as the horizontal axis of coordinates when outputting the data. When different detection subsystems use common mileage data as a horizontal axis of a coordinate system, synchronization of output data of different subsystems is achieved.
The disadvantages of using the mileage data directly as the synchronization reference signal are as follows:
1) the error is large. The odometer itself has a large error, typically a measurement error of one percent of the measurement length, that is, an error of up to one kilometer in a pipe test of hundreds of kilometers is possible. And because the magnetic leakage and inertial navigation systems are arranged in the two capsule bodies, one space cannot be shared, and one mileage data cannot be shared, so that the mileage data and the data of the magnetic leakage and the inertial navigation cannot be accurately matched. The mileage data is only the 'reference' of the space positions of the magnetic flux leakage and inertial navigation data, and a rough data corresponding relation can be obtained only by researching the relative position relation of the three data installed on the PIG carrier, and a certain error can be brought in the process. Therefore, when offline processing is performed, the accuracy of synchronization is seriously affected by using mileage data of hundreds of kilometers as a synchronization basis.
2) Are prone to failure. The odometer operates outside the protective housing of the PIG, with a higher probability of data failure relative to other detection subsystems. Inside the oil and gas pipeline, the working environment is very bad, and the mechanical and electrical structure failure rate of the odometer is very high. Even if the odometer keeps mechanical and electrical structures without deformation and damage in a severe environment of about one hundred hours, serious problems of slippage, blockage, failure of electrical parts and the like of the odometer can be caused by high-viscosity crude oil, highly corrosive natural gas, defects of the inner wall of a pipeline and the like. Once the mileage data is partially or completely invalid, all offline synchronization operations cannot be performed.
3) The mileage correction causes the relevant synchronous data to be corrected again. After the measurement, the accuracy of the mileage data also needs to be corrected, for example, compensation calculation for the slippage of the odometer, or the like. However, the mileage data is used as synchronization reference data, and once the mileage data is corrected, the detection data of all the related subsystems are also corrected in synchronization. That is, before the synchronization operation of the two subsystems, in order to ensure that the output data inside the two subsystems and the current mileage output data are "bound" together, an "internal synchronization" operation must be performed inside the subsystem output data, and the "internal synchronization" operation of the subsystem may be performed multiple times. This significantly increases the complexity of the system data processing and reduces the system reliability.
Disclosure of Invention
Object of the Invention
The invention aims to solve the problems of a magnetic flux leakage and inertial navigation subsystem mileage synchronization method in a PIG device, and output data of an inertial navigation system is passed through by utilizing the characteristic of high time management precision of the inertial navigation systemUSB2.0 portOutput to the main control computer of the PIG system in real time, and passHigh-speed data acquisition cardThe obtained real-time output data of the magnetic flux leakage system directly carries out online data synchronization, thereby realizing higher data synchronization precision.
Technical scheme
The method comprises the steps that a PIG runs in a pipeline, and the magnetic flux leakage and inertial navigation detection subsystems simultaneously execute an online measurement task; the two subsystems are respectively arranged in the two bins and cannot share one group of mileage data; the detection data of the inertial navigation system and the magnetic leakage system are respectively input into a main control computer of the PIG through a high-speed port in real time, and online real-time data synchronous processing is carried out in the main control computer, and the method is characterized in that: the method comprises the following steps:
step one, a PIG main control computer collects inertial navigation data in real time;
extracting an inertial navigation data frame structure currently sent by an inertial navigation subsystem by a main control computer; including at least the following data items: SINS _ time (sampling time of current data, which is coding of physical time), WX, WY, WZ (three-dimensional angular velocity), AX, AY, AZ (three-dimensional acceleration), Od1, Od2, Od3 (three-way mileage), T1, T2(IMU internal temperature), etc., all data do not exceed 1 kbyte;
all inertial navigation data of sampling points at SINS _ time are defined as
SINS_od_output(SINS_time)＝{SINS_time，WX，WY，WZ，AX，AY，AZ，Od1、Od2、Od3，T1，T2}
At any moment, the sampling time of the inertial navigation data sampling point which is received by the main control computer most recently is defined as SINS _ time _ on, and the time of the last sampling point is defined as SINS _ time _ before;
the USB2.0 port sends a data packet to the main control computer every 1 millisecond, and each data packet encapsulates effective data with at least 256K bytes; the sampling frequency F _ IMU of the IMU is far less than 1KHz, so that the communication delay caused by the USB2.0 port does not exceed 1 millisecond, and the requirement on the data synchronization precision (0.1 second) of the detection engineering in the pipeline can be ignored; therefore, when the host computer obtains a frame of data from the USB port, the frame of data at most includes a current time data from the inertial navigation system, i.e. SINS _ od _ output (SINS _ time _ on);
step two, the PIG main control computer collects magnetic flux leakage data in real time;
the magnetic leakage data consists of N sensor data channels, the sampling frequency of a high-speed data acquisition card of the main control computer is defined as M, the N sensor channels share the high-speed data acquisition card in a time-sharing manner, and F _ LC is defined as the sampling frequency of the magnetic leakage subsystem, so that the magnetic leakage data has the frequency of M
Obviously, the current ith (0)I is less than or equal to N) output data of the data channel of the magnetic flux leakage sensor is defined as LCi(ii) a The sampling frequency is F _ LC; a data set (defined as LC _ output) acquired by one-time circulation of sensor channels with subscripts of 0 to N-1 is regarded as a sampling point, and a sampling point time LC _ time is shared, wherein LC _ output is described as
LC_output(LC_time)＝{LC_time，fresh，LC0，LC1，…，LCN-1}
The LC _ time is sampling time of current data output by the magnetic leakage system, is a code of physical time, an initial value of the LC _ time is provided by the magnetic leakage system, does not consider the precision problem of the physical time, and is only used for sequencing LC _ output data; the fresh is a 'time updated' mark, the initial value is 0, if the fresh is made to be 1, the LC _ time is indicated to be refreshed, and the current LC _ output (LC _ time) data record has completed the synchronization operation;
the PIG system is designed and is easy to realize
F_LC≥1KHz
The sampling frequency of the magnetic leakage system is usually far more than 1KHz, namely the period of the LC _ output data output by the magnetic leakage system is far less than that of the inertial navigation system; after the system is powered on, all LC _ output (LC _ time) data form a matrix table according to the sequence of LC _ time, and the matrix table is defined as LC _ output _ list
LC_output_list＝{LC_output(LC_time_j)∣j＝0,1,...,N-1}
Step three, synchronizing online real-time magnetic flux leakage and inertial navigation data;
the data synchronization algorithm is as follows:
1) after the whole PIG system is electrified and works, the magnetic leakage system is ensured to generate LC _ output _ list at first, namely, at least one LC _ output (LC _ time) is ensured to be contained in the LC _ output _ list; the method comprises the following steps:
the method comprises the steps that a power supply management subsystem of the PIG delays to be powered on to an inertial navigation subsystem, and the power supply management subsystem is powered on to the inertial navigation subsystem after the magnetic flux leakage subsystem completes the actions of being powered on, starting, self-checking and the like;
or in the second method, after receiving the first LC _ output (LC _ time) data, downloading and processing the data sent by the inertial navigation subsystem through the USB port;
2) monitoring a USB port by a USB _ IMUdata _ reader program, and receiving current inertial navigation data SINS _ od _ output (SINS _ time _ on);
3) let the last LC _ output (LC _ time) in the current LC _ output _ list be recorded
LC_time＝SINS_time_on
And order
fresh＝1
Marking this leakage data record as "time updated";
4) j LC _ outputs of all the fresh ═ 0 are extracted from the current LC _ output _ list, and with LC _ outputs (SINS _ time _ on) and LC _ outputs (SINS _ time _ before), in the order in which these leakage magnetic data are generated, a sequence set unfresh _ LC _ list of the form:
unfresh_LC_list＝{LC_output(SINS_time_before),LC_output(LC_time_1),LC_output(LC_time_2),...,LC_output(LC_time_j),LC_output(SINS_time_on)∣j＝0,1,...}
j is a positive integer greater than 0, and represents the number of magnetic flux leakage data records between two consecutive inertial navigation data without updating the time of the sampling point
j is small in value and stable, and when the time complexity of the algorithm is calculated later, j is treated as a constant;
5) updating LC _ time _ k and fresh _ k, k being 0,1, and j of LC _ output records with all fresh being 0 in the unfresh _ LC _ list by interpolation, wherein the updated interpolation algorithm for all positive integers k with the value equal to 0 and less than or equal to j is as follows:
then all LC _ time _ k are correlated
fresh_k＝1,k＝0,1,...,j
Finally order
SINS_time_before＝SINS_time_on
The synchronous operation of the inertial navigation magnetic flux leakage data is completed;
6) at this time, LC _ time data items of all the magnetic leakage data LC _ output received by the current main control computer are updated, and are synchronized with all the received SINS _ od _ output data in time; jump to 2), continue the loop of 2) through 6) until all PIG subsystems are powered down and out of service.
Advantages and effects
Compared with the prior art, the invention has the beneficial effects that:
firstly, the method does not rely on mileage data as a synchronization basis, and remarkably solves the problem that the synchronization operation cannot be carried out when the odometer fails. Meanwhile, the problem that the previous synchronous operation result is invalid due to partial correction of the odometer data is solved.
Secondly, the precision of synchronization is greatly improved. The estimation of the synchronization precision of the invention can use the following method:
taking JC-24B type IMU developed by Beijing automation control equipment research as an example, the time management precision of the inertial navigation system can reach microsecond level, and the sampling frequency is 300 Hz; in the communication process with the main control computer, a USB2.0 port is adopted, and 1 millisecond frame data can be obtained, namely 1 millisecond delay at most; the time precision of real-time data output from the inertial navigation system to the main control computer can be said to reach millisecond level.
The magnetic flux leakage data itself is a continuous analog signal; the real-time data output to the main control computer is realized by a high-speed data acquisition card, taking a DMM-32X-AT acquisition card as an example, the highest sampling rate is 250KHz, and even if 250 probes use the acquisition card in a time-sharing manner, each path of signals can realize a sampling period of 1 millisecond; the time precision of the real-time data output from the magnetic flux leakage system to the main control computer can also reach millisecond level.
The data synchronization calculation performed in the main control computer can also ensure real-time performance, for example, a PC104 industrial computer is adopted, a 266MHz MIPS processor of HS3210I is adopted, the instruction period can reach 10 nanoseconds, the algorithm of the invention has no complex calculation, the time complexity of the algorithm is O (1), namely, the time of each data synchronization calculation is approximately constant, and the time of each data synchronization calculation can be completely ensured to be less than 1 millisecond.
In conclusion, the invention fully utilizes the characteristics of strong communication capability and communication delay far exceeding the synchronization requirement of the modern computer system, converts the requirement of data synchronization output by two subsystems into the calculation process of online real-time data synchronization, achieves the millisecond-level synchronization precision and completely meets the engineering requirement of detection in a pipeline.
Drawings
FIG. 1 shows a mechanical arrangement of a typical flux leakage-inertial navigation subsystem on a PIG platform;
FIG. 2 shows an electrical structure design of a typical flux leakage-inertial navigation subsystem on a PIG platform;
FIG. 3 is a flow chart of an online real-time magnetic flux leakage and inertial navigation data synchronization algorithm.
Description of reference numerals:
1-a pipeline; 2-a power cabin; 3-a universal joint; 4-a magnetic flux leakage detection subsystem; 5-a main control computer; 6-excitation end of multi-path magnetic flux leakage detection sensor; 7-a signal receiving end of a multi-path magnetic flux leakage detection sensor; 8-inertial navigation detection subsystem; 9-milemeter; 10-low frequency transmitting and receiving device; 11-debugging part; 12-high speed data acquisition card.
Detailed Description
The invention is further described below with reference to the accompanying drawings:
as shown in fig. 1, a pipeline internal detection device (PIG) is arranged in a pipeline 1, a power cabin 2 is arranged at the most front end of the PIG, the power cabin 2 is connected with a magnetic leakage detection subsystem 4 through a universal joint 3, an excitation end 6 of a multi-path magnetic leakage detection sensor is arranged inside the magnetic leakage detection subsystem 4, the rear end of the magnetic leakage detection subsystem 4 is connected with a main control computer 5 through the universal joint 3, the rear end of the main control computer 5 is connected with a signal receiving end 7 of the multi-path magnetic leakage detection sensor, the rear end of the signal receiving end 7 of the multi-path magnetic leakage detection sensor is connected with an inertial navigation detection subsystem 8 through the universal joint 3, and a odometer 9 is arranged at the rear end of the inertial.
As shown in fig. 2, the main electrical structure of the PIG system is a main control computer 5, and a signal receiving terminal 7 of a multi-path magnetic flux leakage detection sensor of the magnetic flux leakage detection subsystem 4 is connected to the main control computer 5 through a high-speed data acquisition card 12; the power cabin 2 is connected to a main control computer 5; the odometer 9 is connected to the main control computer 5; the inertial navigation detection subsystem 8 is connected to the main control computer 5; the debugging subsystem 11 is connected to the main control computer 5; the low frequency transceiver 10 operates independently.
As shown in fig. 3, a flow chart of online real-time magnetic flux leakage and inertial navigation data synchronization algorithm.
The method comprises the steps that a PIG runs in a pipeline, and the magnetic flux leakage and inertial navigation detection subsystems simultaneously execute an online measurement task; the two subsystems are respectively arranged in the two bins and cannot share one group of mileage data; the detection data of the inertial navigation system and the magnetic leakage system are respectively input into a main control computer of the PIG through a high-speed port in real time, and online real-time data synchronous processing is carried out in the main control computer; the method is characterized in that: the method comprises the following steps:
step one, a PIG main control computer collects inertial navigation data in real time; the main control computer receives data sent by the inertial navigation subsystem through real-time USB data acquisition equipment, and the equipment installs a resident USB port data acquisition program on an operating system framework of the main control computer, wherein the resident USB port data acquisition program ensures that the main control computer can acquire inertial navigation data through a USB2.0 port in real time. The programming of the real-time USB data collection device is not proprietary and is part of the equipment provided by the USB port device provider.
Extracting an inertial navigation data frame structure currently sent by an inertial navigation subsystem by a main control computer; including at least the following data items: SINS _ time (sampling time of current data, which is coding of physical time), WX, WY, WZ (three-dimensional angular velocity), AX, AY, AZ (three-dimensional acceleration), Od1, Od2, Od3 (three-way mileage), T1, T2(IMU internal temperature), etc., all data do not exceed 1 kbyte.
All inertial navigation data of sampling points at SINS _ time are defined as
SINS_od_output(SINS_time)＝{SINS_time，WX，WY，WZ，AX，AY，AZ，Od1、Od2、Od3，T1，T2}
At any moment, the sampling time of the inertial navigation data sampling point which is received by the master computer most recently is defined as SINS _ time _ on, and the time of the last sampling point is defined as SINS _ time _ before.
The USB2.0 port sends a data packet to the main control computer every 1 millisecond, and each data packet encapsulates effective data with at least 256K bytes; the sampling frequency F _ IMU of the IMU is far less than 1KHz, so the communication delay caused by the USB2.0 port does not exceed 1 millisecond, and the requirement on the data synchronization precision (0.1 second) of the in-pipeline detection engineering can be ignored. Therefore, when the host computer obtains a frame of data from the USB port, the frame of data at most includes a current time data from the inertial navigation system, i.e. SINS _ od _ output (SINS _ time _ on).
Step two, the PIG main control computer collects magnetic flux leakage data in real time;
the magnetic flux leakage data consists of N sensor data channels. Defining the sampling frequency of the high-speed data acquisition card of the main control computer as M, sharing the high-speed data acquisition card by time sharing of N sensor channels, defining F _ LC as the sampling frequency of the magnetic leakage subsystem, and then having
Obviously, the output data of the data channel of the ith (0 ≦ i < N) magnetic leakage sensor is defined as LCi(ii) a The sampling frequency is F _ LC; a data set (defined as LC _ output) acquired by one-time circulation of sensor channels with subscripts of 0 to N-1 is regarded as a sampling point, and a sampling point time LC _ time is shared, wherein LC _ output is described as
LC_output(LC_time)＝{LC_time，fresh，LC0，LC1，…，LCN-1}
The LC _ time is sampling time of current data output by the magnetic leakage system, is a code of physical time, an initial value of the LC _ time is provided by the magnetic leakage system, does not consider the precision problem of the physical time, and is only used for sequencing LC _ output data. The fresh is a "time updated" flag, the initial value is 0, if the fresh is made to be 1, it indicates that LC _ time has been refreshed, and the current LC _ output (LC _ time) data record has completed the synchronization operation.
The PIG system is designed and is easy to realize
F_LC≥1KHz
The sampling frequency of the magnetic leakage system is usually far greater than 1KHz, namely the period of the output LC _ output data of the magnetic leakage system is far less than that of the inertial navigation system. After the system is powered on, all LC _ output (LC _ time) data form a matrix table according to the sequence of LC _ time, and the matrix table is defined as LC _ output _ list
LC_output_list＝{LC_output(LC_time_j)∣j＝0,1,...,N-1}
Step three, synchronizing online real-time magnetic flux leakage and inertial navigation data;
the data synchronization algorithm is as follows:
1) after the whole PIG system is electrified and works, the magnetic leakage system is ensured to generate LC _ output _ list firstly, namely, at least one LC _ output (LC _ time) is ensured to be contained in the LC _ output _ list. This setting can be achieved by a number of methods, possible ones being as follows:
the method comprises the steps that a power supply management subsystem of the PIG delays to be powered on to an inertial navigation subsystem, and the power supply management subsystem is powered on to the inertial navigation subsystem after the magnetic flux leakage subsystem completes the actions of being powered on, starting, self-checking and the like;
and in the second method, after receiving the first LC _ output (LC _ time) data, downloading and processing the data sent by the inertial navigation subsystem through the USB port.
2) Monitoring a USB port by a USB _ IMUdata _ reader program, and receiving current inertial navigation data SINS _ od _ output (SINS _ time _ on);
3) let the last LC _ output (LC _ time) in the current LC _ output _ list be recorded
LC_time＝SINS_time_on
And order
fresh＝1
Marking this leakage data record as "time updated";
4) j LC _ outputs of all the fresh ═ 0 are extracted from the current LC _ output _ list, and with LC _ outputs (SINS _ time _ on) and LC _ outputs (SINS _ time _ before), in the order in which these leakage magnetic data are generated, a sequence set unfresh _ LC _ list of the form:
unfresh_LC_list＝{LC_output(SINS_time_before),LC_output(LC_time_1),LC_output(LC_time_2),...,LC_output(LC_time_j),LC_output(SINS_time_on)∣j＝0,1,...}
j is a positive integer greater than 0, and represents the number of magnetic flux leakage data records between two consecutive inertial navigation data without updating the time of the sampling point
j is small in value and stable, and when the time complexity of the algorithm is calculated later, j is treated as a constant;
5) updating LC _ time _ k and fresh _ k, k being 0,1, and j of LC _ output records with all fresh being 0 in the unfresh _ LC _ list by interpolation, wherein the updated interpolation algorithm for all positive integers k with the value equal to 0 and less than or equal to j is as follows:
then all LC _ time _ k are correlated
fresh_k＝1,k＝0,1,...,j
Finally order
SINS_time_before＝SINS_time_on
The synchronous operation of the inertial navigation magnetic flux leakage data is completed;
6) at this time, LC _ time data items of all the magnetic leakage data LC _ output received by the current main control computer are updated, and are synchronized with all the received SINS _ od _ output data in time; jump to 2), continue the loop of 2) through 6) until all PIG subsystems are powered down and out of service.
Claims (1)
1. The method comprises the steps that a PIG runs in a pipeline, and the magnetic flux leakage and inertial navigation detection subsystems simultaneously execute an online measurement task; the two subsystems are respectively arranged in the two bins and cannot share one group of mileage data; the detection data of the inertial navigation system and the magnetic leakage system are respectively input into a main control computer of the PIG through a high-speed port in real time, and online real-time data synchronous processing is carried out in the main control computer, and the method is characterized in that: the method comprises the following steps:
step one, a PIG main control computer collects inertial navigation data in real time;
extracting an inertial navigation data frame structure currently sent by an inertial navigation subsystem by a main control computer; including at least the following data items: SINS _ time (sampling time of current data, which is coding of physical time), WX, WY, WZ (three-dimensional angular velocity), AX, AY, AZ (three-dimensional acceleration), Od1, Od2, Od3 (three-way mileage), T1, T2(IMU internal temperature), etc., all data do not exceed 1 kbyte;
all the inertial navigation data of the sampling points at the time of the SINS _ time are defined as SINS _ Od _ output (SINS _ time) { SINS _ time, WX, WY, WZ, AX, AY, AZ, Od1, Od2, Od3, T1, T2}
At any moment, the sampling time of the inertial navigation data sampling point which is received by the main control computer most recently is defined as SINS _ time _ on, and the time of the last sampling point is defined as SINS _ time _ before;
the USB2.0 port sends a data packet to the main control computer every 1 millisecond, and each data packet encapsulates effective data with at least 256K bytes; the sampling frequency F _ IMU of the IMU is far less than 1KHz, so that the communication delay caused by the USB2.0 port does not exceed 1 millisecond, and the requirement on the data synchronization precision (0.1 second) of the detection engineering in the pipeline can be ignored; therefore, when the host computer obtains a frame of data from the USB port, the frame of data at most includes a current time data from the inertial navigation system, i.e. SINS _ od _ output (SINS _ time _ on);
step two, the PIG main control computer collects magnetic flux leakage data in real time;
the magnetic leakage data consists of N sensor data channels, the sampling frequency of a high-speed data acquisition card of the main control computer is defined as M, the N sensor channels share the high-speed data acquisition card in a time-sharing manner, and F _ LC is defined as the sampling frequency of the magnetic leakage subsystem, so that the magnetic leakage data has the frequency of M
Obviously, the output data of the data channel of the ith (0 ≦ i < N) magnetic leakage sensor is defined as LCi(ii) a The sampling frequency is F _ LC; a data set (defined as LC _ output) acquired by one-time circulation of sensor channels with subscripts of 0 to N-1 is regarded as a sampling point, and a sampling point time LC _ time is shared, wherein LC _ output is described as
LC_output(LC_time)＝{LC_time，fresh，LC0，LC1，…，LCN-1}
The LC _ time is sampling time of current data output by the magnetic leakage system, is a code of physical time, an initial value of the LC _ time is provided by the magnetic leakage system, does not consider the precision problem of the physical time, and is only used for sequencing LC _ output data; the fresh is a 'time updated' mark, the initial value is 0, if the fresh is made to be 1, the LC _ time is indicated to be refreshed, and the current LC _ output (LC _ time) data record has completed the synchronization operation;
the PIG system is designed and is easy to realize
F_LC≥1KHz
The sampling frequency of the magnetic leakage system is usually far more than 1KHz, namely the period of the LC _ output data output by the magnetic leakage system is far less than that of the inertial navigation system; after the system is powered on, all LC _ output (LC _ time) data form a matrix table according to the sequence of LC _ time, and the matrix table is defined as LC _ output _ list
LC_output_list＝{LC_output(LC_time_j)∣j＝0,1,...,N-1}
Step three, synchronizing online real-time magnetic flux leakage and inertial navigation data;
the data synchronization algorithm is as follows:
1) after the whole PIG system is electrified and works, the magnetic leakage system is ensured to generate LC _ output _ list at first, namely, at least one LC _ output (LC _ time) is ensured to be contained in the LC _ output _ list; the method comprises the following steps:
the method comprises the steps that a power supply management subsystem of the PIG delays to be powered on to an inertial navigation subsystem, and the power supply management subsystem is powered on to the inertial navigation subsystem after the magnetic flux leakage subsystem completes the actions of being powered on, starting, self-checking and the like;
or in the second method, after receiving the first LC _ output (LC _ time) data, downloading and processing the data sent by the inertial navigation subsystem through the USB port;
2) monitoring a USB port by a USB _ IMUdata _ reader program, and receiving current inertial navigation data SINS _ od _ output (SINS _ time _ on);
3) let LC _ time recorded by last LC _ output (LC _ time) in current LC _ output _ list be SINS _ time _ on
And order
fresh＝1
Marking this leakage data record as "time updated";
4) j LC _ outputs of all the fresh ═ 0 are extracted from the current LC _ output _ list, and with LC _ outputs (SINS _ time _ on) and LC _ outputs (SINS _ time _ before), in the order in which these leakage magnetic data are generated, a sequence set unfresh _ LC _ list of the form:
unfresh_LC_list＝{LC_output(SINS_time_before),LC_output(LC_time_1),LC_output(LC_time_2),...,LC_output(LC_time_j),LC_output(SINS_time_on)∣j＝0,1,...}
j is an integer greater than or equal to 0 and represents the number of magnetic leakage data records of the sampling point time which is not updated between two continuous inertial navigation data because
j is small in value and stable, and when the time complexity of the algorithm is calculated later, j is treated as a constant;
5) updating LC _ time _ k and fresh _ k, k being 0,1, and j of LC _ output records with all fresh being 0 in the unfresh _ LC _ list by interpolation, wherein the updated interpolation algorithm for all positive integers k with the value equal to 0 and less than or equal to j is as follows:
then let all LC _ time _ k associated fresh _ k be 1, k be 0,1
Finally order
SINS_time_before＝SINS_time_on
The synchronous operation of the inertial navigation magnetic flux leakage data is completed;
6) at this time, LC _ time data items of all the magnetic leakage data LC _ output received by the current main control computer are updated, and are synchronized with all the received SINS _ od _ output data in time; jump to 2), continue the loop of 2) through 6) until all PIG subsystems are powered down and out of service.
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