CN111132201B - Wireless measurement system based on UWB - Google Patents
Wireless measurement system based on UWB Download PDFInfo
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- CN111132201B CN111132201B CN202010021173.7A CN202010021173A CN111132201B CN 111132201 B CN111132201 B CN 111132201B CN 202010021173 A CN202010021173 A CN 202010021173A CN 111132201 B CN111132201 B CN 111132201B
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Abstract
The invention belongs to the field of wireless measurement systems, and relates to a wireless measurement system based on UWB, which comprises: the sensor node is connected with the sink node through a UWB network, and the sink node is connected with the measurement and control center through a wireless network; the sink node and the sensor node adopt a low-power consumption design, the sink node acquires electric energy through solar energy, and the sensor node acquires electric energy through an alternating magnetic field formed by power line current; the sink node obtains standard time and position information through GPS, the sensor node does not contain GPS, and time synchronization is realized between the sink node and the sensor node in the data communication process through a time synchronization mechanism; the sensor node marks a time stamp and a sampling period on the sampling data and sends the time stamp and the sampling period to the sink node, and the sink node forwards the sampling data of the sensor node to the measurement and control center and simultaneously temporarily stores the sampling data locally. The invention realizes time synchronization in the data communication process, and has low power consumption and realization cost.
Description
Technical Field
The invention belongs to the field of wireless measurement systems, and relates to a wireless measurement system based on UWB.
Background
The wireless measurement system provides a feasible networking solution for occasions inconvenient to connect through a wired network. The time stamp attribute is an attribute as important as a dimension attribute, a position attribute, etc. of a physical quantity (such as temperature, humidity, light intensity, etc.), and it is meaningless that one sample data object has only a value and no time and place of generating data. In data communication, the physical quantity is given by a variable name, and for the occasion that the communication is very reliable (such as wired communication) and the requirement on time synchronization is not high, the current time of data sampling obtained after the communication can be used as a time stamp; however, in situations where the communication is not very reliable (such as wireless communication) or where the accuracy requirements for the time stamps are high, such as multi-point seismic wave measurement, power system fault wave measurement, fault location, etc., the time stamp error requirements are on the order of microseconds, and it is necessary to keep the clocks of the nodes in the network very accurately. Therefore, time synchronization is very important for such wireless measurement systems, and the time stamping error of the sampled data must be within an allowable range, otherwise the error of fault location is very large, and even normal location cannot be achieved.
At present, the time synchronization of a wireless measurement system generally adopts satellite time service such as GPS or Beidou system, the time synchronization precision of satellite time service and UTC can be controlled within 100 nanoseconds, the contrast precision is controlled within 2.25 nanoseconds, and the time synchronization requirements of most wireless measurement systems can be met. However, this requires that each wireless measurement node be equipped with a GPS or beidou system timing module, which not only increases cost, but also increases power consumption, which is not acceptable in many wireless measurement systems. Therefore, it would be of positive significance to invent a wireless measurement system that does not significantly increase power consumption and is low cost.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a wireless measurement system based on UWB.
The invention is realized by adopting the following technical scheme:
A UWB-based wireless measurement system, comprising: the sensor node is connected with the sink node through a UWB network, and the sink node is connected with the measurement and control center through a wireless network; the sink node and the sensor node adopt a low-power consumption design, the sink node acquires electric energy through solar energy, and the sensor node acquires electric energy through an alternating magnetic field formed by power line current; the sink node obtains standard time and position information through a GPS, the sensor node does not contain a GPS module, and time synchronization is realized between the sink node and the sensor node in the data communication process through a time synchronization mechanism; the sensor node marks a time stamp and a sampling period on the sampling data and sends the time stamp and the sampling period to the sink node, and the sink node forwards the sampling data of the sensor node to the measurement and control center and temporarily stores the sampling data in a local place; the measurement and control center analyzes and calculates the sampling data of different sink nodes, and controls or configures parameters of the sink nodes and the sensor nodes.
Preferably, the sink node and the sensor node adopt micro-steps to correct the local clock in real time, so as to ensure unidirectional smooth increase of macroscopic time and time stamp.
Preferably, the backward secondary time stamp correction is performed on the sampling data of which the time synchronization interval is longer.
Preferably, the sink node comprises: the sink node MCU module, the GPS time service and positioning module, the 4G communication module, the UWB communication module, the solar battery and the electric energy storage module are connected with the sink node MCU module; wherein:
The sink node acquires current sampling data of each phase of the power line from the sensor node through the UWB communication module, stores the current sampling data in FLASH and periodically transmits the current sampling data to the measurement and control center through the 4G communication module; the sink node acquires UTC standard clocks and positions through the GPS time service and positioning module, and then time synchronization is carried out on each sensor node through the UWB network.
Preferably, the sink node MCU module includes a sink node local clock correction module, where: the sink node local clock correction module comprises a temperature compensation crystal oscillator, a TIM2 timer of the MCU, a real-time clock buffer, a GPS standard clock, a real-time clock compensation module and a real-time clock reading module which are connected with each other.
Preferably, the TIM2 timer of the MCU is a 32-bit counter, to realize local clock timing of the sink node, the TIM2 is configured to interrupt once every 10 ms, the TIM2 interrupt program obtains the compensation amount through the real-time clock compensation module, reads the buffered clock value at the last interrupt from the real-time clock buffer, obtains the current real-time clock value after +10 ms+the compensation amount according to the buffered clock value at the last interrupt, and stores the current real-time clock value into the real-time clock buffer again.
Preferably, the MCU acquires the GPS timestamp of the GPS standard clock in an interrupt manner, and also acquires the local timestamp of the sink node through the real-time clock reading module, and the sink node acquires the compensation amount Tac required by the real-time clock compensation module for calculating each interrupt of the TIM2 through the following formula:
Wherein: tgps1 and Tgps are GPS time stamps obtained twice consecutively, tagg1 and Tagg2 are local time stamps of sink nodes corresponding to Tgps1 and Tgps respectively, and Tap is a periodical micro-step correction time of the sink nodes.
Preferably, the error Tc of the local clock of the sensor node is calculated according to the following formula:
Wherein: TA1 and TA2 are respectively standard time of the sink node received by the sensor node twice continuously, TS1 and TS2 are respectively local time stamps of the sensor node corresponding to TA1 and TA2, and Tp is periodical micro-step correction time of the sensor node.
Preferably, the standard time of the sink node received by the sensor node is obtained by extracting a real-time clock from a data packet received by the sink node and adding Tmm1 delay, wherein:
Tmm1＝(Tmu+Tum)+Tuu1
Tmu is the delay between MCU to UWB; tum is the delay from UWB to MCU; tuu1 is the sum of time from the transmit register to the transmit antenna, the transmit antenna to the receive antenna, and the receive antenna to the receive register of the UWB transceiver chip.
Preferably, the sensor node comprises: the sensor node MCU module and UWB communication module, current detection module and electric energy collection and storage module that are connected with it, wherein:
The power harvesting and storage module includes: the device comprises a mutual inductance power taking coil, a rectifying filtering and voltage limiting circuit, a BQ 24650-based lithium iron phosphate charging circuit and a lithium iron phosphate battery; wherein: the mutual inductance electricity taking coil is equivalent to a transformer, an opening magnetic ring of the mutual inductance electricity taking coil clamps a power line, the power line is taken as a primary side coil, and a coil wound on the magnetic ring is taken as a secondary coil; the electric energy in the power line coupling process is changed into direct-current voltage after passing through a rectifying and filtering circuit and a voltage limiting circuit, the direct-current voltage charges a lithium iron phosphate battery through a BQ24650 lithium iron phosphate charging circuit, and the lithium iron phosphate battery stores the electric energy;
The current detection module is used for converting a current signal of the high-voltage power line into an ADC voltage input signal of the MCU, and comprises the following components: high-precision current transformer, precision resistor and voltage amplifier.
Compared with the prior art, the invention has obvious advantages and positive effects, including:
(1) Aiming at the time synchronization problem of a wireless data measurement system, the invention provides a time synchronization mechanism adopting UWB (Ultra Wide Band) communication technology, realizes time synchronization in the data communication process, does not obviously increase power consumption and realization cost, has high communication rate and strong anti-interference capability in a UWB communication mode, and has good application prospect.
(2) According to the asymmetric characteristics of the energy of the sink node and the sensor node in practical application, the GPS time service and positioning module is only installed on the sink node, the sink node communicates with the sensor node in a UWB mode, time synchronization is completed in the data communication process, and high-efficiency, energy-saving and low-cost time synchronization is achieved.
(3) UWB communication is adopted, so that the communication rate is high, the communication period is short, and the anti-interference capability is strong; the sensor node and the sink node have simple structure, low cost, small volume, convenient installation and long service life, and are suitable for long-term operation in the field.
(4) The sink node and the sensor node adopt micro-steps (10 milliseconds) to correct the local clock in real time, so that the unidirectional smooth increase of macroscopic time and time stamp is ensured; for the sampling data with longer time synchronization interval (more than 10 seconds), the sampling data in the time interval is subjected to secondary time stamp correction, so that the error of the time stamp of the sampling data is further reduced.
Drawings
FIG. 1 is a block diagram of a UWB based wireless measurement system according to one embodiment of the invention;
FIG. 2 is a block diagram of a sink node in one embodiment of the invention;
FIG. 3 is a block diagram of a sensor node in one embodiment of the invention;
FIG. 4 is a flow diagram of local clock correction information for sink nodes in one embodiment of the invention;
FIG. 5 is a flow diagram of a sensor node local clock correction information in one embodiment of the invention;
FIG. 6 is a schematic diagram of time-of-flight measurements of a sensor node and sink node in one embodiment of the invention.
Detailed Description
The following describes specific embodiments of the present invention with reference to the drawings, but the embodiments of the present invention are not limited thereto.
The invention relates to a wireless measurement system, in particular to a method for marking a sampling data time stamp and a specific implementation, which relate to a communication mode and a time synchronization mechanism between nodes based on UWB (Ultra Wide Band).
A UWB-based wireless measurement system, comprising: the sensor node is connected with the sink node through a UWB network, and the sink node is connected with the measurement and control center through a wireless network. The sink node and the sensor node adopt a low-power consumption design, the sink node obtains electric energy through solar energy, and the sensor node obtains electric energy through an alternating magnetic field formed by power line current. The sink node obtains standard time and position information through GPS, the sensor node does not contain a GPS module, and the synchronous time is obtained through the sink node. The sink node and the sensor node realize time synchronization through a time synchronization mechanism. The sensor node marks the time stamp and the sampling period on the sampling data and sends the sampling data to the sink node, the sink node forwards the sampling data of the sensor node to the measurement and control center, meanwhile, the sink node stores the data temporarily in the local area, and the measurement and control center analyzes and calculates the sampling data of different sink nodes. The measurement and control center controls or configures parameters of the sink node and the sensor node through opposite communication paths.
In a preferred embodiment, the sink node is further connected to the portable terminal in a USB and/or UWB manner, and the portable terminal may download the collected data of the sink node and perform operations such as partial software upgrade through the USB or UWB. Portable terminals include, but are not limited to, laptop computers, mobile terminals, IPAD, and the like.
In this embodiment, fault detection of a high-voltage transmission line of a power system is taken as an application scenario. The sink nodes are arranged at the position 3 meters away from the ground on the power transmission tower, the sensor nodes are fixed on the power line, and one sink node supports real-time connection of 9 sensor nodes with high-speed UWB; the sink node and the sensor node are designed with low power consumption, the sink node obtains electric energy through solar energy, and the sensor node obtains electric energy through an alternating magnetic field formed by power line current. The sink node and the measurement and control center communicate by adopting a wireless public network, the sensor node and the sink node communicate by adopting a IEEE802.15.4A network based on UWB, and the sink node also provides a USB and/or UWB mode to be connected with the portable computer. After the sensor nodes collect data, the data are transmitted to the sink nodes in a UWB communication mode at regular intervals, the sink nodes are transmitted to a measurement and control center through a wireless public network, the measurement and control center configures working parameters for the sink nodes and the sensor nodes through opposite communication paths, remote measurement and remote control are carried out, and a laptop can download the collected data of the sink nodes and carry out partial software upgrading through USB or UWB.
The sink node comprises an MCU module, a GPS time service and positioning module, a 4G communication module, a UWB communication module, a solar battery and an electric energy storage module, wherein the GPS time service and positioning module, the 4G communication module, the UWB communication module, the solar battery and the electric energy storage module are connected with the sink node. The sensor node includes: MCU module and UWB communication module, current detection module and the electric energy collection and storage module that are connected with it, the sensor node does not contain the GPS module, and the synchronous time passes through the sink node and obtains, consequently, sink node and sensor node realize low cost.
The sink node obtains standard time and position information through a GPS, and the sensor node measures communication delay between each sensor node and the sink node through a UWB bilateral delay measurement method and compensates in each sensor node; the sensor node obtains a real-time clock of the sink node in a UWB communication mode, obtains real-time errors of the sensor node clock and the sink node clock through an algorithm, and compensates the local clock of the sensor node in real time by applying the real-time errors. The sensor node marks the time stamp and the sampling period on the sampling data and sends the sampling data to the sink node, the sink node forwards the sampling data of the sensor node to the measurement and control center, and the measurement and control center software analyzes and calculates the sampling data of different sink nodes and combines different position information of each sink node to obtain power failure information and failure positions.
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, a UWB-based wireless measurement system includes: the system comprises sensor nodes, sink nodes and a measurement and control center, wherein the sensor nodes and the sink nodes form a star-shaped personal area network through 802.15.4A based on UWB, and one sink node supports 9 sensor nodes; the aggregation node and the measurement and control center communicate through a wireless public network (such as a 4G network), the number of the aggregation node supported by the measurement and control center depends on the communication capacity, and the wireless measurement system can cover the whole power system when the communication capacity is enough. The data collected by the sensor nodes are transmitted to the sink nodes through the UWB network, the sink nodes are transmitted to the measurement and control center through the public 4G network, and meanwhile the sink nodes temporarily store the data locally; and data such as telemetry and remote control instructions, parameter configuration and the like of the measurement and control center are transmitted to the sink node and the sensor node through opposite communication paths.
In a preferred embodiment, referring to fig. 2, the sink node comprises an MCU and peripheral circuits (including FLASH memory) M20, and a solar energy collection and electrical energy storage circuit M21, a UWB transceiver circuit M22, a GPS timing and positioning module M23 and a 4G communication module M24 connected thereto. Wherein:
the MCU and peripheral circuit M20 comprises STM32L4R5ZGT6, a FLASH chip W29N08GV of 40MHz temperature compensation crystal oscillator TG2520SBN and 8Gb connected with the STM32L4R5ZGT6 and the peripheral circuit of the MCU.
The solar energy collection and electric energy storage circuit M21 comprises a 10W/18V silicon battery plate, a BQ 24650-based lithium iron phosphate charging circuit, a 12V/12AH lithium iron phosphate battery and a 12V-to-3.3V DC/DC circuit, wherein a 3.3V power supply supplies power to circuits except a 4G communication module, and the 4G communication module directly obtains 12V power from the lithium iron phosphate battery.
The UWB transceiver circuit M22 includes a UWB transceiver chip DW1000 and its peripheral circuits and a ceramic antenna.
The GPS timing and positioning module M23 comprises NEO-LEA-M8T and peripheral circuits thereof.
The 4G communication module M20 includes ME909s-821LTE and its peripheral circuits.
The sink node obtains current sampling data of each phase of the power line from the sensor node through the UWB receiving and transmitting circuit, the current sampling data are stored in FLASH, and the current sampling data are sent to the measurement and control center through the 4G communication module periodically. The sink node acquires UTC standard clocks and positions through the GPS time service and positioning module, and then time synchronization is carried out on each sensor node through the UWB network.
Referring to fig. 3, the sensor node includes an MCU and peripheral circuits M30 and power line energy harvesting and storage circuits M31, UWB transceiving circuits M32 and power line current measurement circuits M33 connected thereto. Wherein:
the MCU and peripheral circuit M30 comprises STM32L4R5VGT6, and a 40MHz temperature compensation crystal oscillator TG2520SBN and an MCU peripheral circuit which are connected with the same.
The power line energy harvesting and storage circuit M31 includes: the device comprises a mutual inductance power taking coil, a rectifying filtering and voltage limiting circuit, a BQ24650 lithium iron phosphate charging circuit and a 3.2V/1.5AH lithium iron phosphate battery. The mutual inductance electricity taking coil is equivalent to a transformer, an opening magnetic ring of the mutual inductance electricity taking coil clamps a power line, the power line is taken as a primary side coil, and a coil wound on the magnetic ring is taken as a secondary coil; the electric energy in the power line coupling process is changed into direct-current voltage after passing through a rectifying filtering and voltage limiting circuit, the direct-current voltage charges a lithium iron phosphate battery through a BQ24650 lithium iron phosphate charging circuit, and the electric energy is stored in the lithium iron phosphate battery; when the power line is currentless or very low, the system is supplied with power for a sufficiently long time.
The UWB transceiver circuit M32 includes a UWB transceiver chip DW1000 and its peripheral circuits.
The power line current measurement circuit M33 is configured to convert a current signal of the high voltage power line into an ADC voltage input signal of the MCU, and includes: high-precision current transformer, precision resistor and voltage amplifier. The high-precision current transformer converts the current of a power line (primary side) into the current of a secondary side of the transformer according to the proportion of 1200:1, the current flows through a precision resistor to become a voltage signal, and the voltage signal is amplified by a voltage amplifier and then is connected with the ADC input of the MCU. In a preferred embodiment, the high precision current transformer is a high precision 1200/1 current transformer; the precision resistor is a precision resistor of 1 ohm.
The sensor node sends the sampling data to the sink node through the UWB network, and meanwhile time synchronization with the sink node is achieved.
Fig. 4 is a local clock correction information flow chart of the sink node, which is implemented by the MCU and the peripheral circuit M20 of fig. 2, and includes: the temperature compensation crystal oscillator M41, the TIM2 timer M42 of the MCU, the real-time clock buffer M43, the GPS standard clock M44, the real-time clock compensation module M45 and the real-time clock reading module M46. The functions of fig. 4 are mainly implemented by the MCU and peripheral circuit M20 of fig. 2, and in fig. 4: the temperature compensation crystal oscillator M41 adopts a temperature compensation crystal oscillator TG2520SBN with the frequency of 40MHz and the precision of 2ppm, and provides a system clock for the MCU, and is also a timing clock of a TIM2 timer. The TIM2 timer of the MCU is a 32-bit counter, realizes local clock timing of the sink node, the TIM2 is configured to interrupt once every 10 milliseconds, the TIM2 interrupt program obtains the compensation quantity through the real-time clock compensation module M45, reads the cache clock value when interrupted last time from the real-time clock buffer M43, obtains the current real-time clock value according to the cache clock value +10 milliseconds+the compensation quantity last time, and stores the current real-time clock value into the real-time clock buffer M43 again. The real-time clock buffer M43 organizes and saves the current time of the TIM2 interrupt time in terms of a data structure of year (1 byte), month (1 byte), day (1 byte), time (1 byte), minute (1 byte), second (1 byte), millisecond (2 byte), microsecond (2 byte), nanosecond (2 byte).
The real-time clock reading module M46 obtains the current real-time by adding the real-time offset (the count value of TIM2 multiplied by 25 ns) to the time value stored in the real-time clock buffer (the time of the last time TIM2 interrupt time) from the TIM2 counter of the MCU.
The UWB receiving and transmitting circuit of the sink node adopts a 38.4MHz temperature compensation crystal oscillator TG2016SBN, the MCU acquires the GPS time stamp of a GPS standard clock M44 in an interrupt mode every 1 second, meanwhile, the sink node acquires the local time stamp of the sink node through a real-time clock reading module M46, the sink node calculates the compensation amount required by each interrupt of the TIM2 through a real-time clock compensation module M45, and the compensation amount is obtained through the following formula (1).
In the formula (1), tgps and Tgps are GPS timestamps acquired twice in succession, tagg1 and Tagg2 are local timestamps of the sink node corresponding to Tgps and Tgps, respectively, tap is a periodic micro-step correction time of the sink node, 10 ms (10 7 ns), namely, the local clock is corrected once every 10 ms, and Tac is an error, namely, compensation amount, of the local clock of the sink node calculated according to the formula (1).
Fig. 5 is a local clock correction information flow chart of a sensor node, which is implemented by the MCU and the peripheral circuit M30 of fig. 3, and includes: the temperature compensation crystal oscillator M51, the TIM2 timer M52 of the MCU, the real-time clock buffer M53, the UWB network data packet M54, the real-time clock compensation module M55, the real-time clock reading module M56 and the TIM1 timer M57 of the MCU. The temperature compensation crystal oscillator M51 adopts a temperature compensation crystal oscillator TG2520SBN of 2ppm of 40MHz to provide a system clock for the MCU, and is also a timing clock of TIM2 and TIM1 timers. The timer TIM2 of the MCU is a 32-bit counter, realizes the local clock timing of the sensor node, the TIM2 is configured to interrupt once every 10 milliseconds, the TIM2 interrupt program obtains the compensation quantity through the real-time clock compensation module M55, reads the buffer clock value when interrupted last time from the real-time clock buffer M53, obtains the real-time clock value this time according to the buffer clock value +10 milliseconds+the compensation modified value last time, and stores the buffer clock value in the real-time clock buffer M53 again. The real-time clock buffer (M53) organizes and stores the clock value at the time of TIM2 interrupt in terms of a data structure of year (1 byte), month (1 byte), day (1 byte), time (1 byte), minute (1 byte), second (1 byte), millisecond (2 byte), microsecond (2 byte), nanosecond (2 byte).
The UWB receiving and transmitting circuit adopts a 38.4MHz temperature compensation crystal oscillator TG2016SBN, when the sink node performs data communication with the sensor node by adopting a UWB network, the local real-time of the sink node is put into a communication data packet, so that the sensor node can acquire a data packet with a real-time timestamp, namely a UWB network data packet M54, through each communication of the sensor node and the sink node, and the sensor node is used for calculating the compensation amount required by each interruption of the TIM2 through a real-time clock compensation module M55. The real-time clock reading module M56 obtains the current real-time clock by adding the real-time offset to the time value of the real-time clock buffer from the TIM2 counter.
The distance between the sink node and each sensor node is 10-40 m, the sink node is from the real-time clock of MCU to its UWB transceiver chip, the UWB transceiver chip of the sink node is from the UWB transceiver chip of the sensor node to the UWB transceiver chip of the sensor node through electromagnetic wave, the real-time clock module in the MCU of sensor node from UWB transceiver chip of the sensor node has time delay, these all need to compensate in the time synchronization, in order to improve the time synchronization precision.
In order to improve time synchronization precision of a wireless measurement system, the invention provides a time synchronization mechanism and a UWB bilateral delay measurement method, delay is measured and estimated from end to end, the delay from a sink node MCU to a sensor node MCU is set to be Tmm, and the delay from a sink node UWB chip to a sensor node UWB chip is set to be Tuu.
The delay between the UWB transceiver chip of the sink node and the sensor node is measured by bilateral bidirectional flight time, tuu is the sum of the time from the transmitting register to the transmitting antenna, the transmitting antenna to the receiving antenna, and the receiving antenna to the receiving register of the UWB transceiver chip DW1000, and tuu is determined according to the following formula with reference to fig. 6:
Tuu is the flight time of electromagnetic waves between the sensor node and the UWB chip of the sink node, in fig. 6, the sensor node sends a data packet with a timestamp (the timestamp is the value of a real-time clock register in the UWB chip DW1000, is relative time, is not the real-time clock in the MCU) to the sink node at the S1 moment, and the sink node DW1000 receives at the R1 moment; then the sink node DW1000 sends a data packet with a time stamp (the value of a real-time clock register in the DW 1000) at the moment S2, and the sensor node DW1000 receives the data packet at the moment R2; the sensor node then sends a data packet with a timestamp (the value of the real-time clock register inside DW 1000) at time S3 for the second time, and the sink node DW1000 receives the data packet at time R3. The sensor node and the sink node can calculate respective sending and receiving time intervals T1, T2, T3 and T4 according to respective UWB receiving and transmitting chip internal real-time clocks, wherein: t1 is the time difference between the sensor node UWB chip sending the 1 st data packet to the sink node UWB chip and the sensor node UWB chip receiving the 1 st data packet of the sink node UWB chip; t2 is the time difference between the sink node UWB chip receiving the sensor node UWB chip and sending the 1 st data packet to the sink node UWB chip sending the 1 st data packet to the sensor node UWB chip; t3 is the time difference between the sensor node UWB chip receiving the sink node UWB chip and sending the 1 st data packet to the sensor node UWB chip and sending the 2 nd data packet to the sink node UWB chip; t4 is the time difference between the sink node UWB chip sending the 1 st data packet to the sensor node UWB chip and the sink node UWB chip receiving the 2 nd data packet sent by the sensor node UWB chip. The flight time between the sensor node and the sink node UWB chip can be calculated by the formula (2).
The method for measuring the delay Tmm from the sink node MCU to the sensor node MCU needs to be based on Tuu measuring methods, and the time required by software in the MCU for reading the real-time clock, namely the running time of the real-time clock reading module M56, is set as Tread, and the value is determined by respectively reading the value of the timer in the same running before and after the running of the real-time clock reading module and differencing. To ensure consistency and certainty of the running time of the real-time clock reading module M56, interrupt processing needs to be started before the module is run and after the module is run, so as to avoid random interference of interrupt on the execution time of the real-time clock reading module M56. Similar to Tuu, the time difference between transmitting and receiving data between the sensor node and the MCU of the sink node is:
tmm is the time difference between the transmission and reception of data between the sensor node and the MCU of the sink node; t5, T6, T7 and T8 are similar to T1, T2, T3 and T4 in meaning, and are therefore labeled together in FIG. 6, with the difference that T1, T2, T3 and T4 are the time differences between the transmission and reception of data packets by the UWB chips of the sensor node and sink node, and T5, T6, T7 and T8 are the differences between the real-time clocks read by the software of both the transmission and reception nodes between the sensor node and sink node MCU, as further detailed: t5 is the difference of real-time clocks between the sensor node sending the 1 st data packet to the sink node and the sensor node receiving the 1 st data packet of the sink node; t6 is the difference of real-time clocks between the sink node receiving the 1 st data packet sent by the sensor node and the sink node sending the 1 st data packet to the sensor node, and T7 is the difference of real-time clocks between the sensor node receiving the 1 st data packet sent by the sink node and the sensor node sending the 2 nd data packet to the sink node; t8 is the difference of real-time clocks between the sink node sending the 1 st data packet to the sensor node and the sink node receiving the 2 nd data packet from the sensor node.
The same meaning as that of Tuu. Tmm can be determined through testing under the condition of a certain distance (such as 30 meters) during node production and manufacture, and Tuu can be determined under the condition of the distance, so that the delay error between the MCU and the UWB is as follows:
Tmu+Tum＝Tmm-Tuu (4)
Tmu and Tum are the delays from MCU to UWB and from UWB to MCU, the sum of these two parameters is determined after the product is set, and after the measurement of the production process, the product is fixed in MCU and then directly called. When the sensor node and the sink node are installed on site, tuu is performed after the system is started, and the value is Tuu, and then the communication delay value between the sensor node and the MCU of the sink node is Tmm1 according to the formula (5).
Tmm1＝(Tmu+Tum)+Tuu1 (5)
The sensor node extracts a real-time clock (real-time clock of MCU) from the data packet received by the sink node, and adds Tmm1 delay as the standard time TA of the received sink node. Similarly to the sink node, the error of the local clock of the sensor node is calculated according to equation (6):
In formula (6), TA1 and TA2 are respectively standard times of sink nodes received twice consecutively, TS1 and TS2 are respectively local time stamps of sensor nodes corresponding to TA1 and TA2, tp is a periodic correction time of the sensor nodes, 10 ms (10 7 ns), i.e. the local clock is corrected once every 10 ms, and Tc is a correction value calculated according to formula (6). For example, the sensor local time detection (TS 2-TS 1) is 1 second (10 9 ns), and the difference between the received standard times (TA 2-TA 1) is 1 second zero 2 microseconds (10 9+2×103 ns), then the time required to be corrected every 10 milliseconds (10 7 ns) is:
i.e. the sensor local clock needs to be increased by 20 ns every 10 ms to reduce the accumulated error of the local clock.
The sensor node samples 256 values per cycle of the power line current, i.e., the ADC samples the current at 78.125 microsecond cycles, the ADC is configured to trigger the transition by TIM1 timer M57. The auto-load register of the TIM1 timer is configured 3125 to enable an ADC conversion trigger signal output of 78.125 microsecond period. After ADC conversion, the converted data are stored in an internal RAM of the MCU in a DMA mode, and when the stored data reach 256, DMA interruption is carried out. The DMA interrupt program performs the following tasks: (1) turn on TIM1 interrupt; (2) The main program informing the MCU by the flag processes 256 data just sampled. The main program converts 256 pieces of sampling data into measurement currents according to the flag, and stores the measurement currents in a memory real-time data block. The main program allows the TIM1 to be interrupted in the initialization stage, and the following tasks are completed in the TIM1 interruption program: (1) Closing the self interrupt, and then waiting for the DMA interrupt program to start the TIM1 interrupt again, namely carrying out the TIM1 interrupt once every 256 initial moments of sampling data; (2) The current time is obtained by the real-time clock reading module M56 and is used as the starting time stamp of 256 sampling data, and the time stamp is placed in front of the 256 sampling current real-time data and is used as the starting time of the 256 sampling data, so that accurate time stamp marking of the sampling data is realized.
When the time synchronization interval of the sink node and the sensor node is long (more than 10 seconds) for some reason, in order to further reduce the time stamp error of the sampled data, the time stamp of the sampled data that has been sampled between the two time syncs is subjected to the backward secondary time stamp correction according to equation (7).
In equation (7), tuwb and Tuwb are two standard times (propagation delay correction has been performed) of the sink node received twice consecutively, tstamp and Tstamp correspond to local clocks of the sensor nodes in time synchronization twice, tstampx is a time stamp recorded when the ADC samples, and Tstampxnew is a corrected time stamp. The secondary correction reduces errors in the time stamp of the sampled data.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (7)
1. A UWB-based wireless measurement system, comprising: the sensor node is connected with the sink node through a UWB network, and the sink node is connected with the measurement and control center through a wireless network; the sink node and the sensor node adopt a low-power consumption design, the sink node acquires electric energy through solar energy, and the sensor node acquires electric energy through an alternating magnetic field formed by power line current; the sink node obtains standard time and position information through a GPS, the sensor node does not contain a GPS module, and time synchronization is realized between the sink node and the sensor node in the data communication process through a time synchronization mechanism; the sensor node marks a time stamp and a sampling period on the sampling data and sends the time stamp and the sampling period to the sink node, and the sink node forwards the sampling data of the sensor node to the measurement and control center and temporarily stores the sampling data in a local place; the measurement and control center analyzes and calculates the sampling data of different sink nodes, and controls or configures parameters of the sink nodes and the sensor nodes;
the sink node comprises: the sink node MCU module, the GPS time service and positioning module, the 4G communication module, the UWB communication module, the solar battery and the electric energy storage module are connected with the sink node MCU module; wherein:
The sink node acquires current sampling data of each phase of the power line from the sensor node through the UWB communication module, stores the current sampling data in FLASH and periodically transmits the current sampling data to the measurement and control center through the 4G communication module; the sink node acquires UTC standard clocks and positions through a GPS time service and positioning module, and then performs time synchronization on each sensor node through a UWB network;
The TIM2 timer of the MCU is a 32-bit counter, so that local clock timing of the sink node is realized, the TIM2 is configured to be interrupted once every 10 milliseconds, a TIM2 interrupt program obtains compensation quantity through a real-time clock compensation module, reads a cache clock value when interrupted last time from a real-time clock buffer, obtains the real-time clock value at this time after +10 milliseconds+the compensation quantity according to the cache clock value when interrupted last time, and stores the real-time clock value at this time into the real-time clock buffer again;
The MCU acquires the GPS time stamp of the GPS standard clock in an interrupt mode, and simultaneously acquires the local time stamp of the sink node through the real-time clock reading module, and the sink node acquires the compensation quantity Tac required by the real-time clock compensation module to calculate each interrupt of the TIM2 through the following formula:
Wherein: tgps1 and Tgps are GPS time stamps obtained twice consecutively, tagg1 and Tagg2 are local time stamps of sink nodes corresponding to Tgps1 and Tgps respectively, and Tap is a periodical micro-step correction time of the sink nodes.
2. The wireless measurement system of claim 1, wherein the sink node and the sensor node employ micro-steps to correct the local clock in real time for ensuring a unidirectional smooth increase in macroscopic time and time stamp.
3. The wireless measurement system of claim 1, wherein the backward secondary timestamp correction is performed on sampled data having a longer time synchronization interval.
4. The wireless measurement system of claim 1, wherein the sink node MCU module includes a sink node local clock correction module, wherein: the sink node local clock correction module comprises a temperature compensation crystal oscillator, a TIM2 timer of the MCU, a real-time clock buffer, a GPS standard clock, a real-time clock compensation module and a real-time clock reading module which are connected with each other.
5. The wireless measurement system of claim 2, wherein the error Tc of the local clock of the sensor node is calculated according to the formula:
Wherein: TA1 and TA2 are respectively standard time of the sink node received by the sensor node twice continuously, TS1 and TS2 are respectively local time stamps of the sensor node corresponding to TA1 and TA2, and Tp is periodical micro-step correction time of the sensor node.
6. The wireless measurement system of claim 5, wherein the standard time of the sink node received by the sensor node is obtained by the sensor node extracting a real-time clock plus Tmm1 delay from a data packet received by the sink node, wherein:
Tmm1＝(Tmu+Tum)+Tuu1
Tmu is the delay between MCU to UWB; tum is the delay from UWB to MCU; tuu1 is the sum of time from the transmit register to the transmit antenna, the transmit antenna to the receive antenna, and the receive antenna to the receive register of the UWB transceiver chip.
7. The wireless measurement system of any of claims 1-6, wherein the sensor node comprises: the sensor node MCU module and UWB communication module, current detection module and electric energy collection and storage module that are connected with it, wherein:
The power harvesting and storage module includes: the device comprises a mutual inductance power taking coil, a rectifying filtering and voltage limiting circuit, a BQ 24650-based lithium iron phosphate charging circuit and a lithium iron phosphate battery; wherein: the mutual inductance electricity taking coil is equivalent to a transformer, an opening magnetic ring of the mutual inductance electricity taking coil clamps a power line, the power line is taken as a primary side coil, and a coil wound on the magnetic ring is taken as a secondary coil; the electric energy in the power line coupling process is changed into direct-current voltage after passing through a rectifying and filtering circuit and a voltage limiting circuit, the direct-current voltage charges a lithium iron phosphate battery through a BQ24650 lithium iron phosphate charging circuit, and the lithium iron phosphate battery stores the electric energy;
The current detection module is used for converting a current signal of the high-voltage power line into an ADC voltage input signal of the MCU, and comprises the following components: high-precision current transformer, precision resistor and voltage amplifier.
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