CN101561245A - Bridge strain detection sensor based on wireless sensor network interface - Google Patents

Abstract

The invention discloses a bridge strain detection sensor based on a wireless sensing network interface. The data acquisition module of the sensor is connected with the weak signal conditioning amplifier module, the weak signal conditioning amplifier module is connected with the data processing module, the data processing module is connected with the wireless transmission module, the wireless transmission module is connected with the wireless receiving module, finally, the wireless receiving module is connected with the PC terminal, the ATmega128L singlechip in the data processing module is provided with ten-bit ADC conversion ports of eight channels, accordingly, the strain detection sensor can detect strain signals of the eight channels, and therefore wireless transmission is carried out through the CC2420 radio frequency chip of the wireless transmission module. And after being received by the wireless receiving module, the data is transmitted to the PC terminal through the SPI bus. The invention tests the bearing capacity of the existing bridge and verifies the structural design of the developed bridge, and has the characteristics of no wiring, high detection efficiency, real-time monitoring and the like.

Description

A bridge strain detection sensor based on wireless sensor network interface

technical field

The invention relates to a bridge load detection technology, in particular to a bridge strain detection sensor based on a wireless sensor network interface.

Background technique

Bridge strain detection plays an important role in the research, design, construction and acceptance of bridges. At present, the commonly used bridge strain detection method is bridge strain detection based on cable transmission.

In the bridge strain detection of wired cable transmission, the transmission is completed by wired cable. First of all, although this technical method has the advantages of high data transmission efficiency and mature technology, in the test of long-span bridge structures, as the span of the bridge continues to increase, the number of sensors and the amount of wired cables increase sharply, resulting in on-site Arranging and evacuating wired cables requires a lot of work, a long test cycle, and low efficiency, which may even make it difficult to implement the wiring workload of several kilometers of wired cables. The distribution of many wired cables is complicated and messy, and it is easy to connect the wrong wires, which will bring irreparable losses to the later data processing. Secondly, analog signal transmission is used in the traditional wired cable transmission mode, which makes crosstalk between cables easy to occur. Not only that, but the signal is especially disturbed by temperature and electromagnetic waves. As a result, the data cannot correctly reflect the bridge strain detection information. Finally, the current existing bridge strain detection sensors are expensive, so they are not suitable for the national consumption level of our country.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a bridge strain detection sensor based on a wireless sensor network interface. Since the data transmission between the sensor and the Sink node uses digital signals, this effectively improves the anti-interference of the data. And the present invention highly integrates collection, processing, and wireless transmission together, so that the integration degree of this node is greatly improved.

Technical scheme of the present invention is realized like this:

A bridge strain detection sensor based on a wireless sensor network interface, including a data acquisition module, a weak signal conditioning amplifier module, a data processing module, a wireless transmission module, a wireless receiving module, a 5V power supply module and a 3.3V power supply module. The data acquisition module of the sensor is connected with the weak signal conditioning amplifier module, and the two parts are powered by the 5V power supply module. The weak signal conditioning amplification module is connected to the data processing module, the data processing module is connected to the wireless transmission module, the wireless transmission module is connected to the wireless receiving module, and finally the wireless receiving module is connected to the PC terminal through the SPI bus. The wireless transmission module and the wireless receiving module are powered by a 3.3V power supply module.

The single chip chip ATmega128L in the data processing module has an eight-channel ten-bit ADC conversion port, so the strain detection sensor can detect eight-channel strain signals, which are sent wirelessly by the radio frequency chip CC2420 of the wireless transmission module.

The data acquisition module is composed of a balanced electric bridge, which contains two 1K strain gauges connected from Q1 and Q2 respectively, and two precision fine-tuning potentiometers R1 and R2, half of the bridge arm is controlled by a strain gauge The plate and a precision fine-tuning potentiometer are connected in series. At the non-ground ends of the two potentiometers, two signal lines are drawn out as the differential input signal of the amplifier module. When the strain gauge is deformed by force, the bridge loses balance, resulting in Differential signal, the differential signal is connected to the weak signal conditioning amplifier module, and connected to pins 2 and 3 of the instrumentation amplifier AD620AN of the weak signal conditioning amplifier module.

The bias voltage is essentially a voltage divider, which is composed of a 1K resistor and a 2K precision trimmer in series, and a voltage of +5V is added to both ends of it, and then a signal is drawn from the connection point of the resistor and the potentiometer The line is connected to the 5-pin of the instrumentation amplifier AD620AN to change the negative voltage into a positive voltage. Pin 6 outputs the amplified voltage. Connect this voltage signal to the analog-to-digital conversion (ADC) port of the single-chip microcomputer chip ATMega128L connected to the data processing module. The voltage signal is converted into a digital signal through A/D, and the digital signal is connected with the radio frequency chip CC2420 of the wireless transmission module.

The data communication between the data processing module and the wireless transmission module is based on the SPI bus. The radio frequency chip CC2420 in the wireless transmission module corresponds to the ports SI, SO, CSN, and SCLK respectively and the MOSI, MISO, SS, The SCK port is connected for data communication. The wireless transmission signal is a digital signal. The transmission frequency of CC2420 is 2.4G～2.4835GHz, and there are 16 transmission channels in total. The transmission path is determined by the routing information generated by the routing simulation platform, so as to realize the multi-hop wireless transmission of data.

The combination of the data processing module and the wireless transmission module realizes data processing and wireless transmission. Their combination is the same as the structure of the wireless receiving module, the difference is that the data processing module is connected with the weak signal conditioning amplifier module to realize the AD conversion of the data, and then the data is sent wirelessly by the radio frequency chip; while the wireless receiving module is The total sink node of the whole wireless sensor network. It is used to connect with the host computer to realize receiving the data sent from the transmission module.

The wireless receiving module is composed of AVR microcontroller chip ATMega128L, memory AT45DB041, radio frequency chip CC2420 and peripheral circuits. It communicates the digital signal received wirelessly with the PC terminal through the SPI bus. The AVCC and VCC ports in ATmega128L are connected to the 8 ports of the 3.3V power supply module. Connect the 28, 30, 48 and 27 pins of ATmega128L to the 1, 2, 4 and 8 pins of the memory AT45DB041 respectively to realize the communication between the microcontroller and the auxiliary memory. Pins 10, 11, 12 and 13 are connected to pins 31, 32, 33 and 34 of CC2420 respectively to realize data communication between the single-chip microcomputer and the radio frequency chip. The pins 51, 50 and 49 of ATmega128L are respectively connected to three light-emitting diodes, which are used to indicate the data sending status, data receiving status and routing receiving status. Pins 2 and 3 are connected to the serial port of the host computer to realize the communication between the Sink node and the host computer. ATmega128L pins 18 and 19 are externally connected to a 32.768KHz active crystal oscillator, and pins 23 and 24 are externally connected to a 7.3728MHz passive crystal oscillator. The two crystal oscillators of ATmega128L are used for the working state and sleep state of the node respectively. CC2420 only needs very few peripheral components, and its peripheral circuit includes three parts: crystal oscillator clock circuit, radio frequency input/output matching circuit and microcontroller interface circuit. Pins 38 and 39 of CC2420 are externally connected with a 16MHz crystal oscillator and two 22pF load capacitors. The RF input/output matching circuit is mainly used to match the input and output impedance of the chip so that the input and output impedance is 50Ω, and at the same time provide DC bias for the PA and LNA inside the chip. CC2420 can set the working mode of the chip through the 4-wire SPI bus (SI, SO, SCLK, CSn) and realize read/write cache data read/write status register, etc. The transmit/receive buffer can be set by controlling the state of the FIFO and FIFOP pin interface.

First of all, the data acquisition module forms a Wheatstone bridge by arranging distributed equidistant multiple strain gauges and the same number of precision adjustable potentiometers on the most unfavorable positive bending moment section of the bridge, so that real-time representative bridges can be measured Differential signal of physical properties - pressure deformation signal. Then the signal is connected to the weak signal conditioning amplifier, through the AD620AN chip, the collected analog signal is appropriately amplified, and the system performs A/D conversion on the received data through the data processing core chip AVR microcontroller, and then through the special radio frequency chip CC2420 converts the digital signal into a data frame and sends it to the Sink node in the form of 802.15.4 protocol. Finally, the wireless receiving module communicates with the host computer through the SPI bus. The host computer obtains the detection data by analyzing the frame format. In this way, real-time and accurate analysis and judgment can be made on the health status and damage status of the bridge structure.

The present invention has the following advantages:

1. The bridge strain detection sensor adopts IEEE802.15.4/Zigbee protocol for data transmission. It avoids large-scale wiring of traditional bridge strain testing equipment, realizes the advantages of no wiring in the testing process, shortened testing cycle, and improved efficiency.

2. The sensor adopts digital signal wireless transmission, which avoids the problems of cable crosstalk, temperature and electromagnetic wave interference caused by analog signals in wired transmission. Thereby effectively improving the anti-interference ability.

3. The bridge strain detection sensor has the advantages of small size, portability, and low energy consumption. Because data acquisition, signal conditioning, data processing and data wireless transmission modules all use low-power chips, and the single-chip microcomputer has a unique sleep mode, which effectively guarantees the characteristics of low power consumption and long life of sensors and networks.

4. The sensors communicate with the Sink node at a transmission rate of not less than 250kbps, and the transmission adopts an intermediate multi-hop mode, thereby improving the security of data transmission and extending the transmission distance, which is suitable for the detection of long-span bridges.

In the invention, the node realizes technical difficulties such as no need for wiring, strong anti-interference, high transmission rate, large bridge span detection, shortened test cycle, etc., and completes a high-precision, high real-time, and cost-effective wireless sensor network interface Development of a multi-channel bridge strain detection sensor.

Description of drawings

Figure 1 is a flow chart of the system structure

Figure 2 is a circuit design diagram

(a) Connection circuit diagram of data acquisition module and weak signal conditioning amplifier

(b) SCM chip circuit diagram in the data processing module

(c) Circuit diagram of the radio frequency chip in the wireless transmission module and the wireless receiving module

(d) 5V power supply module circuit diagram

(e) 3.3V power supply module circuit diagram

Fig. 3 is a functional block diagram of the present invention;

Figure 4 is a flow chart of the lower computer software of the wireless sensor network.

The content of the present invention will be described in further detail below in conjunction with the accompanying drawings.

Detailed ways

The multi-channel bridge strain detection sensor with a wireless sensor network interface of the present invention is composed of an adhesive strain gauge bridge, a power supply circuit, an amplification conditioning filter circuit, a single-chip microcomputer chip ATmega128L, a CC2420 radio frequency circuit and a computer.

Referring to Figure 1, the data acquisition module is connected to the weak signal conditioning and amplification module to collect the deformation of the bridge when it is under pressure. The data acquisition module is a bridge circuit composed of strain gauges and precision trimmer potentiometers. Signal conditioning amplifies and filters the collected millivolt level voltage to the range of 0-3.3V, and then sends it to the data processing module for A/D conversion. The data processing module is composed of ATmega128L chip and its power supply module. This one-chip computer has 10 ADC ports of 8 channels, has guaranteed the characteristic that A/D changes the precision and is high. The data processing module is connected with the wireless transmission module, and is used for wirelessly sending the converted digital signal through the built-in PCB antenna. The wireless transmission module can send data to the Sink node, and can also receive the wireless route sent by the Sink. The data frame is sent to the Sink node through the PCB antenna based on the 802.15.4 protocol. The wireless receiving module is connected with the PC terminal. The Sink node parses the received data frame and extracts the required detection data. Since the data collected at this time is voltage information, it is necessary to calibrate the physical quantity through the strain gauge. Thus the PC can display the collected bridge load parameters.

As shown in Figure 2, the data acquisition module is composed of a balanced bridge, the data acquisition and weak signal conditioning amplifier module is provided by the 5V power supply module to connect the working voltage of this part of the circuit, and the VCC terminal in the figure is connected to the 5 port of the 5V power supply module . The bridge contains two 1K strain gauges (respectively connected from Q1 and Q2), two fine-tuning potentiometers (R1 and R2), half of the bridge arm is composed of a strain gauge and a fine-tuning potentiometer It is formed in series, and at the non-ground ends of the two potentiometers, two signal lines are drawn out as the differential input signals of the amplifier module. When the strain gauges are deformed by force, the bridge is out of balance and a differential signal is generated. The differential signal is connected to the weak signal conditioning amplifier module, and connected to pins 2 and 3 of the instrumentation amplifier AD620AN of the weak signal conditioning amplifier module for amplification and conditioning. The weak signal conditioning amplifier module is mainly composed of the instrumentation amplifier chip AD620AN. The output bias voltage is provided by pin 5, and the amplified voltage is output by pin 6.

Since the ADC port of the single chip microcomputer can only recognize positive voltage, and the amplified output of the differential signal has positive and negative signals, a bias voltage is added to the weak signal conditioning amplifier module. The bias voltage is a voltage divider, which is composed of a 1K resistor and a 2K precision trimmer in series, so that the amplified output signal is always positive. The AD620AN amplified output pin (pin 6) is connected with the A/D conversion pin (pin 59) of the AVR microcontroller.

Referring to Figure 2(b), the AVCC and VCC ports in the chip are connected to the 8 ports of the 3.3V power supply module. The 28, 30, 48 and 27 pins of the chip are connected with the 1, 2, 4 and 8 pins of the memory AT45DB041 respectively to realize the communication between the single-chip microcomputer and the auxiliary memory. Pins 10, 11, 12 and 13 are connected to pins 31, 32, 33 and 34 of CC2420 respectively to realize data communication between the single-chip microcomputer and the radio frequency chip. Pins 51, 50 and 49 are respectively connected to three light-emitting diodes, which are used to indicate data sending status, data receiving status and routing receiving status. Pins 2 and 3 are connected to the serial port of the host computer to realize the communication between the Sink node and the host computer. Pins 18 and 19 are externally connected to a 32.768KHz active crystal oscillator, and pins 23 and 24 are externally connected to a 7.3728MHz passive crystal oscillator. The two crystal oscillators of this system are used for the working state and sleep state of the node respectively. In order to prolong the transmission distance in the process of wireless transmission, a multi-hop relay method is adopted. This method will cause the processor of a certain node to collect a large amount of data, and the internal storage space of the processor is very limited. , adding an auxiliary memory module - AT45DB041, which contains 2048 pages, each page has a space of 264 bytes, thus greatly increasing the storage capacity of each processing node. The communication between the single-chip microcomputer and the auxiliary memory is based on the SPI bus, and the single-chip microcomputer completes the reading and writing operation of the auxiliary memory under strict clock control according to the reading and writing operation codes of the auxiliary memory.

Referring to Figure 2(c), the 8 ports of the 3.3V power supply module are connected to the DVDD_3.3V port of the CC2420 chip to provide the working voltage of the chip. Reset (pin 21), frame start delimiter (pin 27), channel idle flag (pin 28), FIFO (pin 29), FIFOP (pin 30), chip select signal (pin 31), SPI clock signal (pin 32 pin), SPI input (33 pins), SPI output (34 pins), and voltage regulator enable (41 pins) are connected to ATmega128L. It uses SPI interface, when CS goes low, the SPI communication cycle of CC2420 starts. After the chip is "selected", start driving the SCLK clock signal. On the rising edge of SCLK signal, CC2420 samples the data on SI and SO. On the falling edge of SCLK signal, if the operation mode of SO is output, CC2420 will change the data on SO. When this cycle is complete, stop driving SCLK and bring the CS signal high. The 30 port of CC2420 is connected with the port 17 of the one-chip computer. When the FIFO (30 pin) is high level, it means that there is data in the receiving buffer, and when it is low level, it means that the buffer is empty. When the FIFOP (pin 29) of CC2420 is high level, it means that the receiving buffer overflows, otherwise there is no overflow. When CCA (28 pins) is high level, it means that the data transmission channel is idle, otherwise the channel is busy. When the SFD (pin 27) is at a high level, it means that the start of frame character has been received and data (including address information) is started to be received, and the port will remain at a high level until the data is received. In the process of receiving data, if the address identification is wrong, the level of SFD will jump to low level, thus terminating the receiving of data.

Referring to Figure 2(d), it mainly provides a working voltage of 5V for the data acquisition module and the weak signal conditioning amplifier module. First, two dry batteries are used to provide an input voltage of 1.5V to 3.0V for the MAX631 chip. Port 4 of the MAX631 is used as the input of the battery voltage, ports 1, 3 and 7 are grounded, and then port 5 is used as the output port after boosting. When the battery power supply is normal, the output voltage of this port is +5V. At the same time, the peripheral circuit of MAX631 is very simple. A 330mH energy storage inductor is connected between port 4 and the positive pole of the battery, and a 100uF electrolytic capacitor is connected between port 5 and ground to remove noise. The VCC shown in the figure is connected to port 5 of MAX631.

Referring to Fig. 2(e), the power supply module is mainly used to supply power to the single-chip microcomputer chip ATMega128L of the data processing module, the radio frequency chip CC2420 in the wireless transmission module and the wireless receiving module. The power supply module uses the MAX1678 chip. The positive input of two dry batteries is connected to its ports 1, 4, and 7, and the ports 5 and 6 are connected to the negative electrode of the battery. Port 8 outputs a boosted 3.3V voltage. A 47uH inductance is connected between the 7 ports, and a 10uF electrolytic capacitor is connected between the 8 port and the ground. The 8 ports are connected to AVCC and VCC in Figure 2(b) to provide the working voltage of the ATMega128L chip; the 8 ports are connected to DVDD_3.3V in Figure 2(c) to provide the working voltage of the RF chip CC2420.

As shown in Figure 3, the indicator light component mainly controls the on-off and flickering of the three indicator lights to indicate the current working state of the system; the clock component realizes the control of the timer, closes and opens the timer, sets the timing interval, and Generate timing interrupts; the serial port component realizes the communication between the embedded node and the host computer, performs data transmission and generates debugging information; the EEPROM component controls the read and write operations of the EEPROM; the data sampling component is responsible for analog acquisition and analog-to-digital conversion, and generates conversion Interrupt; the wireless communication component controls the communication channel, the working status of the radio frequency chip, and performs wireless data transmission and reception, thereby realizing communication between networks. The entire embedded system realizes the overall function of wireless detection by calling and cooperating among the above modules.

Referring to Figure 4, after the program is started, it starts to initialize the ports, registers and radio frequency chips of the single-chip microcomputer. After the initialization is completed, check whether the node exists in the network. path, start to collect data and prepare to receive data, when the node collects data or receives data packets, judge whether it is control command information, if so, execute the command, sleep or wake up the node; if it is not command information, then judge the node number Whether it is 0, if not, it will be forwarded according to the routing path; if it is, it will be sent to the host computer through the serial port.

Claims (3)

1, a kind of bridge strain detection sensor based on wireless sensing network interface, comprise data acquisition module, weak signal conditioning amplifier module, data processing module, wireless transport module and wireless receiving module five parts are formed, it is characterized in that, the data acquisition module of this sensor is connected with weak signal conditioning amplification module, weak signal conditioning amplification module is connected with data processing module, data processing module is connected with wireless transport module, wireless transport module is connected with wireless receiving module, last wireless receiving module connects the PC terminal, and wherein the singlechip chip ATmega128L in the data processing module has ten ADC conversion port of eight passages.

2, sensor according to claim 1, it is characterized in that, described data acquisition module is made up of a balanced bridge, the foil gauge that comprises two 1K in the electric bridge inserts respectively from Q1 and Q2, the potentiometer R1 and the R2 of two Precision trimmings, half brachium pontis of electric bridge is made of a foil gauge and a Precision trimming potentiometer series connection, non-earth terminal at two potentiometers, draw the differential input signal of two signal wires as amplification module, when foil gauge during because of stressed generation deformation, the electric bridge out of trim, thereby generation differential signal, this differential signal is connected with weak signal conditioning amplifier module, inserts 2,3 pin of the instrument amplifier AD620AN of weak signal conditioning amplifier module.

3, sensor according to claim 1, it is characterized in that, the data communication of data processing module and wireless transport module is based on spi bus, its corresponding port SI, SO, CSN, SCLK link to each other with MOSI, MISO, SS, the SCK port of single-chip microcomputer respectively to realize data communication, the signal of this wireless transmission is a digital signal, transmission frequency has 16 transmission channels at 2.4G～2.4835G Hz.

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