CAN bus based distributed grid sub-health monitoring system

Abstract: In view of the need for safety monitoring of a grid design of a distributed health monitoring system, introduced in the distributed system using controller area network (CAN) communication network module form a distributed program. Detail based on the CAN bus controller SJAl000 acquisition system design and specific design of hardware and software design to solve easily in the problems encountered.

In the construction of a large network structure, because of the special network structure and its geographical location in the typhoon-prone coastal areas, requiring high-speed data acquisition system designed network structure of the health status of the real-time monitoring, and data real-time analysis and assessment. Due to the need by the force conditions on the grid on the multi-point monitoring, consider Dao hardware Jizhongkongzhi Kuozhannengli Chai and Zai Xian Chang construction has Jiaoda the wiring Kunnan for this reason, a widely used in 分布式 system design, Jiang Ge Ge control unit located in the collection point on the scene. In order to achieve a distributed system monitoring and control functions, need to establish good communication in order to complete the system host with the intelligence unit of information exchange and communication between. According to the characteristics of the data acquisition system, its communications system should have good reliability, adaptability, scalability and simplicity of connection, and can meet the needs of long-distance transmission. Because this data collection system over the number of nodes (100 Lu), on the signal transmission speed is high and low bit error rate, using 485 data acquisition system built the traditional way, the maximum control point can only have 32 of the more than lkm speed routing structure only lOOkbps, and the "data collision" and "deadlock" and other issues not easily resolved, with 485 clearly does not meet design requirements.

CAN bus based distributed grid sub-health monitoring system

Compared with the traditional 485 speaking, the controller area network CAN (Controller Area Network) as a field bus, with its time-sharing multi-master, non-destructive automatic bus arbitration and error detection re-issued so flexible and reliable communications technology solve the 485 on-site commissioning difficulties, problems and long development cycle [1]. Especially in the more difficult installation environments, efficient on-site commissioning performance is particularly useful. As a decentralized, Shu Zi technology, two-way multi-point, high reliability, high-speed characteristics of the communication system, CAN can Goujianlinghuo of multi-master communication system, also can create a master Cong-style Jie Gou, and these two kinds of modes of hardware Wuli exactly the same connection. The automatic data encoding, CRC redundancy check, error automatic retransmission of data is assured with the accuracy of a serious error when a node from the bus automatically guarantee the stability of the system, and its load with a very strong band ability to drive up to 110 nodes, the system can meet the high-speed, precision, multi-load requirements.

An acquisition card hardware design

1.1 CAN bus Distributed System Design

System architecture shown in Figure 1. The system consists of host PC, monitor, CAN bus adapter and control unit composed of three parts. Upper monitor PCs using IBM-PC compatible machine, is mainly responsible for receiving and managing system data and control commands sent and the dynamic parameters of the control units and equipment, real-time status display; CAN bus adapter can easily connect to PC, to the CAN bus; control unit with microcontroller core, primarily responsible for on-site state of Huanjingcanshu and Shebei to monitor, for packaging of data from processing and handling of Shuozixinhao Guo Tong Xin by CAN controller SJA1000 CAN bus into .

CAN bus based distributed grid sub-health monitoring system

1.2 Control Unit module design and solution of key issues

The main function of the control unit is on-site collection of analog signals into digital signals, after processing through the CPU package sent by the CAN bus CAN bus controller for receiving and processing host computer; to receive control signal PC, the specific operation for field control . Specific issues need to be addressed: ① CAN module design; ② A / D Module.

1.2.1 CAN Module

Control unit with 8-bit microcontroller AT89C51 core, used as a device SJA1000 CAN controller and 82C250 and 6N137 silicon used as the CAN controller interface and opto-isolation. Hardware circuit shown in Figure 2.

System uses the CAN bus communication controller PHILIPS SJA1000 is a stand-alone company CAN device, the block diagram shown in Figure 3. It CAN2. OB-compatible [1], while supporting 11 (BasicCAN mode) and 29 (PeliCAN mode) identifier.

Figure 2 AT89C51 MCU ALE, WR, RD control the SJA1000, respectively end of ALE / AS, WR, RD client, address and data lines ADO ~ AD7 by the P0 port time division multiplexing to achieve. SJA1000 interrupt request signal INT interrupt in the interrupt occurs to allow and there, from high power to the transition to a low level, so the INT0 AT89C51 INT and directly connected. GAL chip select signal CS from the decoder circuit control, when the CS receives low when, SJA1000 is selected, CPU can SJA1000 to read / write operations. In order to enhance the control node of anti-interference ability, to prevent crosstalk between lines, SJA1000 is connected through the optocoupler 6N137 and 82C250, so that each CAN bus isolation between nodes in order to protect the CAN controller is working properly. 82C250 is a CAN bus transceiver is a CAN controller SJA1000 CAN Bus to work with the interface device, the differential CAN bus to be sent. The RS pin is used to select the work 82C250 mode (high-speed, slope control, or wait). RS pin to ground, 82C250 work in high-speed mode, RS incorporates a foot after the grounding resistance R, if the 82C250 CAN bus network in the terminal, bus interface part of the match to add a 120Ω resistor to protect the 82C250 from over-current shocks.

CAN bus based distributed grid sub-health monitoring system

1.2.2 A / D Module

A / D chip select 12-bit high-speed acquisition chip AD574. In this design, A / D module is the function of the external analog signal into digital signal through the AD574 after the parallel input to the AT89C51, AT89C51 then be packed, parallel output to the CAN bus communication controller SJA1000, by bus to the CAN transceiver bus. The control circuit DS1232, which has the power monitoring, manual reset and watchdog functions, but also output the two-way high-low reset signal, respectively, AT89C51 and SJA1000 output to the reset terminal to meet the requirements of this design.

2 Software

The health monitoring system requirements for the software part of the digital signal with on-site show, the scene detection and drive signal equipment and so on. In this design was completed for two Bufen tasks: first yes part of the upper Ji PC machine display, the main Tongguojicheng Kaifahuanjing PC software designed Chu Jian Shi display interface, with its emphasis on PC, and Xian Chang nodes of the Tong Xin; second is scene node control design, that device driver functions to achieve the purpose of the control PC to receive the signal, so the scene nodes work according to the established way of working.

According to the system requirements for the work, work will focus on CAN bus communication procedures, watchdog initialization, A / D sampling control program, the implementing agency control procedures and control algorithms, the main process shown in Figure 4. Due to space limitations, here focuses on designing SJA1000 initialization, sending programming, to receive programming and A / D conversion process design.

2.1 SJA1000 initialization Design

Initialization flow chart shown in Figure 5. AT89C51 power on or reset, call the reset procedure to reset terminal SJA1000 (RST) to provide reset signals to enter the reset mode SJA1000. SJA1000 only in the reset initialization mode for that. Initialization process was completed for the design of the following registers: (1) by the clock frequency register SJA1000 definition, determine the use of BassicCAN mode or use PeliCAN mode; is enabled CLOCKOUT and output clock frequency; whether to use the bypass CAN enter more device; TX1 output is interrupted by a special receiver. (2) by written acceptance code register and the acceptance mask register defines the acceptance code to receive messages, and the acceptance packet and compare the code definition of the relevant bit acceptance mask code. (3) bus timing register by writing the definition of the bus bit rate and sampling points within the bit period and a number of samples within a bit period. (4) the output register by writing the definition of CAN-bus output pin TX0, TX1 output mode and output configuration. (5) removal of the reset request flag SJA1000 into normal mode, so SJA1000 before proceeding to send and receive packets.

2.2 send and receive programming

MCU will send the message to be sent to the sending buffer SJA1000, SJA1000 command register and then send the request flag (TR) set, the sending process independently from the SJA1000. Send a message to write in the new buffer, you must check the status of the sending buffer status register flag (TBS), if "1", then send the buffer to be released, you can write a new message to send buffer device; Otherwise, send buffer is locked, new packets can not be written, can be used to send program interrupt and query method. In this design, the use of the query.

Packet reception is completed independently by the SJA1000. Received packets stored in the FIFO through the receiver filter, the first message into the receiver buffer, the status register to receive buffer status flag (RBS) and receive interrupt flag (RI) are marked. SCM removed from the receiving buffer after a packet to the command by setting the bit SJA1000 to release the receiver buffer register. In this design, the receiving program is designed with the interrupt.

CAN bus based distributed grid sub-health monitoring system

2.3 A / D converter design

In this design uses a 12-bit successive approximation A / D converter AD574. Way to check the design process, through the continuous query A / D converter conversion end flag to judge whether the end. When the conversion finished, add anyone to the CPU in processing the data and save the processed data to the 6264 chip.

High-speed CAN bus design based on distributed data acquisition system has some value, but low price and high reliability. While the system is also scalable, multi-channel acquisition is required under the circumstances to maintain only a small amount of sample chips can be. Approved by this bus system's communication ability test, Bingqiangshangshu system in place for Lian Xu Jiang Ganraohuanjing experiments, found that the use of communication Sulvwanquan Ke Yi ensure data of Shi Shi Kekaochuanshu, Qi Tongxinxiaoguo fully meet the requirements, while the upper Jihe bottom node can ensure mutual coordination.