CAN bus based power meter reading system
About CAN Bus
CAN multi-master mode work, a node of the network office at any time can take the initiative to other nodes on the network to send information; CAN nodes on the network information into different priorities, can satisfy different real-time requirements; CAN bus using non-destructive arbitration techniques; CAN message filtering can be simply achieved by point to point, multipoint, and global broadcast data is sent and received in several ways; CAN direct communication distances of up to 10km (rate 5kbit / s below) communication speed up to 1Mbit / s (at this time communication distance up to 40m); CAN messages for each frame has a CRC checksum error detection and other measures to ensure that the data error rate is very low; CAN communication medium for double stranded wire, coaxial cable or optical cable, select flexible.
System Design
System consists of the following components: pulse meter, electricity collector, CAN converter, modem, PC. System block diagram shown in Figure 1.
CAN bus based power meter reading system
Figure 1 Block diagram of the power meter reading system
Can see from Figure 1, real-time acquisition charge collector residential building output pulse meter pulse signals transmitted by the CAN interface, CAN bus, and then the CAN converter conversion and Modem host computer and lower computer communications, in order to complete data collection, storage, measurement, display and other functions, on the whole cell situation of each user to achieve real-time monitoring.
System works
Electrical measurement of the acquisition
Rotary meter according to the structure, its pulse and dial the number of cycles of change is proportional to the number of pulses multiplied by the coefficient can be accumulated before the corresponding electrical measurement. To improve the accuracy of pulse measurement, software design methods with regular continuous sampling. An effective electric pulse width of 50ms or more, designed with the time period of 16ms. For the normal pulse, regular pulse measured by continuous sampling for the high frequency of ≥ 2, see Figure 2. If the pulse width is too small, not measured by the number 2, then you can get rid of this pulse.
Figure 2 Schematic diagram of pulse sampling inspection
Collector power
Power collector is the main function of pulse data, and communicate with the host computer. Its core components are AT89C52 microprocessor and interrupt controller 8259A. Systems, interrupt sources more than eight, so 8259A using cascade. Collector of each power under 5 8259A cascade, to meet the 32-way power signal input. Collector power block diagram shown in Figure 3.
CAN bus based power meter reading system
Figure 3 Block diagram of the collector charge
System, 8259A to control the external interrupt sources with AT89C52. 8259A for the AT89C52 analyze, judge, decide the priority of interrupt request signal. Interrupt signals from multiple meter was then taken by the input processing circuit 8259A. Which way is high, 8259A of the IRR (interrupt request register) the corresponding bit; then, 8259A its IRR and IMR (interrupt mask register ) for the situation analysis and processing, when a road is not IMR mask interrupt sources, and the way the priority level of interrupt source CPU is higher than the level of the transaction when, 8259A 17-pin to generate a high level, through the specialized application and respond to interrupt the circuit into a low power meter based on CAN bus system, the interrupt request made to the AT89C52, while waiting in line the rest of the interrupt and save. This pulse will not be lost, signal acquisition to ensure the accuracy of the system. , The instrument technologies and sensors would be more disruption for the AT89C52 interrupt the currently running application program and the priority level for and response by the interruption of the circuit response to the 8259A interrupt signal back to the electricity meter reading based on CAN bus system. At this time, AT89C52 turn to the implementation of the interrupt service routine.
For the protection of the data collected, the design of memory used. Storage area can be divided into two areas: a work area, storage, real-time power measurement, repeat it some time to refresh 1; a backup area for 6 months of electrical backup measure to prevent the loss of useful information.
For the convenience of the user query, the system can be displayed in the collector circuit was designed LCM103, to achieve local display. To its pin CS, WR, DA2TA and microcontroller interface can be achieved related to its display. Multiple interrupt sources of data used in LCM103 rotation display. LCM03 of 10 were defined as the user account can do, and do not display the data table. No. 10 for the household income, section 8 for the table do not, the remaining bit that the energy consumption figures of all tables, the first 3 digits of the decimal point. No. 9 and No. 7 as a space for clear reading.
Design, in LCM103 the VDD and VLCD plus 511kΩ resistor between pins to allow moderate display brightness.
CAN Interface Converter
CAN controller SJA1000 CAN converter and by the CAN driver PCA82C250 composition. CAN converter is responsible for receiving commands issued to the host computer to transmit the power site, a group linked to CAN bus up to 110 sites, the block diagram shown in Figure 4.
CAN bus based power meter reading system
Figure 4 CAN Controller Interface Functional Block Diagram
CAN converter
In order to achieve communication with the host computer microcontroller designed with TTL level conversion between RS-232 interface, as shown in Figure 5. AT89C52 itself does not contain the controller, so using the CAN controller SJA1000, and CAN drive PCA82C250.
CAN bus based power meter reading system
Figure 5 RS232/CAN functional block diagram of converter
CAN bus communication baud rate
Calculate the district control room PC with the power collector in the MCU communication baud rate 40.5Kbit / s, take 50Kbit / s, this time CAN bus communication distance up to 1.5km, if the control room was built in load center, the communication meet the requirements from. At this point bus timing register BTR0 and BTR1 were BTR0 = 47H = 01000111B, BTR1 = 2FH = 0011111B. Moreover, in order to make the site work within the system simultaneously, the PC must be the whole point of time when the school issued an order to the site.
Software Design
Mainly on the design of the collector for a brief description of the main program. It includes the initialization and data acquisition and processing of two parts. Initialization procedure includes initialization 8259A. In the data collection, the collector main program loop to take the way of data collection, and to classify the received command, and then switch to the appropriate command processing subroutine. The main program flow chart shown in Figure 6.
Anti-jamming measures
(1) in the system design, the use of the X5045 chip, the chip has a watchdog circuit. Watchdog circuit for real-time monitoring of CPU, if the CPU into an infinite loop, the watchdog circuit can discover and to reset the entire system. In software programming, set to visit every 1s 1 watchdog circuit. If the program running or flying over a set time (the system set to 1.4s) did not visit the watchdog chip, X5045 chip will automatically reset pulse output until the program runs properly.
(2) data acquisition device with filter circuit, the various forms produced by electrical pulse signal is filtered to prevent the signal during transmission may be subject to interference.
(3) the use of X5045 chip power supply monitoring circuit monitoring feature set and power down protection circuit to prevent data loss after power-down.
CAN bus based power meter reading system
Conclusion
CAN bus based power meter reading system uses a smart data acquisition, data communication via CAN bus exchange, the system response speed, anti-jamming; network reliability high, communication baud rate, data transfer volume; structure simple to install, easy to maintain. System can easily achieve real-time monitoring, high-speed data acquisition, look-up table printing, system monitoring and other functions, has a good prospect.