Design of Data Acquisition and Dispatch System of Radio Station Center

I. Introduction

This article describes the design of a radio station data acquisition and control system implemented by MTU (Master Terminal Unit central dispatcher) and RTU radio telemetry technology using AVR single-chip microcomputer and dedicated MODEM chip. The system uses remote RTUs (the system can carry 256 RTUs) distributed on the city's pipeline monitoring points for data collection, and then sends data to the central dispatcher through the radio station. The central dispatcher receives the data and performs data processing. The data is stored and sent to the analog screen for display.

2. Design Ideas

In the use of the original system, there are mainly the following problems: 1. Low baud rate of wireless communication (300 bps), high bit error rate, slow patrol speed, up to 32 RTU terminals; 2. When a certain remote RTU The radio station at the end has been in the state of long-term mistransmission (abbreviated as "long hair") has been occupying the system frequency point, because the system shares a set of radio frequency points, which will make all other radio stations in the system unable to communicate, the entire system is paralyzed and is in a fault The radio cannot send valid data, so it is impossible to determine the fault point. The pressure measurement points are distributed in a wide and scattered area, making fault finding very difficult, often requiring several days; 3. Low RTU board integration, high failure rate, and difficult components purchase.

Considering the versatility of the system and the actual situation of the company, it is required that the RTU system can make full use of the original radio station, antenna, power supply, analog screen, detection instrument, etc., and can achieve the following functions: 8 channels of 10-bit analog input , 8-channel switch input and two-channel pulse input, of which 8-channel switch input can be expanded to 64-channel switch input, can store 24-hour historical data (15 minutes / time) in RTU station, and has power-off protection function.

Through the organic cooperation of hardware and software, we have solved the existing system problems and system functional requirements cost-effectively, so that the MTU board and RTU board are completely consistent in hardware, and wireless modulation and demodulation that are usually independent of the RTU board MODEM is integrated on the RTU board, which simplifies the hardware structure of the system. The RTU board of this system has a wireless communication baud rate of 1200bps, a low bit error rate, and up to 256 RTU terminals, which effectively solves the problem of system paralysis caused by the "long hair" of the radio station, high data collection accuracy, and high RTU board integration , Strong versatility, easy software upgrades and other advantages.

3. Design of RTU

1. Selection of components

The CPU selects ATMEL's AVR series microcontroller AT90S8535. This chip is a relatively new type of microcontroller. Its internal resources are as follows: 8K byte FLASH program memory, 512 byte EEPROM data memory, 8-channel 10-bit precision A / D converter, a standard Serial port, one 16-bit timer / counter, one 8-bit timer / counter, one real-time clock, two external interrupts, built-in watchdog circuit, etc. The functions required by RTU and the data acquisition function can be basically realized on this single chip microcomputer; the connection with the radio station selects the MSM7512B MODEM chip of OKI company for modulation and demodulation, the communication with the computer selects the MAX232 chip, and the historical data storage selects 8K words The serial EEPROM memory chip AT24C64, the power supply of the radio is controlled by the CPU, and is provided through the relay.

2. Data communication

(1) Communication between RS-232 serial port and PC

Because the only serial port of the single-chip microcomputer is used for the communication of the radio station, the accuracy of the wireless communication is first guaranteed. Communication with PC through MAX232 chip converts the TTL level of the single-chip microcomputer into the standard RS-232 level, using the external interrupt INT0, INT1 port and I / O port of the single-chip microcomputer, application software simulation to achieve two baud rates 9600Bps half-duplex three-wire serial communication, its receiving data uses interrupt mode.

(2) Wireless communication between radio stations

We integrated the wireless modem MODEM, which is usually independent of the RTU board, on the RTU board, which simplifies the hardware structure of the system, reduces the cost, and improves the reliability of communication, and realizes the close combination of RTU and MODEM. The MODEM chip selects the MSM7512B modulation and demodulation chip from OKI. The MSM7512B is a relatively mature chip with a communication baud rate of 1200Bps and a working mode of half-duplex mode. In practice, we found that there is a period of unstable state at the moment when the radio station changes from the receiving state to the transmitting state or from the transmitting state to the receiving state. The data at this time is prone to error codes. According to the experiment, a more suitable delay is obtained. Time and time, we delay the appropriate time after controlling the radio station to send and receive conversion, so that the reliability and accuracy of data transmission has been greatly improved. In the process of data transmission, system code, RTU station code, checksum of low value of sum value are added to ensure the reliability and correctness of system communication.

4 Layer PCB

4 layer PCB Board

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