Key words: OPTO 22 SNAP I / O; PLC; control system; MODBUS; agreement

1, an overview of
Daqing Oilfield red pressure cryogenic gas plant is the largest branch of the gas and natural gas treatment plant, the volume of natural gas per day to deal with
90 Million, more than 200 tons of light hydrocarbon production. According to the cryogenic gas separation plant automation control system design requirements,
as a result of the PLC-related equipment are widely distributed monitoring requirements of a high degree of automation and the rapid access to information and treatment and to manage and easy. Therefore, automatic control system to OPTO 22's SNAP I / O system as the backbone of the framework, combined with its extremely easy-to-use-the-art application development software configuration Factory Floor Suit 4.0c, in the 32-bit WINDOWS operating platform, which is developed Will be completed in a simple system to monitor a variety of functions, but also has flexibility in the use of man-machine interface of cryogenic gas separation plant automation control system application software to monitor the process at the district unit of temperature, pressure, pressure, valve and so on. Device inside the compressor, expander, propane refrigerator, ESD systems and emergency parking OPTO 22 SNAP I / O through the communications system for data exchange, as the unit's own PLC system from multiple manufacturers, telecommunications standard, a technical difficulty Great.
we continue to explore, practice, in a relatively short time, the successful completion of a number of communication problems between the system so that the system has high reliability and compatibility, easy to operate, and other advantages and savings for investment projects.

2, communications systems require
1) with real-time data communication capabilities, the use of OPTO 22 products, strong communication advantages, real-time production data will be transmitted to the OPTO 22 SNAP I / O system.
2) improve the safety monitoring functions. OPTO 22 SNAP I / O system to receive reports of the Alarm unit communication signals can be recorded in a timely manner and implement appropriate control procedures at the scene.
3) to support more communication protocols.
4) a good Chinese people Machine interface.
5) the use of industrial configuration software for easy maintenance, expansion and upgrade.

3, the technical realization of
red cryogenic pressure by the compressor unit control system, control sub-system expansion, propane control sub-system, ESD
emergency stopping system and OPTO 22 companies OPTO22 SNAP I / O control system (ME system) of five parts. The first four of which system is only partial control of the unit, and OPTO 22 SNAP I / O control system through the exchange of data communications networks. OPTO 22 SNAP I / O system (ME system) in the entire system to control and monitor the overall situation in the crucial position.
in this project we use OPTO 22 SNAP I / O control system OPTO 22 SNAP LCM4 as a main controller, the CPU controller using 32-bit Motorola 68EC030 processor, 4MB RAM with battery backup, 2MB flash can read and write Memory, four serial interface, a fixed RS-485, the three can be set to independent RS-232/485. We use the controller's own serial interface for programming.
applications in the field, first of all, we analyze the ESD system. ESD is a red emergency stop system pressure cryogenic equipment to ensure the safety of the base, using SIEMENS S7-400 PLC to realize that their main station designed to work with PC displays, in full control OPTO 22 SNAP I / O To achieve. OPTO 22 SNAP I / O control system LCM4 controller COMO ---- COM3 communication ports can be set according to need 232 or 485 ways, according to the scene of many experimental communications, telecommunications standard MODBUS can not be achieved. The main reason is the ESD system is the main way station, if the station changed from the means of communication need to replace all the ESD software and hardware. The cost is too high, can not be achieved. Through ESD, PLC for further analysis, we have decided to free the mouth communication to SIEMENS S7 --- 400 communications port 485 by way of wiring to connect to the LCM4 compatible with the standard controller on COM3. Through the establishment of procedures for data exchange, setting the initial code, parity, the median of each of the array, transmission rate and so on. Debugging process, DCS received the ESD to send data, but the stability of poor online (ONLINE) process that sometimes the wrong stack space, running to communicate abnormal logic, and repeated the experiment many times, in the process Increase the data can be processed simultaneously, thus completely normal communications with the ESD, the realization of the DCS and ESD (ESD) of the communication.
in the compressor and PLC communication system, the system uses a compressor GE's 90-70, we have adopted a way of MODBUS RTU corresponding procedures in the preparation process is completed, through the download, run continuously debug and eventually carried out smoothly Connection.
in achieving the above-mentioned two communication units based on the use of the accumulated experience and the characteristics of the unit, with the full realization of a DCS communications unit.

Second, the structure and system configuration
in the configuration of the system, the use of OPTO 22 advanced and mature and reliable OPTO 22 SNAP I / O system, which is a serial communication applications repeatedly re-issued three-tier distributed network technology. The present system controlled by the central control of the host PC and four OPTO 22 of the main controller OPTO 22 SNAP-LCM 4 and 7 can be installed to place the distribution of the front-end smart I / O unit B3000, the structure of the system, see the following The icon.


(structure of the icon)
figure shown in the three-tier structure of the network, the most by a layer of the PC, using the ETHERNET network connection, the monitoring system as the man-machine interface, dynamic display a variety of devices running real-time status, display and recording devices Abnormal and fault alarm, the device automatically set the time and conditions, the operator can switch between systems by way of automatic or manual operation. In addition, if the user has requested, to monitor for the host to set up WEB SERVER, the monitoring of all the pictures into a WEB PAGE, the user can be on the Internet and local area network, using standard web browser Internet Explorer, to monitor the implementation of the system operation and control .
second by four OPTO 22 controller OPTO 22 SNAP---LCM 4, the host controller and control communication between the use of Ethernet, the composition of the Monitoring Network (C - NET). One of two on-site controller with I / O connected to each other linked to the PLC controller at the scene.
the third layer is made of multiple PLC and 7 I / O intelligence unit composition of the B3000. I / O unit and between the controller between the RS-485 component I / O network (I / O - NET), I / O unit is the distance between the 1000M, plus re-issued communications device to extend the distribution of distance. This could be I / O modules and I / O modules dispersed placed in the vicinity of related equipment, so that the connection lines to minimize the signal, greatly reducing the signal transmission was interfered with. I / O device unit direct access to the work of the state of alarm and signal detection device signal values at the same time can be automatically or manually control the operation of the PID control loop operation of the local operation and regulation has greatly strengthened the system Real-time control and quick reaction capability.

conclusion
Practice has proved that through the OPTO 22 SNAP I / O system and the multi-unit communication between the PLC is stable and convenient, real-time, high reliability. Reflects the OPTO 22 SANP I / O system is flexible, dynamic, powerful communication and adaptability of a wide range of characteristics.
Author About
Gao Baoguo men, strangers in January 1967. In 1991 graduated from the Shanghai Institute of Mechanical work is in the Daqing Oil Field Automation Instrumentation Co., Ltd., engineers, the current project's deputy manager. Tel :0459-5105428
Tian Fei Ji male stranger in 1974. Op Beijing Science and Technology Co., Ltd. plans, technical managers, engineers.
Tel :010-64830920 - 16