Abstract: This paper designs a natural gas gate station process control system based on AnKong SUPER E40 RTU and E-spider industrial configuration software. The structure and functions of the process control system platform, as well as the design of the host computer configuration software, are introduced. This process control system adopts a modular design approach, has expansion capabilities, and is easy to build multi-site remote monitoring and control systems. It has certain practicality and is suitable for harsh industrial environments.
0 Introduction
Natural gas and its transmission are one of the economic lifelines of the country, and the reliable realization of its transmission and pressure regulation functions is related to the national economy and people's livelihood. With the development of automation technology, the monitoring of natural gas gate stations, pressure regulating stations and transmission and distribution pipelines has become an indispensable part of the industry. Among them, RTU (Remote Terminal Unit) is an important device in the automation system. Its communication distance is relatively long and it is suitable for various harsh industrial sites, which makes it widely used in natural gas dispatch and other industries. The Super E40 series RTU is a new RTU product designed by Ankong Company based on years of development and engineering experience. It can realize the acquisition of industrial field signals and the control of field equipment. Compared with commonly used programmable logic controllers (PLCs), it has better communication capabilities [1] . This paper designs a natural gas pipeline process control system based on the lower computer of Ankong RTU and the industrial configuration software of E-spider. It realizes the process monitoring and control of natural gas and fluid pressure regulating stations and pipelines.
1. Hardware Design and Implementation of Process Control System
1.1 System Overview
This system aims to achieve common monitoring functions such as data acquisition, data monitoring, parameter control, curve display, and alarms. Utilizing PLC module technology, the system can be used for safety monitoring of natural gas and fluid pressure regulating stations and pipelines.
This system consists of a network layer, a field control section, and a control section. The network layer uses Ethernet to connect the industrial control computer with lower-level machines, enabling centralized management of the industrial site. The field control section comprises a pipeline platform, water tank, temperature transmitter, differential pressure transmitter, electromagnetic flowmeter, pressure transmitter, and electric ball valves. The monitoring section consists of an industrial control computer running an AnKong SUPERE40 RTU, a Siemens S7-200 system, and E-spider industrial configuration software. The system block diagram is shown in Figure 1.
1.2 System Design
The system can be autonomously controlled by the front-end computer and industrial control computer according to the actual situation of the industrial site. Under normal operating conditions, the upper computer configuration software can set the actual required natural gas pipeline flow rate according to the temperature and flow rate in the pipeline platform. It can also analyze and calculate the reasonable ball valve opening value through the AnKong SUPER E40 RTU and communicate with the Siemens S7-200 PLC via the free port to make the ball valve act in real time and achieve the expected effect.
In addition, the system is also equipped with an emergency alarm function. When the temperature, flow rate, and differential pressure values on both sides of the electric ball valve received by the SUPER E40 RTU of the lower-level computer are abnormal or exceed the normal operating range, it indicates that the system is in a dangerous state. The system will issue alarm signals at the industrial site and in the control room where the industrial computer is located. The lower-level computer will also issue an interrupt signal to the ball valve and water pump to stop their operation. Alternatively, the industrial computer can directly interrupt the front-end program through the E-spider industrial configuration software to issue a stop command to carry out the next inspection work, which is beneficial to the safety protection of the system.
1.3 System Implementation
An industrial PC is used as the host computer, and the E-spider industrial configuration software communicates with the AnKong SUPER E40 RTU slave computer via Ethernet to achieve field control. The slave computer consists of a power supply module, a CPU module A32-M1, an analog input module AC101, a communication connection module A32-L3, a digital output module AC112, a pulse input module AC141, and an S7-200 analog output interface.
The AC101 analog input module accepts 4-20mA current signals from DP1151 differential pressure transmitters, BT2007 electromagnetic flowmeters, electric ball valves, and temperature and pressure transmitters, converting them into digital values of 10000-50000. Its channel address is determined by the card slot location. In this system, the AC101 analog input module's module address is 2, corresponding to OpenPCS direct variable addresses of %512.0 to %2558.0; parameters for other modules are shown in Table 1.
Signal | Number of registers | OpenPCS direct variable address | Modbus address |
DI | 4096 | %0.0～%511.7 | 10001～14096 |
AI | 1024 | 512.0～2558.0 | 30001～31024 |
DO | 4096 | %0.0～%511.7 | 00001～04096 |
AO | 9999 | %512.0～%20508.0 | 40001～49999 |
Table 1 Module Parameter Table
The DP1151 differential pressure transmitter, BT2007 electromagnetic flowmeter, pressure transmitter, differential pressure transmitter, and temperature transmitter in the field operation section convert flow and other signals into 4-20mA current signals, which are then sent to the AC101 module of the AnKong RTU. Utilizing the Siemens S7-200's unique free-port communication mode, the AnKong RTU converts the acquired analog signals and sends them to the Siemens S7-200 PLC. The Siemens then outputs current through the analog output port, driving the ball valve to the corresponding opening degree.
2. Software Design and Implementation of Process Control System
The software design mainly consists of the Infoteam Openpcs ladder diagram program for the SUPER E40 RTU, the ST text language for the S7-200 PLC, and the E-spider industrial configuration software for the host computer.
2.1 Infoteam Openpcs Ladder Diagram Programming
The front-end software design utilizes the SUPER E40 RTU series programming software Infoteam Openpcs at the monitoring level to complete the programming and debugging of the lower-level program, and then downloads the debugged program to the RTU. The lower-level software mainly implements subroutines for communication between the RTU and the configuration software and Siemens S7-200 PLC, control of field flow by the upper-level computer, fault alarms, and diagnosis. The program flowchart of its software design is shown in Figure 2.
Figure 2 System Program Flowchart
2.2 Espider Configuration Software Design
The host computer software design utilizes Espider industrial configuration software, which comes with a large number of I/O device drivers, allowing users to easily build real-time monitoring systems. To provide a good human-computer interaction environment for the process control system experimental platform, process flow charts, monitoring screens, real-time adjustment curves, historical curve graphs, data reports, and alarm screens were developed in Espider, enabling real-time monitoring of the site. The monitoring system block diagram is shown in Figure 3.
3. Conclusion:
The natural gas pipeline process control system, based on a safety control RTU and a Siemens S7-200 PLC as the lower-level computer and an Espider HMI as the upper-level computer, has been verified to be a safe and reliable system. After adjustment, the flow rate fluctuation range is within +5% to -5% mm. After one flow rate adjustment, it can achieve balance within three calculations, meeting the actual needs of industrial sites. Furthermore, this system serves as a simulation experimental platform to support scientific experiments and research for students, especially graduate students. Its structure, control methods, and hardware and software systems can be directly applied to actual industrial sites involving natural gas and other fluids.
Note: This project was funded by the Southwest Jiaotong University SRTP (Undergraduate Research Training Program) project (Project No.: 090207).
References
[1] Super E40 Series RTU User Manual
[2] ESet Configuration Manual (V5.2.2)
[3] OpenPCS Programming Manual_5.2.2
[4] Wang Hongmeng. Design and Implementation of Process Control System Based on PLC [J] Automation Technology and Application
[5] Liao Changchu. PLC Programming and Application (Second Edition) [M] Beijing: Machinery Industry Press, 2005
