In process control projects, communication problems between DCS and lower computer PLC or field instruments are often encountered. Many chemical plants now adopt a general contract plus subcontracting model when constructing. Each supplier provides its own control system (usually mostly PLC), but in the central control room of the factory, operators hope to monitor these control systems. operating parameters. Therefore, these PLC operating data need to be transmitted to DCS through communication. In addition, some large instruments provide more data and usually use communication methods. Modbus was launched relatively early and is relatively mature. Now most PLC manufacturers and large instrumentation manufacturers support the Modbus protocol. Therefore, if you agree to use Modbus from the beginning of the engineering design, it will be convenient, unified and time-saving. Save effort .
RS232 serial port server principle
RS232 serial port server is a kind of serial port server, and its serial port has RS232 serial port. Therefore, its principle is the same as that of the serial port server. Since the RS232 serial port has developed very well, the RS232 interface is Internationally called “one of the most popular interface methods for peripheral devices” and can provide an integrated solution for software and hardware communication.
Where is the RS232 serial port commonly used? Will it continue to be used in the future?
Most modern electronic instruments, including measurement tools and laboratory instruments (balances, electrochemical meters, spectrometers, spectrophotometers, etc.) use standard RS232 serial lines to connect to a computer. The RS232 protocol has been around for many years, and many cost-effective hardware and software solutions have been established. More than 90% of computers are equipped with at least one RS232 port with add-on adapters. There are also hundreds of software applications available for communicating with instruments over RS232 connections. Due to the flexibility and ubiquity of the RS232 standard, it is likely that it will continue to remain relevant in the future.
What are the limitations of RS232 communication?
The problem with RS232 communication is that it requires point-to-point serial line connection and transmission, and the distance of the serial line is limited. This requires each instrument it communicates with to use a separate serial cable connected to a unique RS232 port on the PC. If you want to connect multiple devices to a single PC, you must install multiple RS232 ports on your PC.
If the RS232 standard were to be improved, it would allow multiple connections through one serial line, with no limit on serial line length, and would remain 100% compatible with all existing RS232 communication software.
Is there any way to improve it?
Fortunately, there’s a very simple way to do it. The original local serial port control function is extended through the virtual serial port software, and you do not need to modify the original serial port program, you can still use it.
The virtual serial port application software can map TCP/IP connections, UDP broadcasts and devices connected to Zongheng Cloud to the local virtual serial port. Applications can complete remote control, data transmission and other functions by accessing the virtual serial port.
Using MOXA NPort 5630 can better and more conveniently solve the problem of bidirectional data transmission between on-site serial devices and Ethernet network interfaces. Compared with some other manufacturers that use serial communication and card methods, it is cheap, flexible and convenient. But in terms of loading capacity, its loading capacity is not as good as that of the serial communication card. The author has done experiments. According to the definition of Modbus communication protocol, a communication bus can theoretically connect up to 248 slave communication devices. However, it is not easy to use a serial port of NPort5630 to connect several devices at the same time for communication. If communication cards used by other manufacturers are used, there will be no problem in practical applications if multiple devices are connected to one communication bus.