1 Introduction
The rolling steel production line includes a total of 5 parts including finish A line, finish B line, intermediate rolling line, rough rolling zone, and sizing machine. The electrical part includes PLC, man-machine interface, frequency converter, low-voltage electrical appliances and others. Because this five-part production line is far away, five human-machine interfaces are used to realize the operation display of different systems. At the same time, a PLC controls the system. , ie N:1 multiple connection. Previously, the design institute conducted communication tests on several professional human-machine interface manufacturers' products, but the results were not satisfactory, and some of the connected units were not enough or even failed to communicate.
2, communication options
We provide users with two options: that is, Ethernet is connected and RS-485 is used for direct communication.
(1) Mount Ethernet
Since the GE90-70 itself can be connected to Ethernet, the proposed solution is to put Ethernet on five human-machine interfaces and PLCs at the same time. The man-machine interface selects UG30 series products newly introduced by Fuji Electric. One high-performance man-machine interface comes with a 10M Ethernet interface. It does not require any accessories to build an Ethernet-based network system. It has its own communication gateway function. The two-way communication from the PLC to the computer or from the computer to the PLC can send and receive data through it. The connection between the UG30 and the PLC on the Ethernet can perform N:N protocolless communication. The man-machine interface chooses UG330H-VH4, the function and the characteristic are as follows: 8.4 inches, 32768 colors TFTs, comes with Ethernet interface, can communicate with all PLCs that can be sold on the market, can also directly and frequency converter, temperature control table and series printer,etc. Peripheral devices pass through.
(2) Direct communication via RS-485
Because the communication module of GE90-70 PLC has two communication ports, we fully use these two communication ports to hang two and three man-machine interfaces, respectively, and communicate with each other in RS-485 mode.
1# as host 2#, 3# as slave, 4# as master 5# as slave, the maximum communication distance between them is 500m, baud rate is 115200bps, host and PLC communication baud rate is 19200bps, It can guarantee that there will be no communication delay and communication interference. The original 2#, 3#, and 5# man-machine interfaces need to add an RS-485 communication module. After repeated communication tests, we canceled the communication module. As long as several communication cables are connected in parallel, they can communicate normally. Users save thousands of dollars in costs. Man-machine interface selection UG320H-SC4, 128 colors, 7.7 inches, more reasonable than the UG330H-VH4 cost-effective.
After careful consideration and multiple investigations, the user decides to use the second option that is economical and reasonable under the premise of not affecting the use of functions.
3, solve the communication delay
After the completion of all programming, an unexpected communication delay occurred when commissioning the machine. That is, when 1# is switched from the display screen to the operation screen in the operation screens 2# and 3#, both the human-machine interface and the PLC appear. Obvious lag, time is probably 2 - 3 seconds, which is not allowed in any system, especially in the rolling line. Through multi-analysis, we propose the following suggestions: All the PLC addresses involved in the man-machine interface are mapped to the internal address of the man-machine interface $u. $u is the user memory in the man-machine interface, and can be from $u0--- -$u16383 A total of 16384 words are arbitrarily set. For example, the data of the register R1----R10 in the PLC can be mapped to $u1----$u10, so that the communication hysteresis disappears. These experiences are worth our use in future communications.
4 Conclusion
This scheme has been successfully applied to the scene, and there is no communication delay and communication interference at the production site. The equipment with a large area and controlled by a single PLC, such as textile machinery and tobacco machinery, is greatly promoted.