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In the modern industrial landscape, the integration of computer networks and fieldbus technologies has revolutionized automation systems. PLCs (Programmable Logic Controllers) and touch screens have become essential components in industrial control and building automation. Fieldbus technology, along with its interface modules, intelligent instruments, and control equipment, forms the backbone of integrated monitoring systems that are shaping the future of automation. The combination of PLCs and touch screen technology has gained widespread acceptance among engineers due to its intuitive interface, ease of programming, strong communication capabilities with PLCs, and robust anti-interference features. This synergy is rapidly expanding across industries, offering unparalleled advantages in automated control.
PROFIBUS offers two main communication protocols: DP (Decentralized Periphery) and FMS (Fieldbus Message Specification). The Fuji UG series touch screen supports the DP protocol, ensuring strong compatibility with a wide range of PLC manufacturers—over 30 different brands. Additionally, it can communicate with computers using open communication protocols. Through an interface unit, the UG031-P communication card, and the PROFIBUS bus, the UG touch screen can function as a slave station while communicating with Siemens S7-300 or S7-400 series PLCs as the master station. This network configuration is illustrated in Figure 1.
The system under discussion consists of several key components, including raw material mixing lines, potato cake production lines, packaging lines, steam boiler systems, water systems, air systems, lighting systems, ventilation systems, and fire protection systems. These subsystems are spread out across the facility, involving over 140 motors, 29 inverters, and 15 temperature and humidity control points. Due to the complexity of the setup, a layered control strategy was implemented. Two host computers manage plant-level monitoring and data management, while the touch screen and PLC handle field-level control via PROFIBUS. The host computers are equipped with LAN and WAN interfaces for future scalability. The system includes more than 900 digital input points, 400 digital output points, and 20 analog input points.
As an example, this food processing plant employs a centralized control system, as shown in Figure 2. The main system uses a Siemens S7-300 CPU315-2DP, while the auxiliary system uses an S7-200 CPU226. The PID module is FM355C, the communication module is CP342-5, and the expansion module is IM153-1. Digital inputs use SM321, digital outputs use SM322, and analog inputs use SM331. An industrial PC from Siemens is used as the upper-level computer, featuring a built-in PCI interface (CP5611 card) for communication with the PLC.
The selection of the IM153-1 module depends on the distance between the central controller and the I/O modules. If all I/O modules are housed in the same control cabinet, an IM153-1 with a 5-meter communication range is suitable. For longer distances, an IM module with a 100-meter range can be used.
The touch screen model used is the Fuji UG420H-SC1, a 10.4-inch STN display with 128 colors. It runs on Windows 95/98/NT and offers a user-friendly interface, reducing development time significantly. The software includes extensive graphic libraries (switches, lights, bar graphs, etc.) and supports BMP and DXF file conversions. It also allows users to customize process graphics according to their needs.
After hardware connections are established, system configuration and communication parameters must be set in the configuration software. The touch screen type is selected (UG420, 640x480), followed by the PLC type (SIEMENS S7-PROFIBUS). System parameters such as read/write areas, MPI address, frame length, parity, data bits, stop bits, and communication mode (RS-485) are configured. The MPI address must match the PLC's hardware configuration to avoid communication errors.
Fuji UG00S-CW simplifies configuration by handling technical details internally. When a button is created, it is pre-defined in the PLC (in Siemens PLCs, both digital and analog values are stored in DB blocks). For example, if the button address is DB2.DBX2.0, the touch screen address would be DB2:2-0. No additional variable definitions or communication frame structures are required.
For analog values, the number of bytes occupied by the analog value must be specified. However, in complex scenarios, issues may arise. In a food production line, trend graphs were used to display PID-controlled analog values. During online debugging, communication errors occurred when trend graphs were included. After testing, it was found that removing the trend graph resolved the issue. Further investigation revealed that the problem stemmed from a mismatch in data storage formats between the Siemens PLC and the Fuji touch screen.
Siemens PLC stores analog values in low-word first, then high-word, while the Fuji touch screen expects high-word first. This caused incorrect data interpretation, leading to anomalies like infinite curve values when the analog value was non-zero. To resolve this, the high and low words were reversed in the touch screen’s internal memory before assigning the trend graph addresses. A macro command was used to implement this correction.
Using the macro commands in UG00S-CW, the program reads analog values into the touch screen, reverses the high and low words, and updates the trend graph addresses accordingly. For example, after reading DB10:DBD0–DB10:DBD8 into $u500–$u505, the high and low words are swapped using W instructions. The corrected data is then assigned to the trend graph curves (PV, SP, OP).
This approach ensures accurate data synchronization between the PLC and the touch screen. After implementing these changes and conducting online tests, the system operated smoothly without communication errors.
In conclusion, the combination of Fuji touch screens and Siemens PLCs provides a stable and efficient solution for industrial control. Despite minor compatibility challenges, the system can be optimized through careful configuration and macro programming. As the IT industry continues to evolve, hardware limitations can be addressed through software enhancements. With proper design and implementation, the integration of these technologies can deliver powerful and reliable automation solutions.