Since the advent of the first programmable logic controller (PLC), programmable control technology has undergone 30 years of development. Especially with the rapid advancements in computer and microelectronics technologies in recent years, it has made significant progress in both hardware and software. The programmable computer controller (PCC) launched by the Austrian company B&R Industrial Automation represents this development trend.
Compared to conventional PLCs, the biggest advantage of PCCs lies in their time-sharing multitasking operating system and diverse application software design. Conventional PLCs mostly use single-task clock scanning or monitoring programs to handle the program's own logic operations and the acquisition and refreshing of external I/O channel status. This means the PLC's execution speed depends on the size of the application program, which undoubtedly contradicts the high real-time control requirements of the I/O channels. PCC system software solves this problem. It uses a time-sharing multitasking mechanism to build its application software's operating platform. Thus, the application program's execution cycle is independent of the program's length but determined by the operating system's cycle. This distinguishes the application program's scanning cycle from the actual external control cycle, meeting the requirements of true real-time control. Of course, this control cycle can be arbitrarily adjusted according to the user's actual requirements, provided the CPU's computing power allows.
Based on this operating system, PCC applications consist of multi-task modules, which greatly facilitates the development of project application software. This is because it allows for the easy creation of control program modules (tasks) according to the different functional requirements of each part of the control project, such as data acquisition, alarm, PID control calculation, and communication control. These modules operate independently while maintaining a certain degree of interrelationship between their data. After these modules are independently developed and debugged step by step, they can be downloaded together to the PCC CPU and run in parallel under the scheduling and management of the multi-task operating system to jointly achieve the project's control requirements. This feature can be illustrated as follows:
Based on the aforementioned powerful and specialized operating system, the PCC offers unparalleled flexibility in application design compared to conventional PLCs.
Because PCC is designed for a multi-tasking environment and adopts the modular design concept of large application software, the functional descriptions of each task module are clearer and more concise. When developing their own tasks, users can easily encapsulate the extracted functions as independent functional modules for reuse in other application projects in the future, as the extraction of functions is universal.
PCC's programming hardware utilizes a standard PC paired with a powerful development software suite as an online development tool. This approach not only saves users on hardware investment but, more importantly, leverages the PC's strong hardware and software advantages as an online programming development tool. It provides users with various debugging methods at the source code level, including single-stepping, breakpoints, single-cycle debugging, and PCC's online error self-diagnosis, making application development highly flexible and convenient. Furthermore, through the numerous functions provided by the programming software package on the PC, users can quickly create efficient and complex control programs.
PCC offers flexibility in using different programming languages when developing various individual task modules. This means that not only can the instruction list language used on conventional PLCs be reused on PCC, but users can also utilize more efficient and intuitive high-level languages (PL2000). It is a text-based language entirely geared towards control; technicians familiar with BASIC will find its syntax familiar, and its description of control requirements is very simple and intuitive. Furthermore, PCC application software development also has the capability to integrate C language programs.
What makes it particularly unique is that PCC uses "complementary variables" to identify external I/O channels and internal register units for all these programming languages. Software developers do not need to be familiar with the distribution of hardware resources inside PCC, but only need to focus on the requirements of the project itself to quickly develop their own control programs.
In terms of hardware structure, the PCC has significant features. Inside its core computing module, the PCC equips its CPU with a storage unit (100K-16M) several times larger than that of a conventional PLC, undoubtedly providing a robust hardware foundation for powerful systems and application software monitoring. Externally, it features a fully modular plug-in structure, allowing for convenient hot-swappable connections in industrial environments. Furthermore, it boasts sophisticated designs in areas such as terminal blocks, module power supply, and operational status display.
The PCC's hardware features are also reflected in its many dedicated interface modules designed for various signals in industrial settings, such as temperature, high-frequency pulse, incremental pulse encoders, weighing signals, and ultrasonic signal interface modules. These modules easily connect various forms of field signals to the PCC-based digital control system. Users can expand and network the application system's hardware I/O channels as needed, using single channels, dozens of channels, or even hundreds or thousands of channels as modules.
The flexibility of PCC in remote communication is a significant feature that distinguishes it from conventional PLC. As one of the main players in the future distributed field I/O control, PCC provides a wide variety of flexible solutions.
In addition to the above-mentioned open fieldbus network solutions, PCC also provides various local master-slave network protocols on the RS485 bus. Users can not only use PCC's own network protocols, but also easily network and communicate with PLCs and other industrial control equipment from other manufacturers (such as Siemens, AB, Modicon, etc.). In some special cases, PCC also provides users with tools to create custom protocols (frame driver). Due to these technical advantages, PCC can often solve many communication problems that conventional PLCs cannot solve, and easily achieve interconnection with various products and different communication protocols.
Through the above discussion, we have gained a relatively comprehensive understanding of the characteristics of PCC. Here, we might as well compare it with the traditional PLC in tabular form.
In summary, although PCC evolved from PLC, it possesses unparalleled advantages. Its larger memory capacity, more flexible programming methods, and superior control mechanisms enable PCC to perform many functions that are difficult for ordinary PLCs to accomplish, such as temperature control accurate to ±1℃; precise servo control; and remote communication capabilities. Furthermore, PCC can be continuously updated and upgraded with the development of current computer and network technologies, offering better upgrade capabilities. Therefore, PCC is widely used in industrial control, particularly suitable for the precision control of plastic machinery, where it has achieved excellent application results and received high praise from industry professionals.
