PC-Based Control - More Than Just Cost Savings

The use of PC-based system control technology can greatly reduce the cost of the control system, of course, another non-cost reason, but also determine the reason why PC-based control is increasingly popular, the advantage of this technology is to have an open-ended The control platform can continuously upgrade the operating system and optimize the system performance, processing speed, control modules, and other components through multiple suppliers.

In the past five years, from the perspective of industry development, it can be seen that the application of PCs in the field of industrial control has become more and more significant. The most common application is the use of computers in factories to perform “secondary” control of production, including the supervision of control systems, access to data, and The report replaces the previous operation on the light board by managing the flow of information between actual control devices and providing an operation interface.

PC hardware has also become increasingly powerful and standard, and this change is also evident in industrial applications. Today, getting a high-performance, low-cost industrial computer hardware is as easy as or even better than getting other types of controllers. Industrial PC I/O devices and operating interfaces are gradually being standardized, including Profibus, Interbus, Fieldbus, DeviceNet, SERCOS, and others.

With the increasing demand for PCs from businesses and households, people’s awareness and acceptance of computers is also increasing. Even professional controllers such as PLCs do not require special "black boxes". Users understand that by choosing the right hardware for PC hardware components and software control packages, they can get a very reliable control system.

Because most of the PC network technology vendors have common technologies, there will be no single case of controlling the vendor's exclusive technological advantage. Users want to easily obtain information from the factory's workshop to the management and MIS systems. This is difficult for individual computer networks to support. The PC-based control system uses standard network cards, modems, and LANs to build a standard network architecture (TCP/IP Ethernet) to achieve a standardized solution.

Recently, users began to use PC-level control on a large scale to directly control I/O devices, hoping to allow PCs to replace PLCs, RTUs, and DCS systems. The reason for this trend is that many times the classification will involve the cost problem: PC hardware is less expensive than the general controller, a single PC can replace other controllers when applying secondary control; however, consider the control system The total cost, the use of CPU control can save 2000 to 10,000 US dollars, how will people make choices?

Case 1
Applications: High-speed sorting conveyors, such as those used in postal systems, courier companies, etc., are mainly sorting letters.
Problem: The system is based on a read bar code to control whether the sorting device passes the letter or package. Two PLCs are generally used to control 20 sorters. The problem is that the original PLC system is too slow and mail cannot be sorted correctly unless the conveyor belt speeds down. If it is sorting work between two controllers, its communication is more complicated.
Solution: Using a software PLC controller system can reduce the scan time from 200 ms to 8 ms, allowing the PC to run faster and have better data processing capabilities than a single PLC. Equipped with a special custom code reading function, the logic control of the program becomes the control of the I/O, and the algorithm of the sorting action is controlled by the computer program. In addition, by using the bus I/O to replace the traditional PLC I/O, the production speed is increased and the step line is reduced.
Benefits: Fast, custom configuration

Case 2
Application: Food processing issues: Machines used for meat processing are generally complex structures that can use not only I/O control but also multi-axis motion control. The original system consists of a PLC with basic modules plus a motion controller. The problem is that because the communication speed between the basic components and the PLC is slow, only 50% of the ideal production effect can be achieved, and at the same time it cannot be adjusted timely.
Solution: A PC-based system includes a multi-function processor and software PLC control software running on a 486 CPU to control the I/O and basic components, eliminating timely tuning and communication issues. The PC-based motion card is used to control the motion, and a loadable instruction of the software PLC controller is integrated to store the information stored in the RAM of the PC bottom plate. With this solution, the output of the machine can be doubled.
Benefits: Optimize and simplify machining, integrate components from multiple vendors

Case 3
Application: Tobacco processing issues: Each cigarette needs to be matched to its own data input card (DI). Reading of the DI takes at least 1.5 ms. If using a conventional PLC, even with a fast digital I/O card, Nor can you meet the same fast input as reading. Even if you use a program module, you cannot achieve the desired output. In addition, the installation is adjusted according to the PLC and network configuration that the supplier can provide.
Solution: Using a software PLC controller with a data input card, the I/O and PC bus can be read directly in less than 1 megasecond. In addition, this method can support the factory-wide PLC communication network, which is the same as the logic control of the PC system. The operator does not need to be trained.
Benefits: I/O optional, compatible with existing devices

Case 4
Application: Glass fiber processing issues: This processing system requires an I/O control interface and an 18-bit continuous motion controller. The traditional PLC needs to install a series of expensive basic modules to obtain a series of serial ports needed; at the same time, the customized application PC also needs to be equipped with a series of serial communication controls.
Solution: The software PLC system not only has a multi-port serial card, but also can communicate with the motion controller to complete multiple controls on communication and data processing.
Benefits: I/O optional, compatible with existing devices

Case 5
Application: Process control issues: The integration of PLC and DCS functions on a single controller does not always work well. Because of circuit control and process control, different description languages ​​are required.
Solution: The software PLC can provide an open system for handling DCS (Distributed Control System) modules. These modules can operate in a ladder logic language, but if the operator is not familiar with this logic language, digital I/O control cannot be performed.
Benefits: Customized according to user needs

Source: Modern Packaging