Plc designers must know the five insider - Solutions - Huaqiang Electronic Network

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When selecting a PLC, there are several key factors to consider. First, it's important to choose a model that you're familiar with, especially if you're new to programmable logic controllers. Many users find themselves confused about which PLC to choose due to the variety of manufacturers available. However, if you've already worked with a specific type of PLC in previous projects or on imported equipment, it’s often best to stick with that model for new developments. This approach not only reduces the learning curve but also allows for better resource sharing and support. Another consideration is whether to go with an imported or domestic PLC. Some joint-venture manufacturers in China produce PLCs that match the performance of their international counterparts. These domestic options often come with better after-sales service and easier access to spare parts. Additionally, they tend to be significantly cheaper—often around one-third the cost of imported models. That said, for large-scale or critical projects, well-known international brands may still be the preferred choice due to their proven reliability and advanced features. It's also crucial to evaluate the performance requirements of your project. For small-scale applications with only a few digital inputs and outputs, using a PLC with more advanced capabilities like analog I/O could be unnecessary and costly. In such cases, choosing a simpler, more cost-effective model can save money without compromising functionality. As PLC technology evolves rapidly, it's important to stay updated with the latest models. I once encountered a situation where a user was trying to replace an old F1-20MR PLC from a 1980s machine. They struggled to find an exact match, but in reality, a modern FXON-20MR or even another compatible model would have worked just as well. Always check for equivalent alternatives when upgrading or replacing older systems. When it comes to installation and wiring, proper placement is essential. The PLC should not be installed alongside high-voltage devices or components that generate electromagnetic interference, such as relays, contactors, or high-power machinery. If these components are in the same cabinet, ensure they are equipped with RC snubber circuits to minimize voltage spikes. For wiring, signal lines and power cables should be kept separate to reduce noise and interference. Use shielded cables for long-distance analog or high-speed signals, and route them close to ground conductors whenever possible. If the signal distance exceeds 300 meters, consider using intermediate relays or remote I/O modules. Also, avoid running power and signal cables in the same conduit unless shielded cables are used. When transmitting analog signals, it's better to use current-based transmission (like 4-20 mA) rather than voltage-based signals, especially over long distances. Shielded cables for analog signals should be grounded at one end, while digital signal shields should be connected to a potential equalization line and grounded at both ends to reduce high-frequency interference. Power supply stability is vital for reliable PLC operation. Interference from the power line can affect the system, so using a dedicated power circuit for the PLC can help isolate it from other equipment. In environments with strong interference or high reliability demands, consider adding a shielded isolation transformer and a low-pass filter to the AC input. This setup helps suppress external disturbances and absorb power glitches. Finally, protecting the user program is essential. While many PLCs store programs in RAM with backup power, this isn't always sufficient in noisy environments. A common practice is to write the program into EPROM using a PLC programmer and protect it from accidental overwriting during operation. This ensures long-term data integrity and system reliability.