DDC is developed from PLC, which is specially designed by the manufacturer for the detailed market. Its biggest advantage with PLC is only a fixed part of the control program.
Note : DDC (Direct Digital Control) direct digital control, usually called DDC controller. The composition of DDC system usually includes central control equipment (central control computer, color monitor, keyboard, printer, uninterruptible power supply, communication interface, etc.), on-site DDC controller, communication network, and corresponding sensors, actuators, regulating valves, etc. Components.
Regarding PLC and DDC, which application has more advantages in building automation system, do the following comparison:
1. Application field
DDC is developed from PLC. PLC is specially used in industrial automation. In China, almost all industrial production line control systems, thermal power plant control systems, and steel plant control systems are all using PLC systems. Part of the building control system also uses PLC. The building automation DDC is developed by the manufacturer according to the building automation features. The difference from the PLC is that it only solidifies a part of the program inside, but it also lacks the flexibility of the PLC and the ability to deal with complex electromagnetic interference environments.
2. Structural differences
After years of development, the current PLC is actually the same as DDC in terms of network. It also supports multiple protocols and is also a layered structure. It can also achieve point-to-point communication. PLCs distributed on the site do not need to pass the host computer. For communication management.
3. Software features
The host computer software of the DDC system is mostly dedicated software. In fact, it is incompatible from the other side. The software of each manufacturer is different, and many of them are in English. This is a nightmare for technicians. The PLC software of the host computer can be both special software and general configuration software. Now the domestic general configuration software is pure Chinese, and the configuration is flexible and convenient. The general configuration software can cope with complex industrial control systems, and it's all about building control. Besides, whether it is the debugging of the PLC system or the DDC system, there are professional debuggers to complete the configuration, and then to train the owner to operate and manage, it is actually the same for the owner. Can realize many functions that professional software can not achieve (such as high simulation interface, vocal alarm, user customized functions, etc.).
4. Professionalism
Many building control projects now use PLC systems. Facts have proved that the above DDC function PLC system can also be completed. Experienced PLC building control implementers have also accumulated all control process procedures, energy management and energy saving procedures. All process programs have source programs, so you can quickly make tailor-made functions for different projects. Because there are also ready-made process procedures, the on-site debugging work is also very short, and it will also be smoother than DDC debugging, because the built-in DDC program only has interface functions and is in a fixed format. If you have special needs, you have to contact a manufacturer engineer who is thousands of miles away. Contact, and whether it can be resolved is not necessarily.
5. Scalability
Everyone knows that the PLC system is a universal and open system. At this stage, most PLC systems and most DDC system operator stations use TCP / IP protocol, and all can be accessed with a network. At present, DDC system software charges expensive fees according to the number of users, making most of the completed building control systems dare not think about the sub-control operation station! The PLC system has this advantage.
6. Security
In fact, just imagine this problem: a thermal power plant is generating electricity, and suddenly a PLC module is broken. As mentioned above, the entire system must be shut down to be replaced. What will be the consequences, and the boiler may explode! Ha ha! The consequences are much more serious than the floor control! Now many PLC system modules are hot pluggable and hot standby redundant (these functions, building control seems to have learned from PLC in recent years), PLC is developed for industrial environment, in a complex industrial control environment The failure of the next module or system shutdown may cause major accidents or casualties, and the reliability requirements are more than DDC! I don't know how the above discussion came about. The PLC control core can operate in a harsh environment for long-term reliable, trouble-free operation, and is easy to wire, easy to maintain, good isolation, strong corrosion resistance, can adapt to a wide range of temperature changes, the mean time between failures (MTBF) is greater than 15 years.
7. Debugging complexity
The most commonly used PLC programming is the ladder diagram language. This language is visualized and you can see what you see. It does not require English level, and ordinary electricians can learn it.
The current PLC system, like the DDC system, can be fully debugged by sitting in a comfortable computer room with a laptop and a network cable. As for accuracy, take a look at the product technical parameters! Just want to say one thing: Is the accuracy requirement of industrial control lower than building control? I do n’t think anybody would think so! Haha! The control system of a modern industrial production line is tens of thousands of points (basically all adopt PLC, but none of them use DDC), and it requires millisecond network connection. Can DDC do it?
Summary
In fact, DDC is developed by PLC, which is specially designed by the manufacturer for the detailed market. Its biggest advantage with PLC is only a fixed part of the control program, and other performance aspects should be worse than PLC. Since DDC is only aimed at the professional market segment of building control, the national market capacity is not large, which also causes the fundamental reason why DDC performance is not outstanding, but the price is higher.
A part of the control program is fixed in the DDC. The initial starting point of the manufacturer is that the contractor of the building control system is mostly a weak current system integrator. This group has relatively little contact with the automatic control technology, so the manufacturer must make an easy product for its debugging. But because of this, it loses its flexibility.
If you encounter an experienced automatic control engineer, the fixed procedures in its products become a burden to its ability. After the building control system is completed and delivered to the user, because the user maintenance engineer has more contact with PLC in the society, the most commonly used PLC programming is the ladder diagram language. This language is visualized, what you see is what you need, and no English level is required. , Ordinary electricians can learn, so its maintenance technology and cost are lower.
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