In the building automation system, who is better with PLC and DDC?

DDC is developed by PLC, which is designed by the manufacturer for the refinement of the market. The biggest advantage of PLC is that it has only a fixed part of the control program.

Note : DDC (Direct Digital Control) direct digital control, commonly referred to as DDC controller. The composition of the DDC system usually includes central control equipment (centralized 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 the building automation system, do the following comparison:

1. Application field

DDC is developed by PLC. PLC is specially applied in industrial automation. In almost all industrial production line control systems in China, thermal power plant control systems, steel plant control systems are all applied to PLC systems, and currently there are quite Some building control systems also use PLC. The building automation DDC is developed by the manufacturer from the PLC according to the building automation characteristics. The difference between the PLC and the PLC is actually only a part of the program is solidified inside, but at the same time, the flexibility of the PLC and the ability to cope with the complex electromagnetic interference environment are also lacking.

In the building automation system, who is better with PLC and DDC?

2. Structural differences

Through years of development, the current PLC is actually the same as DDC in terms of network. It also supports multiple protocols. It is also a layered structure, and can also realize point-to-point communication. PLCs distributed on the site do not need to pass the host computer. Conduct communication management.

3. Software features

The host computer software of the DDC system is mostly dedicated software. In fact, it is incompatible with the other side. The software of each manufacturer is different, and many of them are in English. This is the beginning of a nightmare for technicians. The PLC system PC software 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 the complicated industrial control system, and it is also a matter of how to control the district. Besides, whether it is PLC system or DDC system debugging, there are professional debugging personnel to complete the configuration, and then train the owner's operation management, which is actually the same for the owner. In contrast, the configuration software can realize all the functions of professional software, and It can realize many functions that professional software can't realize (such as high simulation interface, vocal alarm, user customization function, etc.).

4. Professionalism

Now many building control projects have applied PLC systems. It turns out that the above DDC function PLC system can also be completed. The experienced PLC building control implementers have also accumulated all control flow procedures, energy management and energy saving procedures, and at the same time All process programs have source programs, so you can quickly make tailored features for different projects. Because there are also ready-made process programs, the on-site debugging work is also very short, and it will be smoother than DDC debugging, because the DDC built-in program only has interface functions, which is a fixed format. If there are special requirements, it must be with engineers who are thousands of miles away. Contact, and can not be solved is not necessarily.

5. Scalability

Everyone knows that PLC systems are versatile and open systems. At present, most PLC systems and most DDC system operator stations use TCP/IP protocol, which can be accessed by a network. At present, the DDC system software charges an expensive fee according to the number of users, so that most of the completed building control systems do not dare to 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. Suddenly a PLC module is broken. If the whole system is shut down to be replaced as mentioned above, what will happen? The boiler may explode! Ha ha! It is much more serious than the consequences of building control! Now many PLC system modules are hot plugging and hot standby redundancy (these functions, building control seems to be learned from PLC in recent years), PLC is developed for industrial environment, in complex industrial control environment Failure of the lower module or system shutdown may result in major accidents or casualties, and the reliability requirements are higher than DDC! I don't know how the above discussion came about. The PLC control core is capable of long-term reliable and trouble-free operation in harsh environments, and is easy to wire, easy to maintain, has good isolation, and strong corrosion resistance. It can adapt to a wide range of temperature changes, and the mean time between failures (MTBF) is greater than 15 years.

7. Debugging complexity

The most commonly used PLC programming is the ladder language. This language is visualized and what you see is right. You don't need English level, and ordinary electricians can learn it.

The current PLC system, like the DDC system, can be fully debugged in a comfortable computer room with a laptop and a network cable. As for the accuracy problem, take a look at the technical parameters of the product! Just want to say: Is the industrial control's accuracy requirements lower than the building control? I don't think anyone would think so! Haha! The control system on the modern industrial production line is tens of thousands of points (basically using PLC, but no one uses DDC), and requires millisecond network connection. Can DDC do it?


In fact, DDC is developed by PLC. It is designed by the manufacturer for the refinement of the market. The biggest advantage of PLC and PLC is only a fixed part of the control program. Other performance aspects should be worse than PLC. DDC is only for the professional segment of the building control, the national market capacity is not large, which also causes the DDC why the performance is not outstanding, the price is higher.

A part of the control program is fixed in the DDC. The initial starting point of the manufacturer is because the contractor of the building control system is mostly a weak system integrator. This group has relatively little contact with the self-control technology, so the manufacturer must make an easy product for debugging. But because of this, it lost its flexibility.

If you run into an experienced self-control engineer, the fixed program in the product becomes a burden for your ability. After the building control system is completed and delivered to the user, since the user maintenance engineer is more in contact with the PLC in the society, the most commonly used PLC programming is the ladder language. This language is visualized, what you see is what you need, and you don’t need English level. Ordinary electricians can learn, so their maintenance technology and cost are even lower.

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