MVI69-MNET 19-01-21 現(xiàn)貨卡件備件

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Difference between DCs and PLC
Control processing capacity
We know that a PLC controller can often handle thousands of I / O points. DCS controller can only handle hundreds of I / O points. As far as the requirements of DCS are concerned, centralized control is not allowed. Controllers with too many I / O points are useless in practical application. DCS developers do not need to develop controllers with many I / O points. Their main focus is to provide the reliability and flexibility of the system. But PLC is not the same, as an independent flexible control device, with a point ability is very strong.
In people's impression, the operation speed of PLC is much faster than that of DCS. From a certain point of view, it is true that PLC has a high efficiency in logic operation. The execution time of 1K logic program is less than 1 millisecond, and its control cycle (taking Di input to do output as an example) can be controlled within 50 ms; DCS uses the same way to deal with logic operation and analog operation, and its control cycle is often more than 100 ms. When we use PID algorithm to compare, we can find that PLC performs a PID operation in a few milliseconds, while the t2550 controller of network6000 + DCs also needs one millisecond to solve a PID, which shows that PLC and DCs have the same actual calculation ability, and a certain type of DCS controller is even stronger. The difference of control cycle is mainly related to the scheduling design of controller. The new DCS controller has learned the design of large PLC, and its performance in control cycle has been greatly improved. Take t2550 controller of network6000 + DCs as an example. The controller can set four tasks with different priorities, and the minimum operation cycle can be set as 10ms. With high-speed I / O card, the control cycle can reach 15 ~ 20ms. The analog operation is set in other tasks with long cycle.
Data communication exchange
DCs has inherent advantages in this aspect. From the early development of DCS, network has become the core technology direction of DCS manufacturers. Redundancy technology and narrowband transmission technology are the earliest research and development or successful application of DCS manufacturers. PLC is mainly designed according to independent device, its "network" is actually serial communication.
The problem of PLC data communication exchange is mainly due to the fact that PLC has been developing as an independent device for a long time, and there is no system concept; And mainly used in small control system, the problem is not obvious, so the development is slow. At present, there are some large PLC in this aspect has been improved, but to achieve the level of DCS still needs a long process.