TRICONEX-3902AX PLC and DCS
The emergence of PLC and DCS is from different professional mouth, the most important difference is the following:
First, the response speed is different
TRICONEX-3902AX The earliest purpose of PLC is to replace relay logic, because the response speed of relay logic is generally less than a few milliseconds, so the response speed of PLC is required to be fast; The purpose of the earliest appearance of DCS is to replace the secondary instrument, the general instrument is to measure pressure, flow, temperature, level, etc., the response speed is in a few hundred milliseconds to a few seconds, the response speed is not high, but TRICONEX-3902AX the calculation method of control is generally more complex than the relay logic, so DCS sacrifices the speed to complete the complex calculation.
Second, the scanning methods of the two are different
PLC scans from the beginning of the program to the end of the program, and then continuously cycle scanning, can be said to be a gut to the end of the way; DCS is to scan the surface according to the control ring, which can be said to be a multitasking way of working simultaneously.
3. I/O redundancy
DCS and PLC can achieve CPU redundancy, power redundancy, backboard redundancy, network redundancy, but at present, no matter which brand of PLC has not achieved I/O redundancy, and DCS can achieve I/O redundancy.
TRICONEX-3902AX That’s all I can say about it. Huh.
With the development of the computer, DCS and PLC are both close to each other, the function is getting closer and closer, some people advocate that the two can replace each other, in fact, for DCS, fast response control (such as motion control) is not competent, and for PLC, a large number of PID and other advanced computing control, the CPU can not withstand.
Therefore, I personally believe that when the switching quantity control is more, the control response speed is faster, it is recommended to use PLC, and the analog quantity control is more, it is recommended to use DCS.
There are many kinds of control products and different names. Commonly used control products include DCS, PLC two categories. We then extended the DCS concept to FCS.
TRICONEX-3902AX DCS (Distributed Contorl System), also known as distributed control system.
PLC (Program Logic Control) : Programmable logic controller.
FCS (FieldBus Contorl Syestem) is a field bus control system
Now, there is no strict boundary between DCS and PLC, in most people’s eyes, the big system is DCS, the small system is called PLC. Of course, it’s not impossible to say that, but it’s not right. Now let’s re-establish that idea.
First, what is the difference between DCS and PLC?
1. In terms of development.
DCS evolved from the traditional dashboard monitoring system. Therefore, DCS is more focused on the control of the instrument from the congenital point of view, such as the ABB Freelance2000 DCS system we use does not even have a limit on the number of PID (PID, proportional differential integration algorithm, is the standard algorithm for closed-loop control of regulating valves and inverters, usually the number of PID determines the number of regulating valves that can be used).
TRICONEX-3902AX PLC developed from the traditional relay circuit, the original PLC did not even have analog processing power, therefore, the PLC from the beginning to emphasize the logical computing power.
2, from the scalability and compatibility of the system.
There are many control products on the market, whether DCS or PLC, there are many manufacturers in the production and sales. For PLC systems, there is generally no or little need for expansion, because PLC systems are generally used for equipment. In general, there are few compatibility requirements for PLC, such as two or more systems that require resource sharing, which is also very difficult for PLC. And PLC generally use a dedicated network structure, such as Siemens MPI total linear network, and even adding an operator station is not easy or costly.
TRICONEX-3902AX DCS in the process of development is also the manufacturer’s own system, but most of the DCS system, such as Siemens, ABB, Honeywell, GE, Schneider, etc., although the internal system (process level) of the communication protocol is not the same, but the operating level of the network platform is the same choice of Ethernet network, using standard or deformed TCP/IP protocol. This provides very convenient scalability. In this kind of network, the controller and the computer exist as a node, as long as the network reaches the place, you can arbitrarily increase or decrease the number of nodes and arrange the node position. In addition, based on windows OPC, DDE and other open protocols, the system can also be very convenient communication, in order to achieve resource sharing.