How to choose a control system: Process controller, PLC, DCS
Thread Content
How to choose a control system: Process controller, PLC, DCS. When to choose PLC control system and when to choose DCS system? There is the following statement: There are very few points, so you can consider process controllers ； 50~100 points consider PLC system ； When the scale is larger, choose DCS. I think it makes some sense, but I always feel it's not convincing enough. I wonder if there are any other considerations? ? Especially between PLC and DCS.
Process controller: Generally used for simple equipment or complete sets of control, such as temperature control modules, etc. The number of such points is generally small.； PLC: There are applications from the simplest systems to more complex systems. PLC applications are generally environments where the system's reliability and performance requirements are not very stringent, that is, environments where the system can shut down. ； PLC is a programmable logic controller. DCS: Generally, DCS can be considered if the points exceed 600. DCS is a distributed control system, which means centralized management and decentralized control. In addition, the concept of redundancy (power supply, CPU, cards, etc.) is more powerful than PLC. Even if a failure occurs, the system can be switched to a backup system. Of course, there are fewer and fewer differences between PLC and DCS in high-end fields. However, industries with higher reliability requirements such as electric power, chemicals, and aerospace generally use DCS, and others generally use PLC. The simplest principle is: Can your system be discontinued? You can use PLC, but you can't use DCS.
Do current PLCs also have redundant configurations?
Generally speaking, PLC will not be equipped with redundant configurations. As mentioned on the second floor, the controls that require redundancy are for higher production safety. If you think the objects you control need redundancy, then use DCS.
1. Definitely choose based on the size of the system first. A system that is too small is not suitable for DCS. 2. Choose according to the number and complexity of the regulating control loop. 3. If there is a DCS system first, then if conditions permit, if the system is not large, it is best to use a DCS system to facilitate problem handling, accident inquiry and spare parts management. Others include environment and personal * habitual problem.
As mentioned on the second floor, "Nowadays, there are fewer and fewer differences between PLC and DCS in the high-end field." Redundancy, communication, configuration, etc. are all on par. For example, AB's ControlLogix5K series, Siemens' PCS7, etc. are all very powerful PLCs. They are not as simple as the traditional impression of having fewer points, fewer circuits, and fewer functions.
The working method of plc is cyclic scanning； The working mode of DCS is a multi-process real-time system. In addition to the conceptual things, the S7-400 can be used as a PLC or a DCSAC800M. ； Emphasis on "aggregation" and "dispersion", with strong management functions ； PLC is relatively small in scale, with not many points and mainly switches. ； ”Set "/" Scatter " are very simple;
Their differences are becoming increasingly blurred,
Generally speaking, I think PLC focuses on the logic control of switching values, and the processing of analog values is relatively troublesome. DCS is good at analog control in process control, such as PID configuration, which is very simple and convenient. However, the scan time of DCS is longer than that of PLC, so it has some disadvantages for high-speed motion control. For example, it is not suitable for high-speed compressor control.
The working method of plc is cyclic scanning； DCS works as a multi-process real-time system. Is DCS more powerful?