- 上一篇：建筑抗震评价方法英文文献和中文翻译
- 下一篇：开槽板翅式换热器英文文献和中文翻译
Now that we're familiar with these terms, let's see how they are used in describing the available PLC network options.
PLC network options
PLC networks provide you with a variety of networking options to meet specific control and communications requirements. Typical options include remote I/O, peer-to-peer, and host computer communications, as well as LANs. These networks can provide reliable and cost-effective communications between as few as two or as many as several hundred PLCs, computers, and other intelligent devices.
Many PLC vendors offer proprietary networking systems that are unique and will not communicate with another make of PLC. This is because of the different communications protocols, command sequences, error-checking schemes, and communications media used by each manufacturer.
However, it is possible to make different PLCs "talk" to one another; what's required is an ASCII interface for the connection(s), along with considerable work with software.
Remote I/0 systems
A remote I/O configuration, as shown in Fig. 4A, has the actual inputs and outputs at some distance from the controller and CPU. This type of system, which can be described as a "master-and-slave" configuration, allows many distant digital and analog points to be controlled by a single PLC. Typically, remote I/Os are connected to the CPU via twisted pair or fiber optic cables.
Remote I/O configurations can be extremely cost-effective control solutions where only a few I/O points are needed in widely separated areas. In this situation, it's not always necessary, or practical for that matter, to have a controller at each site. Nor is it practical to inpidually hard wire each I/O point over long distances back to the CPU. For example, remote I/O systems can be used in acquiring data from remote plant or facility locations. Information such as cycle times, counts, duration or events, etc. then can be sent back to the PLC for maintenance and management reporting.
In a remote I/O configuration, the master controller polls the slaved I/O for its current I/O status. The remote I/O system responds, and the master PLC then signals the remote I/O to change the state of outputs as dictated by the control program in the PLC's memory. This entire cycle occurs hundreds of times per second.
Peer-to-peer networks
Peer-to-peer networks, as shown in Fig. 4B, enhance reliability by decentralizing the control functions without sacrificing coordinated control. In this type of network, numerous PLCs are connected to one another in a daisy-chain fashion, and a common memory table is duplicated in the memory of each. In this way, when any PLC writes data to this memory area, the information is automatically transferred to all other PLCs in the network. They then can use this information in their own operating programs.
With peer-to-peer networks, each PLC in the network is responsible for its own control site and only needs to be programmed for its own area of responsibility. This aspect of the network significantly reduces programming and debugging complexity; because all communications occur transparently to the user, communications programming is reduced to simple read-and-write statements.
In a peer-to-peer system, there's no master PLC. However, it's possible to designate one of the PLCs as a master for use as a type of group controller. This PLC then can be used to accept input information from an operator input terminal, for example, sending all the necessary parameters to other PLCs and coordinating the sequencing of various events.
Host computer links
PLCs also can be connected with computers or other intelligent devices. In fact, most PLCs, from the small to the very large, can be directly connected to a computer or part of a multi drop host computer network via RS232C or RS422 ports. This combination of computer and controller maximizes the capabilities of the PLC, for control and data acquisition, as well as the computer, for data processing, documentation, and operator interface.
-
PLC工业机器人英文文献和中文翻译
-
PLC相关问题英文文献和中文翻译
-
电气系统的可编程序控制...
-
PLC可编程逻辑控制器英文文献和中文翻译
-
S7-200PLC组态英文文献和中文翻译
-
闪存微控制器英文文献和中文翻译
-
PLC6层立体车库设计英文文献和中文翻译
十二层带中心支撑钢结构...
电站锅炉暖风器设计任务书
中考体育项目与体育教学合理结合的研究
河岸冲刷和泥沙淤积的监测国内外研究现状
当代大学生慈善意识研究+文献综述
酸性水汽提装置总汽提塔设计+CAD图纸
乳业同业并购式全产业链...
杂拟谷盗体内共生菌沃尔...
大众媒体对公共政策制定的影响
java+mysql车辆管理系统的设计+源代码