（ 5 ）對在線和離線編程的挑選
離線編程示指主機(jī)和編程器共用一個(gè) CPU ，經(jīng)過編程器的辦法挑選開關(guān)來挑選 PLC 的編程、監(jiān)控和運(yùn)轉(zhuǎn)作業(yè)狀況。編程狀況時(shí)， CPU 只為編程器服務(wù)，而不對現(xiàn)場進(jìn)行操控。專用編程器編程歸于這種狀況。在線編程是指主機(jī)和編程器各有一個(gè) CPU ，主機(jī)的 CPU 完成對現(xiàn)場的操控，在每一個(gè)掃描周期結(jié)尾與編程器通訊，編程器把修正的程序發(fā)給主機(jī)，在下一個(gè)掃描周期主機(jī)將按新的程序?qū)ΜF(xiàn)場進(jìn)行操控。核算機(jī)輔佐編程既能實(shí)現(xiàn)離線編程，也能實(shí)現(xiàn)在線編程。在線編程需置辦核算機(jī)，并配置編程軟件。選用哪種編程辦法應(yīng)依據(jù)需求決議。
Different loads have corresponding requirements for the output method of PLC. For example, for inductive loads that are frequently switched on and off, transistor or thyristor output type should be selected instead of relay output type. However, the relay output PLC has many advantages, such as small conduction voltage drop, barrier effect, relatively cheap price, strong ability to withstand instantaneous overvoltage and overcurrent, flexible load voltage (AC and DC) and large voltage level. Therefore, AC and DC loads with infrequent actions can choose relay output type PLC.
(5) Selection of online and offline programming
Offline programming indicates that the host and programmer share a CPU, and the programming, monitoring and operation conditions of PLC are selected by selecting the switch through the programmer. When programming, the CPU only serves the programmer and does not operate on site. Special programmer programming is attributed to this condition. Online programming refers to that the host and programmer have a CPU respectively. The CPU of the host completes the control of the site, communicates with the programmer at the end of each scanning cycle, and the programmer sends the modified program to the host. In the next scanning cycle, the host will control the site according to the new program. Computer aided programming can realize both offline programming and online programming. Online programming requires an accounting machine and programming software. Which programming method should be selected should be determined according to the requirements.
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