不同的負(fù)載對(duì) PLC 的輸出辦法有相應(yīng)的要求。例如，頻頻通斷的感性負(fù)載，應(yīng)挑選晶體管或晶閘管輸出型的，而不該選用繼電器輸出型的。但繼電器輸出型的 PLC 有許多長(zhǎng)處，如導(dǎo)通壓降小，有阻隔效果，價(jià)格相對(duì)較便宜，承受瞬時(shí)過(guò)電壓和過(guò)電流的才干較強(qiáng)，其負(fù)載電壓靈活（可交流、可直流）且電壓等級(jí)規(guī)模大等。所以動(dòng)作不頻頻的交、直流負(fù)載能夠挑選繼電器輸出型的 PLC 。
（ 5 ）對(duì)在線(xiàn)和離線(xiàn)編程的挑選
離線(xiàn)編程示指主機(jī)和編程器共用一個(gè) CPU ，經(jīng)過(guò)編程器的辦法挑選開(kāi)關(guān)來(lái)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(duì)現(xiàn)場(chǎng)進(jìn)行操控。專(zhuān)用編程器編程歸于這種狀況。在線(xiàn)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(duì)現(xiàn)場(chǎng)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(chǎng)進(jìn)行操控。核算機(jī)輔佐編程既能實(shí)現(xiàn)離線(xiàn)編程，也能實(shí)現(xiàn)在線(xiàn)編程。在線(xiàn)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.