除了模塊，PLC還有外部設備。
盡管用PLC完結對體系的操控可不必外部設備，裝備好適宜的模塊就行了。但是，要對PLC編程，要監(jiān)控PLC及其所操控的體系的作業(yè)狀況，以及存儲用戶程序、打印數(shù)據(jù)等，就得運用PLC的外部設備。故一種PLC的功用怎么，與這種PLC所具外部設備豐厚與否，外部設備好用與否直接有關。
PLC的外部設備有四大類：
編程設備：簡略的為簡便編程器，多只承受助記將編程，單個的也可用圖形編程（如日本東芝公司的EX型可編程操控器）。雜亂一點的有圖形編程器，可用梯形圖語編程。有的還有專用的核算機，可用其它高檔語編程。編程器除了用于編程，還可對體系作一些設定，以斷定PLC操控辦法，或作業(yè)辦法。編程器還可監(jiān)控PLC及PLC所操控的體系的作業(yè)狀況，以進行PLC用戶程序的調(diào)試。
監(jiān)控設備：小的稀有據(jù)監(jiān)督器，可監(jiān)督數(shù)據(jù)；大的還也許有圖形監(jiān)督器，可經(jīng)過畫面監(jiān)督數(shù)據(jù)。除了不能改動PLC的用戶程序，編程器能做的它都能做，是運用PLC極好的界面。功用好的PLC，這種外部設備已越來越豐厚。

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