組成PLC的模塊是PLC的硬件基礎(chǔ)，只有弄清所選用的PLC都具有那些模塊及其特點(diǎn)，才能正確選用模塊，去組成一臺完整的PLC，以滿足控制系統(tǒng)對PLC的要求。常見的PLC模塊有：CPU模塊，它是PLC的硬件核心。PLC的主要性能，如速度、規(guī)模都由它的性能來體現(xiàn)。電源模塊，它為PLC運(yùn)行提供內(nèi)部工作電源，且，有的還可為輸入信號提供電源。I/O模塊，它集成了I/O電路，并依點(diǎn)數(shù)及電路類型劃分為不同規(guī)格的模塊。內(nèi)存模塊，它主要存儲用戶程序，有的還為系統(tǒng)提供輔加的工作內(nèi)存。在結(jié)構(gòu)上內(nèi)存模塊都是附加于CPU模塊之中。底板、機(jī)架模塊，它為PLC各模塊的安裝提供基板，并為模塊間的聯(lián)系提供總線。若干底板間的聯(lián)系有的用接口模塊，有的用總線接口。不同廠家或同一廠家但不同類型的PLC都不大相同。箱體式的小型PLC的主箱體就是把上述幾種模塊集成在一個(gè)箱體內(nèi)的，并依可能提供I/O點(diǎn)數(shù)的多少，劃分為不同的規(guī)格。

The modules that make up the PLC are the hardware basis of the PLC. Only by understanding which modules the selected PLC has and their characteristics, can the modules be correctly selected to form a complete PLC to meet the requirements of the control system for PLC.
Common PLC modules are:
CPU module, which is the hardware core of PLC. The main performance of PLC, such as speed and scale, is reflected by its performance.
Power module, which provides internal working power for PLC operation, and some can also provide power for input signals.
I/o module, which integrates i/o circuits and is divided into modules of different specifications according to the number of points and circuit type.
Memory module, which mainly stores user programs, and some also provide auxiliary working memory for the system. In structure, memory modules are attached to CPU modules.
Base plate and rack module, which provide base plate for the installation of PLC modules and provide bus for the connection between modules. Some backplane connections use interface modules, and some use bus interfaces. Different manufacturers or the same manufacturer but different types of PLC are not the same.
The main box of box type small PLC integrates the above modules into a box, and is divided into different specifications according to the number of i/o points that may be provided.