底板、機架模塊，它為PLC各模塊的安裝提供基板，并為模塊間的聯系提供總線。若干底板間的聯系有的用接口模塊，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箱體內的，并依可能提供I/O點數的多少，劃分為不同的規格。箱體式的PLC還有I/O擴展箱體，它不含CPU，僅有電源及I/O單元的功能。擴展箱體也依I/O點數的多少劃分有不同的規格。除上述模塊，PLC還有特殊的或稱智能或稱功能模塊。如A/D（模入）模塊、D/A（模出）模塊、高速計數模塊、位控模塊、溫度模塊等等。這些模塊有自己的CPU，可對信號作預處理或后處理，以簡化PLC的CPU對復雜的程控制量的控制。智能模塊的種類、特性也大不相同，性能好的PLC，這些模塊種類多，性能也好。通訊模塊，它接人PLC后，可使PLC與計算機，或PLC與PLC進行通訊，有的還可實現與其它控制部件，如變頻器、溫控器通訊，或組成局部網絡。通訊模塊代表PLC的組網能力，代表著當今PLC性能的重要方面。掌握PLC性能，一定要了解它的模塊，并通過了解模塊的性能，去弄清楚PLC的性能。除了模塊，PLC還有外部設備。
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.
The box type PLC also has an i/o expansion box, which does not contain CPU, but only has the function of power supply and i/o unit. The expansion box also has different specifications according to the number of i/o points.
In addition to the above modules, PLC has special or intelligent or functional modules. Such as a/d module, d/a module, high-speed counting module, position control module, temperature module, etc. These modules have their own CPU, which can preprocess or post process the signal, so as to simplify the PLC CPU's control of complex programmed control quantities. The types and characteristics of intelligent modules are also very different. PLC with good performance has many kinds of modules and good performance.
Communication module, which can communicate between PLC and computer, or between PLC and PLC after being connected to PLC. Some can also communicate with other control components, such as frequency converter and temperature controller, or form a local network. The communication module represents the networking ability of PLC and the important aspect of PLC performance today.
To master the performance of PLC, we must understand its module, and understand the performance of PLC by understanding the performance of the module.
In addition to modules, PLC has external devices.
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