Answer: The interface between PLC and electrical circuit is completed through the input and output part (I/O). The I/O module integrates the PLC's I/O circuit. Its input register reflects the input signal status, and the output point reflects the output latch status. The input module converts the electrical signal into a digital signal and enters the PLC system, while the output module does the opposite. I/O is divided into switch input (DI), switch output (DO), analog input (AI), analog output (AO) and other modules.
Switch quantity refers to a signal with only two states: on and off (or 1 and 0), and analog quantity refers to a continuously changing quantity. Commonly used I/O classifications are as follows:
(1) Switch quantity. According to the voltage level, there are 220VAC, 110VAC, and 24VDC; according to the isolation method, there are relay isolation and transistor isolation.
(2) Analog quantity. According to the signal type, there are current type (4~20mA, 0~20mA), voltage type (0~10V, 0~5V, --10~10V), etc.; according to the accuracy, there are 12, 14, 16bit, etc.
In addition to the above-mentioned general I/O, there are also special I/O modules, such as thermal resistors, thermocouples, pulse modules, etc. The module specifications and quantity are determined by the number of I/O points. The I/O modules can be more or less, but their maximum number is limited by the basic configuration capabilities that the CPU can manage, that is, the maximum number of baseboards or rack slots.
The PLC power supply is used to provide working power for the integrated circuits of each PLC module. At the same time, some also provide 24V working power for the input circuit. The power input types include AC power (220VAC or 110VAC) and DC power (commonly 24VAC).
Most modular PLCs use a baseboard or rack, whose functions are: electrically, to achieve communication between modules so that the CPU can access all modules on the baseboard; mechanically, to achieve connection between modules so that each module forms a whole.
