PLC's IO module input sampling stage works

PLC works: When the PLC into operation, their work is generally divided into three stages, namely the input sample, a user program execution and output refresh three stages. Completion of the three phases is called a scan cycle. During the entire operation, PLC's CPU to a scanning speed of repeating the above three phases. (A) input sampling stage: input sampling stage, PLC scan mode sequentially reads all input status and data stored within them plc analog io module image area corresponding the unit. After the end of the plc input module sample, into the user program execution and output refresh period. In both stages, and even if the input data changes state, status, and data g-input-output-module/">IO module plc of the image area of ​​the corresponding cell is not changed. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than one scanning cycle, in order to ensure that in any case, the input can be read.