HOW PLC SCAN CYCLE WORKS
HOW PLC SCAN CYCLE WORKS? Hi Friends … Greetings , Today want to share with you how PLC actually works. PLC’s work on the principal on SCAN CYCLE. Lets find out how PLC Work? It works in Following Stages. STAGE 1.Regenerate input signal Before the execution of the program, PLC reads the On/Off status of the external input signals into the input signal memory at a time. The On/Off status of the input signal during the execution of the program will not change the signal status in the input signal memory. The new On/Off status will be read in the next scan. There will be approximately a 10ms delay from the On→Off or Off→On changes to the status being recognized by the contact in the program. The delay time may be affected by the scan time in the program. STAGE 2.Program processing After the PLC reads the On/Off status of every input signal in the input signal memory, it will start to execute every instruction in the program in order starting from address 0. The e...