PLC is the key component to manipulate electrical equipment in the electrical equipment automatic control system. Therefore, the performance of PLC is an important place related to the safety, reliability and efficient operation of the entire automatic control system. When designing PLC control cabinets and PLC control system software, the following basic principles should be followed:
Consider the control requirements of the target to the greatest extent. 2. To ensure that the automatic control system is simple, economical, easy to use, and easy to maintain.
3. Maintain the safety factor and stability of the automatic control system. 4.
The operation is simple and convenient, and there are safety precautions to avoid operating errors. 5. Consider various performance indicators and environmental requirements of PLC.
Generally speaking, when the PLCPLC electric control cabinet is running, its working process can be divided into input sampling stage, program execution stage and output updating stage. Carrying out the three phases is referred to as one scanner cycle time. PLC stores each input situation into the corresponding input image register, at this time, the input image register is updated, and then enters the program execution stage.
In the program execution stage or the output update stage, the input component image register is isolated from the outside, no matter how the input data signal changes, its content remains unchanged until the input sampling stage of the next scanner cycle time to update the new content of the input terminal Load again.