Any person or PLC programmer usually have own a way to program the PLC that he thinks the best and easy. In a simple sense in the process of editing, structured, nice views, and as much as possible minimize the error rate.
Usually in a plant PLC programming automation divided into 4 levels:
1. Field Level
At this level of process map from equipment level to the field level or the address of the inputs and outputs are connected to the PLC input output module.
2. Equipment Level
It is the object of existing equipment. Such as: Valve, Motor, Analog Input, Control Valve, Digital Input, etc. Or equipment that working in a separate function described in a programming language. Object here is to provide the interface with the unit level to enable the equipment level.
3. Unit Level
Level where the logic of programming is put, whether it is the delay time of the process, activation of the equipment used, Interlock list for equipment, PID control, and enable / disable of the process. A master sequence must have at least 1 or more units.
4. Master Sequence Level
The highest level and it is a supervisory to summon all levels, it is the main part of the process that will be made in the plant. Master sequence is also an interface for the operator to operate its plant, from here can see the status whether that is happening in these sequences, i.e., “run”, ”stopped”, “stopping”, “hold”, “aborting”, etc.