Q Series PLC ladder diagrams, the statement table programmatically in addition, you can also execute SFC program. SFC is designed to satisfy both structured and standardized programming language. It is that will represent it in a series of actions to control the object directly with the program, so easy to understand.
Compared with ladder, it has the following features.
(1) the interlock SFC is simple
In the ladder diagram processing method, is used the method, a statement repeated from the beginning of the program to the last scan, and the procedures for the execution and control of all movements. In other words, in this way, no matter what device actions take place, the system always handle both before and after the action. Therefore, in order to coordinate action and actions before processing, which includes many interlocking signal. In order to define an interlock signal must be fully understood before and after treatment. If a does not fully understand and discuss, define interlock signal would have no meaning, there will be double interlock signals. Because of the existence of these interlocking signal, make the program more difficult to understand.
In contrast, in the SFC, procedure for dealing with current device corresponds to the action, action and action not addressed before. So, in the current process, only need to interlock signals which are relevant and current, which makes programs more concise.
(2) the SFC way easy to show action in order
Ladder diagram are by the contact and coil combination to be a way in the procedure cannot be action sequence. For example: device has some unusual had to stop working, in order to understand the program corresponds to the stop must read all programs.
In contrast, SFC modes, using a flow chart of the procedure in the form shown, the SFC and the order of the device action is essentially uniform, so to understand programs written in it is very easy.
(3) the SFC is easy to implement standardization
In ladder diagrams, contacts are connected, the coil would be put ON, this is one of the most fundamental principles, design must be in accordance with. In other words, program design freedom is very high, the action to implement a device in several ways. This makes designers design for different programs may vary, it difficult to standardize. In addition, persons other than the designer to understand the program is difficult.
In contrast, in SFC in order to produce the equipment line with the SFC, restricts freedom of programming, making it consistent with the action. Therefore, designers to people outside the program is very easy to understand, so as to realize the standardization of procedures.
(4) the SFC does not apply to non-sequential control
Ladder diagram in the way, because there is no record of the order, so that it also applies to the external interrupt signals and monitoring procedures to be used when.
In contrast, in the SFC, is recorded with the SFC action sequence. It does not apply to that kind of control regardless of the order.
In the PLC, SFC and ladder diagram can be used simultaneously, but can control objectives can be differentiated from use.