Sfc Program And Step Ladder; Sfc Program; Outline; Explanation Of Function And Operation - Mitsubishi Electric MELSEC FX3U Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition

35. SFC Program and Step Ladder

This chapter explains the programming procedures and sequence operations for the "SFC" and "step ladder"
programming methods in GX Developer.
35.1

SFC Program

35.1.1 Outline

Sequence control using the SFC (sequential function chart) is available in FX PLCs.
In SFC programs, the role of each process and the overall control flow can be expressed easily based on
machine operations, so sequence design is easy. Accordingly, machine operations can be easily transmitted
to any person, and created programs are efficient in maintenance, specifications changes and actions against
problems.
When SFC programs and step ladder instructions are programmed conforming to the same rules, they are
compatible with each other.
As a result, the same contents can be handled in relay ladder charts which are familiar and easy to
understand.

35.1.2 Explanation of function and operation

In SFC programs, a state relay State S is regarded as one control process, and the input conditions and
output control sequence are programmed in each process.
Because the preceding process is stopped when the program execution proceeds to the next process, a
machine can be controlled using simple sequences for each process.
Operation of state relay State S and driven instruction
In SFC programs, each process performed by the machine is expressed by a state relay.
• When a state relay turns ON, a connected circuit (internal circuit) is activated.
When a state relay turns OFF, a connected internal circuit is deactivated.
After one operation cycle, non-driving of an instruction (jump status) is not available.
• When a condition (transfer condition) provided between state relays is satisfied, the next state relay turns
ON, and the state relay which has been ON so far turns OFF (transfer operation).
In the state relay ON status transfer process, both state relays are ON only momentarily (for one operation
cycle).
In the next operation cycle after the ON status is transferred to the next state relay, the former state is reset
to OFF.
When the transfer state relay S is used in a contact instruction, however, the contact image is executed in
the OFF status immediately after the transfer condition is satisfied.
• A state relay number can be used only once.
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35 SFC Program and Step Ladder
35.1 SFC Program