5. Sequential Function Chart
action and the transition from one step to another generally requires some transition criteria
(condition). The action of the previous step finishes as long as all criteria is true. When next step
begins, the action of previous step will be cleared. The step-by-step transition process is the
concept for designing sequential function chart (SFC).
Features:
1. Users do not have to consider the sequential relationship
between outputs as general ladder logic because STL
operation process can execute multiple outputs or interlocked
outputs automatically. An easy sequential design between the
steps is the only thing required to control the machines.
2. The actions in SFC are easy to understand. Also, it’s easy to
do a trial operation, error detecting or period maintenance.
3. SFC functions as a flow chart. The STL operation works on
the internal step relay S, which is also the step points
representing each state in SFC. When current step is finished,
the program proceeds to the next step according to the
transition condition and the desired continuous control
purpose can be achieved by this process.
4. Cycle process can be performed. Please refer to the SFC
opposite. Initial step S0 transfers to general step S21 by
transition condition X0. S21 transfers to S22 or jumps to S24
by the condition X1 and X2. The process finally proceeds to
S25 then a single cycle process is completed when S25
returns to S0 with transition condition X6 fulfilled.
SFC:
S0
S21
S24
S25
S0
X0
X1
X5
X6
X2
S22
X4
X3
S24
Explanation on SFC Toolbar Icons in Ladder Editor (WPLSoft)
Ladder diagram mode. The icon inserts general ladder diagram before the STL
diagram, usually the instructions for initializing the STL program.
Initial step in SFC. S0 ~ S9.are applicable
General step. S10 ~ S1023 are applicable.
5-3
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