Programming Actions and Conditions
S7-GRAPH for S7 300/400 Programming Sequential Control Systems
7-14
C79000-G7076-C526-01
Example: Action table with counters and arithmetic as alternative to counting step
activations
S1 CU
Z23
S4
S1 N
A:=A+1
Step4
Step4
1
2
Two alternatives for counting production cycles:
(1): As soon as the step is active, the counter C23 is incremented by 1. The
counter therefore counts the number of times the step is activated.
(2): As soon as the step becomes active, the value of A is incremented by 1. In this
way, the arithmetic can be used to count actions based on the number of
activations of the step.
7.5 Conditions
Conditions are binary states of the process that are combined with each other as
LAD or FBD elements (normally-open contact, normally-closed contact, AND box,
OR box, comparator) in the LAD diagram or in the function block diagram
according to Boolean logic. The result of the logic operation (RLO) can influence
individual actions of a step, the entire step, the enabling of the next step or the
entire sequencer. Logic operations are programmed in Ladder Logic or FBD.
Conditions are :
•
Events (for example active step is exited) and
•
States (for example input I 2.1 is set)
Areas in which Conditions Can Occur
Conditions occur in the following areas:
•
Transition (enabling the next step)
•
Interlocks
•
Supervisions
•
Permanent instructions (conditions and block calls at the start and/or at the end
of the sequencer)
