
B-63983EN/02 1.OVERVIEW OF PMC
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1.2.6 Difference Between Relay Sequence Circuit and Ladder
Sequence Program
In general relay sequence circuits, because of a limited number of relay
contacts, one contact may be shared by several relays to minimize the
number of contacts used. Fig. 1.2.6 (a) gives an example.
R1
R2
B
Fig. 1.2.6 (a)
With the PMC, relay contacts are considered to be unlimited, so ladder
diagrams are created as shown in Fig. 1.2.6 (b).
R1
R2
B
Fig. 1.2.6 (b)
In a relay sequence circuit having no contact between a branch point
and a coil as shown in Fig. 1.2.6 (c), a similar ladder diagram can be
created even for the PMC.
R1
R2
B
Fig. 1.2.6 (c)