
B-63983EN/02 1.OVERVIEW OF PMC
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(1) For relay sequence circuit
(A) and (B) in Fig. 1.4.1 (b) operate in the same manner. When A
(P.B) is turned on, current flows through coils B and C, turning on
B and C simultaneously. After C is turned on (after relay
operation time), B is turned off.
(2) For PMC programming
In (A) in Fig. 1.4.1 (b), as with the relay sequence circuit, when A
(P.B) is turned on, B and C are turned on, then B is turned off after
a certain time elapses (after a time required for one cycle of the
PMC sequence). In (B) in Fig. 1.4.1 (b), turning on A (P.B) turns
on C but does not turn on B even momentarily.
1.4.2 Repetitive Operation
A sequence program is executed until the end of the ladder diagram
(the end of the program) is reached, then program execution is repeated
from the beginning of the ladder diagram (the beginning of the
program).
The execution time from the beginning to the end of the ladder diagram
(the time required for one cycle) is a time for processing the sequence
program once and is called a scan.
This processing time depends on the sequence control scale (the
number of steps) and the size of the 1st level sequence described below.
A shorter processing time results in a better signal response in the
sequence.