The PLC can be, in effect, considered as an aggregate
of relays and timers.
The PLC is an electronic device mainly comprised of a microcomputer.
However in effect…
The user does not need any knowledge of a microcomputer to operate a PLC and it can be regarded
as an aggregate of relays, timers, and counters.
Signal Flow of PLC
● When the pushbutton switch PB1 is pushed, the coil of the input relay X1 is
energized.
● When the coil of the input relay X1 is energized, the N.O. contact of X1 is closed and the
coil
of the output relay Y0 is energized.
● When the coil of the output relay Y0 is energized, the contact of Y0 is closed, then the
pilot
lamp PL is illuminated.
● When the pushbutton switch PB1 is released, the coil of the input relay X1 is de-energized
and
the N.O. contact of X1 is opened.
But the output relay Y0 is still energized since the N.O. contact is closed. (Self-maintaining action)
● When the input relay is energized by closing the limit switch LS1, the N.C. contact of X3 is
opened, then the coil of the output relay Y0 is de-energized (Reset).
As a result, the pilot lamp; PL distinguishes and the self-maintaining action of the output
relay
Y0 is cleared.
Internal operation of PLC
X1
S/S
X0
X1
X2
X3
X4
X5
X6
X7
X3
X5
Y0
COM0
Y0
Y1
Y2
Y3
X3
X7
X5
M100
X1
X1
Y0
PB
1
LS
1
PB
2
PL
MC
0V
24V
OUT
T0
K100
Activate input relays
with external signals
Activate output
relays
Activate external
loads
Activate the internal sequential
circuit with input relay contacts
PLC
Power supply
Fuse
Input Wiring
Internal Signals
Output Wring
Output relay
Timer
M100
Auxiliary relay
Load
Contacts for
external output
Input relay
4
Содержание FX5U Series
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