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31
FX
3G
/FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
2 Overview (Sequence Program)
2.5 Introduction of Devices Constructing PLC
1
Int
roduct
ion
2
O
ver
view
3
In
str
uc
tion
Li
st
4
D
evices
in D
etail
5
Spec
ified t
he
D
evice &
C
onst
ant
6
Bef
ore
Pr
ogr
am
m
ing
7
B
asic
In
st
ru
ct
io
n
8
FN
C
00-FN
C
09
P
rogr
am
F
low
9
FN
C
10
-FN
C
19
Mo
ve
&
Co
mp
are
10
FNC2
0-F
NC2
9
Ar
ith.
&
Logic
O
per
ation
2.5
Introduction of Devices Constructing PLC
Many relays, timers, and counters are built into an FX
3G
/FX
3U
/FX
3UC
PLC, with many NO (normally open)
contacts and NC (normally closed) contacts.
These contacts and coils are connected to make a sequence circuit.
A PLC is also equipped with data registers (D) and extension data registers (R) functioning as memory
devices to store numeric data values.
2.5.1
Relationship among devices
Arrows show transfer of signals.
4
1 2 3
Input terminal or
input connector
Input relay: X
Input relays function as receiving ports when the PLC receives signals from external
input switches.
The assigned device mnemonic is "X".
The PLC has built-in input relays in accordance with its scale.
Auxiliary relay: M
There are many
auxiliary relays
inside the PLC.
The assigned
device mnemonic
is "M".
State relay: S
There are many
state relays inside
the PLC.
The assigned
device mnemonic
is "S".
Timer: T
There are many
timers inside the
PLC.
The assigned
device mnemonic
is "T".
Counter: C
There are many
counters inside the
PLC.
The assigned
device mnemonic
is "C".
Output relay: Y
Output relays
function as ports
when the PLC
drives external
loads.
There are many
output relays inside
the PLC.
The assigned
device mnemonic
is "Y".
Output terminal
or output
connector
Contact for external output from output relay
(one NO contact)
The PLC has built-in output contacts in accordance with its
scale.