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FX Series Programmable Controllers Basic Program Instructions 2
2-5
2.5.2 Double Coil Designation
Double or dual coilin
g
is not a recommended
practice. Usin
g
multiple output coils of the
same device can cause the pro
g
ram
operation to become unreliable. The example
pro
g
ram shown opposite identifies a double
coil situation; there are two Y3 outputs. The
followin
g
sequence of events will occur when
inputs X1 = ON and X2 = OFF;
1.The first Y3 tuns ON because X1 is ON. The
contacts associated with Y3 also ener
g
ize
when the coil of output Y3 ener
g
izes. Hence,
output Y4 turns ON.
2.The last and most important line in this
pro
g
ram looks at the status of input X2.
If this is NOT ON then the second Y3 coil does NOT activate. Therefore the status of the Y3
coil updates to reflect this new situation, i.e. it turns OFF. The final outputs are then Y3 = OFF
and Y4 = ON.
Input durations:
The ON or OFF duration of the PLC inputs
must be lon
g
er than the operation c
y
cle
time of the PLC.
Takin
g
a 10 msec (standard input filter)
response dela
y
into account, the ON/OFF
duration must be lon
g
er than 20 msec if
the operation c
y
cle (scan time) is 10 msec.
Therefore, in this example, input pulses of
more than 25Hz (1sec/(20msec ON +
20msec OFF)) cannot be sensed.
There are applied instructions provided to
handle such hi
g
h speed input requests.
: Input ON state NOT reco
g
nized
: Input ON state reco
g
nized
: Input OFF state NOT reco
g
nized
: 1 pro
g
ram processin
g
: Input processin
g
: Output processin
g
: A full pro
g
ram scan/operation c
y
cle
X1
Y3
X2
1.
2.
Y3
Y3
Y4
Use of dual coils:
•Alwa
y
s check pro
g
rams for incidents of dual coilin
g
. If there are dual coils the
pro
g
ram will not operate as expected - possibl
y
resultin
g
in unforeseen ph
y
sical
The last coil effect:
• In a dual coil desi
g
nation, the coil operation desi
g
nated last is the effective coil. That
is, it is the status of the previous coil that dictates the behavior at the current point in
the pro
g
ram.
1
2
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4
4
7
t secs