Double Output (Double Coil) Operation And Countermeasures - Mitsubishi Electric MELSEC FX3U Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
6.2.2

Double output (double coil) operation and countermeasures

1. Operation of double outputs
When a coil gives double outputs (double coils) in a sequence program, the priority is given to the latter one.
Suppose that the same coil Y003 is used in two positions as
shown in the figure on the right.
For example, suppose the X001 is ON and X002 is OFF.
In the first coil Y003, the image memory turns ON and the output
Y004 turns ON also because the input X001 is ON.
In the second coil Y003, however, the image memory is set to
OFF because the input X002 is OFF.
Accordingly, the actual output to the outside is "Y003 = OFF,
Y004 = ON".
2. Countermeasures against double outputs
Double outputs (double coils) do not cause illegal input (program
error), but the operation is disrupted as described above.
Change the program as shown in the example below.
A B
C E
D
SET, RST or jump instruction can be used instead, or a same output coil can be programmed at each state by
step ladder instructions.
When step ladder instructions are used, if an output coil located in the main routine is also used in a state, it is
handled as a double coil. It is better to avoid such programming.
Y000
Ignored
Y000
or
6 What to Understand before Programming
6.2 Cautions on Creation of Fundamental Programs
Input processing
X001 = ON X002 = OFF
First
X001
Y003
Second
X002
Output processing
Y003 = OFF Y004 = ON
A B
Y000
C E
D
A B
M100
C E
M101
D
M100
Y000
M101
1
2
Y003
3
Y004
4
Y003
5
6
7
8
9
10
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