External Wiring Precaution - Mitsubishi Electric MELSEC-F FX1N Series Hardware Manual

FX1N Series Programmable Controllers
6.3.4

External wiring precaution

1) Contact protection circuit for inductive loads
Transistor outputs use internal zener diode (50V)
as protection circuitry. When driving the inductive
load with transistor output, a reverse-current
protection diode can be installed in parallel with the
load if necessary.
The reverse-current protection diode needs to satisfy the following specifications.
- Choose a commutating diode that has a reverse voltage strength over 5 - 10 times the
load voltage, and a forward current over the load current.
2) Mechanical Interlock
Ensure all loads are applied to the same side of
each PLC output, see previous figures. Loads
which should NEVER simultaneously operate
(e.g. direction control of a motor), because of a
critical safety situation, should not rely on the
PLC's sequencing alone. Mechanical interlocks
MUST be fitted to all critical safety circuits. (See
proceeding figure.)
DC (+)
Inductive load
Reverse-current
PLC
protection diode
output
PLC output
MC2 LSF
MC1
MC2 MC1 LSR
PLC output
Mechanical
interlock
6-9
Outputs 6.
1
DC (-)
2
3
4
5
Forward
operation
6
Reverse
operation
7
8