Mitsubishi Electric LCPU-U-HW Safety Manuallines page 3

[Design Precautions]
(2) Machine OPR (Original Point Return) of the CPU module's positioning
function is controlled with two kinds of data: an OPR direction and an OPR
speed. Deceleration starts when the near-point watchdog signal turns on.
If an incorrect OPR direction is set, motion control may continue without
deceleration. To prevent machine damage caused by this, configure an
interlock circuit external to the programmable controller.
(3) When the CPU module detects an error during operation of the CPU
module's positioning function, the motion slows down and stops.
(4) When the programmable controller detects an abnormal condition, it stops
the operation and the output status is as follows:
• If the overcurrent or overvoltage protection of the power supply
module is activated, all outputs are turned off.
• If the self-diagnostics function of the CPU module detects an error
such as a watchdog timer error, all outputs are held unchanged or
turned off according to the parameter setting.
All outputs may turn on if an error occurs in a part, such as an I/O control
part, where the CPU module cannot detect any error. To ensure safety
operation in such a case, provide a safety mechanism or a fail-safe circuit
external to the programmable controller. For a fail-safe circuit example,
refer to "GENERAL SAFETY REQUIREMENTS" in this manual.
(5) Outputs may remain on or off due to a failure of an output circuit relay or
transistor. Configure an external circuit for monitoring output signals that
could cause a serious accident.
● In an output circuit, when a load current exceeding the rated current or an
overcurrent caused by a load short-circuit flows for a long time, it may cause
smoke and fire. To prevent this, configure an external safety circuit, such as a
fuse.
● Configure a circuit so that the programmable controller is turned on first and
then the external power supply. If the external power supply is turned on first,
an accident may occur due to an incorrect output or malfunction.
● Configure a circuit so that the external power supply is turned off first and then
the programmable controller.
If the programmable controller is turned off first, an accident may occur due to
an incorrect output or malfunction.
WARNING
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