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Mitsubishi Electric Artisan MELSEC-Q Series Manual Page 11

General-purpose programmable controllers, large/small.
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● Configure safety circuits external to the programmable controller to ensure that the entire system operates
safely even when a fault occurs in the external power supply or the programmable controller. Failure to do so
may result in an accident due to an incorrect output or malfunction.
(1) Configure external safety circuits, such as an emergency stop circuit, protection circuit, and protective
interlock circuit for forward/reverse operation or upper/lower limit positioning.
(2) The mechanical zero return of the positioning function is controlled based on two parameters, zero
return direction and zero return speed, and deceleration is started when the near-point dog is turned
on. Therefore, if the zero return direction is set incorrectly, the positioning function may continue the
operation without deceleration. Configure an interlock circuit for prevention of mechanical damage on the
outside of the programmable controller.
(3) When the CPU module detects an error during operation of the positioning function, the function will
decelerate and stop.
(4) The programmable controller stops its operation upon detection of the following status, and the output
status of the system will be as shown below.
• When the overcurrent or overvoltage protection of the power supply module is activated, all outputs
will be turned off.
• When the CPU module detects an error such as a watchdog timer error by the self-diagnostic
function, all outputs will be held or turned off according to the parameter setting.
All outputs may turn on when an error occurs in the part, such as 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 LOADING AND INSTALLATION in the LCPU User's Manual (Hardware Design,
Maintenance and Inspection).
(5) Outputs may remain on or off due to a failure of a transistor on an output circuit. 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 before the programmable controller is
turned off.
If the programmable controller is turned off first, an accident may occur due to an incorrect output or
malfunction.
● For the operating status of each station after a network communication failure, refer to relevant manuals for
the network. Incorrect output or malfunction due to a communication failure may result in an accident.
● When changing data of the running programmable controller from a peripheral connected to the CPU
module, configure an interlock circuit in the program to ensure that the entire system will always operate
safely.
For other controls for the running programmable controller (program modification and operating status
change (status control)), read relevant manuals carefully, and ensure the safety before operation.
Especially, in the case of a control from an external device to a remote programmable controller, immediate
action cannot be taken for a problem on the programmable controller due to a communication failure.
Configure an interlock circuit in the program, and determine corrective actions to be taken between the
external device and CPU module in case of a communication failure.
● If an absolute position is recovered by the positioning function, the servo ON signal may be kept off (the
servo may be kept off) for approx. 20 ms, and the motor may operate. If any problem is caused by the motor
operation when the servo ON signal is turned off, provide an electromagnetic brake so that the motor will be
locked during absolute position recovery.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
Design Precautions
WARNING
8

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