Mitsubishi Melsec-Q Series User Manual page 216

DANGER
CAUTION
When the programmable controller is powered on and off, normal control output may not be done momentarily due to
a delay or a start-up time difference between the programmable controller power supply and the external power supply
(DC in particular) for the control target.
For example, if the external power supply for the controlled object is switched on in a DC output module and then the
programmable controller power supply is switched on, the DC output module may provide false output instantaneously
at power-on of the programmable controller. Therefore, it is necessary to make up a circuit that can switch on the
programmable controller power supply first.
Also, malfunction may occour if an external power supply or the programmable controller is faulty.
To prevent any malfunction which may affect the whole system and in a fail-safe viewpoint, provide a external circuit to
the areas which can result in machine breakdown and accidents (e.g. emergency stop, protective and interlock
circuits) must be constructed outside the programmable controller.
The following page gives examples of system designing in the above viewpoint.
10 - 2
When changing data of the running programmable controller from a
peripheral connected to the CPU module or from a personal computer
connected to an intelligent function module, configure an interlock circuit
in the sequence program to ensure that the entire system will always
operate safely.
For program modification and operating status change, 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.
To prevent this, configure an interlock circuit in the sequence program,
and determine corrective actions to be taken between the external
device and CPU module in case of a communication failure.
Do not install the control lines or communication cables together with the
main circuit lines or power cables.
Keep a distance of 100mm (3.94 inches) or more between them.
Failure to do so may result in malfunction due to noise.
When a device such as a lamp, heater, or solenoid valve is controlled
through an output module, a large current (approximately ten times
greater than normal) may flow when the output is turned from off to on.
Take measures such as replacing the module with one having a
sufficient current rating.