9 LOADING AND INSTALLATION

MELSEC-Q

! DANGER

When connecting a peripheral device to the CPU module or connecting

 

 

a personal computer or the like to the special function module to

 

 

exercise control (data change) on the running PLC, configure up an

 

 

interlock circuit in the sequence program to ensure that the whole

 

 

system will always operate safely.

 

 

Also before exercising other control (program change, operating status

 

 

change (status control)) on the running PLC, read the manual carefully

 

 

and fully confirm safety.

 

 

Especially for the above control on the remote PLC from an external

 

 

device, an immediate action may not be taken for PLC trouble due to a

 

 

data communication fault.

 

 

In addition to configuring up the interlock circuit in the sequence

 

 

program, corrective and other actions to be taken as a system for the

 

 

occurrence of a data communication fault should be predetermined

 

 

between the external device and PLC CPU.

 

 

 

 

CAUTION

Do not bunch the control wires or communication cables with the main

 

 

circuit or power wires, or install them close to each other. They should

 

 

be installed 100 mm (3.94 inch) or more from each other.

 

 

Not doing so could result in noise that would cause erroneous

 

 

operation.

 

 

When controlling items like lamp load, heater or solenoid valve using an

 

 

output module, large current (approximately ten times greater than that

 

 

present in normal circumstances) may flow when the output is turned

 

 

OFF to ON. Take measures such as replacing the module with one

 

 

having sufficient rated current.

 

When the PLC power supply is switched ON-OFF, correct control output may not be

 

performed temporarily due to differences in delay time and starting time between the

 

PLC power supply and the external power supply for the controlled object (especially

 

DC).

 

 

For example, if the external power supply for the controlled object is switched on in a

 

DC output module and then the PLC power supply is switched on, the DC output

 

module may provide false output instantaneously at power-on of the PLC. Therefore, it

 

is necessary to make up a circuit that can switch on the PLC power supply first.

 

Also, an abnormal operation may be performed if an external power supply fault or

 

PLC failure takes place.

 

To prevent any of these abnormal operations from leading to the abnormal operation of

 

the whole system and in a fail-safe viewpoint, areas which can result in machine

 

breakdown and accidents due to abnormal operations (e.g. emergency stop, protective

9

and interlock circuits) should be constructed outside the PLC.

The following page gives examples of system designing in the above viewpoint.

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