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10.1 General Safety Requirements
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LOADING AND INSTALLATION
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, an abnormal operation may be performed if an external power supply fault or
programmable controller 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 and interlock
circuits) should be constructed outside the programmable controller.
The following page gives examples of system designing in the above viewpoint.
DANGER
When connecting a peripheral device to a CPU module, or a PC to an
intelligent function module to control a programmable controller in opera-
tion (data change), configure an interlock circuit on the sequence pro-
gram so that the entire system operates safely at any time.
Also before exercising other control (program change, operating status
change (status control)) on the running programmable controller, read
the manual carefully and fully confirm safety.
Especially for the above control on the remote programmable controller
from an external device, an immediate action may not be taken for pro-
grammable controller trouble due to a data communication fault.
In addition to configuring up the interlock circuit in the sequence pro-
gram, corrective and other actions to be taken as a system for the occur-
rence of a data communication fault should be predetermined between
the external device and programmable controller 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 hav-
ing sufficient rated current.
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