Safety Measures; Safety Circuit; Momentary Power Drop - Panasonic FP7 Series User Manual

4.4 Safety Measures

4.4.1 Safety Circuit

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Precautions regarding system design
● In certain applications, malfunction may occur for the following reasons:
• Power on timing differences between the PLC system and input/output or mechanical
power apparatus.
• Response time lag when a momentary power drop occurs.
• Abnormality in the PLC unit, external power supply, or other devices.
In order to prevent a malfunction resulting in system shutdown take the following measures as
adequate:
■
Install the interlock circuit outside PLC
● When a motor clockwise/counter-clockwise operation is controlled, provide an interlock
circuit externally.
■
Install the emergency stop circuit outside PLC
● Install an emergency stop circuit outside PLC to turn off power supply to the output device.
■
Start up other devices before PLC
● The PLC should be started after booting the I/O device and mechanical power apparatus.
● When stopping the operation of PLC, have the input/output devices turned off after PLC has
stopped operating.
■
Install safety measures in case of alarm outside the PLC body
● When an alarm is released, PLC output is turned off and its operation is stopped. In order to
prevent a malfunction resulting in system shutdown under the above conditions, install safety
measures outside PLC.
■
Perform secure grounding
● When installing PLC next to devices that generate high voltages from switching, such as
inverters, do not ground them together. Use an exclusive ground for each device which
should be grounded at a grounding resistance of 100 Ω or less.

4.4.2 Momentary Power Drop

Operation in the case of momentary power drop varies depending on the combination of units,
the power supply voltage, and other factors. In some cases, operation may be the same as that
for a power supply reset.
● When a power supply unit (AC) is being used, operation is continued in the case of
momentary power drop shorter than 10 ms.
● When 24V DC is being supplied to the CPU unit, operation is continued in the case of
momentary power drop shorter than 4 ms.
WUME-FP7CPUH-09

4.4 Safety Measures

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