Rockwell-automation 1761 MicroLogix 1000 Programmable Controllers Bedienungsanleitung PDF herunterladen (Seite 28)

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101

Preface

MicroLogix 1000 Programmable Controllers User Manual

1–12

Power Distribution

There are some points about power distribution that you should know:

• The master control relay must be able to inhibit all machine motion by

removing power to the machine I/O devices when the relay is de-energized.

• If you are using a dc power supply, interrupt the load side rather than the ac line

power. This avoids the additional delay of power supply turn-off. The dc

power supply should be powered directly from the fused secondary of the

transformer. Power to the dc input and output circuits is connected through a

set of master control relay contacts.

Periodic Tests of Master Control Relay Circuit

Any part can fail, including the switches in a master control relay circuit. The

failure of one of these switches would most likely cause an open circuit, which

would be a safe power-off failure. However

, if one of these switches shorts out, it

no longer provides any safety protection. These switches should be tested

periodically to assure they will stop machine motion when needed.

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