Cutler-Hammer D320 PLC, Руководство пользователя

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Chapter 8: Troubleshooting Noise Problems
185
Isolation and Filtering Techniques
Isolation
There are several methods of isolation:
•
Attach an isolation transformer between the PLC power supply and the VAC source to help
remove noise that flows in the power cable. Try to attach the isolation transformer as near to
the PLC power supply input terminal strip as possible.
•
Some isolation transformers come with a shield that can be grounded. This shield, when
properly grounded, enhances the transformers ability to remove unwanted spikes.
•
Be certain to size the isolation transformer to handle the necessary power rating required by
the system. A good practical rule in specifying an isolation transformer is to multiply the
required load capability by 1.35 (35% additional deliverable power). This allows expansion of
the PLC system at a later date without the immediate need to upgrade the isolation
transformer.
•
When heavy noise is expected, also use an isolation transformer on the AC control power to
the I/O modules and devices. A cost-effective way of specifying the isolation transformer for
this requirement would be to specify a transformer with multiple primary and secondary
windings and wiring the PLC as shown below. Again, be certain to size the isolation
transformer to handle the necessary power required plus a 35% surplus and additional
windings to allow for future expansion of the system.
AC input
Ground
terminal
Triple ground (Less than 100 Ω
of ground resistance)
I
Isolation Transformer PLC
AC power
Breaker
Breaker
AC power
PLC power
Load
PLC input
Isolation Transformer