PLC Shielding and Grounding

There are two problems that occur in these systems,

  1. Different power sources in the same system can cause different power supply voltages at opposite ends of a wire. As a result a current will flow, and an unwanted voltage appears. This can destroy components and create false signal levels.

  2. Magnetic fields crossing the long conductors or in conductor loops can induce currents, and destroy equipment, give false readings, or add unwanted noise to analog data signals.

Typical sources of grounding and shielding problems are,

  • electrostatic

  • magnetic

  • electromagnetic

  • resistance coupled circuits

  • ground loops

General shielding design points,

  • choose a metal cabinet that will shield the control electronics

  • avoid “noisy” equipment when possible

  • separate voltage levels, and AC/DC wires from each other when possible.

  • use shielded cables and twisted pair wires

Grounding problems include,

Resistance coupled devices can have interference through a common power source, such as power spikes or brownouts caused by other devices in a factory.

Ground loops are caused when too many separate connections to ground are made creating loops of wire that become excellent receivers for magnetic interference that induces differences in voltage between grounds on different machines. The common solution is to use a common ground bar…

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