Types of PLC (Based on Output configuration)

1. Relay type
2. Transistor type
3. Triac type

Relay Type

With relay type, the signal from the PLC output is used to operate a relay and so is able to switch currents of the order of few amperes in an external circuit. The relay isolates the PLC from the external circuit and can be used for both d.c and a.c switching Relays are relatively slow to operate.

Transistor Type

The transistor type of output (fig) uses a transistor to switch current through the external circuit. This provides a faster switching action. Opto isolators are used with transistor switches to provide isolation between the external circuit and the PLC. The transistor output is only for D.C. switching.

Triac Type

Triac outputs can be used to control external loads which are connected to the a.c power supply. Opto isolators are again used to provide isolation.

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