Electrical Outputs for Incremental Encoders！

Incremental encoders offer several types kinds of electrical outputs: Line Driver, NPN Open Collector, or Push-Pull (Totem Pole).A Line Driver output is a differential signal and requires two unique output wires per channel (Image 3). Typical wire designations are A, A- (A “not”), B, B- (B “not”), etc. When channel A is ON there’s a positive voltage between A and A-. When channel A is OFF, there’s a negative voltage differential between A and A-. The magnitude of the voltage
differential will be greater than 2.5V. The same happens for the B and Z channels. Line Drive outputs provide a high quality signal and are fairly immune to electrical noise.Line Driver encoders are very straightforward to wire to line driver-equipped PLC or motion controller inputs. Each output (A, B, Z) requires two wires, plus two wires for power supply (usually 5VDC).

A second output type is an Open Collector (NPN transistor) (Image 4). NPN Open Collector encoders “sink” current from sourcing (PNP) PLC inputs. Sinking and sourcing inputs simply refer to the current flow in a transistor.
An Open Collector encoder has A, B, Z, and 0V wires (and a wire for +DC to power the electronics). NPN Open Collector (sinking) encoders require the master PLC or motion controller to have PNP (sourcing) inputs. Open collector encoders usually accept a wide range of voltage.

The third type of encoder output is a Push-Pull circuit, also known as a Totem Pole output (Image 5). The Push-Pull output is a special circuit that can sink or source current to the PLC. The key to this encoder’s circuit is the pair of transistors in the encoder. When one transistor is ON, the other is OFF.
If the PLC supplies current (the PLC has sourcing, or PNP inputs), the Push-Pull encoder can sink current through the lower transistor. If the PLC sinks current (the PLC has sinking or NPN inputs), the encoder will source current through the upper transistor

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