How do I choose a digital input sensor?

Limit and Home sensors are split into two main groups:

• A NPN sensor is one that provides a sinking output. In other words, when the sensor is triggered, the output is sunk to GND. However, in the un-triggered state, the sensor outputs the high voltage.
• A PNP sensor operates opposite of an NPN sensor.

Most Arcus input opto-isolators trigger when the input is shorted to GND of the opto-supply. Therefore, a NPN sensor is the correct choice.

Other issues to note are the maximum sink/source current and voltage allowed. This will need to be addressed by the choice of the voltage supply and the current limiting resistor (if necessary).