What does Non-Polarized refer to on Optically Isolated inputs?

Non-polarized means that the input trigger condition measures the voltage magnitude across the input, or alternatively the current magnitude through the input, regardless of the actual direction of the voltage polarity or current direction. This distinguishes these optically isolated inputs from polarized inputs because the optical isolator uses a back-to-back arrangement of light emitting diodes. Inexpensive optical isolators will only trigger when the voltage across the input has a specific polarity or the current through the input is in a specific direction.

All Sealevel I/O products with isolated inputs use non-polarized optical isolators for trouble-free field wiring and improved reliability.