Incremental encoder connected to a Compactlogix PLC using and arduino 

Why use an Arduino - you say?, well for once; my PLC has no high speed inputs nor hardware counters, so I needed a dedicated controller to read the pulses count them up/down and then transmit them- and what else to use but the old trusty humble and mighty Arduino Nano!
With a choice of either Serial or Ethernet, I choose Serial maybe a do a Ethernet shield later on.