Hi Robert. POE is Power Over Ethernet. It just provides device power through the ethernet cable (CAT5, CAT6e, etc.) It does not, by itself, provide the necessary protocols for network communications. Normally, if you’re using POE, you have a network device that will accommodate that network connection (i.e., has an RJ45 jack, capable of hardwired connection, etc.).
But in the case of the PA sensor, I do not believe the existing models have the capability to be “hardwired” via an ethernet cable. They are designed to use wireless network connectivity only.
So why use POE if PurpleAir doesn’t have an RJ45 jack to accept a network or POE connection? Simple, the PA sensor requires 5v .08 amps of DC power in the physical form of a USB connector. It does not care how you provide that power, as long as it’s stable, correct voltage and current, and is in the form of that USB connector.
A simple “POE splitter” takes the power from the ethernet cable and converts it into a USB connector.
So to do away with the messy electrical cords hanging from the side of the house just to power the sensor, one can simply use a POE source to power the sensor. It’s the same power, just provided in a different manner. In my case, I already had POE capabilities in my rafters for other devices, so it was very simple to provide another connection for my sensor (see my pictures on this thread: Relocating Sensor and Power resource issue - #2 by KurtH)
Keep in mind that this configuration does require an ethernet cable and a POE capable device to feed that POE power (i.e., switch, injector, etc.). But it’s much simpler to run an ethernet cable on the outside of your house that it is to mess with 120v AC cables, connections, etc.). Much safer too.
As with anything, the devil is in the details. What works for me may not work for you or others. But modifying the configuration to meet your requirements is easy, and it simplifies the entire cable run/configuration.
While I do not advocate for any specific equipment vendors, I do recommend using POE technology when it can benefit and simplify your needs.
Did that at least answer some of your question?
Kurt