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Power over Ethernet (App Note)

Power over Ethernet (PoE) standards celebrates 15 years of official adoption by IEEE 802.3af in 2018. While most 15 year old technology is obsolete or mothballed, PoE is just as relevant today as ever. Mainstream adoption of PoE devices has driven down costs of switches, splitters and  injectors combined with an exploding number of PoE capable/compatible devices. This has offered expanded opportunities to not only established industrial processes but also experiments, prototypes and projects on a shoestring budget.

PoE offers innovators a variety of creative applications to the world of data acquisition (DAQ). Recently, LabJack performed thorough product testing to better serve those clients wishing to utilize PoE for their upcoming deployments. Using one of a variety of  inexpensive splitters/adapters our Ethernet capable LabJacks (T7 family, T4, & UE9 Family) can be used with PoE, eliminating the need for nearby AC power. Using Cat 6 cable, PoE can reliably transmit power and data 100 meters/328 feet. The benefits of PoE are well documented so we won’t turn readers off with another white paper provided by LabJack. We wish to share testing we have performed on 3rd party devices in conjunction with LabJacks' so you can incorporate PoE into your next LabJack project with confidence.

Consider using PoE the next time you deploy a LabJack in a remote setting that is without convenient AC power such as: factories, warehouses, outbuildings, outdoors, underground, other farming/agriculture applications, and other distributed data collection and automation applications.

LabJack PoE Testing Notes:

A customer reported noisy thermocouple readings with PoE on a T7-Pro, so we tested a number of different injectors and splitters to confirm that noise on grounded AIN0 stayed around 1-2uV with Range=0.1 and ResIndex=Auto=9.

Indeed, with all tested PoE equipment noise was always within acceptable limits.  All our LabJack devices have excellent power supply rejection and thus analog input readings are generally not noticeably affected by noise and instability of the supply voltage.  *LabJack Note: The customer's problem in this case was that upon device reset the analog inputs were being set to Range=10, which has substantially more noise than is seen with the Range=0.1 that is normally used with thermocouples.

3rd Party PoE Devices Tested:

 

Switches:

Injectors:

All injectors were tested with the WT-AF-USB splitter, and some injectors were tested with other splitters.

All devices performed without errors or excessive noise.

 

Splitters:

Many of these splitters seemed to have auto power shutdown.  They might take a few seconds to power up, and might not power up at all if the load (T7) is not connected.

All tested splitters had one of the following connectors for power output and we used the listed cables to connect to a T7-Pro:

The first 2 tested splitters have a switch to select 5V, 9V, or 12V output.  They have no other indication of what is selected so could see easily having the switch in the wrong spot and damaging a T7:

The next 2 tested splitters also have a switch to select 5V, 9V, or 12V output, but have an LED that shows what is selected so should make it more difficult to use the wrong voltage. Note* All LabJack devices require 5V only

The last tested splitter has fixed 5V output and also is available in the following specific model that includes a female USB connector.  This seems to be a great splitter:

 

 

References:

https://en.wikipedia.org/wiki/IEEE_802.3

http://www.bb-elec.com/Learning-Center/All-White-Papers/Ethernet/Benefits-of-PoE-for-Industrial-Applications.aspx

https://www.lorextechnology.com/articles/poweroverEthernet-PoE/R-sc15300042

http://www.veracityglobal.com/resources/articles-and-white-papers/poe-explained-part-1.aspx