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Power over Ethernet (App Note)

 

The T7 does not have Power over Ethernet (PoE) built-in, but it is quite convenient to use an external splitter so you can just run 1 cable (Ethernet) to the T7 rather than 2 (Ethernet & Power).  This application note documents Power over Ethernet testing done September 2016.

A customer had reported noisy thermocouple readings with PoE on a T7-Pro, so we tested a bunch 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 good.  All our devices have excellent power supply rejection and thus analog input readings are generally not noticeably affected by noise and instability of the supply voltage.  BTW: The customer's problem in this case was that on 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.

 

Injectors:

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

  • NETGEAR GS308P 8-port switch with PoE
  • TRENDnet TPE-S44 switch with PoE
  • BV-Tech POE-I100
  • TRENDnet TPE-113GI
  • TP-Link TL-POE150S

No problems with any of these.

 

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:

  • Female Barrel 5.5 x 2.1:  Tensility 10-00240 and Tensility 10-00648
  • Male Barrel 5.5 x 2.1:  Amazon B00QHL2PTA and Belkin F3U133-06INCH
  • Female Type A USB:  Belkin F3U133-06INCH

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:

  • TP-Link TL-POE10R, female barrel power output.
  • TRENDnet TPE-112GS, female barrel output and also includes a cable to provide male barrel output.

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:

  • TRENDnet TPE-104S, female barrel power output.
  • Amcrest Splitter, Amazon B00CDT7KPO.  Female barrel output and also includes a cable to provide male barrel output.

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:

 

D-Link WAPPOE kit or POES5 splitter:

We tried 3 of these splitters.  2 from the kits and 1 ordered standalone.  Tried with the WAPPOE injector and with other injectors but could not get any of the splitters to work at all.  Not sure what the problem is as we have used these with no problems in the past.