I'm doing a big project, where I will connect a lot of sensors to my Arduino Mega 2560. Eagerly, I bought boards of this type, but I can't get them to give me any voltage output! I've connected them with +24V, and my 2 wire 4-20mA sensor, a pressure transmitter, to the other end. There's no documentation to be found about the board, despite it looking like a popular product.
I have Vout measured with a voltmeter, it says 0.13. It's no different than the other cards, where there is no sensor attached at all. I was expecting there to be +24 between I+ and I-, but there is nothing. It's 100ohm resistance between them internally in the card. I have 16 of them, and they all behave the same, so there must be somehing I'm not doing right Could it be that they are made for 3-wire sensors? How can I wire it differently in order to make it work? Here's a photo of the card: