Who would think a two wire system could be so confusing?

I have setup the 2108 system we have to connect to passive sensors so therefore i supply the 24V to power the device.

Now i have a flowmeter that is an active sensor, it supplies its own power to the 4-20mA transmitter. same two wire output but it's just signal and ground. How do I go about connecting that? I cant quite get my head round it.

Thanks