Are there any 4-20mA devices that are NOT loop powered? I though that was the whole point of 4-20mA. The 4mA floor is the minimum power required for the device to output "zero".
Yes there are. In the process control world they are sometimes called "4-wire transmitters", where two of the wires are for a input power supply for the transmitter, and the other two wires are the now 'powered' 4-20ma current loop output. This allows measurement of the loop at the 'receiver' end to just use a passive 250 ohm resistor, with one of the wires also grounded to the measurement systems ground.
So a 2-wire 4-20ma transmitter device requires that the loop is powered externally, while a 4-wire transmitter can power the loop.