According to precisioin digital, the term 'loop-powered' is synonymous with the term '2-wire'. Meaning that only 2 connections/wires are involved in any of the connections between the transmitter, the power source and the output device.
However, PRtrans and M-System, Japan, distinguish between 2-wire and loop-powered elements. For example PRetrans 6185 is Loop-powered signal isolation device, and PRtrans 5131 is 2-wire device.
Is there really a difference between 2-wire and loop-powered devices? In other words, can a 2-wire device NOT be loop-powered or a loop-powered device not be 2-wire?
Thank you in advance
> Is there really a difference between 2-wire and loop-powered devices?
Answer: No. "Loop powered" is a passive 2 wire device.
> In other words, can a 2-wire device NOT be loop-powered or a loop-powered device not be 2-wire?
Answer: One has to specify the 'signal', not the 'device'. A device might be 4 wire and line powered. But the 4-20mA output could be active (powered from a DC power supply internal to the device) or passive, requiring external DC power.
So if the signal output (not the device) is 2 wire, it is loop powered. But the device might be a 4 wire device.
You have to be aware that because a 4-20mA isolator (a device) has both an input side (a 4-20mA signal and output side (a 4-20mA signal). So a device has two 4-20mA signals to deal with and they might be the same (both passive or active) or different (one passive, one active).
There's a variety of isolator models - where the input or output are active or passive depending on what the field device signals require.