FieldBus Signal -Power

I am not a Fieldbus Man.

1. But I know that, since about 130 years ago, series inductors have been used to feed the power from a telephone battery to a telephone circuit.
2. The working load resistance of a telephone overhead wire line and telephone set is about 600 ohms.
3. The inductor value L henries is chosen (with telephone set load DC current flowing) so that its impedance (2 x ∏ x f x L) is many times 600 ohms at audible frequencies (f) which are f = 300 - 2700 Hz for a typical speech circuit.
4. Consequently, most of the AC speech current goes down the line and very little into the inductors.
5. I expect the principle is the same for a FieldBus telemetry signal which uses a certain AC bandwidth.

Fieldbus segments use the inductor after the power supply, but before the input to the DCS (or whatever host). This causes the AC of the communications to go to the other devices, but blocks the signal from being absorbed by the windings etc. of the power supply. MTL and Pepperell& Fuchs have good descriptions on their websites of how this is done.