For many industrial electronics the following rule of thumb holds: you can never have to many galvanic isolations. Especially between devices that are placed at some distance between each other, potential differences can disturb communication or deteriorate analog signals.
A common scenario is when one device powers the other (via a + en 0 wire), and communicates (via signal wires that are related to 0). Fast fluctuations in de current draw, for instance caused by switching power supplies, cause voltage drops when long cables are used. This can disturb communication, especially at higher baud rates.
Contrary to what is common belief this can occur even with RS485 communication!
For proper functioning of RS485 3 wires are required, plus 2 for the power supply. The 0 of the RS485 and that of the power supply should be galvanically separated.
Transferring energy over a galvanic isolation generally requires a transformer. The costs of these transformers can be relatively high, especially with Ex galvanic isolattions, where the distances in the transformer need to comply with special requirements. As a result, these Ex transformers can seldom be bought of the shelf, and must be especially designed and tested.
A lower cost alternative is applying PCB transformers. Here the PCB tracks are used for the windings and the PCB material is used as isolator.
Exalon Delft has the technology to design Ex PCB transformers.
A galvanic isolation is actually a switching power supply. A high power a high efficiency is required because of heat development.
For instrumentation, the available power is often so small (for example 12V x 4 mA in HART transmitters) that it needs to be used as economically as possible.
Exalon Delft has the technology to realize galvanic isolations that dissipate less then 1 mW.
For the signal transmission between primary and secondary circuit in principal optocouplers can be used. These are generally slow or dissipate much power.
For analog signal transmission it is also difficult to limit the signal’s distortion.
When additionally the galvanic isolation needs to comply with Ex i standards the distances internal to the optocoupler need to be considered.
The combination of requirements generally leads to complex circuits with high costs.