Hello,
>
> I have a design problem regarding a system with RS485 bus in it.
> Ones in a while, some parts of the system needs to get physically
> disconnected from the RS485 line.
> This can be done using something simple like a relay that will
> disconnect the signal.
>
> Now here comes the problem, RS485 is a differential balanced signal,
> with known impedance, and should have low levels of noise.
>
> Can a coil based relay handle those requirements? Will the coil
> introduce noise? What about impedance? Is there a simpler way - like
> solid-state switch?
>
Why would the coil introduce noise? It's not connected to the RS485 bus is it? Only the relay's contact should be connected. I've done this to switch nodes from one RS485 bus to another and it works fine. The relay contact essentially has zero impedance at such low currents hence does not affect the bus.