Its not a very electrically noisy environment, just the usual fluorescent lighting, general 13 amp plugs with 'bits' plugged in like kettles, lamps, the odd computer, printer, etc.
The Slave units are divided (not equally) between a number of 'station positions' (about 7 in all).
Each Station has a series of 'modules' that collect the local data, and pass to a 'Station' handler module .... this will be on the network.
The cabling between the slave stations and the master will be in 2 core screened cable (using the Screen as the 'Ground') - or would it be better to use a 3 core screened cable, as Tx, Rx, Gnd and Screen as Earth (at the master end only) ?
The only other cables that 'could' be near to the comms cable would be 20vdc, 15vdc, and 7.5vdc .... there will be NO Mains or AC circuits within about 2 meters of cable ...... quit a nice 'electronic friendly' area.
I indicated in my original post that the last slave is a maximum of about 25 metres away .... I was thinking that I could split the network into 2 completely seperate networks, and cable them in both directions.
Its basically an area 7 meters by 5 meters square, and I was baseing the comms link on going right round, hence 24 meters (not as a ring, just end to end) ... I can't cable as 'star' from point to point as there is equipment in the middle, the cabling MUST go round the sides.
If I split it into 2 networks, the max lenght of either network would only be 12 meters ..... Hmm or could I just cable it that way anyway, and then place the master half way along the 25 metre network ? ... there's a thought !
I've done plenty of Ethernet, Modbus, Profibus .... but not too clued up on network wiring of this 'hybrid' type, all suggestions greatfully received.
Roy