in reply to: Multidropping 4 wire HART devices posted by John Emmett on 23 July 2010 at 08:56:59.
I think, if you connect them appropriately, you can regard all these devices as current sources (not sinks). (That is, unless they are output devices - valve positioners etc.) If a device really sinks current from the live signal wire to ground, it would generate a negative voltage across the load resistor; I've never seen that.
So I don't see a conflict, as long as the combined currents don't add to more than 20mA. I've put a diagram and more comments at www.romilly.co.uk/mixedmultidrop.htm .