As many know, one can implement a simple node to node rs485 communication by using only two wires, A and B. Well, the standard specify to connect the ground of the two node together.
In addition to the A and B connections, the EIA standard also specifies a third interconnection point called C, which is the common signal reference ground.
I stumbled upon tens of articles that speak about this third connection but still couldn't understand the concept.
- Why can't the receiver just act as a simple voltmeter? measuring the voltage between A and B?
- If both nodes are battery operated(different battery for each node) does the ground connection make any difference?
- Why is it better for (outdoor) nodes to be earthed when cables are long?
- How is this ground connection good for protection from transient?