External U vs. I
The External U vs. I () feature connects an arbitrary current measurement (for example, a coil domain from another physics interface) as a current source between two nodes in the electrical circuit. The resulting circuit voltage between the first node and the second node is typically coupled back as a prescribed voltage source in the context of the current measurement.
Node Connections
Specify the two Node names for the connecting nodes for the current source. The current flows from the first node to the second node.
External Device
Enter the source of the Current. Voltage excited terminals or lumped ports defined on boundaries in other physics interfaces are natural candidates but do not appear as options in the Voltage list because those do not have an accurate built-in current measurement variable. A User defined option must be selected and a current variable entered, for example, using a suitable coupling operator.
The voltage variable must be manually coupled back in the electrical circuit to the context of the current measurement. This applies also when coupling to a voltage excited terminal or lumped port. The name of this voltage variable follows the convention cirn.UvsIm_v, where cirn is the tag of the Electrical Circuit interface node and UvsIm is the tag of the External U vs. I node. The tags are typically displayed within curly brackets {} in the Model Builder.
Connecting to Electrical Circuits
Nonlocal Couplings and Coupling Operators in the COMSOL Multiphysics Reference Manual