This is a model for an electrical resistor where the generated heat is dissipated to the environment via connector heatPort and where the resistance R is temperature dependent according to the following equation:
R = R_ref*(1 + alpha*(heatPort.T - T_ref))
alpha is the temperature coefficient of resistance, which is often abbreviated as TCR. In resistor catalogues, it is usually defined as X [ppm/K] (parts per million, similarly to percentage) meaning X*1.e-6 [1/K]. Resistors are available for 1 .. 7000 ppm/K, i.e., alpha = 1e-6 .. 7e-3 1/K;
When connector heatPort is not connected, the temperature
dependent behaviour is switched off by setting heatPort.T = T_ref.
Additionally, the equation heatPort.Q_flow = 0
is implicitly present
due to a special rule in Modelica that flow variables of not connected
connectors are set to zero.