The present invention relates to a field device adapted to determine a process parameter value related to a tank, the field device comprising a terminal block with: a first interface configured to connect to two wires of a loop; a first electrical conductor and a second electrical conductor for connecting the first interface with field device electronics, the second electrical conductor having a voltage drop generating element; a first power supply conductor connected to said second electrical conductor upstream of the voltage drop generating element and a second power supply conductor connected to said second electrical conductor downstream of the voltage drop generating element; and a second, auxiliary interface adapted for wired connection to an external device and configured at least for communication with said external device, wherein the second auxiliary interface comprises a communications connector which is galvanically isolated from the field device electronics.