A field device adapted to determine a process parameter value related to a tank, the field device comprising: a housing having an opening closed by a removable cover; a terminal block located in the housing and accessible via said opening; and field device electronics located in the housing, wherein the terminal block comprises: - a first interface configured to connect to two wires (108a-b) of a loop for power supply to and signal output from the field device; - a first electrical conductor and a second electrical conductor for connecting the first interface with the field device electronics, the second electrical conductor having a voltage drop generating element (54; 54'); - 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, wherein the second auxiliary interface is further configured to power the external device by means of a lift-off voltage taken from the loop, wherein the second auxiliary interface further comprises first and second power supply connectors (46a-b), the first power supply connector being connected to said first power supply conductor and the second power supply connector being connected to said second power supply conductor, and wherein the housing comprises a first compartment accommodating the terminal block, and a second compartment accommodating the field device electronics. a housing having an opening closed by a removable cover; a terminal block located in the housing and accessible via said opening; and field device electronics located in the housing, wherein the terminal block comprises: - a first interface configured to connect to two wires (108a-b) of a loop for power supply to and signal output from the field device; - a first electrical conductor and a second electrical conductor for connecting the first interface with the field device electronics, the second electrical conductor having a voltage drop generating element (54; 54'); - 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, - a first interface configured to connect to two wires (108a-b) of a loop for power supply to and signal output from the field device; - a first electrical conductor and a second electrical conductor for connecting the first interface with the field device electronics, the second electrical conductor having a voltage drop generating element (54; 54'); - 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, wherein the second auxiliary interface is further configured to power the external device by means of a lift-off voltage taken from the loop, wherein the second auxiliary interface further comprises first and second power supply connectors (46a-b), the first power supply connector being connected to said first power supply conductor and the second power supply connector being connected to said second power supply conductor, and wherein the housing comprises a first compartment accommodating the terminal block, and a second compartment accommodating the field device electronics.