The invention relates to a measuring device for measuring a process variable, which device exhibits the least sensitivity to disturbance possible and allows flexible use, comprising an input circuit (1) having a line pair, which comprises a supply line (9) and a return line (11) and can be connected to a higher-level unit and via which, during operation, the measuring device is supplied with power and signals, in particular an output signal reflecting the process variable, are transmitted between the measuring device and the higher-level unit, and via which an input voltage (Uin) is present at the measuring device during operation, further comprising an in-phase regulator (13) inserted in the supply line (11) for setting a current flowing over the line pair, a quadrature regulator (15), which is connected downstream of the in-phase regulator (13) and is inserted in a shunt arm (17); connecting the supply line (9) to the return line (11), and a unit (19) for adjusting a voltage drop (deltaU) present over the in-phase regulator (13), which unit adjusts the voltage drop (deltaU) over the in-phase regulator (13) in accordance with the input voltage (Uin) that is present for input voltages (Uin) greater than a predetermined minimum input voltage (Uin min) to a value which is predetermined by a characteristic (deltaUsoll(Uin)) for the respective input voltage (Uin) and is above a minimum value (deltaUmin) required for the operation of the in-phase regulator (13), and a measuring sensor (3), which is connected to the input circuit (1) and supplied with power by the input circuit (1), for determining the process variable and for generating a measurement signal (M) reflecting the process variable.