Measuring device for measuring a process variable with - an input circuit with -- a pair of cables which can be connected to a higher-level unit, said cable pair consisting of a supply cable and a return cable and via which, during operation, energy is supplied to the measuring device and a signal is transmitted, particularly an output signal representing the process variable, between the measuring device and a higher-level unit, and via which an input voltage (U in) is applied at the measuring device during operation, -- a linear regulator inserted into the supply cable, said regulator being designed to regulate a current flowing through the pair of cables, -- a shunt regulator located downstream from the linear regulator and inserted into a cross branch connecting the supply cable to the return cable, and -- an apparatus designed to regulate a voltage drop (ΔU) present via the linear regulator, which regulates the voltage drop (ΔU) over the linear regulator - depending on the input voltage present (U in) for input voltages (U in) that are greater than a predefined minimum input voltage (U in min) - to a value, which is predefined by a characteristic curve (ΔU soll (U in)) for the input voltage (U in) and greater than a minimum value (ΔU min) required for the operation of the linear regulator, in such a way that the predefined value of the voltage drop (ΔU) for input voltages (U in) which are greater than the predefined minimum input voltage (U in min) increases to a predefined maximum value (ΔU max) as the input voltage (U in) increases, wherein the apparatus to regulate the voltage drop (ΔU) has an intelligent electronic unit, which regulates the voltage drop (ΔU) via the linear regulator to the predefined value on the basis of the input voltage (U in) present at the measuring device and the voltage drop (ΔU) via the linear regulator by appropriately controlling the shunt regulator, and - a sensor connected to the input circuit and powered via the input circuit, said sensor being designed to measure the process variable. - an input circuit with -- a pair of cables which can be connected to a higher-level unit, said cable pair consisting of a supply cable and a return cable and via which, during operation, energy is supplied to the measuring device and a signal is transmitted, particularly an output signal representing the process variable, between the measuring device and a higher-level unit, and via which an input voltage (U in) is applied at the measuring device during operation, -- a linear regulator inserted into the supply cable, said regulator being designed to regulate a current flowing through the pair of cables, -- a shunt regulator located downstream from the linear regulator and inserted into a cross branch connecting the supply cable to the return cable, and -- an apparatus designed to regulate a voltage drop (ΔU) present via the linear regulator, which regulates the voltage drop (ΔU) over the linear regulator - depending on the input voltage present (U in) for input voltages (U in) that are greater than a predefined minimum input voltage (U in min) - to a value, which is predefined by a characteristic curve (ΔU soll (U in)) for the input voltage (U in) and greater than a minimum value (ΔU min) required for the operation of the linear regulator, in such a way that the predefined value of the voltage drop (ΔU) for input voltages (U in) which are greater than the predefined minimum input voltage (U in min) increases to a predefined maximum value (ΔU max) as the input voltage (U in) increases, wherein the apparatus to regulate the voltage drop (ΔU) has an intelligent electronic unit, which regulates the voltage drop (ΔU) via the linear regulator to the predefined value on the basis of the input voltage (U in) present at the measuring device and the voltage drop (ΔU) via the linear regulator by appropriately controlling the shunt regulator, and -- a pair of cables which can be connected to a higher-level unit, said cable pair consisting of a supply cable and a return cable and via which, during operation, energy is supplied to the measuring device and a signal is transmitted, particularly an output signal representing the process variable, between the measuring device and a higher-level unit, and via which an input voltage (U in) is applied at the measuring device during operation, -- a linear regulator inserted into the supply cable, said regulator being designed to regulate a current flowing through the pair of cables, -- a shunt regulator located downstream from the linear regulator and inserted into a cross branch connecting the supply cable to the return cable, and -- an apparatus designed to regulate a voltage drop (ΔU) present via the linear regulator, which regulates the voltage drop (ΔU) over the linear regulator - depending on the input voltage present (U in) for input voltages (U in) that are greater than a predefined minimum input voltage (U in min) - to a value, which is predefined by a characteristic curve (ΔU soll (U in)) for the input voltage (U in) and greater than a minimum value (ΔU min) required for the operation of the linear regulator, in such a way that the predefined value of the voltage drop (ΔU) for input voltages (U in) which are greater than the predefined minimum input voltage (U in min) increases to a predefined maximum value (ΔU max) as the input voltage (U in) increases, - a sensor connected to the input circuit and powered via the input circuit, said sensor being designed to measure the process variable.