A field device for measuring a measurement variable, comprising: - a sensor, which is designed to measure the corresponding measured value; - an interface having at least four electrical contacts; - a first current regulator, which is designed o to set a first current (a 1) between the first contact and the second contact when the field device is contacted via the interface such that a first voltage source (Q 1) is connected between these contacts (111, 112), characterized in that the field device furthermore comprises - a second current regulator, which is designed o to set a second current (a 2) between the first contact and the third contact when the field device is contacted via the interface such that a second electrical voltage source (Q 2) is connected between these contacts (111, 113), and o in the other case to generate a second signal (s f2); and - a control unit, which is designed: o to transmit the measured value according to a predefined digital standard via the fourth contact when the second current (a 2) is settable between the first contact and the third contact, and o to control the first current regulator such that the current strength of the first current (a 1) corresponds to the measured value according to a predefined current signal standard when the second current regulator generates the second signal (s f2). - a sensor, which is designed to measure the corresponding measured value; - an interface having at least four electrical contacts; - a first current regulator, which is designed o to set a first current (a 1) between the first contact and the second contact when the field device is contacted via the interface such that a first voltage source (Q 1) is connected between these contacts (111, 112), o to set a first current (a 1) between the first contact and the second contact when the field device is contacted via the interface such that a first voltage source (Q 1) is connected between these contacts (111, 112), - a second current regulator, which is designed o to set a second current (a 2) between the first contact and the third contact when the field device is contacted via the interface such that a second electrical voltage source (Q 2) is connected between these contacts (111, 113), and o in the other case to generate a second signal (s f2); and o to set a second current (a 2) between the first contact and the third contact when the field device is contacted via the interface such that a second electrical voltage source (Q 2) is connected between these contacts (111, 113), and o in the other case to generate a second signal (s f2); and - a control unit, which is designed: o to transmit the measured value according to a predefined digital standard via the fourth contact when the second current (a 2) is settable between the first contact and the third contact, and o to control the first current regulator such that the current strength of the first current (a 1) corresponds to the measured value according to a predefined current signal standard when the second current regulator generates the second signal (s f2). o to transmit the measured value according to a predefined digital standard via the fourth contact when the second current (a 2) is settable between the first contact and the third contact, and o to control the first current regulator such that the current strength of the first current (a 1) corresponds to the measured value according to a predefined current signal standard when the second current regulator generates the second signal (s f2).