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 (111-114); - 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 , 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 , 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 (111-114); - 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 , 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 , - 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 , 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 , 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 ). <EOS>