Measuring device for a non-electrical variable, - having a measuring unit that is intended to convert the non-electrical variable indirectly into an electrical measurement signal by means of an electrical alternating current of a frequency (f), wherein the electrical measurement signal contains a useful signal portion (3), which is dependent on the non-electrical variable and is of the double frequency, and a fault signal portion (3(f)), which is dependent on the alternating current (I(f)) and is of the frequency (f), - having a signal pre-processing device for pre-processing and digitalisation of the measurement signal to give a digital signal, and - having a signal processing device for processing the digital signal by means of signal processing software to give a measured value, wherein the signal processing software is intended to: - detect the digital signal in a phase-sensitive manner, by multiplication with a reference signal at the double frequency, and process it by subsequent low-pass filtering to give the measured value, which is proportional to the non-electrical variable, and - detect the digital signal in a phase-sensitive manner, by multiplication with a further reference signal at the single frequency (f), and process it by subsequent low-pass filtering to give a fault signal value, characterised in that - the signal processing device has a normalising stage that is intended to normalise the measured value by forming the quotient using the square of the fault signal value, and to output it as a normalised measured value. - having a measuring unit that is intended to convert the non-electrical variable indirectly into an electrical measurement signal by means of an electrical alternating current of a frequency (f), wherein the electrical measurement signal contains a useful signal portion (3), which is dependent on the non-electrical variable and is of the double frequency, and a fault signal portion (3(f)), which is dependent on the alternating current (I(f)) and is of the frequency (f), - having a signal pre-processing device for pre-processing and digitalisation of the measurement signal to give a digital signal, and - having a signal processing device for processing the digital signal by means of signal processing software to give a measured value, wherein the signal processing software is intended to: - detect the digital signal in a phase-sensitive manner, by multiplication with a reference signal at the double frequency, and process it by subsequent low-pass filtering to give the measured value, which is proportional to the non-electrical variable, and - detect the digital signal in a phase-sensitive manner, by multiplication with a further reference signal at the single frequency (f), and process it by subsequent low-pass filtering to give a fault signal value, - detect the digital signal in a phase-sensitive manner, by multiplication with a reference signal at the double frequency, and process it by subsequent low-pass filtering to give the measured value, which is proportional to the non-electrical variable, and - detect the digital signal in a phase-sensitive manner, by multiplication with a further reference signal at the single frequency (f), and process it by subsequent low-pass filtering to give a fault signal value, - the signal processing device has a normalising stage that is intended to normalise the measured value by forming the quotient using the square of the fault signal value, and to output it as a normalised measured value.