Arrangement to determine at least one electrical feature of an electrical device, the arrangement comprising • a signal injection unit configured to inject a first test signal (t 1) at a first main frequency (f 1) into a first electric circuit, and to inject a second test signal (t 2) at a second main frequency (f 2) into the first electric circuit or into a second electric circuit, • a signal conversion unit configured to measure a first and a second electrical quantity in the first electrical circuit resulting from the first test signal (t 1), and to measure the first and second electrical quantity in the first or second electric circuit resulting from the second test signal (t 2), and • a processing device including at least two analogue input channels (16,17) configured to receive said measured electrical quantities and to determine said electrical feature based on the measured electrical quantities, characterized in that the arrangement comprises • a mixing unit configured to ∘ add the measurements (U 1, U 2) of the first electrical quantity resulting from the first and second test signals and based thereon generate a first mixed signal, ∘ add the measurements (I 1, I 2) of the second electrical quantity resulting from the first and second test signal and based thereon generate a second mixed signal, ∘ to supply the first mixed signal to a first input channel of the processing device and to supply the second mixed signal to a second input channel of the processing device, and • the processing device is configured to decompose the mixed signals to obtain the measurements of the first and second electrical quantities. • a signal injection unit configured to inject a first test signal (t 1) at a first main frequency (f 1) into a first electric circuit, and to inject a second test signal (t 2) at a second main frequency (f 2) into the first electric circuit or into a second electric circuit, • a signal conversion unit configured to measure a first and a second electrical quantity in the first electrical circuit resulting from the first test signal (t 1), and to measure the first and second electrical quantity in the first or second electric circuit resulting from the second test signal (t 2), and • a processing device including at least two analogue input channels (16,17) configured to receive said measured electrical quantities and to determine said electrical feature based on the measured electrical quantities, characterized in that the arrangement comprises • a mixing unit configured to ∘ add the measurements (U 1, U 2) of the first electrical quantity resulting from the first and second test signals and based thereon generate a first mixed signal, ∘ add the measurements (I 1, I 2) of the second electrical quantity resulting from the first and second test signal and based thereon generate a second mixed signal, ∘ to supply the first mixed signal to a first input channel of the processing device and to supply the second mixed signal to a second input channel of the processing device, and ∘ add the measurements (U 1, U 2) of the first electrical quantity resulting from the first and second test signals and based thereon generate a first mixed signal, ∘ add the measurements (I 1, I 2) of the second electrical quantity resulting from the first and second test signal and based thereon generate a second mixed signal, ∘ to supply the first mixed signal to a first input channel of the processing device and to supply the second mixed signal to a second input channel of the processing device, and • the processing device is configured to decompose the mixed signals to obtain the measurements of the first and second electrical quantities.