A difference measurement circuit having a first port and a second port for connection to a first set of nodes and a second set of nodes of a sensor unit. The circuit further has switching units for switching excitation signals emanating from excitation nodes from being applied to the first set of nodes (A, B) via the first port to being applied to the second set of nodes via the second port and for switching differential measurement signals measured at sensing nodes from being obtained from the second set of nodes via the second port to being obtained from the first set of nodes via the first port. The circuit further includes redundancy testing circuitry for evaluating the similarity or deviation between measurement signals obtained in different states of the switching units.