Analytical apparatus for analysing at least one substance has an array of sensors (1) driven by an electronic driver (14) for operating each sensor. The signals produced by the sensors are received by a receiver (82), and the apparatus includes one or more calibration elements connected to the driver and the receiver for enabling changes in parasitic losses in the apparatus to be determined. The invention is particularly applicable to apparatus in which the sensors are electrical-mechanical transducers, individually connectable (in sequence) to the driver and receiver by a corresponding array of switches forming part of an interface (4).