An addressable transducer interface which may be associated with a particular electrical transducer, comprises means (107) for storing correction data for the correction of errors as herein defined relating to that transducer so that on addressing of the interface by external control means, the correction data may be transmitted to the control means together with measurement data from the transducer. The storing means is arranged to store said correction data in digital form. The interface includes an analogue to digital converter circuit which comprises means (305, 306) for charging a capacitor (303) of a given value from a source of constant current of a given value, voltage comparator means (310, 311, 312) arranged to compare the value of an analogue voltage signal on an input with the charge voltage in said capacitor, a digital counter (301) arranged to start a count of cycles of a reference frequency when charging the capacitor is commenced from zero charge, a shift register (316, 317, 318) and a loading circuit arranged to cause the instantaneous count in said counter to be loaded into said shift register at the time when the charge in said capacitor is detected by said comparator as being equal to the value of the analogue signal.