Abstract: The amplitude of an electrical signal is converted into a current of proportional intensity which is integrated and an integration voltage appears at the terminals of the integrating circuit. There is produced a signal which initiates stopping of the current integration and a signal which initiates the start of a following integration at the instant when the integration voltage attains a threshold value V.sub.O. Stopping of the integration occurs after a time-delay .theta., when the integration voltage has overstepped the threshold value V.sub.O and attained a maximum value V'.sub.O. The threshold value V.sub.O is adjusted so as to control the maximum value V'.sub.O in dependence on a reference voltage V".sub.O which is higher than V.sub.O. The frequency of integrations is measured, with the result that the conversion frequency is thus determined.