Abstract: First and second spaced apart optical emitter-receiving pairs are located along a liquid carrying conduit. A regulator circuit is coupled to each emitter-receiver pair to control the operation of that pair inside a maximum response range regardless of the transparency of the liquid. The regulator circuit is so arranged as to supply the emitter with a voltage which is a function of the difference between a voltage supplied by the receiver portion of an optical-receiver pair and a reference voltage. A differential circuit produces a differential signal representing the difference between the signals produced by the receiver portions of the optical emitter-receiver pairs and a comparator circuit is connected to the differential circuit in order to generate an alarm signal as a function of the differential signal. The detector is particularly useful as an air bubble detector in a transfusion or perfusion system, and can also provide a container-empty alarm in such systems.

Abstract: This invention relates to the monitoring of the correct operation of a respirator with single source of energy constituted by a cylinder of pressurized oxygen, to which is annexed a device for connection to a patient. Such monitoring is effected with the aid of a pneumatically operating device which comprises a comparator with adjustable threshold, connected to the mask for connecting to the patient and followed by an amplifier whose output signal takes the binary logic level 1 during the time when the insufflation pressure in the mask is greater than said threshold, and takes the other binary logic level 0 in the opposite case, and a circuit for processing this signal, which triggers off an alarm device if the duration of the time intervals when this latter is at level 1 is too long or too short with respect to a predetermined normal value.