Detector of air bubbles in a circuit of liquid

A detector for detecting air bubbles or other liquid discontinuities in a circuit of liquid, comprising:

• first and second spaced apart optical emitter-receiver pairs spaced apart from each other along a conduit carrying said liquid, each emitter-receiver pair comprising a light emitting means and a light receiving means placed in a facing relationship on opposite sides of said conduit;
• a regulating circuit having a first input connected to said light receiving means, a second input of said regulating circuit connected to a source of a reference voltage and an output of said regulating circuit connected to said light emitting means in order to supply said light emitting means with a voltage which is a function of the difference between a voltage supplied by said light receiving means and said reference voltage such that said emitter-receiver pairs operate throughout a predetermined response range, independently of transparency of said liquid;
• processing means comprising a differential circuit including first and second inputs connected to said first and second emitter-receiver pair, respectively, in order to produce a differential signal representative of the difference between a first voltage supplied by said light receiving means in said first emitter-receiver pair and a second voltage supplied by said light receiving means in said second emitter-receiver pair;
• and
• said processing means operative to generate an alarm signal upon the appearance of an air bubble or liquid discontinuity in said conduit as a function of said differential signal.