Device for controlling a liquid flow in a tubular duct and particularly in a peristaltic pump

A monitoring device for monitoring the flow of a liquid in a tubular duct, comprising:

• a support structure of a peristaltic pump including a deformable tube having an outlet portion forming the tubular duct;
• a first piezoelectric cylinder whose vibration axis is substantially orthogonal to said duct in a detection zone and which is mounted on said support structure to be disposed on a first side of said duct, said first cylinder being fixed relative to said support structure;
• means for exciting said first piezoelectric cylinder in an axial mode at a predetermined frequency F lying in the range 100 kHz to 1500 kHz, in order to transmit ultrasound waves;
• a second piezoelectric cylinder whose axis coincides substantially with that of the first cylinder and that is disposed on a second side of said duct, whereby said second cylinder receives said ultrasound waves after they have passed through said duct;
• said second piezoelectric cylinder being secured to a moving support moveable in translation relative to said support structure along the direction of the axis of the cylinder;
• a resilient means interposed between said support structure and said moving support tending to press said second cylinder against the wall of the duct,
• a displacement detection means for detecting displacement of said moving support relative to the support structure under the effect of deformation of said duct because of excess pressure of the liquid flowing along said duct;
• means for picking up an electric signal representative of the amplitude of axial vibration of said second cylinder;
• and
• processor means for processing said electric signal to deduce therefrom the presence of a gas bubble in the liquid flowing in said duct through the detection zone.