Acoustic cleaning of optical probe window

The present invention relates to a system for removing deposits from measuring instruments measuring chosen characteristics of a fluid medium contained in a pipe or container, the measuring instrument comprising a window (10) and a first surface (12) having contact with said medium, said first surface (12) being positioned on one end defining a probe head (2) of an elongated member (13) adapted to be extending through the wall (6) of said pipe or container, the outer end of said member (13) being positioned outside said wall (6), the cleaning system comprising an acoustic transducer (5) positioned on the other end of said elongated member (13), wherein said acoustic transducer (5) is acoustically coupled to the elongated member (13) so as to couple acoustic energy thereto, the acoustic energy propagating along said member (13) to the end (2,12) of the probe (1) being in contact with the fluid inside the pipe or container, the resulting vibrations of which removing any contaminations from said window (10) by inducing cavitation.