Abstract: A device for the measurement of time at which the physical state of a fluid medium is modified, comprises a vertical cup which contains the fluid and the necessary reagents, and in which a ferromagnetic ball is placed and is driven in rotation by an external magnetic field. The cup has at its lower part an annular travel path for the ball and it comprises a detection device which delivers an electric signal whenever the ball passes in front of it which is associated with a measurement unit determining the variation of the time interval between two consecutive passages of the ball.

Abstract: The invention relates to a method and device for determining the time of modification of the physical state of a fluid medium of the kind in which a ferromagnetic ball is placed in the bottom of a cup containing the fluid to be studied and driven with a periodic movement under the effect of an external magnetic field and in which the modifications of the movements of this ball, due to the modification, are detected. The method is characterized by the fact that the ball always follows at each period the same imposed path and in that the amplitude variations and/or the frequency of its movement are detected.