Abstract: The invention concerns a device for the precise positioning of a measurement probe along a probe axis A and which can rotate around this axis. By the coaxial arrangement of adjustment units for rotating and longitudinal displacement of the probe as well as by an rpm step-down gear arranged therebetween, a compact construction of the device is made possible and a coaxially situated passage is kept free, through which the probe shaft can be inserted and removed.

Abstract: The device is constructed to position a measuring sensor, especially a sensor head at an angle to a sensor shaft, precisely at the point of measurement and in the direction of a fluid flowing in a test tube, in which there is an adjuster through which the measuring sensor, in a coaxial arrangement, can be adjusted via a first adjusting motor about its axis and/or by a second adjusting motor along its axis. A control device communicates with an electronic computer for controlling the sensor adjustment. An adjuster (4) is coupled to the sensor to rotate in unison therewith and has a rotatable pendulum which, in the position of rest transversely to the test tube axis defines the zero position of the sensor. Limit positions of the pendulum are predetermined from a relative movement of the adjuster about the axis which can be photometrically converted into position signals.