Abstract: A pipette body extends along a longitudinal axis and a piston mounted in sliding fashion along this axis inside the said pipette body so as to define a chamber of variable volume emerging at a sampling orifice, said piston being driven over a limited distance of travel in the direction of the sampling orifice by means of pressure manually exerted on a push rod mounted in sliding fashion in the pipette body, and in the opposite direction by the reaction of elastic return means until it abuts against an axial extremity of a metal sheath extending along the said longitudinal axis in side the pipette body. The sheath has an external thread which works by engaging with a thread inside the pipette body in such a way as to move the sheath longitudinally when driven in rotations, in order to adjust the distance of travel of the piston in the opposite direction and the volume of the chamber.

Abstract: A pump comprising at least a pump body having a chamber (110) communication with an inlet duct (130) and an outlet duct (140) via respective inlet and outlet valves (136, 146), a piston (120) moveable in sealed manner within said chamber, a cyclical actuator (400) of the rotary cam type for co-operating with said piston to cause it to slide, and a motor (500) for driving the cam in an unchanging predetermined direction while injecting volumes greater than the cylinder capacity of the pump, wherein the pump includes control means (404, 220, 600) adapted, on detecting that a required volume has been injected, to determine the position occupied by the rotary cam and to return the piston to the initial position of its delivery stroke prior to injecting a following volume by reversing the direction of rotation of the motor during reinitialization of the piston whenever the rotary cam is positioned on its delivery slope on such detection, and in contrast reinitializing the piston without reversing the direction of

Abstract: The output signal of an effluent detector, disposed, for example, downstream of a liquid phase chromotography column, is digitalized and then compared to a LEVEL signal, fixed in relation to the base line of the detected signal, plus a deviation value (LO). A slope threshold is defined. As long as the slope of the detected signal is below the threshold, the pilot signal follows the detected signal. When the slope of the detected signal is higher than the threshold, a peak has occurred, and the value of the pilot signal locked, at least during a pre-established time. Thereafter the pilot signal resumes its evolution substantially parallel with the base line. This enables an outstanding detection of the useful peaks in the analysis of effluents.

Abstract: In a stepping motor (M), the windings (L1 to L4) can be switched with the aid of switches (111 to 114). Two windings of each pair (e.g. L1 and L2) cannot be brought into the circuit simultaneously and are together arranged in series with a resistor (146) and a transistor circuit (150) adapted to cut off the supply voltage of 25 volts. A comparison and control circuit (130) compares the winding current from the resistor (146) with a reference value which is determined by a digital balancing resistor network (120) controlled by a permanent memory (102) and consequently acts on the form factor of the interruptions of the 25 volt supply current by the transistor circuit (150). The invention enables the multiplication of the number of steps per revolution which can be carried out by a stepping motor.