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: A precision-delivery and precision-pressure piston pump is actuated by a cam controlled by a finestep stepping motor. The initial delivery pressure is precisely regulated by fixing the commencement of the delivery stroke at the cam with the aid of the stepping motor, as well as the time required for this delivery. Delivery is also regulated very precisely, for example in a ratio of 1 to 1000 by controlling the delivery stroke with the aid of the stepping motor. The pump is of use in particular in high-pressure liquid-phase chromatography.

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.