Metering apparatus

Abstract

The metering apparatus for small volumes of liquid in the milliliter and microliter range comprises a piston/cylinder system driven by a direct-current motor. The piston stroke is measured by means of an optical path-length measuring system. For this purpose, a slide-rule pulse scale provided with a regular line grid is affixed to the piston. The light from a light transmitter passes through the slide-rule pulse scale and a stationary scanning plate which likewise is provided with a regular line grid, and to a light receiver. The pulses of the light receiver are digitalized in a pulse conditioning circuit and fed to a counter adapted to be preset by means of a coding switch. The counter position acts upon a braking and rotative-speed regulating circuit in such a way that regardless of the preset desired value of the rotative speed the speed of rotation of the motor is reduced to a small value as the final value is approached. As soon as the preset volume has been metered and the counter has reached the zero position, the motor is brought to a dead stop through a motor-control logic circuit with the aid of a reverse voltage. During the stopping process the no-load voltage of the motor is measured by means of a zero-voltage comparator at regular intervals. A pulse monitoring circuit serves to measure and regulate the piston-stroke speed and to turn off the motor in case of a mechanical defect. Motor and electronic systems are supplied with current from dry cells or storage batteries, a power supply being optionally provided to charge them.