Abstract: Current to the stator coils 21-24 of a brushless DC motor is commutated by making transistors 42 and 43 alternately conductive by current through magnetically actuated switches 37 and 33 (or 51 and 52). These switches are actuated by magnetic fields from the permanently magnetized poles of a magnet 31 (or 47) attached to, but spaced from the rotor 11 and the stator poles 17-20. Depending on the polarity of the magnetic fields, the switches 37 and 33 (51 and 52) permit one of the transistors 42 or 43 to be biased by a voltage source that causes that transistor to become conductive and, simultaneously, connects the base of the other transistor to a voltage that causes that transistor to become non-conductive. Conductivity of the transistors 42 and 43 alternates as the rotor 11 rotates.

Abstract: A vacuum pump controlled by a timer periodically evacuates a metering chamber to draw liquid samples into the chamber from a source. A switch is actuated when the liquid level reaches a predetermined point and causes the motor to stop. An electrically controlled valve is connected to the metering chamber above the level of the intake nozzle of the pump and is closed when the pump is operating and open when the pump is stopped, thereby allowing air to enter the upper part of the chamber to relieve the vacuum and allow the metered sample to flow out through an outlet tube to a sample receptacle. The outlet tube is controlled by a vacuum operated pinch valve to be closed during sample intake so that the pump will not have to evacuate the sample container before starting to draw liquid into the metering chamber.