Abstract: An apparatus and a method for using at least two multiphase AC power sources to provide seamless uninterruptible power to a common load by isolating a faulty phase or source upon detection of a fault in one of the sources or in one of the phases thereof. To combine at least two three-phase power sources in parallel, for example, the apparatus includes a power paralleling circuit comprising two three-phase silicon controlled rectifier (SCR) bridges and a controller. Each bridge receives power from one of two separate and/or independent three-phase power sources. The controller monitors the status or condition of respective phases of power and selectively gates an associated SCR in each bridge so as to simultaneously power the common load from the two sources. Isolation switches are located in series with each phase circuit of each power supply. In the event of a fault, e.g.

Abstract: A method for controlling the air-to-fuel ratio fed to an engine or other combustion device provides for periodically adjusting the air-to-fuel ratio to stoichiometric or near stoichiometric, within the response range of the conventional exhaust gas sensor employed. This establishes a reference point from which the setting of an air-to-fuel ratio proportioning device (e.g., carburetor) is established by moving its adjustment means a selected distance from its setting at the reference point. The selected value may be outside the normal response range of the sensor, either rich or lean of stoichiometric. The apparatus may include a sensor which generates an output signal which is compared against a reference signal by a comparator. When the output signal exceeds (or falls below) the reference signal, a timer to operate the proportioning device adjustment means in the desired direction for a stated interval of time is actuated.