Abstract: A three phase transformer having a pair of additional coupled windings on the secondary side of each phase, with these coupled windings properly connected in series to develop a voltage in phase with a particular secondary voltage but driven from alternate phase primaries. The primary and secondary windings are connected in a Y or .DELTA. configuration. One coupled winding from each of the two phases, other than the desired secondary phase which is to be balanced, are joined in negative series so that when summed, they are aligned with the secondary phase being corrected. The series coupled windings are connected in parallel with the third secondary. The unbalanced current is split between the secondary winding and between the two coupled windings, each of which is coupled to the primary of another phase. The coupled winding combined voltages and resistances are approximately equal to the voltage and resistance of the secondary.

Abstract: An apparatus and method for automatically determining the measurement accuracy of an uncalibrated field fluid flow meter by comparing its fluid flow volume, measurement, V.sub.f, to a fluid flow volume measurement, V.sub.m, of a master meter of known accuracy. The apparatus comprises fluid flow device operably coupled to the field and master meters for passing a common fluid stream through each of the meters at a predetermined flow rate until a predetermined volume of fluid has been registered by the field meter; a first measurement signalling device for a generating data representing the fluid volume registered by each of the meters; a second signalling device for generating data representing input temperatures and pressures to each of the meters; and a computer coupled to the fluid flow device for automatically controlling the flow rate and calculating the accuracy of the field meter.

Abstract: An inverter is provided, especially for use in an uninterruptible power supply, with its switching transistors being ground referenced and its output voltage fed back and compared to a single reference waveform for a self-setting duty cycle control of the switching transistors. The switching transistors are activated only when the output voltage is outside of a predetermined error band from the desired level, with the control system activating the switching transistors to drive the output voltage to the desired level and deactivating the switching transistors when the output voltage is within the error band. A current limit circuit provides current limit control which varies depending on the angle and magnitude of the output voltage.