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Abstract

An automatic transfer switch is taught which includes as part thereof a voltage sensing device which is interconnected with one of the lines to be monitored and controlled by the automatic transfer switch and neutral. This voltage may vary over a wide range and it is desired to provide a universal transfer switch control for operation over the wide range. The output analog voltage is provided to an analog-to-digital converter which has a maximum number of output bits. In order to keep the resolution of the output digital signal from the analog converter as high as possible, it is necessary to range the input voltage according to a menu of potential ranging values which are stored in the memory of a microprocessor. A programming device is utilized to input the line voltage and the microprocessor determines the maximum value for the ranging constant as a function thereof. The output analog voltage is reduced by this factor then provided to the analog-to-digital converter. The greater the reduction, the lower the sensitivity. However, the microprocessor chooses only that amount of discrete reduction necessary to prevent the expected input line voltage from exceeding the maximum digital output capacity of the A-to-D converter. The output of the A-to-D converter is then supplied to the microprocessor for processing and the amount of reduction is compensated for by multiplying the output signal by the increase of the conversion factor.

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