Importance

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Abstract

A range switching device for an electric meter, e.g. voltmeter, having a pair of input terminals, an impedance converting operational amplifier high in input impedance but low in output impedance having its input connected to one of said input terminals, a variable resistance and fixed resistance are connected in series between the output of said amplifier and the other input terminal, and the terminals of an electric meter made high in the input impedance by an impedance converting amplifier are connected across the ends of the fixed resistance, wherein the variable resistance is the aggregate of a plurality of groups of serially connected individual resistors, the individual resistors of each such group having the same resistance value while the resistance values of successive groups are successive multiples to a common base number of the fixed resistance value, each such group having switching contacts between the individual resistors of each group and at the ends of each group for selective engagement by a switch connected to one end of the next group to vary the number of functional individual resistors in that group. The number of individual resistors in each group normally will be one less than the common base number except that the number in the group corresponding to a multiple of one preferably equals the base number less two.

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First Claim