Abstract
A wide-range logarithmic response function is approximated by cascading a series of ``ramp'' functions, each representing the plate current of a triode driven toward cutoff by a diode rectifier in its grid circuit. Proper apportionment of the ac signal between the biasing diode and the triode makes the ramp symmetrical so that complementary deviations from linearity cancel when two or more ramp functions are cascaded. The wide-range voltmeter consists of a cascade of such amplifier stages driven successively to cutoff. Each stage is held at cutoff after reaching it by a diode-coupled holding bias fed forward from preceding stages. This arrangement prevents overloading of any stage and makes the range of the voltmeter approximately equal to the voltage gain of the cascade amplifier. Even without invoking compensation techniques, the response at all input levels can be made independent of frequency over a range extending from 50 cy/sec to 100 kc/sec. A simple alignment procedure is adequate to compensate normal tube variations, and a logarithmic response linear within ±1 db is readily obtained over the 80-db voltage range extending from 1 millivolt to 10 volts. The range can be changed easily, in both the number of db covered and in the input voltage for full-scale deflection, by connecting the indicating milliammeter to different numbers and combinations of ramp elements.
Published Version
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