GB635562A - Improvements in and relating to electrical logarithmic converters - Google Patents

Abstract

635,562. Thermionic valve voltmeters. SCOPHONY, Ltd., and FRANKLIN, D. P. Nov. 28, 1946, No. 35363. [Class 37] [Also in Group XL (c)] An apparatus for producing from an input voltage applied at 12 an output voltage at terminals 14 which is a linear function of the logarithm of the input voltage in order, for example, to expand the scale of a meter at lower readings, comprises a generator 11 of a waveform, a substantial part of which is exponential an amplitude limiter 10 to which the generated wave and the input voltage is applied and means 13 for producing from the resulting pulses a voltage proportional to the duration of the pulses and constituting the desired logarithmic output voltage. As decribed, the generator produces an exponential sawtooth wave 18, for example by charging a condenser through a resistance and discharging it rapidly and this wave is applied to a limiter which starts conducting at an amplitude corresponding to line 17 and limits on a small signal increment at 16. Input signals of voltage E1 or E2 (Fig. 3), alter the position on the curve at which the limiter operates, with the result that the output from the limiter is in the form of pulses 19, 19<1> whose width varies as the logarithm of the input voltage. These pulses may be converted into a steady signal by passing them through a low-pass filter. The D.C. component may alternatively by extracted- and the resulting pulses applied to a peak voltmeter.