A logarithmic time base generator or counter

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Abstract
A number of output pulses linearly related to the logarithm of elapsed time or of input pulse count is generated by a circuit including two counters and a comparator. A fraction 1/a of the input pulses is applied to a continuous counter. A second, cycling counter receives all input pulses above a selected starting count, counts to equality with the continuous counter, and resets with production of an output pulse. Repetition of the cycle yields an output pulse series according to the equation ti /t 0=[a/(a − 1)] i , where t represents time or pulse count depending upon the source of pulses, periodic or aperiodic, and i is the number of output pulses. Conformance to the logarithmic relation log (ti /t 0)=i log [a/(a − 1)] is within 0.01%−0.1% for reasonably large input counts. This circuit has been applied to generation of a logarithmic time base for direct linear plotting of data from thermal conductivity measurements of liquids by the transient hot‐wire method.

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