Design and Construction of a Four-Decade Digital Log Ratemeter

A four-decade digital log ratemeter using integrated circuits for all active components has been designed and tested. The ratemeter is capable of measuring pulse rates ranging from 1.11 ×10-1 to 2.0 × 107 pulses per second. With a very simple modification the ratemeter can be made to have any desired number of decades in its output. The input pulse rate is determined by digital counting circuits and the logarithm of the pulse rate is approximated by seven digital functions which are generated by a series of combinational logic networks. The output is available in either digital or analog form. The system is composed of the following sections: Timing and Control, Counting, Transfer, Round-off, Log Converter, Storage, and Digital-to-Analog Converter. Experimental results have shown that the digital log ratemeter has for the same statistical accuracy a much faster response time than conventional log ratemeters. It was shown also that the digital log ratemeter is capable of being used to measure much lower pulse rates than is practical with conventional log ratemeters.