A Wide Range Time Constant Measuring Technique

A method is presented and analyzed that allows the implementation of a technique for the direct measurement of the time constant of single and/or multiple event exponentially decaying signals of the form: Y = K exp (-αt). The decaying exponential signal is fed into monolithic comparators which detect two preselected voltage levels of the signal. By means of TTL logic circuitry the output of the comparators are converted into a pulse. The duration of the pulse is directly proportional to the time constant of the signal and can thus be measured by different means. The technique described is capable of a dynamic range with a lower limit of 50 ns and a measured higher limit of several milliseconds, however, there is no theoretical upper limit with this method. The accuracy of the measurements remains within 1 percent, utilizing standard inexpensive components. Both lower limit and accuracy can be improved by the use of selected components. Inaccuracies of the measurements due to temperature variations from 0 to 80°C could not be detected by standard laboratory methods.