Low-Current Measurements Using Transistor Logarithmic DC Electrometers

A nine-decade (10-13 to 10-4 amp) and a five-decade (4 ?? 10-12 to 4 ?? 10-7 amp) dc logarithmic electrometer have been designed, and their performance evaluated. The problems of drift, linear-to-log conversion accuracy, temperature dependence, and frequency response are considered. An accuracy of better than ??0.6%/decade (~2% of reading) was achieved.