Digital Picoammeter

This is a very versatile multipurpose equipment for the measurement of low dc currents. It has 6 decade ranges with-9 -4 100% over-ranging from 10 A to 10 A. For the ease, readings are directly obtained on a 3½ digit DPM. The instrument uses a well designed precision FET input electrometer operational amplifier AD549, which offers the lowest input bias currents  (5OfA with ±5V supplies) available in any standard operational amplifier. The excellent characteristics of AD549, ultra low bias current, low offset voltage, low drift and low noise have been fully utilized to obtain best results in the present picoammeter. The first operational amplifier AD549 is used in low level current to voltage configuration and the output has been directly read on a 3½ digit panel meter. The instrument is capable of  accepting either polarity of the input current. Well-regulated power supplies are incorporated to use the instrument upto 10% changes in a.c. main's voltage