An Electronic Zero Resistance Ammeter with Instantaneous Null Characteristics

A brief review is made of the operating principles and shortcomings of the traditional manual null balancing zero resistance ammeter. It is demonstrated qualitatively how this instrument, when off balance, can affect the validity of corrosion current data obtained on short circuited elements. The design and operating principles of a modified electronic null balancing zero resistance ammeter are described, with which most of the objections raised against the manual null balance instrument can be overcome. The use of an operational amplifier as a voltage controller to replace the manual balance part of a conventional instrument allows a continuous readout of corrosion current versus time to be made under conditions of short circuit coupling.