A Coordinated System of Maintaining and Disseminating the Volt

Groups of standard cells may be used to maintain the volt with an uncertainty of 1/4 parts per million (ppm) using a separate transportable group of cells to transfer the value from the National Bureau of Standards (NBS). An enclosure to hold 24 standard cells has been designed in which temperature control is better than 100 ¿K in an environment varying as much as 3 K. The volt thus maintained is transferred over coaxial cables to service groups about l/2 km away. This is done by generating a constant current that produces a 1-V drop across standard resistors located at both ends of each cable group. Accuracy of the transferred volt is about 1 ppm.