New voltage standard.

New voltage standard

The National Bureau of Standards (NBS) is beginning to use a new device for producing standard voltages that should make life easier for electrical laboratories. The modern voltage standard is related to frequency, which can easily be measured, says Richard L. Kautz of NBS in Boulder, Colo. Frequency can be turned into voltage by a Josephson junction, which, when bathed in radio waves of a certain frequency, puts out a certain voltage.

The trouble with the previous devices is that, using one or two Josephson junctions, they put out either half a millivolt or a millivot. This makes it difficult to calibrate the 1.018-volt Weston cells that the other laboratories use as secondary standards. Furthermore, the primary standard had to be kept at NBS, and so from time to time the laboratories had to send their Weston cells to NBS.

The new standards use microlithography to make series arrays of large numbers of Josephson junctions to produce higher voltages -- 2,000 for 1 volt, 19,000 for 10 volts. They can also be kept in other laboratories, lessening the need for travel, and technicians can operate them. They "don't need a PhD physicist to twiddle the dials," says Kautz.