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A new type of Josephson junction array has been developed with nonhysteretic characteristic, whose output voltage V = nf/KJ is stable. The number of internal nodes of the junction array in accordance with binary segmentation, thus the output voltage is defined by digitally programming with a step number n. With this new type of junction array, voltage standard has been established as a programmable Josephson voltage standard (PJVS).
The Programmable Josephson Voltage Standard (PJVS) has been developed at National Institute of Metrology (NIM), China. The accuracy of the system is estimated to be better than 2.0×10-9.
The precision measurement system consists of a program controlled bias current source, a set of auto-reversing switch system and a scanner switch. All of them are home-made. The whole automatic switching units perform very well with thermal EMF of less than 1nV.
On basis of PJVS, a precise AC waveform synthesis at NIM has also been developed. A Josephson system has been applied in the precise AC waveform synthesis with a frequency of up to 1 kHz with an uncertainty of 10-6. The circuits of the system includes a newly home-made 32-channel bias source, whose output current has a rise-time less than 50ns on an 100ohm resistor.
A new approach of magnetic flux measurement has been developed: it determines magnetic flux by measuring the flux difference between the flux under test and the rectangular pulse which is synthesized by the output of the programmable voltage standard (PJVS). PJVS can produce rectangular pulse with given volt-second area (precise amplitude and pulse width), which can be considered as a volt-second generator (a magnetic flux standard). By using this method, the precision measurement of magnetic flux can be greatly improved with a repeatability in an order of 106.