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  Cryogenic Current Comparator

 Cryogenic Current Comparator



1. Introduction


Cryogenic current comparator is at low temperature measuring electrical measuring instruments, current ratio is the proportion of current international the most accurate measuring tool and its proportion accuracy can reach more than 10, and the proportion of any value can be realized, in the electromagnetic measurement plays an important role in the establishment of standard, its main use is by comparing the measured current and resistance to correction.

Cryogenic current comparator in solving the error due to magnetic flux leakage, make full use of the superconducting screen completely diamagnetic effect, namely the meissner effect and superconducting theory and experiment have confirmed the superconductor is a completely diamagnetic material, superconductor internal magnetic field does not exist, external magnetic field on the depth of penetration on the surface of the superconductor is just 10 - magnitude 7 meters. Therefore, as long as the superconductor ACTS as the superconducting shield to isolate the current comparator detection coil and the proportional coil, its isolation effect will be very perfect. In this way, the problem of leakage flux error is solved thoroughly. Superconducting quantum interference devices (SQUID) are used in low temperature current comparator for monitoring the ampere-turns balance conditions. Superconducting quantum interference device is contemporary the most sensitive weak magnetic flux detection means, the sensitivity can reach 10-20 wb level, has been accused of measuring weak magnetic field and magnetic field space creatures got very good application. Moreover, this device has no magnetic hysteresis characteristics and can be used to monitor the ampere-turns balance condition.

Because the ampere-turns balance condition is realized in the low temperature current comparator, the accuracy of its current ratio is very high.


2. Applications


Correction resistance

measured current


3. Specification


Cryogenic current comparator consists of four parts: drive, probe, superconducting quantum interference device and liquid helium. The parameters are as follows:

- Expanded uncertainty (k=2) of 6 x 10e-9 for resistance ratios of 1Ω, 10Ω, 100Ω, 1kΩ, and 10kΩ as well as ratio between 100Ω and the Quantum Hall resistance of 12.9064...kΩ.


- Expanded uncertainty of 1.5 x 10e-8 for comparisons with a 100kΩ resistor.


- Expanded uncertainty of 1.5 x 10e-7 for comparisons with a 1MΩ resistor.



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