DC-Current Control Using SQUID-Gradiometer Systems

Weyand, K.

doi:10.1109/tim.1980.4314944

Cited by 6 publications

(3 citation statements)

References 5 publications

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“…Indeed, several attempts (with different but encouraging success) were made during three last decades to realize a direct current source of fundamental stability based on locking (by means of a SQUID detector) an external direct current to the magnetic flux in a closed superconducting circuit through some intermediate transformer [3][4][5]. This transformer unit being in effect a mutual inductance artifact, was one of key elements of the whole setup and attended the undiverted care.…”

Section: Backiroundsmentioning

confidence: 99%

On Possible Use of Quantized Voltages of Shapiro Steps for Absolute Inductance Calibration and Governing Direct Currents

Frantsuz

Kajastie

Riski

2004

2004 Conference on Precision Electromagnetic Measurements

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It is suggested to make use of Shapiro step quantized voltages for controllable changes of magnetic flux in a superconducting loop. This makes it possible to produce a stable direct current (dc) scale by an external dc controller with the current magnitude adjustable in a ramping manner without unlocking the feedback. Also, a mutual inductance inherent to the setup can be calibrated on practically zero frequency in terms of fundamental constants and the second.

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Section: Backiroundsmentioning

confidence: 99%

On Possible Use of Quantized Voltages of Shapiro Steps for Absolute Inductance Calibration and Governing Direct Currents

Frantsuz

Kajastie

Riski

2004

2004 Conference on Precision Electromagnetic Measurements

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“…The technique of locking an external dc current to the magnetic flux from a persistent superconducting current was first demonstrated by Gallop [4]. Weyand has constructed similar systems using second-order magnetic gradiometers as flux transformers [5]. As an alternative technique, smaller currents may be directly injected into a SQUID input and comparably stabilized.…”

Section: Tmentioning

confidence: 99%

Flux-locked current source reference

Tew

Williams²

1993

IEEE Trans. Instrum. Meas.

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The quantization of flux in a closed superconducting circuit is used to provide a stable reference current. A 10 mA current source is coupled through a toroidal transformer to a dc SQUID input, and the resulting signal is fed back as an error current. The result is a net flux linkage that exhibits shortterm stability of 1 part in 109/h. The net current is quantized with a step size of 59.4 nA, and it will exhibit the same stability as the ftux provided the mutual inductance of the transformer remains constant. This current is passed through a precise 100 n resistor and compared against Zener diode references. The observed temperature coefficient for the flux transformer is 28.5 :t 3 ppm/K at 4.2 K. Possible sources for the temperature dependence are discussed.

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“…Two different kinds of equipment are in use for the stabilization and measurement of direct current to the highest accuracy: instruments based on magnetic resonance [1,2] or superconductivity [3,4] for current stabilization; and voltage and resistance standards for current measurement.…”

Section: Introductionmentioning

confidence: 99%

A high-precision system for direct current reproduction based on atomic magnetic resonance in helium-4

Shifrin¹,

Khorev²,

Park³

1999

Metrologia

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At the D. I. Mendeleyev Institute for Metrology (VNIIM) a high-precision system using helium-4 atomic magnetic resonance has been realized for the automatic reproduction and maintenance of direct current in the range 0.1 A to 1.0 A. A random standard uncertainty of 2 10 -8 was obtained for stabilization at 1 A, with a non-linearity of less than 2 10 -7 in the frequency-to-current conversion factor. The conversion factor was determined experimentally through the gyromagnetic ratio of helium-4 atoms and the calculable coil constant of a high-precision solenoid. The technique was used to determine the gyromagnetic ratio of the proton and for the accurate reproduction of the tesla using the calculable solenoid.

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DC-Current Control Using SQUID-Gradiometer Systems

Cited by 6 publications

References 5 publications

On Possible Use of Quantized Voltages of Shapiro Steps for Absolute Inductance Calibration and Governing Direct Currents

On Possible Use of Quantized Voltages of Shapiro Steps for Absolute Inductance Calibration and Governing Direct Currents

Flux-locked current source reference

A high-precision system for direct current reproduction based on atomic magnetic resonance in helium-4

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