Voltage traceability of Johnson noise thermometry by ac-dc transfer method
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The absolute Johnson noise thermometer (JNT) being developed at INRIM traces temperature measurements to electrical units. A pseudorandom noise signal is employed for calibration: the traceability of its rms value was given by commercial ac voltmeter. To improve the measurement accuracy, a primary ac-dc transfer method with a multi-junction thermal converter, is presently implemented. First results show that ac-dc transfer measurement is compatible with ac voltmeter readings and has a comparable noise; an improvement of an order of magnitude in the voltage measurement accuracy is expected and presently under validation.
[1] Luca Callegaro,et al. A Johnson noise thermometer with traceability to electrical standards , 2009 .