Four Terminal Pair Digital Sampling Impedance Bridge up to 1 MHz

• This paper describes a new four terminal pair digital sampling impedance bridge designed for frequency range up to 1MHz and small impedances, such as shunts. The bridge is capable of comparing impedance standards of arbitrary ratios in a full complex plane from approximately 100 kΩ down to 50mΩ, limited by maximum achievable current 3 A. To keep low uncertainties a new multiplexer was designed and a very simple and fully automated linearity correction method based on the pair of calculable resistors was developed and validated. The paper describes the design and details of the bridge topology, basic uncertainty budget and first results of the validation. The expanded uncertainty of impedance module is about 50 μΩ/Ω at 1MHz for impedance ratios up to 1:16 and voltage drops above 10mV and the expanded uncertainty of a phase angle was about 360 μrad/MHz. Expanded uncertainty for frequency 100 kHz about 10 μΩ/Ω was reached. Typical expanded uncertainty for low impedance ratios below 1:1.1 is only 35 μΩ/Ω. Set of measurement of impedance standards of known values and a small international comparison of ac-dc and phase angle errors of current shunts were carried out to validate the bridge capabilities in wide range of impedances. The validation measurements showed the deviations of the bridge are below 35 μΩ/Ω and below 350 μrad at 1 MHz.

Nyckelord

Bridge circuits

Impedance

Topology

Uncertainty

Standards

Calibration

Multiplexing

impedance measurement

phase comparators

sampling methods

shunts (electrical)

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