Abstract
Abstract. The requirements for precision current-sensing shunts are getting more sophisticated due to further development of fast switch-mode converters and other high-frequency applications. Good AC characteristics are important both for industrial applications and for calibration standard purposes. Low-ohmic foil shunts show excellent DC behavior, but the AC characteristics could be improved. The optimization of foil shunts towards better temperature independency and load stability in the range of a few parts per million per kelvin can lead to significant weaker AC performance. In this work, eddy currents in the mounting body are identified as a cause of the increasing real part of the shunt impedance at higher frequencies by means of a numerical field simulation.
Highlights
The requirements for low-ohmic current shunts, used as precision current-sensing resistors in measuring instruments, are getting more sophisticated due to further development of fast switch-mode converters and other high-frequency applications
For example in the development of measurement systems operating with foil shunts, we observed an increase in the shunt resistance at higher frequencies, which can not be attributed to the skin effect because of its different dependence from the signal frequency
A “perfect” shunt for DC applications and a shunt optimized for AC applications are to a certain degree mutually exclusive
Summary
The requirements for low-ohmic current shunts, used as precision current-sensing resistors in measuring instruments, are getting more sophisticated due to further development of fast switch-mode converters and other high-frequency applications. The inseparability of shunt foil and mounting body does not allow the cause of this frequency behavior to be determined via measurements, so we decided to utilize simulations with the numerical field simulation program Fast Henry (Kamon et al, 1996). Changing resistance due to temperature increases or decreases can be offset by mechanical stretching caused by a carrier plate with an appropriate thermal coefficient of expansion The utilization of this strain gauge effect is an elegant way to compensate for part of the temperature coefficient of the resistive material (Szwarc, 2012 and Zandman and Szwarc, 2013). With a very low distance between the resistive foil and the conductive carrier plate, eddy currents are induced in the carrier plate as well as in the mounting body. The graphical representation is created using Gnu Octave (Eaton et al, 2011)
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