Wire Bundle Current Shunt for High Frequency Measurement
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Solution Overview
Problem
Existing current shunts face challenges in accurately measuring large and rapidly changing currents due to inductive drops and limited bandwidth, especially at high frequencies, as they require small shunt resistances and are affected by the skin effect, which reduces their usability in applications like switching power supplies and motor drives.
Innovation Solution
A current shunt constructed using a wire bundle, such as litz wire, with individually insulated strands minimizes skin-effect-induced changes in shunt resistance with frequency, and can be configured as a coaxial shunt or without a coaxial return path to reduce inductive drops and insertion inductance, using resistive metal alloys like manganin or nichrome to maintain high frequency operation up to 100 MHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a small shunt resistance is used to measure large currents, then the voltage drop and power dissipation are kept within reason, but the usable bandwidth decreases due to increased inductive drop
Solution Approach 1:
The shunt resistor is segmented into multiple parallel resistive elements, which reduces the overall inductance while maintaining the required resistance value. This segmentation allows the shunt to handle large currents with acceptable power dissipation while extending the usable bandwidth by reducing inductive effects at high frequencies.
Solution Approach 2:
The patent employs a coaxial structure where the resistive element is nested within an outer conductive cylinder. The return current path is routed through the outer cylinder, creating a symmetrical configuration that minimizes magnetic field generation and reduces inductive drop, thereby extending bandwidth while maintaining measurement accuracy.
2Measurement precision
If a coaxial shunt is used to eliminate measurement inductance, then the inductive drop is eliminated, but the insertion inductance increases due to the longer current path
Solution Approach 1:
The current path is segmented into multiple parallel conductive paths within the coaxial structure. By dividing the current flow into several strands and routing them in parallel through the shunt, the effective length of the current path is reduced, thereby decreasing the insertion inductance while maintaining the coaxial geometry that eliminates measurement inductance.
3Reliability
If the skin depth approaches the thickness of the resistive cylinder in a coaxial shunt, then the current distribution changes, but the resistive drop decreases significantly reducing measurement accuracy
Solution Approach 1:
The resistive element is divided into multiple parallel resistive strands or segments. This segmentation increases the effective surface area available for current flow at high frequencies, counteracting the skin effect by providing multiple pathways for current distribution. The combined effect maintains a stable resistive drop across a broader frequency range, improving measurement precision.
Solution Approach 2:
The patent applies different geometric characteristics to different parts of the resistive element. By varying the dimensions, materials, or configurations of individual resistive strands within the bundle, the shunt optimizes current distribution locally to compensate for skin effect variations across the frequency spectrum, maintaining consistent resistive drop characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively minimizes the skin-effect-induced change in shunt resistance with frequency, maintaining accurate current measurement across a broader bandwidth without significant inductive drops, enhancing the usability of current shunts in high-frequency applications.
Implementation Method 1
A current shunt constructed using a wire bundle, such as litz wire, with individually insulated strands minimizes skin-effect-induced changes in shunt resistance with frequency
Implementation Method 2
The symmetrical nature and the outer return current path ensure the magnetic field generated by the current circles between the shunt and the outer return path, leaving no magnetic field to impart an inductive drop on the measured voltage inside the shunt
Implementation Method 3
One approach often used is to place a series resistor ('current shunt resistor,' 'current shunt,' or 'shunt') in the current path, measure the voltage drop caused by the current, and divide by the resistance
Data Source
AI summary
A test and measurement accessory includes a shunt configured to be located in a current path including a device under test, the shunt comprising a wire bundle of individually insulated wires as a resistive portion and a sense lead, the wire bundle and the sense lead electrically connected at a first end, a first electrical contact electrically connected to the sense lead at a second end, and a second electrical contact electrically connected to the wires of the wire bundle at the second end to allow measurement of a voltage drop across the first and second electrical contacts. A test and measurement system includes a test and measurement instrument and the test and measurement accessory. A method includes measuring current using the accessory.