Resonant Shunt Resistance Measurement for Accurate Current Sensing
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Solution Overview
Problem
Shunt resistance measurements in current systems are prone to errors due to variations in resistance caused by process tolerances, temperature changes, self-heating, and resistance drift, which degrade the accuracy of current measurements.
Innovation Solution
A resonant circuit comprising an inductor, capacitor, and shunt resistor is used to measure shunt resistance by applying an AC voltage at a different frequency than the input current, processing a superimposed voltage to generate a measured resistance that compensates for variations, thereby improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional shunt resistance measurement is used, then the current measurement system is simple, but measurement precision deteriorates due to resistance variations from process tolerances, temperature, and drift
Solution Approach 1:
The patent introduces an intermediary AC voltage signal at a frequency distinct from the input current frequency. This intermediary signal interacts with the shunt resistance to produce a measurable voltage component that reveals the resistance value without directly measuring the resistance itself. The intermediary signal acts as a mediator between the shunt resistance and the measurement system, enabling precise resistance determination through frequency-separated voltage analysis.
Solution Approach 2:
The patent employs periodic AC voltage signals at a specific frequency to probe the shunt resistance. By using periodic action at a frequency different from the input current, the system creates a time-varying voltage superposition that can be analyzed to extract resistance information. The periodic nature of the AC signal enables consistent, repeatable measurements that compensate for resistance variations over time.
2Measurement precision
If precision resistors are used to address shunt resistance error, then measurement precision improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent enables the shunt resistance measurement system to self-diagnose and self-correct for resistance variations. By injecting an AC voltage signal and analyzing the resulting superimposed voltage across the shunt, the system automatically determines the actual resistance value and uses this information to compensate for deviations from nominal resistance. This self-service approach eliminates the need for external precision resistors or manual calibration procedures.
Solution Approach 2:
The patent implements a feedback mechanism where the measured voltage component from the AC voltage interaction is used to determine the shunt resistance value, which then feeds back into the current measurement calculation. The system continuously monitors the shunt resistance through the AC voltage probe and adjusts the current measurement accordingly, creating a closed-loop feedback system that maintains accuracy despite resistance variations.
3Measurement precision
If calibration circuitry is added to trim resistance error, then measurement precision improves, but manufacturing time and device complexity increase
Solution Approach 1:
The patent replaces mechanical calibration procedures with an electrical measurement and computation approach. Instead of using physical calibration circuits or manual trimming mechanisms, the system uses electrical signals (AC voltage injection) and digital computation to determine and compensate for resistance values. This substitution of mechanical calibration with electrical measurement eliminates the need for additional calibration hardware and manual intervention in the manufacturing process.
4Measurement precision
If specially designed materials are used for the shunt resistor, then temperature-based resistance variations are reduced, but device complexity and cost increase
Solution Approach 1:
The patent changes the measurement parameter from directly measuring voltage drop proportional to current to measuring the AC voltage response at a different frequency. By transforming the measurement approach and using frequency-domain analysis, the system can distinguish between voltage components caused by input current and those caused by shunt resistance characteristics, enabling accurate resistance determination without requiring temperature-stable special materials.
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
This method allows for simultaneous compensation of shunt resistance variations while accurately determining the input current, reducing the need for expensive precision resistors and complex calibration processes.
Implementation Method 1
circuits and methods for measuring a shunt resistance using a resonant circuit
Data Source
AI summary
Apparatus and methods for measuring a shunt resistance through which an input current flows, wherein the input current has a first frequency range, include a voltage source configured to generate an AC voltage having a second frequency range that is higher than the first frequency range. An inductor, a capacitor, and the shunt resistance form an RLC network to which the voltage source is coupled. Processing circuitry coupled to receive a superimposed voltage across the shunt resistance is configured to generate a measured resistance indicative of the shunt resistance in response to the superimposed voltage.