Small Impedance Measurement Using Matching Transformers
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Solution Overview
Problem
Existing methods for measuring small impedances, particularly in the range of units of mΩ, suffer from low accuracy, sensitivity, and lengthy measurement times, especially in the low frequency range of 10^-2 to 10^4 Hz, which complicates applications like electrochemical impedance spectroscopy of batteries.
Innovation Solution
A measuring device utilizing passive matching transformers in parallel with the normal and tested impedances, connected to analog-to-digital converters, processes signals through signal processors to enhance signal/noise ratio and achieve accurate impedance measurements by reconstructing and comparing signal approximations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bridge methods are used to measure small impedances, then measurement accuracy is improved, but sensitivity becomes small when other impedances in the bridge are large
Solution Approach 1:
The measuring device segments the measurement process into multiple independent channels, each with its own passive matching transformer and ADC. This allows each channel to be optimized independently, maintaining high sensitivity for small impedance measurements while preserving the accuracy benefits of bridge methods.
Solution Approach 2:
Passive matching transformers are introduced as intermediary elements between the measurement circuit and the ADC. These transformers provide impedance matching and signal conditioning, enabling high sensitivity detection of small voltage drops across small impedances without compromising measurement accuracy.
2Measurement precision
If manually balanced bridges are used, then accurate comparison of impedance values is achieved, but measurement time becomes very long
Solution Approach 1:
The patent replaces manual mechanical balancing operations with automated electronic measurement. The microprocessor-controlled system automatically adjusts bridge components and performs measurements, eliminating the time-consuming manual balancing process while maintaining accurate impedance comparison through digital signal processing.
Solution Approach 2:
The measuring device enables continuous automated measurements by programmatically adjusting bridge components and sequentially measuring multiple frequency points. This continuous operation eliminates the interruptions and manual reconfiguration required in traditional bridge methods, dramatically reducing total measurement time.
3Adaptability or versatility
If transformer bridges are used for broadband operation, then frequency range is extended, but construction becomes very difficult
Solution Approach 1:
The patent uses simple, easily manufactured passive matching transformers with fixed turns ratios instead of complex broadband transformers. These simpler transformers are optimized for specific frequency ranges and can be easily replaced or reconfigured, making the device easier to manufacture while still achieving broadband operation through multiple measurement channels.
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 device significantly improves measurement accuracy and speed, especially for non-linear objects with impedances of units of mΩ, achieving higher precision and reducing measurement time, particularly useful for battery diagnostics.
Implementation Method 1
Parallel to the normal impedance Rn is connected the primary winding of a first passive matching transformer, whose secondary winding is connected to the input of a first analog-to-digital converter
Data Source
Figure 1A~4
Figure 5A~8
Figure 9~11
AI summary
The series combination of the normal impedance Rn (2) and the tested impedance Ẑ (3) connected in parallel to the generator (1) is connected to the measuring block (A). The normal impedance Rn (2) is connected to the first signal processor (8) via the first matching transformer (4) and the first analog-to-digital converter (6). The tested impedance Ẑ (3) is connected to the second signal processor (9) via an analogue second matching transformer (5) and a second analogue-to-digital converter (7). The output (aN1) of the amplitude of the phasor of the 1st harmonic component of the voltage at the normal impedance Rn (2) from the first signal processor (8) is connected via block (10) of the calculation |RNn|/aN1 to the first input of the first multiplier (11), to the second input of which the output (az1) of the amplitude of the phasor of the 1st harmonic component of the voltage at the tested impedance Ẑ (3) from the second signal processor (9) is connected. Its output is connected to the first input of the second and third multipliers (12, 13). The output (φN1) of the argument of the phasor of the 1st harmonic component of the voltage at the normal impedance Rn (2) from the first signal processor (8) is connected to the first input of the adder (14), to the second input of which the output (φz1) of the argument of the phasor of the 1st harmonic component of the voltage at the tested impedance Ẑ (3) from the second signal processor (9) is connected and to the third input of which the constant (φRNn) representing the phase of the normal impedance RN (2) at the measuring frequency is set. The output of the adder (14) is connected to the inputs of the static functional sine (15) and cosine (16) generators whose outputs are further connected to the inputs of the third multiplier (13) and the second multiplier (12). The output (R) of the magnitude of the real component of the tested impedance Ẑ (3) of the second multiplier (12) is connected to the first input (s) of the control timer (17), and the output (X) of the magnitude of the imaginary component of the tested impedance Ẑ (3) of the third multiplier (13) is connected to the second input (t) of the control timer (17), whose output (x) of the signal is connected to the control input of the generator (1). The output port (V) is the output of the device.