Resistance Measuring Apparatus Using Synchronous Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing resistance measuring apparatus faces challenges including high manufacturing costs due to the need for high-precision components, instability in measurement precision due to temperature and humidity changes, difficulty in achieving suitable measurement precision with adjacent coils, deterioration in dynamic reserve and noise tolerance, susceptibility to noise and offset errors, and issues with safety standards.
Innovation Solution
The resistance measuring apparatus employs a voltage injecting unit that applies a stepped AC signal, a current measuring unit for synchronous detection, and a processing unit that calculates resistance using a reference signal, with coils enclosed in a single clamp-type housing to stabilize their positions and reduce noise, and incorporates a Class D amplifier for efficient power amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-Q band-pass filter is used to extract the second frequency component with high precision, then measurement precision is improved, but manufacturing cost increases due to the need for high-precision components
Solution Approach 1:
The invention changes the frequency parameter from a fixed high frequency (e.g., 100 kHz) to a variable low frequency (e.g., 1-100 Hz) that can be adjusted based on measurement needs. This parameter change allows the use of simple low-pass filters instead of complex high-Q band-pass filters, significantly reducing manufacturing cost while maintaining measurement precision
Solution Approach 2:
The invention replaces expensive high-precision components (high-Q band-pass filters) with inexpensive alternatives (simple low-pass filters). Although low-pass filters have broader frequency response, the use of variable frequency injection and synchronous detection ensures measurement precision is maintained at low cost
2Measurement precision
If a high-Q band-pass filter is used to extract the second frequency component, then measurement precision is improved, but stability deteriorates due to center frequency shift caused by temperature and humidity changes
Solution Approach 1:
The invention changes the operating frequency from fixed high frequency to variable low frequency. Low-frequency signals are much less susceptible to temperature and humidity-induced frequency drift, thereby improving measurement stability while maintaining precision through synchronous detection
Solution Approach 2:
The invention introduces dynamic frequency adjustment capability, allowing the injection frequency to be varied and optimized for different measurement conditions. This dynamic approach enables the system to adapt to environmental changes and maintain stable measurements
Solution Approach 3:
The invention employs synchronous detection with reference frequency comparison, creating a feedback mechanism that continuously tracks and compensates for frequency variations. This feedback system ensures stable measurements even when environmental conditions cause frequency drift
3Adaptability or versatility
If the injection coil and detection coil are clipped onto the measured network separately, then the coils can be independently positioned, but measurement operation becomes troublesome and time-consuming
Solution Approach 1:
The invention merges the injection coil and detection coil into a single integrated clamp-type housing. This integration allows both coils to be clipped onto the measured network simultaneously in one operation, dramatically improving measurement speed and productivity while maintaining the ability to independently position each coil within the housing
4Ease of operation
If the injection coil and detection coil are enclosed in a single clamp-type housing, then clipping operation becomes efficient and coil positions are stabilized, but the magnetic field generated in the injection coil directly encircles the detection coil causing measurement interference
Solution Approach 1:
The invention converts the harmful direct magnetic coupling into a beneficial effect by using synchronous detection. The injection frequency is modulated onto the measurement signal, and synchronous detection at this frequency effectively separates the useful measurement signal from the harmful interference, converting the interference problem into a frequency discrimination opportunity
Solution Approach 2:
The invention employs periodic modulation of the injection frequency and synchronous sampling at the same frequency. This periodic action creates distinct frequency signatures that allow the detection system to distinguish between the injection field and the measurement signal, eliminating interference
5Device complexity
If DC amplification is used in the rectifying amplification circuit, then the circuit is simple to construct, but dynamic reserve deteriorates and noise tolerance reduces
Solution Approach 1:
The invention uses periodic AC injection and synchronous detection instead of DC amplification. The AC signal with its periodic nature inherently provides better noise rejection through frequency discrimination, while synchronous detection maintains circuit simplicity by using the injection frequency as the reference for signal extraction
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 approach reduces manufacturing costs, enhances measurement precision, improves noise tolerance, stabilizes coil positions, and meets safety standards by eliminating the need for high-Q band-pass filters and single-ended detection coils, while maintaining sufficient detection gain and frequency characteristics.
Implementation Method 1
a voltage injecting unit that injects a testing AC signal into a measured circuit by applying an AC voltage to an injection coil
Implementation Method 2
a current measuring unit that detects and measures an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil
Data Source
AI summary
A resistance measuring apparatus includes: a voltage injector that injects an AC signal into a circuit by applying an AC voltage to an injection coil; a current measuring unit that measures an AC current produced in the circuit by the injection coil using a detection coil; a processing unit that calculates the circuit resistance from the AC signal voltage and the measured AC current; and a reference signal generator that outputs a binary reference signal that has a same period as the AC voltage and is synchronized to the clock. The voltage injector generates a stepped wave whose amplitude changes in synchronization with a clock, applies a signal based thereon as the AC voltage. The current measuring unit converts the current in the detection coil to a voltage signal, carries out synchronous detection using the reference signal, and measures the AC current based on the synchronous detection result.