Bidirectional Voltage Bridge Circuit for μK Temperature Sensing
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Solution Overview
Problem
Existing high-precision thermal resistance temperature measurement methods, such as the Wheatstone bridge method and the commutation proportional method, face challenges in achieving μK-level temperature measurement resolution and power spectral density of μK/Hz1/2 due to low-frequency noise and long-term drift issues.
Innovation Solution
A differential proportional temperature measurement circuit based on a bidirectional constant voltage drive is proposed, which includes a bidirectional constant voltage source proportional bridge circuit, differential and single-ended amplifier circuits, an analog-to-digital conversion circuit, a digital filter circuit, a data processing circuit, and an isolated filter power supply circuit. This circuit design eliminates low-frequency drift and noise higher than 1 Hz by switching the voltage excitation direction and using digital filtering techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Wheatstone bridge method is used for temperature measurement, then the measurement accuracy can be improved, but the low-frequency noise and long-term drift cannot be suppressed, making it difficult to achieve μK-level resolution
Solution Approach 1:
The patent employs periodic commutation of the constant current source direction (bidirectional switching) to modulate the measurement signal. By alternating the current direction at a specific frequency and synchronously detecting the output, the method transforms DC drift issues into AC signal processing, enabling effective suppression of low-frequency noise and long-term drift while maintaining μK-level temperature measurement accuracy
Solution Approach 2:
The patent implements synchronous detection (lock-in amplification) where the detection frequency matches the commutation frequency. This feedback mechanism selectively amplifies the signal at the commutation frequency while rejecting other frequencies, effectively suppressing low-frequency noise and drift components, thereby achieving both high measurement precision and long-term stability
2Measurement precision
If the DC current comparator electric bridge method is used, then the measurement accuracy is high, but the measurement time is too long (10-30 s) to meet satellite platform requirements
Solution Approach 1:
The patent uses periodic commutation at a high frequency (e.g., several hundred Hz to kHz) to enable rapid sampling and averaging. This periodic modulation allows the system to achieve high measurement accuracy through synchronous detection while reducing the measurement cycle from 10-30 seconds to milliseconds, meeting satellite platform real-time monitoring requirements
Solution Approach 2:
The patent maintains continuous measurement through high-frequency commutation and synchronous detection, eliminating the need for repeated bridge balancing operations. The continuous sampling and averaging process sustains high measurement accuracy while dramatically reducing measurement time, achieving both precision and speed requirements for satellite applications
3Measurement precision
If variable reference voltage and current limiting resistance are used in the Wheatstone bridge method, then the measurement accuracy is maintained in large temperature range, but the long-term drift of voltage excitation unit and wire resistance cannot be suppressed
Solution Approach 1:
The patent employs periodic commutation of the constant current source to transform the measurement into an AC-based synchronous detection system. This approach converts DC drift issues (excitation voltage drift, wire resistance changes) into frequency-domain separable components, allowing effective suppression of drift while maintaining measurement accuracy across large temperature ranges through ratio-based calculation
Solution Approach 2:
The patent changes the measurement parameter from DC voltage to AC voltage at commutation frequency. By measuring the amplitude and phase of the AC signal rather than DC voltage, the system becomes insensitive to DC drift components (excitation voltage drift, wire resistance changes) while maintaining sensitivity to temperature-induced resistance changes in the thermistor
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 proposed solution effectively improves the temperature measurement resolution to the μK magnitude and reduces noise spectral density, meeting the stringent requirements for satellite platforms, such as gravitational wave detection devices.
Implementation Method 1
the measurement resistor converts the temperature signal into a resistance signal
Implementation Method 2
the constant voltage source converts electrical energy to thermal energy through resistive heating
Data Source
AI summary
A differential proportional temperature measurement circuit and method based on bidirectional constant voltage drive is proposed. The circuit and method applied to the precision temperature measurement of spacecraft, the main components include a bidirectional constant voltage source proportional bridge circuit, a differential and single-ended amplifier circuit, an analog-to-digital conversion circuit, a digital filter circuit, a data processing circuit and an isolated filter power supply circuit. The method adopts the bidirectional constant voltage drive technology, and enlarges and measures the difference between the voltage values of the reference resistor and the resistance to be measured by improving the sensing bridge of the ordinary commutation proportional method, and suppresses the long-term drift of the excitation unit and the voltage measurement unit. The method can meet the requirements of temperature measurement resolution of μK magnitude and the power spectral density of μK/Hz1/2 (0.1 mHz-1 Hz) magnitude in aerospace temperature measurement systems.