Johnson Noise Thermometry Sensor with Calibration Current Injection
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Solution Overview
Problem
Existing temperature measuring systems using thermocouples and resistance temperature detectors require frequent recalibration due to changes in sensor properties over time, especially in demanding environments, leading to measurement uncertainty and reduced efficiency, as they are prone to drift caused by factors like contamination and material degradation.
Innovation Solution
A temperature measuring system that utilizes a Johnson noise generating resistive sensor element with signal processing circuitry and a current injector to inject a calibration current, allowing for the extraction of Johnson noise voltage signals without the need for switching between sensor and reference measurements, enabling higher bandwidth and resistance operation while minimizing errors from cable mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermocouples and resistance temperature detectors are used for temperature measurement, then temperature can be measured, but frequent recalibration is required due to sensor drift caused by contamination and material degradation
Solution Approach 1:
The sensor element serves itself by generating Johnson noise that is used to determine its own temperature. The system measures the voltage across the sensor element and uses the Johnson-Nyquist equation to calculate temperature directly from the sensor's own thermal noise, eliminating the need for external calibration references and making the sensor immune to drift caused by contamination and degradation
Solution Approach 2:
The invention changes the measurement parameter from resistance or EMF (which drift with contamination) to Johnson noise voltage, which is directly proportional to temperature according to the Johnson-Nyquist equation. This parameter change makes the measurement immune to sensor degradation effects
2Measurement precision
If switching between sensor and reference measurements is used for calibration, then measurement accuracy can be maintained, but measurement time increases and bandwidth is limited
Solution Approach 1:
The system continuously measures Johnson noise from the sensor element without interruption or switching to reference measurements. The measurement process is continuous and uninterrupted, allowing for high bandwidth operation and reduced measurement time while maintaining accuracy through the inherent stability of Johnson noise thermometry
Solution Approach 2:
The invention extracts the Johnson noise voltage signal from the total voltage across the sensor element using signal processing techniques. By separating the Johnson noise component from other voltage components through correlation methods, the system achieves accurate temperature measurement without requiring physical switching to reference measurements
3Measurement precision
If higher resistance sensor elements are used to increase Johnson noise signal, then signal strength improves, but cable mismatch errors increase
Solution Approach 1:
The system uses correlation techniques to separate the Johnson noise signal from cable mismatch effects. By correlating the measured voltage with the known characteristics of Johnson noise, the system extracts the true temperature signal while rejecting cable-related errors, enabling the use of higher resistance sensors without penalty
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 measurement time and improves accuracy by eliminating the need for recalibration and allows for faster, more precise temperature measurements, even in challenging environments, by using a pseudo-random noise current and Fourier transform algorithms to extract Johnson noise signals effectively.
Implementation Method 1
In a conductive medium, such as a resistive sensor element, random electrical noise is generated due to the thermal agitation of the charge carriers (usually electrons) inside the medium. This electrical noise, commonly referred to as Johnson noise
Implementation Method 2
a current injector electrically coupled to the signal processing circuitry and the sensor element, and configured to inject a calibration current into the sensor element
Data Source
AI summary
The present invention provides a system and method for measuring temperature accurately by measuring Johnson noise. The system comprising a Johnson noise generating resistive sensor element for detecting temperature; signal processing circuitry electrically coupled to the sensor element; and a current injector electrically coupled to the signal processing circuitry and the sensor element, and configured to inject a calibration current into the sensor element; wherein the signal processing circuitry is configured to: receive a composite voltage signal from the sensor element, the composite voltage signal including a voltage signal arising from the Johnson noise generated by the sensor element and a voltage signal arising from the calibration current; extract the Johnson noise voltage signal and the calibration voltage signal from the received composite voltage signal; and determine the temperature of the sensor element based on the extracted Johnson noise voltage signal and on the extracted calibration voltage signal.