RTD Bridge Circuit for Differential Temperature Measurement
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Solution Overview
Problem
Measuring spatial differences in temperature using resistive temperature devices (RTDs) is challenging due to their non-linear response curves, as simply knowing the resistance difference between two RTDs does not convey the temperature difference, making it difficult to determine temperature differences or gradients accurately.
Innovation Solution
A circuit comprising a bridge network with a first and second node, where a first branch includes a first RTD and a second branch in parallel includes a second RTD, providing a signal representing the difference and average voltage across both RTDs, allowing for accurate determination of differential and average temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistance difference between two RTDs is measured, then temperature sensing capability is provided, but temperature difference determination becomes inaccurate due to non-linear response curves
Solution Approach 1:
The measurement is segmented into two independent components: differential voltage (Vdiff) representing temperature difference and average voltage (Vavg) representing absolute temperature. This segmentation allows each voltage to be processed independently through lookup tables, converting the non-linear resistance-temperature relationship into linear voltage-temperature relationships without requiring complex circuitry.
Solution Approach 2:
Voltage serves as an intermediary quantity that linearizes the non-linear RTD response. By measuring voltage across each RTD rather than resistance directly, and then processing these voltages through lookup tables, the system converts non-linear resistance-temperature characteristics into linear voltage-temperature relationships, enabling accurate temperature difference determination.
2Device complexity
If simple resistance difference measurement is used, then device complexity is minimized, but temperature gradient information is lost
Solution Approach 1:
The circuit segments the measurement information into two distinct voltage outputs: Vdiff containing differential temperature information and Vavg containing absolute temperature information. This segmentation preserves all temperature gradient information that would otherwise be lost in simple resistance difference measurement, while keeping the circuit configuration relatively simple using basic voltage division and differential amplification.
3Device complexity
If non-linear RTD response is directly used, then device simplicity is maintained, but measurement accuracy deteriorates
Solution Approach 1:
Voltage measurements serve as intermediaries that linearize the non-linear RTD response. By converting resistance changes into voltage changes through controlled current sources and voltage dividers, and then processing these voltages through lookup tables, the system achieves linear temperature measurements without modifying the physical RTD characteristics or requiring complex real-time calculation hardware.
Solution Approach 2:
Lookup tables are pre-computed based on the known RTD resistance-temperature characteristics. This preliminary action stores the non-linear conversion relationships in tabular form, allowing the system to perform simple table lookups rather than complex real-time calculations, thereby achieving high measurement accuracy with minimal processing complexity.
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
Enables precise determination of differential and average temperatures from non-linear RTDs, effectively addressing the limitations of existing methods by linearizing the temperature gradient measurements for applications like ring laser gyroscopes.
Implementation Method 1
Resistive temperature devices (RTD) are devices that have temperature sensing elements that vary in resistance as a function of temperature
Implementation Method 2
An example of a temperature measuring circuit using RTDs in a Wheatstone bridge is described in DE 10 2009 028 958A1
Implementation Method 3
Enables precise determination of differential and average temperatures from non-linear RTDs, effectively addressing the limitations of existing methods by linearizing the temperature gradient measurements
Data Source
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AI summary
Systems for determining differential and average temperatures from resistive temperature devices are provided. In one embodiment, a device comprises a bridge network including a first node and second node, wherein the first node receives a constant current from a current source; a first branch coupled between a first node and a second node, the first branch including a first temperature sensing element of a first resistive temperature device; a second branch coupled in parallel with the first branch between the first node and the second node, the second branch including a second temperature sensing element of a second resistive temperature device; a first output that provides a signal representing a difference between a voltage developed across the first temperature sensing element and a voltage developed across the second temperature sensing element; and a second output that provides a signal representing a voltage developed across first node and the second node.