High-Accuracy RTD Measurement Using Single-Channel ADC Ratios
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Solution Overview
Problem
FPGA-based temperature measurements using resistance temperature detectors (RTDs) suffer from accuracy issues due to computational errors associated with voltage-current ratio computations, especially in aerospace applications where FPGAs are optimized for I/O interfaces rather than computational engines.
Innovation Solution
A system comprising an RTD element, a current sense element, and a constant current source, with amplified voltage and current signals fed into a single channel ADC, providing a ratio-based digital output to an FPGA for improved accuracy by eliminating reference-dependent computations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If FPGAs are used for RTD measurements, then I/O interface capability is improved, but measurement precision deteriorates due to computational errors
Solution Approach 1:
The patent extracts the reference voltage computation from the FPGA and performs it externally using a precise voltage reference. This removes the computational burden and potential errors from the FPGA, allowing it to focus on I/O interface functions while maintaining high measurement precision through external reference voltage generation.
Solution Approach 2:
The patent introduces an intermediary reference voltage signal that is generated externally and fed into the FPGA. This intermediary serves as a stable reference that eliminates the need for the FPGA to perform complex voltage-current ratio computations, thereby improving measurement precision while preserving the FPGA's I/O interface capabilities.
2Adaptability or versatility
If computational algorithms are implemented in FPGA, then measurement functionality is improved, but device complexity increases due to logic cell consumption
Solution Approach 1:
The patent extracts complex computational algorithms from the FPGA and implements them externally using precise voltage references and simple ratio computations. This reduces the FPGA to basic I/O and logic functions, significantly decreasing logic cell consumption while preserving full measurement functionality.
Solution Approach 2:
The patent changes the computational approach by using a fixed external reference voltage instead of computing it internally. This parameter change transforms the FPGA's role from performing complex calculations to simply comparing signals against the external reference, thereby reducing device complexity while maintaining measurement functionality.
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
Enhances measurement accuracy and reduces resource consumption by minimizing computational errors and logic cell usage in the FPGA, utilizing a single channel ADC and fixed reference voltage.
Implementation Method 1
The material has an accurate resistance/temperature relationship which is used to provide an indication of temperature
Implementation Method 2
a single channel analog to digital converter (ADC) comprising a first channel input and a reference voltage input
Data Source
AI summary
A resistance temperature detector includes a single channel analog to digital converter (ADC) comprising a first channel input and a reference voltage input. The detector also includes a resistance temperature detector (RTD) element connected to the first channel input and a current sense element in series with the RTD element. The current sense element is connected to the reference voltage input. The detector also includes a power source connected to the RTD element and a controller configured to: receive an output of the single channel ADC to determine a temperature at the RTD element. The output of the single channel ADC comprises a bit representation of a ratio between a first voltage across the RTD element and a reference voltage across the current sense element.