Active grounded thermocouple
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Solution Overview
Problem
Grounded thermocouples are susceptible to electrical noise from ground loops, which affects the accuracy of temperature measurements, especially when measuring small variations in temperature, in caustic or corrosive environments.
Innovation Solution
The temperature measurement system employs isolated voltage and ground for grounded thermocouples, with a power supply that includes overvoltage protection and a regulator to generate isolated voltage and ground, and a multiplexer to selectively bias only one thermocouple during measurement, reducing noise currents and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If grounded thermocouples are used in caustic or corrosive environments, then the response time is fast and the thermocouple can withstand the environment, but electrical noise from ground loops affects measurement accuracy
Solution Approach 1:
The patent introduces an isolated power supply as an intermediary device that provides electrical isolation between the thermocouple measurement circuit and the ground. This mediator blocks the propagation of ground loop noise while maintaining the necessary electrical connections for the thermocouple to function in corrosive environments, thereby resolving the contradiction between environmental durability and measurement precision.
2Speed
If the thermocouple junction is in direct electrical contact with the sheath, then the response time is fast, but the thermocouple is susceptible to electrical noise
Solution Approach 1:
The isolated power supply acts as a mediator that maintains the direct electrical contact between the thermocouple junction and sheath (preserving fast response time) while simultaneously blocking the transmission of electrical noise to the measurement circuit (preserving accuracy). This resolves the contradiction by decoupling the thermal conduction path from the electrical noise path.
3Measurement precision
If isolated voltage and ground are used with a power supply including overvoltage protection and regulator, then measurement accuracy is improved by minimizing noise interference, but device complexity increases
Solution Approach 1:
The power supply circuit is segmented into distinct functional modules: overvoltage protection circuit, voltage regulation circuit, and isolation circuit. Each module performs a specific function and can be independently designed and tested. This segmentation manages the complexity by organizing the circuit into manageable sections while achieving the goal of noise minimization and accuracy improvement.
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 solution enhances the accuracy of temperature measurements by minimizing noise interference, allowing for precise detection of small temperature variations in challenging environments like diesel exhaust systems.
Implementation Method 1
When a junction experiences a change in temperature, a voltage is created. This voltage, in turn, can then be interpreted to calculate the temperature at the junction point.
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
An active temperature measurement system includes at least one grounded thermocouple and a processor in communication with the at least one grounded thermocouple. The processor is configured to receive measurements from the at least one grounded thermocouple. The at least one grounded thermocouple is biased by an isolated voltage when the processor is receiving a measurement from the at least one grounded thermocouple.