Thermocouple Open Circuit Detection via Time Division Multiplexing
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Solution Overview
Problem
Thermocouples in gas turbine engines can fail by going open circuit, producing spurious results that are indistinguishable from valid measurements, leading to inaccurate engine performance assessments, as existing methods for detecting open circuit failures are either intrusive or distort normal operation.
Innovation Solution
A method using a measurement arrangement with a thermocouple, controller/processor, multiplexer/digitiser, and test circuit, where the controller takes temperature readings and switches to a test circuit to stimulate the thermocouple, allowing for dynamic validation of each sensor's integrity by checking for closed or open circuits within a predetermined time frame, ensuring minimal disruption to normal operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermocouple sensor fails by going open circuit, then the sensor cannot provide accurate temperature measurements, but the spurious results are indistinguishable from valid measurements making failure detection difficult
Solution Approach 1:
The system continuously monitors the thermocouple circuit by injecting test signals and comparing the responses against expected values. This feedback mechanism allows the system to detect open circuit failures by observing deviations from normal behavior, thereby solving the detection difficulty while maintaining measurement reliability.
Solution Approach 2:
A test circuit acts as an intermediary between the controller and the thermocouple. This intermediary injects test signals through the thermocouple circuit and measures the response, enabling failure detection without directly interfering with the normal measurement function. The test circuit mediates between the need for continuous monitoring and the requirement to maintain accurate temperature measurements.
2Difficulty of detecting and measuring
If existing methods inject signals to detect open circuit conditions, then failure detection is possible, but the injected current adversely affects the measurement requirements during normal operation
Solution Approach 1:
The system performs signal injection and thermocouple testing periodically rather than continuously. By timing the test signal injection to occur during specific intervals when normal measurements are not being taken, or by using very brief injection pulses, the system can detect open circuit conditions without significantly interfering with the continuous temperature measurement process.
Solution Approach 2:
The system dynamically switches between normal measurement mode and test mode. The controller selectively connects the multiplexer to either the thermocouple for normal measurements or to the test circuit for failure detection. This dynamic reconfiguration allows the system to perform both functions without simultaneous interference, as the test signal injection is isolated in time from the normal temperature measurement process.
3Difficulty of detecting and measuring
If the measurement process is interrupted to test thermocouple integrity, then open circuit detection is possible, but normal temperature measurements are delayed or lost
Solution Approach 1:
The measurement and testing functions are segmented into separate temporal intervals. The multiplexer is configured to switch between connecting to the thermocouple for temperature measurements and connecting to the test circuit for integrity verification. This segmentation allows both functions to be performed without simultaneous interference, and by合理安排 the timing, the interruption to measurements can be minimized while still achieving reliable detection.
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 enables quick and non-intrusive detection of open circuit failures, maintaining accuracy and reliability of sensor measurements with minimal disruption to valid signal acquisition, effectively distinguishing between functioning and malfunctioning thermocouples.
Implementation Method 1
there is an obvious manifestation that an open circuit event has occurred when an electrical current flows through the thermocouple circuit, rather than through the thermocouple which being open circuit will effectively have a higher resistance compared to the thermocouple circuit
Implementation Method 2
if the thermocouples are operating under normal circumstances, then relatively accurate representations of the measured temperatures are received by the storage and processing features
Data Source
AI summary
There are a number of sensors (2, 22) such as thermocouples which can provide a putative measurand signal which is within a predicted range for such signals whilst the sensor is incorrectly operating, such as as due to an open circuit. Techniques and processes are available to determine by interrogation sensor operational validity, but these can distort the measurand signal if correct. By time division multiplex techniques the present arrangement takes a putative measurand signal from a sensor (2, 22) in order that either within the same time division or more normally a separate time division, an interrogation of the sensor is performed in order to determine accuracy and therefore validity of the sensor 22. In such circumstances, the putative measurand signal from the sensor 22 is dynamically verified by the interrogator 23 to allow greater confidence with respect to interpretation, if an invalid sensor operation is determined, then a pre-defined value for that sensor failure can be output for the data signal.