Thermal Flowmeter Abnormality Detection Using Thermopile Voltage Relationships
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Solution Overview
Problem
Existing thermal type flowmeters struggle to detect abnormalities in sensor elements while continuously measuring fluid flow rates, as methods require interrupting the measurement process or cannot differentiate between dust adherence and qualitative changes in thermopiles.
Innovation Solution
A thermal type flowmeter with a sensor element, output circuit, storage unit, and abnormality determination unit that compares the relationship between output signals from upstream and downstream thermo-sensitive elements to a stored referential relationship, allowing for real-time abnormality detection without interrupting flow rate measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the heater is turned off to calculate the resistance value of the thermopile for failure determination, then the failure detection capability is improved, but the flow rate measurement must be interrupted
Solution Approach 1:
The patent applies preliminary action by pre-storing the relationship between upstream and downstream thermopile output voltages at various flow rates before normal operation. This reference data is established in advance, allowing the system to perform abnormality detection during continuous flow rate measurement without needing to interrupt operation or change the heater state.
Solution Approach 2:
The patent makes the flow rate measurement state serve dual purposes: both normal flow rate detection and thermopile abnormality determination. By comparing the actual relationship between thermopile outputs during operation against the pre-stored reference relationship, the system achieves failure detection capability while maintaining continuous flow rate measurement, eliminating the need for separate test modes.
2Measurement precision
If the resistance value of the thermopile is calculated to detect failure, then damage or qualitative change of the thermopile can be detected, but dust adherence to the insulating film cannot be detected
Solution Approach 1:
The patent uses output voltage relationship changes as an indicator of thermopile abnormality. By monitoring how the relationship between upstream and downstream thermopile output voltages deviates from the expected reference relationship, the system can detect various types of abnormalities including dust adherence, which would alter the thermal characteristics and thus the voltage relationship, without requiring direct resistance measurement.
Solution Approach 2:
The patent replaces direct electrical resistance measurement with a functional performance test based on output voltage relationship comparison. Instead of measuring the physical resistance value of the thermopile, the system evaluates the thermopile's actual performance in converting thermal energy to electrical energy by comparing output voltages under known flow conditions, thereby detecting both internal damage and external contamination.
3Ease of manufacture
If a special state is created for failure determination, then the failure detection method can be implemented, but it becomes difficult to determine failure during normal usage with constant measurement demand
Solution Approach 1:
The patent merges the failure determination function with the normal flow rate measurement function. By using the same operational state (heater on, fluid flowing) for both purposes and comparing the actual thermopile output relationship against pre-stored reference data, the system enables continuous abnormality monitoring during normal operation without requiring separate test modes or special operational states.
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 continuous detection of sensor element abnormalities, including dust adherence, without interrupting fluid flow rate measurement, improving reliability and reducing false determinations due to instantaneous malfunctions.
Implementation Method 1
a heater arranged in a flow passage in which a fluid flows to heat the fluid
Implementation Method 2
a first thermo-sensitive element arranged on an upstream side of the flow passage with respect to the heater, and a second thermo-sensitive element arranged on a downstream side of the flow passage with respect to the heater
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A thermal type flowmeter (101) includes a sensor element (10), an output circuit (11), a storage unit (20), and an abnormality determination unit (22). The sensor element (10) includes an upstream-side thermopile (1), a heater (2), and a downstream-side thermopile (3). The output circuit (11) outputs a signal expressing a flow rate of a fluid based on a difference voltage between an output voltage (Vu) of the upstream-side thermopile (1) and an output voltage (Vd) of the downstream-side thermopile (3). A referential relationship, in which a reference of a relationship between the voltages (Vu and Vd) is defined, is previously stored in the storage unit (20). The abnormality determination unit (22) compares the relationship between the voltage (Vu) output from the upstream-side thermopile (1) and the voltage (Vd) output from the downstream-side thermopile (3) to the referential relationship, and determines abnormalities of the upstream-side thermopile (1) and the downstream-side thermopile (3).