Thermal Flowmeter Sensor Drift Diagnosis
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Solution Overview
Problem
Thermal flowmeters face challenges in accurately determining mass flow and flow rate, especially when flow direction is unknown, and in distinguishing between changes in internal and external thermal resistance, leading to measurement errors and the need for frequent sensor replacement.
Innovation Solution
A thermal flowmeter with at least three sensor elements, where each sensor is partially or temporarily in thermal contact with the medium, and an electronics unit that heats two sensors simultaneously while one remains unheated to continuously determine mass flow and flow rate, and analyzes the step response to differentiate between internal and external thermal resistance changes for accurate measurement correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional thermal flowmeters with two sensor elements are used, then the device complexity is low, but the measurement precision deteriorates when flow direction is unknown or sensor drift occurs
Solution Approach 1:
The patent divides the sensing function into three separate sensor elements instead of using two, allowing independent measurement and diagnostic capabilities. This segmentation enables the system to identify which sensor is functioning correctly and to detect flow direction, thereby improving measurement precision without requiring complex additional components
Solution Approach 2:
The three sensor elements serve multiple functions: they can be used individually or in combinations to determine mass flow, detect flow direction, and perform self-diagnostics. This multi-functionality allows the system to maintain high measurement precision under various operating conditions while avoiding the need for separate dedicated components for each function
2Measurement precision
If sensor elements are frequently replaced to ensure measurement accuracy, then the measurement precision is maintained, but the productivity and operational efficiency deteriorate
Solution Approach 1:
The flowmeter performs self-diagnostics by comparing measurements from multiple sensor elements and analyzing step responses to automatically detect sensor drift and determine which sensor is functioning correctly. This self-service capability eliminates the need for frequent manual sensor replacements, maintaining measurement precision while improving operational efficiency
Solution Approach 2:
The system continuously monitors the performance of sensor elements by analyzing step responses and comparing measurements, providing feedback about sensor condition. This feedback mechanism enables early detection of sensor drift and automatic compensation, preventing the need for premature sensor replacement
3Measurement precision
If the flowmeter performs self-diagnostics to distinguish internal and external thermal resistance changes, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent replaces complex mechanical or external diagnostic equipment with an integrated electronic diagnostic system that uses the existing sensor elements to perform self-testing. By applying step inputs and analyzing the thermal response through electronic processing, the system can distinguish between internal and external thermal resistance changes without adding mechanical 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 continuous, accurate determination of mass flow and flow rate while diagnosing sensor drift, allowing for real-time correction and reducing the need for sensor replacement by distinguishing between internal and external thermal resistance changes, thus improving measurement accuracy and operational efficiency.
Implementation Method 1
each of the at least three sensor elements is at least partially and/or temporarily in thermal contact with the medium
Implementation Method 2
there is an additional cooling of the active temperature sensor by the passing colder medium. It takes an additional heat transport due to forced convection
Data Source
Figure 1~2b
Figure 3~4
Figure 5
AI summary
Thermal flowmeter (1), in particular for determining and/or monitoring the mass flow (ΦΜ) and/or the flow velocity (vD) of a flowable medium (3) through a pipeline (2), having at least three sensor elements (4a, 4b, 4c) and an electronic unit (9), wherein each of the at least three sensor elements (4a, 4b, 4c) is at least partially and/or occasionally in thermal contact with the medium (3) and comprises a heatable temperature sensor (5a, 5b, 5c), and wherein the electronic unit (9) is configured to heat each of the three sensor elements (4a, 4b, 4c) with a heating power (P1, P2, P3), to record the temperature (T1, T2, T3) thereof, to heat at least two of the at least three sensor elements (4a, 4b, 4c) at the same time, to determine the mass flow (ΦΜ) and/or the flow velocity (vD) of the medium (3), to make a statement on a change in the thermal resistance of at least one of the at least three sensor elements (4a, 4b, 4c) from a paired comparison of the temperatures (T1, T2, T3) and/or heating powers (P1, P2, P3) of the at least three sensor elements (4a, 4b, 4c) and/or at least one variable derived from at least one of the temperatures (T1, T2, T3) and/or heating powers (P1, P2, P3), to make a statement on a change in the internal thermal resistance of the at least one sensor element from a step response to a sudden change in the supplied heating power ΔΡ at at least one of the at least three sensor elements, and, if a change in the internal and/or external thermal resistance occurs at at least one of the at least three sensor elements (4a, 4b, 4c), to correct the measured value for the mass flow (ΦΜ) and/or the flow velocity (vD) and/or to generate and output a message relating to the state of the at least one sensor element. <sb /> <sb />