Flow Sensor Bubble Detection via Dual Temperature Sensors
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Solution Overview
Problem
Traditional thermal flow sensors face challenges in distinguishing between gas bubbles and zero flow conditions, particularly at low flow rates, and lack sensitivity in detecting air bubbles in medical infusion liquids.
Innovation Solution
A flow sensor design featuring two temperature sensors arranged upstream and downstream of a heat source, with an analyzing circuit that calculates a temperature proportional to the heat source, allowing for differentiation between gas and liquid based on thermal conductivity and heat capacity, enabling effective detection of gas bubbles and accurate measurement of flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a differential measuring procedure with two temperature sensors is used, then sensitivity at low flow rates is improved, but the ability to distinguish gas bubbles from zero flow conditions deteriorates
Solution Approach 1:
The patent segments the temperature measurement function into two independent temperature sensors positioned at different locations (upstream and downstream of the heat source). This segmentation allows the system to obtain two separate temperature signals that can be processed differently - one for flow rate measurement and another for bubble detection, thereby resolving the contradiction between sensitivity and distinguishability.
Solution Approach 2:
The patent transitions from a single-dimensional temperature difference measurement to a two-dimensional measurement space by introducing a second temperature sensor. This enables the system to evaluate temperature at two different positions simultaneously, creating additional information dimensions that allow differentiation between bubble presence and zero flow conditions while maintaining low flow rate sensitivity.
2Productivity
If traditional thermal flow sensors are used, then flow rate measurement is achieved, but the ability to detect gas bubbles deteriorates
Solution Approach 1:
The patent implements multi-functionality by enabling the temperature sensor system to perform both flow rate measurement and gas bubble detection functions. The same thermal field and temperature sensors used for measuring flow rate are also utilized for detecting gas bubbles, eliminating the need for separate detection systems and achieving both objectives simultaneously.
Solution Approach 2:
The patent exploits parameter changes in the thermal field caused by gas bubbles versus liquid flow. By monitoring temperature distribution and its changes in the presence of gas bubbles (which have different thermal conductivity and heat capacity compared to liquid), the system can distinguish between the two conditions while maintaining accurate flow rate measurement capabilities.
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
The solution enhances sensitivity at low flow rates and effectively distinguishes between gas bubbles and standing liquid, ensuring reliable detection of air bubbles while maintaining accurate flow rate measurements.
Implementation Method 1
a heat source and a suitable temperature sensing means are arranged... The flow leads to a change in the temperature distribution generated by the thermal source
Implementation Method 2
the liquid flow rate is deduced from a temperature sensor measuring the cooling effect of the flowing liquid
Data Source
AI summary
The invention relates to a flow sensor (1) and a method for determining the presence of a gas bubble (G) in a liquid (L) flowing through the flow sensor (1).