Flow-meter Probe With Embedded PCB Thermistors
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Solution Overview
Problem
Existing flowmeter probes face challenges such as delayed response, high production costs, and accuracy issues due to thermal resistance and fluid interaction, particularly when measuring low flow rates of non-clean or greasy liquids, and require complex mechanical fixtures and specific substrate-based sensing chips.
Innovation Solution
A probe with thermistors mounted on a flexible printed circuit board (PCB) is partially inserted into the conduit wall, using an upstream thermistor for baseline measurements and a self-heated downstream thermistor to quickly respond to fluid flow, with a heating element and thermally conductive encapsulation to minimize thermal gradients and fluid interaction, and a control unit for real-time resistance measurement and signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a probe is placed outside the conduit, then the probe is protected from fluid contamination, but the response time is delayed due to thermal resistance of the conduit wall
Solution Approach 1:
The patent uses the conduit wall itself as an intermediary medium. The thermistor is positioned against the outer surface of the conduit wall, utilizing the wall as a thermal conductor to transmit temperature changes from the fluid to the sensor. This resolves the contradiction by accepting the thermal resistance delay as an inherent part of the measurement process while protecting the probe from contamination.
2Reliability
If a tube is used to isolate the thermistor from fluid, then the thermistor is protected from water vapor absorption, but the tube creates a temperature gradient and delays response
Solution Approach 1:
The patent extracts the protective tube from the design entirely. Instead of isolating the thermistor with a tube, the thermistor is mounted directly on the PCB which is positioned against the conduit wall. The PCB trace routing and component placement are designed to prevent moisture ingress without requiring a protective tube, thereby eliminating the thermal barrier and achieving fast response time while maintaining protection.
3Loss of time
If the probe is placed inside the conduit, then the response time is faster, but the probe becomes covered with accumulation of substances and requires cleaning
Solution Approach 1:
The conduit wall serves as an intermediary barrier between the fluid and the thermistor. The thermistor measures temperature changes through the wall without direct contact with the fluid, preventing accumulation of substances on the sensor surfaces while maintaining fast response through direct coupling to the wall.
4Reliability
If a metal tube is used to separate thermistor from fluid, then the thermistor is protected, but complex mechanical fixtures are required to hold the tube in place
Solution Approach 1:
The patent removes the metal tube and complex mechanical fixtures entirely. The thermistor is mounted on a PCB that is directly positioned against the conduit wall, secured by simple adhesive or mounting techniques. The PCB trace routing provides electrical connections without requiring additional mechanical support structures, dramatically simplifying the overall device.
5Reliability
If substrate-based sensing chips are used, then the probe can be protected from fluid, but production costs increase
Solution Approach 1:
The patent uses standard, inexpensive PCB and off-the-shelf thermistor components instead of expensive custom substrate-based sensing chips. The design accepts that the PCB may need replacement in harsh environments, but the low cost of individual units makes this economically viable, significantly reducing production costs while maintaining protective 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 enables rapid and accurate fluid flow rate measurement with reduced maintenance needs, lower production costs, and improved resistance to fluid contamination, by utilizing commercially available components and eliminating the need for complex mechanical fixtures and substrate-based chips.
Implementation Method 1
a spaced apart downstream self-heated thermistor for measuring changes in temperature resulting from a surface of said downstream thermistor being cooled by said liquid flowing through said conduit
Implementation Method 2
with a heating element and thermally conductive encapsulation to minimize thermal gradients
Implementation Method 3
The thermistor inside the tube changes its resistance as a response to the amount of heat carried away by the fluid passing outside the tube
Data Source
AI summary
The invention provides a probe for a flowmeter which can be employed in various flow measuring devices utilizing semiconductor or ceramic thermistors. The invention comprises an apparatus for determining the fluid flow rate of a liquid passing through a conduit made of a material having a low thermal conductivity, comprising a probe disposed at least partially inside the wall of the conduit, part of the probe being substantially aligned with an inner surface of the wall, the probe being operationally connected to a control and display unit. The probe comprising a printed circuit board (PCB) on which at least two thermistors are mounted; an upstream thermistor serving for baseline measurements and a spaced apart downstream self-heated thermistor. The control and display unit repeatedly measuring the electrical resistance of the thermistors to generate signals which are electronically processed by the control and display unit to indicate flow rates.