Flow Sensor Bridge Circuit Midpoint Branching
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Solution Overview
Problem
Existing flow quantity measuring apparatuses face issues with detection sensitivity due to long conductive line resistances, which deteriorate the accuracy of air flow quantity sensing and heating temperature control, and are prone to thermal degradation with increased heater resistor temperature.
Innovation Solution
A flow quantity measuring apparatus with a sensor chip featuring a thin wall membrane and conductive lines that minimize conductive line resistance by branching connections at midpoints, ensuring identical temperature characteristics for resistors and reducing the length of conductive lines, thereby improving detection sensitivity and reducing thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the heater resistor temperature is increased to improve detection sensitivity, then the air flow quantity detection sensitivity is improved, but the heater resistor is prone to thermal degradation
Solution Approach 1:
The patent changes the electrical resistance parameters of the bridge circuit components (temperature sensor resistors and fixed resistors) to optimize the circuit operation. By adjusting resistance values rather than increasing heater temperature, the patent achieves improved detection sensitivity while maintaining heater resistor reliability and avoiding thermal degradation.
2Ease of operation
If long conductive lines are used to connect bridge circuit components, then the device layout is flexible, but the conductive line resistance increases and deteriorates detection sensitivity
Solution Approach 1:
The patent transitions the bridge circuit from a distributed layout to an integrated layout where all components are formed on the same sensor chip plane. This dimensional reorganization allows short conductive lines while maintaining layout flexibility through integrated circuit design techniques.
Solution Approach 2:
The patent merges the temperature sensor resistors and fixed resistors onto the same sensor chip substrate, combining previously separate components into a single integrated structure. This merging eliminates long external conductive lines and reduces total resistance, improving detection sensitivity.
3Speed
If the membrane film thickness is reduced to decrease heat capacity, then the thermal response speed is improved, but the structural strength is reduced
Solution Approach 1:
The patent employs a thin film membrane structure that is optimized for thermal response while maintaining sufficient mechanical strength through film composition and structural design. The thin film allows rapid thermal response for quick detection of air flow changes while the material properties ensure the membrane remains structurally sound.
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
Enhances detection sensitivity for air flow quantity and improves the durability of the heater resistor by minimizing conductive line resistance and maintaining required temperature characteristics, leading to more accurate measurements and extended lifespan.
Implementation Method 1
The heat generating resistor generates heat when a heating electric current flows through the heat generating resistor
Implementation Method 2
A resistance value of each of the first and second upstream-side temperature sensitive resistors and first and second downstream-side temperature sensitive resistors is variable depending on a temperature
Implementation Method 3
The membrane of the sensor chip has a film thickness, which is smaller than that of the other portion of the sensor chip, so that a heat capacity of the membrane is small, and thereby it is possible to obtain a quick thermal response in response to a change in the flow quantity of the air
Data Source
AI summary
A sensor chip in a flow quantity measuring apparatus includes a first conductive line, through which a midpoint electric potential of a first series circuit of a bridge circuit is outputted, is branched from a first midpoint connection on a sensor chip. A second conductive line, through which a midpoint electric potential of a second series circuit of the bridge circuit is outputted, is branched from a second midpoint connection on the sensor chip. The output point of the midpoint electric potential of the first series circuit is provided at a midpoint between two temperature sensor resistors, and the first midpoint connection is provided on a center line of a heater resistor. The output point of the midpoint electric potential of the second series circuit is provided at a midpoint between two temperature sensor resistors, and the second midpoint connection is provided on the center line of the heater resistor.