Micromachined Pressure Sensor Diaphragm for Fire Alarm Set Point Precision
Solution Overview
Problem
Existing overheat or fire alarm systems face challenges in consistently achieving a repeatable pressure set point during manufacturing, which is time-consuming and costly, and have a large internal free volume that reduces detection accuracy due to gas entrapment, affecting the system's ability to reset after an alarm event.
Innovation Solution
The use of micromachining techniques to fabricate miniaturized pressure sensors with precise dimensions and complex geometries, allowing for multiple pressure switches on a single substrate with varied set points, and a sensor tube with a low profile, minimizing internal free volume and enhancing detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional pressure forming operations are performed prior to final assembly, then the manufacturing process is simplified, but the pressure set point consistency and repeatability deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-forming the diaphragm to near-final dimensions and pre-positioning it in the assembly before performing the final pressure forming operation. This allows the diaphragm to be pre-prepared and positioned correctly, then finalized after assembly to achieve both manufacturing efficiency and precision pressure set points.
Solution Approach 2:
The manufacturing process is segmented into distinct stages: initial diaphragm forming, assembly preparation, final assembly, and post-assembly pressure forming. This segmentation allows each stage to be optimized independently, with the critical pressure forming operation performed after assembly to ensure precision while maintaining overall process efficiency.
2Manufacturing precision
If the pressure forming operation is performed after final assembly, then the pressure set point repeatability improves, but the manufacturing time and cost increase
Solution Approach 1:
The diaphragm is pre-formed to close tolerances and pre-positioned in the assembly before the final pressure forming step. This preliminary preparation reduces the complexity and time of the post-assembly operation, improving productivity while maintaining the precision benefits of post-assembly pressure forming.
Solution Approach 2:
The patent changes the timing parameter of the pressure forming operation from pre-assembly to post-assembly, and optimizes other parameters such as diaphragm material properties and forming pressure to compensate for the increased manufacturing time, thereby maintaining productivity while achieving better precision.
3Device complexity
If a larger internal free volume is used in the pneumatic pressure switch, then the device complexity is reduced, but the detection accuracy deteriorates due to gas entrapment
Solution Approach 1:
The patent extracts and eliminates the problematic large internal free volume from the pneumatic pressure switch design. By removing the excess volume that causes gas entrapment, the design achieves better detection accuracy while maintaining sufficient simplicity through optimized minimal-volume architecture.
Solution Approach 2:
The patent employs a flexible diaphragm membrane that can be precisely controlled in thickness and material properties. This thin film structure allows for minimal internal volume while maintaining the necessary mechanical compliance and pressure sensing capability, thereby improving detection accuracy without significantly increasing device complexity.
4Length of moving object
If the sensor tube length is reduced to a low profile, then the system compactness improves, but the detection accuracy deteriorates due to increased gas entrapment effects
Solution Approach 1:
The patent uses a flexible diaphragm with optimized thickness and material properties to compensate for the reduced sensor tube length. The enhanced diaphragm sensitivity compensates for the lower pressure signal from the shorter tube, maintaining detection accuracy while achieving the desired compact low-profile configuration.
Solution Approach 2:
The patent changes multiple parameters simultaneously: reduces sensor tube length for compactness, optimizes diaphragm thickness and material for enhanced sensitivity, and adjusts the pressure forming parameters to achieve the desired pressure set point. These coordinated parameter changes maintain detection accuracy despite the reduced tube length.
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
This approach results in a more efficient, reliable, and accurate overheat or fire alarm system with improved detection capabilities and faster reset times, particularly beneficial for aerospace applications.
Implementation Method 1
Exposure of the sensor tube to a high temperature causes the metal hydride core to evolve hydrogen
Implementation Method 2
The pressure sensor is also configured to generate an averaging overheat alarm due to the pressure rise associated with thermal expansion of the inert gas fill
Implementation Method 3
The micromachining step comprises removing material from the first layer to form the pressure sensor
Data Source
Figure 1a~1b
Figure 1c~2
AI summary
A method of manufacturing an overheat or fire alarm detection system, comprises the steps of micromachining a pressure sensor 10 and securing a sensor tube (20, Fig. 2) in fluid communication with the pressure sensor 10. The sensor tube may comprise a hollow tube (24, Fig. 2) containing a material that evolves gas upon heating. The micromachining step may comprise doping at least a portion 13 of a first layer 12, forming a cavity 19 at least partially within the doped portion 13 and forming a deformable diaphragm 14 over the cavity.