Optical Pressure Sensor for Aircraft Fire Alarm
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Solution Overview
Problem
Pneumatic pressure detectors in fire alarm systems face issues with electromagnetic interference due to long electrical cables used for signal routing, especially when the control unit is remotely located from the sensing tube, affecting the reliability and accuracy of temperature and pressure measurements.
Innovation Solution
The implementation of an optical pressure sensor connected via an optical fiber to an interrogator, which processes signals indicative of gas pressure changes and activates alarms based on predefined thresholds, eliminating electromagnetic interference by using light signals instead of electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical cables are used to connect the pressure sensor to the control unit, then the system can transmit pressure signals, but electromagnetic interference affects the reliability and accuracy of measurements
Solution Approach 1:
The patent replaces the electrical cable connection with an optical fiber connection. The pressure sensor converts pressure changes into optical signals that are transmitted through the optical fiber to the control unit. This substitution eliminates electromagnetic interference because optical fibers transmit light signals rather than electrical signals, resolving the contradiction between maintaining signal transmission capability and avoiding electromagnetic interference.
2Adaptability or versatility
If the control unit is remotely located from the sensing tube, then system design flexibility is improved, but long electrical cables are required which introduce electromagnetic interference
Solution Approach 1:
The patent enables remote placement of the control unit by using optical fiber cables instead of electrical cables. Optical fibers can be routed over long distances without suffering from electromagnetic interference, allowing the control unit to be located remotely from the sensing tube while maintaining signal integrity. This resolves the contradiction between design flexibility and electromagnetic interference.
3Reliability
If multiple sensors are connected using separate electrical cables, then each sensor can be independently monitored, but the system weight and complexity increase
Solution Approach 1:
The patent allows multiple pressure sensors to be connected in parallel to a single control unit through optical fiber connections. The optical fiber system can multiplex multiple sensor signals, reducing the number of separate cable runs required. This merging approach maintains independent monitoring capability while reducing overall system weight and complexity compared to using separate electrical cables for each sensor.
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 solution provides a reliable and accurate detection system immune to electromagnetic interference, allowing for continuous monitoring of gas pressure and temperature trends, with the ability to multiplex multiple sensors on a single fiber optic cable, reducing weight and complexity while maintaining high measurement accuracy over a wide temperature range.
Implementation Method 1
an optical pressure sensor, which is responsive to a change in pressure of the pressurized gas and configured to provide a signal that is indicative of that pressure change
Implementation Method 2
The associated pressure rise in the sensor tube causes a normally open pressure switch in the detector to close. This generates a discrete alarm. The pneumatic pressure detector is also configured to generate an averaging overheat alarm due to the pressure rise associated with thermal expansion of the inert gas fill.
Data Source
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AI summary
A pneumatic sensing apparatus for use in an overheat or fire alarm system of an aircraft comprises sensing means (51, 61, 71) containing a pressurized gas coupled to a pressure sensor (52, 62, 72). The pressure sensor (52, 62, 72) is configured to produce a signal that is indicative of the gas pressure, which in turn is directly related to the temperature in the area. The pressure sensor (52, 62, 72) transmits an optical signal indicative of the sensed pressure to a control unit (58, 68, 78), which issues an alarm when the gas pressure exceeds a threshold.