Sample and Hold Circuit Timing Control for Optical Smoke Detectors
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Solution Overview
Problem
Optical smoke detectors face challenges in cost and power consumption due to the use of operational amplifiers and ASIC devices in amplifier circuits, which also lead to increased material costs and susceptibility to false alarms.
Innovation Solution
A smoke detector design utilizing a discrete amplifier circuit without operational amplifiers or ASICs, where the sample and hold circuit's scanning timepoint is controlled relative to the radiation pulse duration to optimize signal digitization, and a calibration method adjusting pulse duration to compensate for variations in the signal path, ensuring reliable smoke detection with reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If operational amplifiers and ASIC devices are used in the amplifier circuit, then the signal amplification performance is improved, but the material costs and power consumption increase
Solution Approach 1:
The patent extracts and removes the operational amplifier and ASIC components from the amplifier circuit, replacing them with a discrete component implementation. This extraction eliminates the high power consumption and cost associated with integrated operational amplifiers while maintaining the necessary signal amplification function through a simplified circuit topology using individual transistors, resistors, and capacitors.
Solution Approach 2:
The patent employs inexpensive discrete components (individual transistors, resistors, capacitors) instead of expensive integrated operational amplifiers and ASIC devices. These discrete components are simpler, cheaper, and consume less power, achieving the amplification function through a more economical approach that trades integration for component simplicity and lower cost.
2Reliability
If operational amplifiers and ASIC devices are used in the amplifier circuit, then the signal amplification performance is improved, but the material costs increase
Solution Approach 1:
The patent extracts and removes the operational amplifier and ASIC components from the amplifier circuit, replacing them with a discrete component implementation. This extraction eliminates the high material costs associated with integrated operational amplifiers while maintaining the necessary signal amplification function through a simplified circuit topology using individual transistors, resistors, and capacitors.
Solution Approach 2:
The patent employs inexpensive discrete components (individual transistors, resistors, capacitors) instead of expensive integrated operational amplifiers and ASIC devices. These discrete components are simpler, cheaper, and easier to manufacture, achieving the amplification function through a more economical approach that trades integration for component simplicity and lower cost.
3Device complexity
If the scanning timepoint is not synchronized with radiation pulse duration, then the circuit design is simpler, but false alarms increase due to signal artifacts
Solution Approach 1:
The patent implements dynamic timing control where the scanning timepoint of the sample and hold circuit is not fixed but is instead synchronized adaptively with the radiation pulse duration. This dynamic synchronization ensures that signal sampling occurs at the optimal moment (when the signal is at maximum level), eliminating artifacts that cause false alarms while maintaining circuit simplicity through coordinated timing control.
Solution Approach 2:
The patent employs feedback mechanisms where the control device monitors the radiation pulse characteristics and adjusts the scanning timepoint accordingly. This feedback-based timing synchronization ensures that the sample and hold circuit captures the signal at the correct moment in response to varying pulse durations, preventing false alarms caused by premature or delayed sampling while keeping the overall system design manageable.
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 results in a cost-effective, low-power smoke detector with reduced false alarms, as the discrete amplifier circuit minimizes unwanted artifacts and the calibration method ensures accurate signal processing by digitizing the output signal at its maximum level, enhancing detection reliability.
Implementation Method 1
optical smoke alarms generally employ the well-known scattered-light method, making use of the fact that clear air reflects virtually no light. However, if smoke particles are present in a measuring chamber, illuminating light emitted by a light source is at least partially scattered by the smoke particles.
Implementation Method 2
The light detector of an optical smoke alarm is typically a photodiode which only produces a very small measurement signal.
Data Source
AI summary
A smoke detector contains a radiation source for transmitting an illuminating radiation having a time sequence of radiation pulses, a radiation detector for receiving measurement radiation impinging on the radiation detector after at least partial scattering of the illuminating radiation, an amplifier circuit for amplifying an output signal of the radiation detector, an analog to digital converter having a sample and hold circuit for converting an analog output signal of the amplifier circuit into a digital measurement value, and a control device coupled to the radiation source and the sample and hold circuit. The control device is equipped for controlling the radiation source and the sample and hold circuit such that the time of a sampling point in time of the sample and hold circuit relative to a radiation pulse depends on the duration of the radiation pulse. A method for calibrating the described smoke detector is also revealed.