Smoke Sensor I-V Circuit With Low-Frequency Ambient Light Correction
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Solution Overview
Problem
Conventional smoke sensors face issues with alarm failures and false alarms due to ambient light interference, which complicates the structure and increases costs, particularly when using batteries as a power source, as the dynamic range of the operational amplifier is narrow and prone to saturation.
Innovation Solution
A smoke sensor design that incorporates a low-frequency correction mechanism within the current-voltage conversion circuit to subtract low-frequency components from the input current, allowing for the suppression of ambient light interference without the need for complex labyrinthine structures, thereby simplifying the prevention of ambient light incidence on the light-receiving section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a labyrinth structure is used to prevent ambient light from incidenting on the light-receiving section, then the prevention of ambient light interference is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts and removes the low-frequency component (ambient light interference) from the input current signal using a correction current source. Instead of using a physical labyrinth structure to block ambient light, the invention electrically extracts the harmful low-frequency component and subtracts it from the total input current, thereby preventing ambient light interference without increasing structural complexity
Solution Approach 2:
The patent replaces the mechanical/optical labyrinth structure with an electrical correction mechanism. The correction current source generates a correction current that corresponds to the low-frequency component, and this correction current is subtracted from the input current through current subtraction circuitry. This electrical substitution eliminates the need for complex mechanical labyrinth structures while achieving the same goal of preventing ambient light interference
2Measurement precision
If a labyrinth structure is used to prevent ambient light incidence, then the accuracy of smoke detection is improved, but the manufacturing cost increases
Solution Approach 1:
The patent extracts the low-frequency component (ambient light interference) from the input current using a correction current source. By electrically extracting and removing this harmful component through current subtraction, the invention improves smoke detection accuracy without requiring expensive labyrinth structures, thereby reducing manufacturing costs
Solution Approach 2:
The patent uses simple, low-cost electronic components (current source, operational amplifiers, resistors) to generate and subtract the correction current. These inexpensive electronic elements replace costly mechanical labyrinth structures, achieving the same function of preventing ambient light interference at a lower manufacturing cost
3Use of energy by moving object
If the operational amplifier operates with a narrow dynamic range, then the power consumption is reduced, but the output voltage becomes prone to saturation
Solution Approach 1:
The patent applies preliminary anti-action by generating a correction current that counteracts the low-frequency component before it causes saturation. The correction current source creates a current that corresponds to the low-frequency component, and this correction current is subtracted from the input current in advance, preventing the operational amplifier from saturating due to the low-frequency component while maintaining narrow dynamic range and low power consumption
Solution Approach 2:
The patent uses feedback mechanisms where the correction current source is controlled based on the output voltage or input current characteristics. The correction current is adjusted to precisely counteract the low-frequency component, ensuring that the operational amplifier operates within its narrow dynamic range without saturation, thereby maintaining both low power consumption and high reliability
4Device complexity
If the low-frequency component is not corrected, then the circuit configuration is simplified, but alarm failures and false alarms increase
Solution Approach 1:
The patent replaces complex mechanical or optical filtering mechanisms with a relatively simple electrical correction circuit. The correction current source and current subtraction circuitry provide a compact and simple configuration that effectively removes the low-frequency component, thereby improving alarm accuracy without significantly increasing circuit complexity
Solution Approach 2:
The patent changes the electrical parameters of the input current by generating and subtracting a correction current. This parameter change removes the low-frequency component from the signal, preventing alarm failures and false alarms. The correction mechanism uses simple parameter adjustments through current subtraction rather than complex circuit configurations
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 design effectively reduces the influence of low-frequency components on the output voltage, preventing saturation and improving the accuracy of smoke detection, thus minimizing alarm failures and false alarms while potentially lowering the overall cost of the sensor.
Implementation Method 1
a photodiode (light-receiving section) PD, which is disposed at a position on which direct light from the LED 6 is not incident, converts the received light into current
Implementation Method 2
an LED (light-emitting section) 6, as illustrated in FIG. 30(a)... the LED 6 outputs light intermittently towards a sensing space within the housing 20
Implementation Method 3
When smoke flows into the sensing space of the smoke sensor A, the smoke gives rise to diffusion and reflection of light from the LED 6 within the sensing space
Implementation Method 4
When smoke flows into the sensing space of the smoke sensor A, the smoke gives rise to diffusion and reflection of light from the LED 6 within the sensing space
Data Source
AI summary
A current-voltage converting circuit (2) is provided with a first feedback circuit (5) and a correcting transistor (Q1). The first feedback circuit (5) outputs, of an output voltage (V10), a voltage according to a magnitude of a low-frequency component that is not greater than or equal to a predefined first cut-off frequency. The correcting transistor (Q1) extracts a correction current (I21) according to a magnitude of an output of the first feedback circuit (5) from a sensor current (I10). The first feedback circuit (5) has a first integrating circuit (9) and a sample-and-hold circuit (10). The first integrating circuit (9) integrates the output voltage (V10) of a conversion section (3). The sample-and-hold circuit (10) samples and holds an output of the first integrating circuit (9) during a sensing period at which a pulsed detection signal is inputted. Means for preventing an incidence of ambient light onto a light-receiving section can be simplified or omitted as a result.