Twilight Switch Illuminance Measurement via Reverse-Biased Photodiode
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Solution Overview
Problem
Existing illuminance measurement devices, particularly in twilight switches, face challenges such as unsuitability for high illuminance levels, temperature dependence, and the use of toxic materials like cadmium, requiring adjustments and additional components like transimpedance amplifiers, which complicate their use across a wide range of illuminance levels.
Innovation Solution
A device with a reverse-biased photodiode and capacitor light sensor connected via two wires, utilizing a control unit with charging and discharge current sources to measure illuminance through discharge times, eliminating the need for adjustments during production, installation, or when replacing the sensor, and allowing operation over a wide range of illuminance levels from 1 to 100,000 lux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a photoresistor is used for illuminance measurement, then the device structure is simple, but it is not suitable for high illuminance levels and has wide temperature-dependent resistance variations
Solution Approach 1:
The patent changes the operating parameters of the photodiode by applying reverse bias voltage and using it in a transimpedance amplifier configuration, transforming it from a simple resistive sensor into a precise current-to-voltage converter that maintains stability across wide illuminance ranges and temperature variations
2Measurement precision
If an accurate photodiode with transimpedance amplifier is used, then measurement precision is improved, but additional supply lines and device complexity are required
Solution Approach 1:
The patent merges the photodiode and transimpedance amplifier into a single integrated sensor module that connects via only two wires to the control unit, eliminating the need for separate supply lines and reducing overall device complexity while maintaining high measurement precision
Solution Approach 2:
The two-wire connection serves multiple functions simultaneously: it provides power to the photodiode, carries the measurement signal, and enables communication, making the sensor universally applicable without requiring additional dedicated supply lines
3Ease of manufacture
If photoresistors are used in twilight switches, then the device is simple to manufacture, but precise adjustment is required and it is not suitable for higher illuminance levels
Solution Approach 1:
The control unit automatically compensates for variations in sensor characteristics through self-calibration routines, eliminating the need for manual adjustment during installation while maintaining ease of manufacture. The system performs self-diagnosis and adapts to the specific sensor installed
4Adaptability or versatility
If the illuminance measurement device must work across a very large range of illuminance levels, then versatility is improved, but device complexity increases due to multiple components
Solution Approach 1:
The patent implements dynamic measurement capabilities where the control unit automatically adjusts measurement parameters such as integration time and gain based on the detected illuminance level, allowing a single sensor to accurately measure across five powers of ten from 1 to 100,000 lux without hardware changes
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
Enables precise measurement of illuminance levels across a very wide range without requiring adjustments, using inexpensive current sources and a simple two-wire connection, ensuring accuracy and usability in twilight switches without operator intervention.
Implementation Method 1
The light sensor consists only of a reverse-biased photodiode and a capacitor connected in parallel
Implementation Method 2
a capacitor connected in parallel. The control unit contains a charging circuit for charging the capacitor to a capacitor voltage and two different discharge current sources that periodically discharge the capacitor with constant currents
Data Source
Figure 1~2
Figure 3~4
AI summary
The device has a photodiode (P) that is arranged parallel to a switched capacitor (C) on a light sensor (1). The photodiode is operated in the reverse direction. A charging circuit charges the capacitor with a voltage source. The current sources discharge the current to capacitor. A time measuring unit measures the discharging times of capacitor. Independent claims are included for the following: (1) method for determining luminance of light in twilight switch; and (2) twilight switch.