LED Pulse Compensation for Gas Sensor Accuracy
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Solution Overview
Problem
Optical absorption gas sensors using LEDs face challenges in accurately measuring gas concentrations due to temperature variations affecting LED output, requiring complex control electronics and high power consumption for short, high-intensity pulses.
Innovation Solution
A method involving multiple measurements of current through the LED during each pulse to determine the shape of the light pulse and generate a compensated signal, which accounts for both photosensor output and LED current measurements, allowing for accurate gas concentration determination without complex pulse shaping circuits and minimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If short pulses of light are generated by an LED to obtain a high signal-to-noise ratio, then measurement precision is improved, but device complexity and power consumption increase due to complex control electronics required for pulse shaping
Solution Approach 1:
The patent measures the actual current waveform through the LED using an ADC and uses this feedback to compensate for deviations from the ideal pulse shape. The microcontroller reads the ADC values and applies compensation algorithms to correct for variations in LED current, thereby maintaining measurement precision without requiring complex analog pulse shaping circuits.
Solution Approach 2:
The patent replaces complex analog pulse shaping electronics with a digital approach using a microcontroller and ADC. Instead of using sophisticated analog circuits to generate precise pulse waveforms, the system uses digital sampling and software-based compensation to achieve the same measurement precision, thereby reducing device complexity and power consumption.
2Measurement precision
If the LED is operated at high current to achieve high peak light intensity, then measurement precision is improved, but the LED temperature increases which affects LED output and measurement accuracy
Solution Approach 1:
The patent uses periodic pulsed operation of the LED instead of continuous operation. By applying current in short pulses, the LED achieves high peak light intensity for accurate measurements while the duty cycle remains low enough to prevent excessive temperature rise. The system allows the LED to cool between pulses, maintaining measurement accuracy without thermal damage.
Solution Approach 2:
The patent measures the LED forward voltage before and/or during the light emission pulse to predict and compensate for temperature effects on LED output. By performing this preliminary measurement, the system can adjust the compensation algorithm to account for temperature-induced variations in LED characteristics, maintaining measurement precision despite temperature changes.
3Measurement precision
If the LED current is increased to compensate for temperature-induced output variations, then measurement precision is maintained, but power consumption increases
Solution Approach 1:
The patent dynamically adjusts the LED drive parameters based on measured temperature and forward voltage. Instead of using a fixed high current to compensate for all temperature variations, the system modifies the pulse width, amplitude, or timing based on real-time measurements of LED characteristics, thereby maintaining measurement precision while minimizing power consumption through adaptive parameter optimization.
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 enables accurate gas concentration measurement while reducing power consumption and eliminating the need for complex electronics, allowing for efficient operation despite temperature variations and achieving a high signal-to-noise ratio.
Implementation Method 1
at least one light emitting diode (LED) and a photosensor
Implementation Method 2
generating a plurality of pulses of light by passing a plurality of pulses of current through the at least one LED
Implementation Method 3
a photosensor (e.g. a photodiode) having an output signal (e.g. a current) sensitive to the amount of light received by the photosensor
Implementation Method 4
Light from the source is directed through a gas sample and detected by the photosensor. The concentration of an analyte gas in the gas sample can be determined from the absorption of light by the analyte gas
Data Source
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Figure 3~4
AI summary
An optical absorption gas sensor for detecting an analyte gas comprises a gas sample receiving chamber, at least one light emitting diode (LED) and a photodiode or other photosensor. A plurality of light pulses are generated by passing pulses of current through the at least one LED. The current through the at least one LED is measured a plurality of times during each pulse and taken into account when generating a compensated output signal. The transfer ratio between LED current and photodiode output signal is calculated a plurality of times during each pulse. An ADC measures the LED and photodiode currents alternately. The LED pulses are generated by inductor discharge flyback and the period of time for which current is supplied to the inductor prior to each pulse is selected so that the photodiode output current is at an optimal region within the input range of the ADC. At least the temperature of the at least one LED is measured and taken into account when generating the compensated output signal. Thus, rather than providing especially careful control of the LED pulses, the pulses are measured, enabling a simpler, lower power circuit which is tolerant of variations in temperature to be provided.