IR Emitter Power Control via PWM Modulation
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Solution Overview
Problem
The sensitivity of non-dispersive infrared detection cells varies due to wide tolerance in emitter resistance, leading to inconsistent power delivery to IR emitters, which affects measurement accuracy.
Innovation Solution
Pulse-width-modulating the voltage applied to the IR emitter during on-time to control power delivery, using a secondary modulation frequency of 800 Hz, which is filtered by the emitter, and adjusting duty cycles to maintain consistent average power, while also applying a primary modulation of 2.5 Hz square wave.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If constant voltage is pulsed to the emitter, then the emitter can operate with simple control, but the power delivered to the emitter varies widely due to resistance tolerance, causing inconsistent NDIR cell sensitivity
Solution Approach 1:
The patent implements a feedback control system where the microcontroller monitors the actual power delivered to the emitter and adjusts the PWM duty cycle accordingly. This closed-loop feedback mechanism compensates for emitter resistance variations, ensuring consistent power delivery and uniform NDIR cell sensitivity across different devices while maintaining simple operational control.
Solution Approach 2:
The patent changes the control parameter from constant voltage to variable voltage with PWM modulation. By dynamically adjusting the voltage parameter through PWM duty cycle control, the system compensates for resistance variations and maintains consistent power delivery, resolving the sensitivity inconsistency issue while keeping the control system relatively simple.
2Manufacturing precision
If PWM modulation is applied to control emitter power, then consistent power delivery is achieved, but the system requires additional modulation circuitry and control complexity
Solution Approach 1:
The patent employs the emitter's inherent thermal inertia as a natural low-pass filter that attenuates the high-frequency PWM signal (800 Hz). This self-service approach allows the emitter to automatically smooth the pulsed power input without requiring additional external filtering circuitry, achieving consistent average power delivery while minimizing added system complexity.
Solution Approach 2:
The patent uses periodic PWM modulation at 800 Hz to control emitter power. This periodic action, combined with the emitter's thermal response time, creates an effective average power control mechanism. The regular pulsing pattern allows precise power delivery control while the thermal filtering effect reduces the need for additional complex circuitry.
3Power
If high frequency PWM is used for power control, then precise power regulation is achieved, but the emitter must respond fast enough to follow the modulation
Solution Approach 1:
The patent applies PWM modulation at 800 Hz, which is significantly faster than the emitter's thermal response time. This excessive modulation frequency ensures that the emitter cannot follow the rapid pulses, but instead responds to the average power level. This approach achieves precise power control through duty cycle adjustment while the emitter's inherent thermal filtering naturally smooths the high-frequency variations.
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 ensures consistent power delivery to IR emitters, reducing variability in NDIR cell sensitivity and improving measurement accuracy by filtering higher frequency secondary modulation, allowing for identical operation of IR emitters across instruments.
Implementation Method 1
The electrical power supplied to the emitter is modulated at a frequency that causes the emitter to heat and cool thereby modulating the optical IR power emitted from its surface
Implementation Method 2
an infrared source or emitter, the sample chamber or light tube, a wavelength filter, and an infrared detector
Implementation Method 3
The PWM is referred to as the secondary modulation. In one embodiment, the secondary modulation occurs at 800 Hz because it is approximately one decade passed the 11 ms temperature response time of a commercially available emitter. Therefore, the emitter will, in effect, filter this higher frequency, and it will appear that an average power is being applied to the emitter during the on-time
Data Source
AI summary
A pulse-width-modulated voltage is applied to an IR emitter during the on-time of a primary drive voltage having a frequency of about 2.5 Hz in order to control the power to a predetermined desired level. The secondary modulation is at about 800 Hz. The lower response time of the emitter will, in effect, filter the higher frequency, and it will appear that an average power is being applied to the emitter during the on-time.