Dynamic DC Biasing Circuit for Flame Sensing Leakage Compensation
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Solution Overview
Problem
DC leakage in flame sensing circuits of residential combustion systems poses challenges due to high impedance resistors used for low-level flame current measurement, exacerbated by modern electronic technology's demand for smaller components, leading to inaccurate flame signal detection and increased sensitivity to leakage.
Innovation Solution
The implementation of a dynamic DC biasing circuit using pulse width modulation (PWM) to control the DC bias level, adjusting the equivalent flame loading resistance with 'tri-state PWM', and employing a 'T network' to replace single capacitors and cancel out leakage effects, thereby reducing leakage sensitivity and improving flame sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high resistance resistors are used for flame current measurement, then measurement precision is improved, but leakage sensitivity increases
Solution Approach 1:
The patent applies dynamic DC biasing where the bias voltage is continuously adjusted based on measured leakage current. The system dynamically adapts the bias level to compensate for leakage effects, transforming a static high-impedance measurement system into a dynamic one that actively counteracts leakage. This resolves the contradiction by making the measurement system adaptive rather than fixed, allowing high precision while compensating for leakage in real-time.
Solution Approach 2:
The patent implements a feedback mechanism where leakage current is measured and used to adjust the DC bias voltage. The system continuously monitors leakage and feeds this information back to modify the biasing, creating a closed-loop control system. This feedback approach allows the system to maintain measurement precision despite varying leakage conditions, directly resolving the technical contradiction between precision and leakage sensitivity.
2Volume of moving object
If smaller components are used to reduce space, then device complexity is reduced, but leakage sensitivity increases
Solution Approach 1:
The patent enables the measurement circuit to self-compensate for leakage effects by automatically adjusting its own bias voltage based on measured leakage current. The system serves itself by using its measurement capability to correct its own leakage vulnerability, eliminating the need for larger components to prevent leakage. This self-service approach allows compact design while maintaining measurement accuracy despite increased leakage susceptibility of smaller components.
3Adaptability or versatility
If DC bias level is increased to improve measurement range, then dynamic range is improved, but leakage current increases
Solution Approach 1:
The patent transforms the static DC bias into a dynamic parameter that automatically adjusts based on leakage conditions. The bias voltage is no longer fixed but varies continuously to maintain optimal measurement conditions. This dynamic approach allows the system to achieve wide dynamic range while preventing excessive leakage current, as the bias adapts rather than remaining constantly high.
Solution Approach 2:
The patent changes the bias voltage parameter dynamically based on measured leakage current. By adjusting this key parameter in response to leakage conditions, the system optimizes the trade-off between dynamic range and leakage current. The bias level becomes a variable parameter rather than a fixed value, allowing the system to achieve adaptability without proportionally increasing leakage.
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 enhances the dynamic range of the measuring circuit, reduces leakage sensitivity, and maintains a constant A/D input voltage, leading to more accurate flame current measurement and compensation for leakage, thereby improving the reliability of flame sensing systems.
Implementation Method 1
One approach may use a pulse width modulation (PWM) output from a microprocessor input/output (I/O) pin to control the DC bias level for an A/D input. The DC bias level may be dynamically modified during run time by changing the duty cycle of the PWM signal.
Implementation Method 2
Capacitor 15 may be a DC blocking device. The other terminal of capacitor 15 may be connected to one end of a resistor 16.
Implementation Method 3
the flame current may be converted to a flame voltage by using a flame load resistor or capacitor. The flame current may be measured by measuring a voltage potential change generated by the flame current.
Data Source
AI summary
A system for adjusting a bias voltage of a flame sensing system. The system may use pulse width modulation to adjust the bias voltage. The system may have a flame sensing rod that conveys an electrical equivalent circuit of a flame presence to a detector via low pass filter. An excitation voltage may be conveyed via a DC blocking mechanism to the sensing rod. A pulse width modulation signal may be conveyed via a bias resistor to a node of the low pass filter and the detector. The input of an A/D converter may be that of the detector for flame signals. Also, leakages between the node of the A/D converter connection and the voltage source and/or ground may be detected and compensated. Further, leakage of the DC blocking mechanism may be minimized.