Flame Sensing System Leakage Current Detection
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Solution Overview
Problem
Existing flame sensors face challenges in detecting weak hydrocarbon flames due to high series resistance, requiring sensitive devices or high AC excitation voltages, which increase costs and vulnerability to leakage, especially when using standard line voltage.
Innovation Solution
The proposed flame sensing system utilizes the leakage resistor of the flame model for diagnostics and detection, employing a floating reference point and AC power supply to differentiate between flame and leakage currents, allowing for low-cost implementation without excitation signals, using resistors and diodes to form a full-wave rectifier and voltage divider circuit for efficient flame detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high AC excitation voltage is used to detect weak flames, then flame detection sensitivity is improved, but system cost and vulnerability to leakage increase
Solution Approach 1:
The patent changes the detection parameter from measuring DC offset voltage (which requires high excitation voltage) to measuring current through the leakage resistor. This parameter change allows detection of weak flames using standard line voltage without increasing leakage vulnerability, while maintaining high detection sensitivity through the relationship I_leakage = V_line / R_leakage.
Solution Approach 2:
The patent introduces the leakage resistor as an intermediary element that converts the flame's electrical properties into a measurable current signal. By measuring the current through this intermediary resistor rather than directly measuring voltage offsets, the system achieves high sensitivity without requiring high excitation voltages that increase leakage risks.
2Ease of manufacture
If standard line voltage is used for flame detection, then system cost is reduced, but detection speed and reliability deteriorate due to high ohm filter resistors
Solution Approach 1:
The patent extracts the detection function from the high-ohm filter resistor path and places it in the leakage resistor path. By taking out the measurement function from the voltage-based detection path (which requires high-ohm resistors that slow detection) and placing it in the current-based leakage path, the system achieves fast detection speed while using standard line voltage and maintaining low cost.
Solution Approach 2:
The patent substitutes the voltage-based detection mechanism (which relies on high-ohm resistors and slow RC time constants) with a current-based detection mechanism. This substitution replaces the slow voltage measurement system with a faster current measurement system, improving detection speed while maintaining compatibility with standard line voltage and low system cost.
3Measurement precision
If sensitive detection devices are used to detect weak flames, then flame detection capability is improved, but system cost increases
Solution Approach 1:
The patent uses standard, inexpensive microcontroller ADC (analog-to-digital converter) capabilities to perform the detection function that would otherwise require expensive specialized sensitive detection devices. By utilizing the readily available ADC functionality in standard microcontrollers and combining it with the current measurement approach through the leakage resistor, the system achieves weak flame detection capability at low cost.
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 reliable detection of weak flames with reduced system cost, improved sensitivity, and enhanced diagnostic capabilities, while minimizing leakage-related issues and potential short circuits, allowing for accurate flame presence and strength determination.
Implementation Method 1
Many flame detectors rely on the flame diode behavior. When a flame exists, because of the flame diode effect, a DC offset voltage may appear.
Implementation Method 2
The present invention may provide a solution to the noted problems by utilizing the leakage resistor of the flame model rather than the diode. Leakage may be used for diagnostic purposes.
Implementation Method 3
The anodes of diodes 16 and 18 may be connected together and to a circuit or control ground 12. Diodes 15, 16, 17 and 18 may form a full-wave rectifier 19.
Data Source
AI summary
A low cost flame sensing system having at last one floating point. For instance, the system may have two grounds. There may be a flame sensing rod for detecting a flame which has a model circuit which appears upon the existence of the flame proximate to the sensing rod. The sensing rod may function without an explicit or dedicated excitation source connected to it. There may be diagnostics in the system for detecting leakage or shorts of the sensing rod to ground. Also, the system may have AC grounding phase detection.