HVAC Flame Sensing Circuit for False Flame Detection
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Solution Overview
Problem
Existing HVAC systems face issues with accurately detecting the presence of a gas flame due to leakage current in inverters or capacitors, leading to false indications of flame presence, which can result in safety hazards and inefficient operation.
Innovation Solution
A method and system for flame detection in HVAC systems using a tank circuit, first and second comparators, and a controller to determine the output states of these components, ensuring accurate notification of flame presence by distinguishing between actual flame and component failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If flame rectification using capacitors and inverters is used to sense flame presence, then the system can detect flame in gas furnaces, but leakage current in inverters or capacitors causes false indications of flame presence
Solution Approach 1:
The patent divides the flame detection function into multiple independent detection circuits, each with its own capacitor and comparator. Instead of relying on a single detection path, the system segments the detection into parallel circuits that can be independently evaluated, reducing the impact of leakage current in any single component on overall system reliability.
Solution Approach 2:
The patent introduces comparators as intermediary components between the flame probe capacitors and the microprocessor. These comparators act as mediators that condition and compare the capacitor voltages against threshold values before presenting the final detection result, thereby filtering out false signals caused by leakage current and improving measurement precision.
2Device complexity
If conventional flame rectification circuitry is used, then the system can operate with simple components, but it cannot distinguish between actual flame and component failures
Solution Approach 1:
The patent implements feedback mechanisms where the microprocessor monitors the output states of multiple comparators and uses this information to determine both flame presence and component health. The system continuously evaluates the consistency of signals from different detection circuits and provides feedback to distinguish between actual flame conditions and component failures, thereby improving measurement precision without significantly increasing device complexity.
Solution Approach 2:
The patent designs the detection system so that the same circuit components (capacitors, comparators, microprocessor) serve multiple functions: detecting actual flame presence, identifying component failures, and providing diagnostic information. This multi-functionality allows the system to maintain relative simplicity while achieving accurate flame presence determination through the coordinated operation of universal components.
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
The solution effectively reduces false flame detection, enhancing safety and operational efficiency by accurately determining flame presence and strength, thereby preventing unnecessary furnace shutdowns and hazardous fuel accumulation.
Implementation Method 1
Flame rectification to sense presence or absence of a flame is conventional in gas furnace controls technology. When a flame is present, the second capacitor discharges to ground through the flame which acts as a poor diode connected in series with a resistor.
Data Source
AI summary
A method of determining presence of a flame in a furnace of a heating, ventilation, and air conditioning (HVAC) system. The method comprises determining, using a controller, whether a processor signal (G) is active, responsive to a determination that the processor signal (G) is active, determining, using the controller prior to assertion of a flame-test input control signal, an output state of a first comparator, responsive to a determination that the output state of the first comparator is high, determining, using the controller prior to assertion of the flame-test input control signal, an output state of a second comparator, and responsive to a determination that the output state of the second comparator is low, transmitting, using the controller, a notification that a flame is present.