Heater Wire Safety Circuit with Dual Sensor Conductors
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Solution Overview
Problem
Conventional electric heating pads and blankets face challenges in effectively detecting and addressing hot spots due to abnormal use conditions, such as bunching or folding, which can lead to overheating, and existing safety systems are costly and complex, requiring multiple components that reduce reliability and increase the time between failures.
Innovation Solution
A heater wire safety circuit with a low resistive conductor and a low melt insulate layer between the heater conductor, where diodes are used to short out the higher resistance heater conductor upon overheating, and a dual heater wire circuit with temperature sensor conductors connected to a microprocessor for temperature control and fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional safety systems with multiple components are used, then safety coverage is improved, but reliability decreases and time between failures reduces
Solution Approach 1:
The patent combines the heater conductor and sensor conductor into a single wire assembly, with the sensor conductor wrapped around the heater conductor. This integration reduces the number of separate components and connections required, thereby improving reliability while maintaining safety functionality. The low melt insulate layer between the conductors further integrates the safety mechanism directly into the wire structure.
Solution Approach 2:
The heater wire assembly serves multiple functions: the heater conductor provides heating, the sensor conductor monitors temperature through resistance changes, and the low melt insulate layer provides both insulation and hot spot detection. This multi-functionality reduces the need for separate safety components, improving reliability while maintaining comprehensive safety coverage.
2Measurement precision
If sophisticated electronic control circuits are used, then temperature control precision is improved, but cost increases
Solution Approach 1:
The sensor conductor utilizes the inherent positive temperature coefficient of copper to automatically sense temperature changes through resistance variations. This self-service approach eliminates the need for separate temperature sensing elements or complex electronic control circuits, reducing manufacturing cost while maintaining adequate temperature monitoring precision for safety purposes.
3Difficulty of detecting and measuring
If low melt insulate layer is used between conductors, then hot spot detection is improved, but manufacturing complexity increases
Solution Approach 1:
The low melt insulate layer utilizes its phase transition from solid to liquid at a specific temperature to detect hot spots. When excessive heat is generated, the insulate layer melts and causes the sensor conductor to contact the heater conductor, creating a detectable electrical connection change. This passive phase-transition-based detection method improves hot spot detection capability while avoiding complex active sensing systems.
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 provides a simple, cost-effective system for detecting and preventing overheating by passively interrupting power to the heater wire, reducing the risk of hot spots and improving reliability by using fewer components, thus enhancing safety and extending the time between failures.
Implementation Method 1
the low melt insulate layer will melt at that hot spot so that the heater conductor and low resistive conductor contact each other
Implementation Method 2
a heater conductor to provide heat to the electric blanket or heating pad
Data Source
AI summary
A dual heater wire circuit for use with a heating pad or electric blanket includes two independent heater wire circuits. Each heater wire circuit includes a heater wire and a temperature sensor conductor. The temperature sensor conductor of each heater wire circuit is connected to a capacitor, or to a resistor, to define with the capacitor or resistor a voltage divider circuit. The juncture between the sensor conductors and either the capacitor or the resistor is provided to the input of a microprocessor. The electrical resistance of the temperature sensor conductors varies with temperature. The signal provided to the microprocessor from the voltage dividers formed between the sensor conductors of the heater wires and either the capacitor or resistor will vary in phase or voltage relative to the temperature of the heater wires. The microprocessor controls the duty cycle of the power signal provided to the heater wires.