Circuit Interrupter Temperature Trip Using Diode Sensor

The patent replaces the mechanical bimetallic strip system with an electronic temperature sensing system using a thermistor and comparator circuit. This substitution eliminates the calibration difficulties inherent in mechanical systems while maintaining reliable temperature-based fault detection. The electronic system provides precise trip temperature control through circuit design rather than manual mechanical adjustment.

The patent changes the sensing parameter from mechanical strip bending to electrical resistance changes in a thermistor. The thermistor's resistance varies predictably with temperature, allowing for precise trip point determination through circuit design. This parameter change enables consistent manufacturing without individual calibration, as the trip temperature is determined by fixed circuit components rather than variable mechanical properties.

The patent replaces the complex mechanical calibration procedure with a simplified electronic circuit approach. The trip temperature is determined by the characteristics of the thermistor and the reference voltage in the comparator circuit, eliminating the need for manual adjustment and testing of each device. This substitution dramatically reduces device complexity related to calibration while maintaining reliable temperature-based tripping.

The electronic temperature sensing system is inherently self-calibrating through the fixed characteristics of the thermistor and reference circuit components. Each device operates at its designed trip temperature without requiring external calibration procedures, as the trip point is determined by the intrinsic properties of the electronic components rather than adjustable mechanical elements.

The patent implements periodic sampling of the thermistor voltage rather than continuous monitoring. The comparator circuit checks the temperature condition at specific intervals during the AC cycle, determining trip status based on the voltage across the thermistor at these discrete moments. This periodic action maintains measurement precision while dramatically reducing power consumption compared to continuous electronic monitoring.

The patent uses the existing voltage waveform in the circuit to sense temperature, rather than introducing a separate powered sensing system. The thermistor's voltage drop, which naturally occurs as part of the circuit operation, is used as the sensing signal. This approach copies the temperature information from the existing electrical parameters, eliminating the need for additional power-consuming sensing electronics.

The patent employs inexpensive, readily available electronic components such as thermistors, resistors, and comparators to achieve precise temperature detection. These standard electronic parts are far cheaper than specialized temperature sensing systems while providing sufficient accuracy for circuit protection applications. The use of common components maintains ease of manufacture and reduces device cost.

The thermistor serves multiple functions: it acts as both a current-carrying conductor and a temperature sensor. By utilizing the voltage drop across this single component, the circuit achieves temperature detection without requiring separate dedicated sensing elements. This multi-functionality reduces component count and overall device cost while maintaining measurement precision.