Oven Heater Power Control Using Temperature Change Rate
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Solution Overview
Problem
Standard thermal and convection ovens experience significant temperature variations within the cooking cavity, leading to uneven cooking and issues like excessive browning and darkening due to rapid energy injection, resulting in temperature deviations of more than 20 degrees Fahrenheit.
Innovation Solution
A control system for ovens that includes a temperature sensor and a controller to calculate the rate of temperature change, allowing for precise adjustment of heater power levels based on both the cavity temperature and the rate of change, using a look-up table to optimize heating element power levels for even temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the heat source is turned on continuously to maintain cavity temperature, then the temperature can be maintained, but the temperature varies significantly (more than 20 degrees Fahrenheit) leading to uneven cooking
Solution Approach 1:
The controller operates the heat source in periodic cycles, alternating between on and off states based on temperature feedback. This periodic operation allows the cavity temperature to be maintained within a tighter range by preventing overheating during continuous operation, thereby reducing temperature variations and improving cooking evenness.
Solution Approach 2:
The system uses a temperature sensor to continuously monitor cavity temperature and feeds this information back to the controller. The controller adjusts the heat source operation based on this feedback, creating a closed-loop control system that maintains more precise temperature control and reduces temperature fluctuations compared to simple on/off control.
2Productivity
If a fan is added to circulate hot air (convection oven), then cooking efficiency is improved, but the system complexity increases
Solution Approach 1:
The patent employs natural convection currents within the oven cavity to circulate hot air without requiring an active fan mechanism. The heated air naturally rises and circulates around the food, providing convection cooking benefits while avoiding the added complexity of fan motors, controls, and maintenance associated with forced convection systems.
3Loss of time
If energy is injected rapidly to heat the cavity quickly, then preheating time is reduced, but temperature control precision deteriorates
Solution Approach 1:
The controller is programmed with preliminary action strategies that anticipate temperature changes and adjust the heat source operation accordingly. By calculating future temperature trends based on current conditions, the system can prevent temperature overshoots and maintain more precise control during the rapid heating phase, achieving both quick preheating and accurate temperature maintenance.
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 solution enables timely and precise control of the oven cavity temperature, reducing thermal gradients and ensuring even cooking by maintaining the temperature within a narrow range (e.g., five degrees Fahrenheit of the steady state), preventing uneven browning and darkening in cooked products.
Implementation Method 1
a temperature sensor configured to detect a cavity temperature within the cavity
Implementation Method 2
at least one heater positioned within the cavity... adjust the power level of the heater
Data Source
AI summary
A control system for an oven includes a temperature sensor configured to detect a cavity temperature within the cavity, and a controller operatively coupled with the sensor. The oven includes a body having a cavity defined therein and at least one heater positioned within the cavity. The controller is also configured to receive a signal from the sensor, to calculate a rate of temperature change of the cavity temperature, and to adjust a power level of the heater based on the cavity temperature and the calculated rate of temperature change.