Forced-Air Heater Control Without Thermocouple Delay
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Solution Overview
Problem
Conventional heated air systems rely on thermocouples for temperature control, which are costly, prone to failure, and cause delays in temperature measurement, leading to inaccurate control and potential product damage due to high failure rates and heat exposure.
Innovation Solution
A system that controls air temperature and mass flow rate or velocity directly without a thermocouple, using a mass flow sensor, input temperature sensor, and controller to adjust air blower output and heater power based on user inputs, with options for air throttle or controllable blower control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermocouple is placed in the heated airflow for temperature measurement, then temperature control is achieved, but the thermocouple deteriorates due to intense heat exposure causing measurement delays and control inaccuracies
Solution Approach 1:
The patent removes the thermocouple from the heated airflow environment entirely. Instead of measuring temperature directly in the hot air stream, the system uses a temperature sensor located in a protected well that measures the temperature of air after it has been heated by the heating element. This extraction eliminates the thermocouple's exposure to intense heat while still enabling temperature control through feedback.
Solution Approach 2:
The patent introduces an intermediary measurement approach where the temperature sensor measures the temperature of air in a protected location (in the well) rather than directly in the heated airflow. This intermediary measurement point acts as a buffer, allowing indirect monitoring of the heating process without subjecting the sensor to damaging conditions.
2Duration of action of stationary object
If a thermocouple is placed in a well to reduce heat deterioration, then thermocouple lifespan is extended, but the distance from airflow and reduced air flow cause significant delay in temperature measurement
Solution Approach 1:
The patent extracts the temperature measurement function from the heated airflow environment and relocates it to a protected well. The temperature sensor is positioned to measure air temperature after heating occurs, eliminating the delay caused by thermocouples being exposed to intense heat while still providing timely temperature data for control purposes.
3Object-affected harmful factors
If a vane switch or air flow detector device is arranged in the airflow to detect loss or stoppage of airflow, then overheating protection is provided, but the delay time causes the heating element to be destroyed before power is switched off
Solution Approach 1:
The patent replaces mechanical airflow detection devices (vane switches) with an electrical sensing system. The temperature sensor continuously monitors air temperature and provides immediate feedback to the control system. When airflow stops, the temperature begins to rise immediately, triggering instant shutdown of the heating element through the feedback control circuit, eliminating the mechanical detection delay.
4Measurement precision
If conventional feedback control using thermocouple is used, then temperature control is achieved, but the direct component cost of the thermocouple and associated circuitry is high
Solution Approach 1:
The patent employs a temperature sensor in a protected well that is not exposed to the harsh heated airflow environment. This allows the use of less expensive, more reliable sensing elements that would otherwise be unsuitable for direct high-temperature exposure. The sensor can be a standard, cost-effective device rather than requiring expensive high-temperature rated thermocouples.
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 provides precise control over air temperature and flow variables, reducing costs, minimizing production downtime, and improving accuracy by eliminating thermocouple-related issues, ensuring consistent and accurate heated air delivery.
Implementation Method 1
a mass flow sensor for detecting a mass flow of air through the air blower
Implementation Method 2
an input temperature sensor for detecting temperature of air entering the electrical air heater
Implementation Method 3
a heater tube having a resistance or other type of electrical heating element that converts electrical energy to heat energy transferable to flowing air
Data Source
AI summary
A blower urges an airflow, at a rate according to a user-controlled flow rate command, through an electric heater and the electrical heater heats the airflow at a heater power based on a user-input temperature command, the user-input flow rate command, and a measured mass flow rate of the airflow. The heater power is calculated based on the heat energy required to heat air to the given reference temperature, at a flow rate corresponding to the measured mass flow rate. Optionally, the temperature of the air entering the electric heater is measured, and the heater power is calculated based on the heat energy required to heat air from the measured temperature to the given reference temperature, at a flow rate corresponding to the measured mass flow rate.