Dual Thermopile Sensor for Microwave Oven Thermal Shock Compensation
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Solution Overview
Problem
Existing non-contact temperature sensors in microwave ovens face inaccuracies due to the 'thermal shock' effect caused by quickly rising air temperatures, and they require a narrow field of view for precise temperature measurement.
Innovation Solution
A temperature sensing device with dual thermopile sensors is used, where one thermopile sensor measures the object's temperature and another compensates for the thermal shock effect by measuring the package cap's thermal radiation. The device incorporates a reflective mirror for a narrow field of view and a Fresnel lens for improved temperature resolution, along with a visible LED illumination for user guidance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a normal thermopile sensor is used for temperature sensing in microwave oven, then the device structure is simple, but the temperature measurement accuracy deteriorates due to thermal shock effect from quickly rising air temperature
Solution Approach 1:
The sensor is segmented into two independent thermopile sensors: one for measuring object temperature and another for measuring package cap temperature. This segmentation allows separate measurement of the two thermal sources (object radiation and package cap radiation), enabling compensation of thermal shock effects while maintaining relatively simple device structure.
Solution Approach 2:
The second thermopile sensor acts as an intermediary that measures the package cap temperature to serve as a reference for compensation. By using the package cap temperature measurement as an intermediary step, the system can calculate and remove the thermal shock contribution from the first sensor's reading, improving accuracy without requiring complex direct measurement methods.
2Ease of operation
If the field of view is widened to facilitate object placement in microwave oven, then the ease of operation is improved, but the temperature measurement precision deteriorates due to inclusion of background radiation
Solution Approach 1:
A spherical mirror is used to define and control the field of view geometry. The curved reflective surface precisely directs thermal radiation from the object onto the thermopile sensor while maintaining a well-defined, relatively narrow field of view angle (approximately 15 degrees), preventing excessive background radiation inclusion while still facilitating object placement.
3Measurement precision
If dual thermopile sensors are used for thermal shock compensation, then the temperature measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
Both thermopile sensors are integrated into a single unified package cap structure with shared optical components (spherical mirror, window). This merging approach allows dual sensing functionality while minimizing the increase in device complexity through shared structural elements and compact arrangement.
Solution Approach 2:
The package cap structure serves multiple functions: it houses both thermopile sensors, provides the spherical mirror for field of view control, and acts as the measurement target for the second sensor. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity despite adding thermal shock compensation capability.
4Measurement precision
If a narrow field of view is used for precise temperature measurement, then the measurement precision is improved, but the ease of operation deteriorates due to difficulty in locating the sensed area
Solution Approach 1:
A visible light source is introduced to illuminate the object and create a visible indication of the sensed area through the window. This allows users to visually locate and identify the precise measurement zone, making it easier to position objects correctly while maintaining the narrow field of view required for accurate temperature measurement.
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 accurate temperature measurements by compensating for thermal shock and offering a narrow field of view, ensuring precise surface temperature measurement of objects within the microwave oven, while also aiding users in correctly positioning the object.
Implementation Method 1
a first reflective module...including a first mirror chamber with a field of view (FOV), and focusing the thermal radiation of an object under measured to a first image plane in the first mirror chamber
Implementation Method 2
The first window cover is disposed on the first reflective module, and allows a selected band of the thermal radiation of the measured object to pass through
Implementation Method 3
The Fresnel lens covers the opening hole, and re-images the first image plane to a second image plane
Implementation Method 4
The active thermopile sensing element is located corresponding to the second image plane to sense the temperature data
Implementation Method 5
The dummy sensing element is located corresponding to the second window and senses the thermal radiation from package cap
Data Source
AI summary
A temperature sensing device includes a substrate, a first reflective module, a first window cover, and a dual thermopile sensor. The first reflective module is disposed on the substrate, including a first mirror chamber with a narrow field of view (FOV), and the first reflective module focuses a thermal radiation from measured object to a first image plane in the first mirror chamber. The first window cover is disposed on the first reflective module, and the first window cover allows a selected band of the thermal radiation to pass through. The dual thermopile sensor is disposed on the substrate and located in the first mirror chamber, and the dual thermopile sensor senses a temperature data from the first image plane. Additional second reflective module, LED source plus pin hole with same FOV of dual thermopile sensor can illuminate the measured object for ease of placement of object to be heated.