Pyranometer Optical Filter for Flat Spectral Response
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Solution Overview
Problem
Pyranometers with micro thermopile-based sensors and optical diffusers experience significant variations in spectral response with wavelength, leading to reduced measurement accuracy due to the combined spectral responses of the thermopile-based sensor and diffusor, which are not adequately compensated by existing technologies.
Innovation Solution
Incorporation of an optical filter in the optical path of the pyranometer to modify the spectral composition of radiation measured by the thermopile-based sensor, compensating for the spectral selectivity of the thermopile-based sensor, diffusor, and dome, ensuring a substantially invariant spectral response across varying atmospheric conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a micro thermopile-based sensor is combined with an optical diffusor to achieve the required field of view, then the field of view is improved, but the spectral response varies considerably with wavelength
Solution Approach 1:
An optical filter is introduced as an intermediary element between the optical diffusor and the micro thermopile-based sensor. This filter compensates for the wavelength-dependent transmission characteristics of the diffusor by introducing opposite spectral variations, thereby flattening the overall spectral response while preserving the 180° field of view provided by the diffusor.
Solution Approach 2:
The spectral transmission parameters of the optical system are modified by inserting the optical filter. The filter's transmission characteristics are specifically designed to counterbalance the wavelength-dependent behavior of the diffusor, changing the overall spectral response from highly variable to substantially flat across the solar spectrum.
2Reliability
If a glass dome is used to protect the thermopile-based sensor from the external environment, then the protection is improved, but the spectral response is limited from about 300 to about 2800 nm
Solution Approach 1:
The optical filter acts as an intermediary that compensates for the spectral cutoff characteristics of the glass dome. By introducing opposite spectral variations through the filter, the system maintains the protective function of the dome while achieving a substantially flat spectral response across the desired measurement range.
3Measurement precision
If a black coated thermopile sensor is used to absorb all radiation, then the spectral response is substantially flat, but the response time is slower and thermal behavior is less stable
Solution Approach 1:
The invention merges the advantages of different sensor types by combining a micro thermopile-based sensor (providing fast response and stable thermal behavior) with an optical filter (providing spectral flatness). This combination achieves both fast response time and substantially flat spectral response, overcoming the limitations of pure black coated thermopile sensors.
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 optical filter achieves a spectrally flat response with a maximum deviation of ±3% from the mean value in the wavelength range of 350 nm to 1500 nm, enhancing measurement accuracy and stability under different solar and atmospheric conditions.
Implementation Method 1
at least one optical filter arranged in an optical path of the radiation in front of the receiving surface of the thermopile-based sensor so as to modify the spectral composition of the radiation measured by the thermopile-based sensor
Implementation Method 2
The diffusor is an optical element (optical diffusor) that is configured to diffuse and transmit the light incident thereon, toward the receiving surface of the radiation sensor
Implementation Method 3
The black coated thermopile sensor is capable of substantially absorbing (almost) all ration (e.g. solar radiation)
Implementation Method 4
the irradiance is measured by a sensor based on thermopiles
Data Source
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AI summary
The claimed invention relates to a pyranometer comprising: a dome, a thermopile-based sensor comprising a receiving surface, a diffusor configured to diffuse radiation external to the pyranometer and passing through the dome, toward the receiving surface of thermopile-based sensor, and at least one optical filter arranged in an optical path of the radiation in front of the receiving surface of the thermopile-based sensor so as to modify the spectral composition of the radiation measured by the thermopile-based sensor. According to the claimed invention, a distance of an optical path between the diffusor and the thermopile-based sensor is set such that the radiation diffused by the diffusor on the receiving surface of the thermopile-based sensor has a substantially cone shape.