Pyranometer Optical Filter for Flat Spectral Response
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Solution Overview
Problem
Pyranometers with micro thermopile-based sensors and optical diffusors 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.
Innovation Solution
Incorporating 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, thereby achieving a spectrally flat response with a maximum deviation of ±3% from the mean value in the wavelength range of 350 nm to 1500 nm.
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 diffusor and the thermopile sensor. This filter compensates for the spectral variations introduced by the diffusor, allowing the system to maintain both a wide field of view and accurate spectral response measurements.
Solution Approach 2:
The optical filter modifies the spectral composition of radiation by changing the transmission characteristics across different wavelengths. This parameter change in the optical path corrects the spectral response deviations caused by the diffusor's wavelength-dependent scattering.
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 compensates for the spectral limitations imposed by the glass dome by introducing complementary transmission characteristics. This allows the system to maintain accurate measurements across the full solar spectrum while preserving the protective function of the dome.
3Measurement precision
If a black coated thermopile sensor is used to absorb all radiation, then the spectral response becomes substantially flat, but the response time is slower and thermal behavior is less stable
Solution Approach 1:
The system combines a micro thermopile sensor (for fast response) with an optical filter (for spectral flatness) as separate functional elements. This segmentation allows each component to optimize its strength: the micro sensor provides speed while the filter ensures spectral accuracy.
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 enhances measurement accuracy by stabilizing the spectral response under varying atmospheric conditions, ensuring a spectrally flat response and improving measurement precision.
Implementation Method 1
at least one optical filter (4) arranged in an optical path of the radiation in front of the receiving surface (22) of the thermopile-based sensor (2) so as to modify the spectral composition of the radiation measured by the thermopile-based sensor (2)
Implementation Method 2
a diffusor (3) configured to diffuse and transmit the light incident thereon, toward the receiving surface of the radiation sensor
Implementation Method 3
the irradiance is measured by a sensor based on thermopiles... the black coated thermopile sensor is capable of substantially absorbing (almost) all ration (e.g. solar radiation)
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. The pyranometer further comprises at least one collimator configured to collimate the radiation impinging on the receiving surface of the thermopile-based sensor.