Capnoscope Calibration Using Colorimetric Reference
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Solution Overview
Problem
Capnoscope devices require calibration gases to accurately measure CO2 concentrations, which is impractical in real-life situations such as monitoring CO2 levels in expired breath during emergencies or anesthesia, where access to calibration gases is limited.
Innovation Solution
A capnoscope assembly with a calibration member having a predetermined calibration color, allowing the device to calibrate without calibration gases by determining and storing control signal values to detect the calibration color, and using these values to establish a CO2 concentration relationship for accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration gases are used to calibrate the capnoscope, then measurement precision is improved, but device complexity and ease of operation deteriorate due to the need for gas handling and availability
Solution Approach 1:
The patent uses a calibration member with a calibration surface that has a predetermined calibration color corresponding to the color of an ideal reference indicator at a predefined CO2 concentration. This copy of the reference indicator's appearance allows calibration without actual calibration gases, replacing the need for physical gas handling with a visual reference that can be captured by the camera.
Solution Approach 2:
The patent changes the calibration approach from using physical calibration gases with specific CO2 concentrations to using a visual calibration surface with a predetermined color. The processing unit adjusts light parameters and determines control signal values based on the captured calibration color, transforming the calibration parameter from gas concentration to color detection.
2Measurement precision
If calibration gases are required for calibration, then measurement precision is improved, but loss of time increases due to the need to obtain and handle calibration gases
Solution Approach 1:
The calibration surface is pre-prepared with a predetermined calibration color that corresponds to the ideal reference indicator appearance at a predefined CO2 concentration. This preliminary preparation eliminates the need for time-consuming gas handling during calibration, as the reference is already in place and ready for immediate use.
3Ease of operation
If a calibration member with predetermined calibration color is used, then ease of operation is improved by eliminating calibration gases, but device complexity increases due to additional calibration components
Solution Approach 1:
The calibration member is integrated into the existing capnoscope assembly, with the calibration surface positioned to be captured by the same camera that measures the indicator. The processing unit uses the same image capture and color analysis mechanisms for both calibration and measurement, merging the calibration function with the existing measurement system rather than adding separate complex calibration equipment.
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
Enables accurate and reliable CO2 measurements without the need for calibration gases, ensuring the capnoscope can function effectively in various real-life scenarios by calibrating based on a reference color and adjusting light parameters for precise CO2 concentration determination.
Implementation Method 1
a colorimetric indicator (10) adapted to exhibit a colour change in response to exposure to carbon dioxide gas
Implementation Method 2
an illumination arrangement (4) comprising a light emitting diode (LED) arranged to illuminate the indicator surface
Data Source
Figure 1~3
Figure 4
AI summary
A capnoscope assembly for measuring carbon dioxide (CO2) concentration, comprising: -a detection unit (2) comprising an illumination arrangement (4) and a camera (6) configured to capture colours of an indicator surface illuminated by light emitted by said illumination arrangement, -an indicator holder (8) configured to hold a colorimetric indicator (10) in front of the detection unit (2), -a processing unit (12) configured to control light parameters, e.g. the colour and intensity, of the light emitted by the illumination arrangement (4) by generating control signals (14). A calibration member (16) is provided having a predetermined calibration colour corresponding to the colour of an ideal reference colorimetric indicator when subjected to a predefined CO2 concentration that is not zero. The processing unit (12) is configured to adjust the light parameters such that the camera (6) detects the predetermined calibration colour. A calibration procedure is then applied that comprises: -arranging a colorimetric indicator (10) to be used in said indicator holder (8), -measuring the colour of the colorimetric indicator surface when illuminated by emitted light being generated by using said determined calibrated control signal values, when no CO2 is present, and storing said measured colour, as a zero CO2 colour value, and -determining a CO2 concentration relationship based upon said measured zero CO2 colour value, wherein said processing unit (12) is configured to apply said CO2 concentration relationship during CO2 concentration measurements provided that the determined calibrated control signal values are applied when emitting light.