CO2 Sensor Calibration via Outside Air Ventilation
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Solution Overview
Problem
Existing CO2 sensors in air conditioning systems face challenges in accurately calibrating their reference values due to CO2 emission in occupied spaces, leading to offsets, making it difficult to match the calibrated values with atmospheric concentrations, especially in environments like homes and offices where it's hard to create a test environment for calibration.
Innovation Solution
A CO2 sensor reference value calibration apparatus that includes a person detection unit, a CO2 sensor, a clock unit, and a calibration unit, which starts introducing outside air after a person is no longer detected, sets a provisional reference value based on CO2 concentration after a waiting period, and adjusts it based on change rates to ensure accurate calibration, reducing power consumption and avoiding erroneous calibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If calibration is performed based on atmospheric CO2 concentration assumption (400 ppm), then calibration can be done in general environments, but the calibrated reference value has offset and does not accurately match atmospheric concentration
Solution Approach 1:
The system performs preliminary ventilation by introducing outside air before calibration to reduce CO2 concentration in the measurement space. This preliminary action ensures that the calibration measurement is taken in a state where CO2 concentration is close to atmospheric levels, improving accuracy while maintaining ease of operation in general environments.
Solution Approach 2:
The system uses feedback from CO2 concentration measurements to determine when calibration should be performed. By continuously monitoring CO2 concentration and comparing it with reference values, the system identifies appropriate calibration timing (when concentration is stable and close to atmospheric levels), thereby ensuring accurate calibration without requiring controlled test environments.
2Loss of time
If CO2 concentration is measured immediately after introducing outside air, then calibration can be performed quickly, but the CO2 concentration is still decreasing and calibration is erroneous
Solution Approach 1:
The system implements feedback control by continuously monitoring CO2 concentration changes after outside air introduction. It calculates the change rate and compares it with a reference change rate to determine when the concentration has stabilized. This feedback mechanism ensures calibration is performed only when reliable conditions are met, preventing erroneous calibration while managing time efficiently.
Solution Approach 2:
The system dynamically adjusts the calibration timing based on real-time CO2 concentration behavior. Instead of using a fixed time delay, it adapts the measurement timing to the actual stabilization rate of CO2 concentration in the specific environment, optimizing both speed and accuracy for each calibration event.
3Measurement precision
If CO2 concentration is continuously monitored during calibration, then accurate calibration can be achieved, but power consumption increases
Solution Approach 1:
The system employs periodic measurement instead of continuous monitoring. It measures CO2 concentration at specific intervals (first measurement after outside air introduction, second measurement after predetermined time elapses) to determine calibration timing. This periodic approach maintains calibration accuracy by capturing critical concentration changes while significantly reducing power consumption compared to continuous monitoring.
Data Source
AI summary
A controller as a CO2 sensor reference value calibration apparatus calibrates a reference value of the CO2 sensor in the following manner. Introduction of outside air is started after a person is not detected. A CO2 concentration, which is acquired when a preset first waiting time elapses, is set as a provisional reference value. The carbon dioxide concentration, which is acquired when a preset second waiting time elapses, is compared with the provisional reference value. In a case where a change rate of the carbon dioxide concentration is out of a preset allowable range, the carbon dioxide concentration is acquired when the second waiting time elapses after newly setting the acquired carbon dioxide concentration as the provisional reference value. In a case where the change rate of the carbon dioxide concentration is in the allowable range, the currently set provisional reference value is set as the reference value.