All carbon dioxide sensors require calibration to maintain accuracy. This can be achieved by calibrating the sensor to a known gas concentration or using the automatic baseline calibration (ABC) method, each with its own advantages and disadvantages.
Most of our CO2 products utilize non-dispersive infrared (NDIR) carbon dioxide sensors. These sensors measure CO2 levels using an infrared light source and detector. Over time, both the light source and detector degrade, leading to slightly lower CO2 readings, a phenomenon known as "drift" in the industry.
Sensor calibration addresses this drift by exposing the sensor to one or more known gases with specific CO2 concentrations. The difference between the new readings and the original factory-calibrated readings is recorded in EPROM memory. This "offset" is then automatically applied to all subsequent readings, ensuring the sensor remains accurate over time.
Zero Point CO2 Sensor Calibration:
Zero point calibration involves exposing the sensor to 100% nitrogen, which signifies the absence of CO2. This process updates the sensor's "zero point" in its internal memory, compensating for drift over time as the sensor ages. While this method effectively removes deviations from the sensor's zero point, it's not a complete factory calibration, nece ssitating additional steps.
Span CO2 Sensor Calibration:
Also known as 2-point calibration, this procedure is conducted at the lowest and highest gas levels for which the sensor is rated. It typically involves exposing the sensor to 0 ppm CO2 using 100% nitrogen and a calibration gas mixture containing specific concentrations of CO2. This calibration is performed at the factory immediately after sensor manufacturing. The sensor's response to both the absence and highest levels of CO2 is recorded in its memory, ensuring accurate readings across its range.
Once the two calibration points are established, a linear response to gas concentration between these points is assumed, forming a calibration curve. Ideally, gas level readings between the two calibration points should align with this curve. However, some sensors may not exhibit a precise linear response, leading manufacturers to perform 4 or more point calibrations to create a curved response line.
Once the calibration curve is determined, the sensor's memory performs calculations to compute concentrations for every gas level. This calculation could involve a simple slope-intercept for a straight line or a more complex formula, such as the derivative for a curved response.
During span calibration, the zero point adjustment is also stored in the sensor's memory. This adjustment reflects what the sensor reads when exposed to zero calibration gas. The difference between this reading and the actual zero point is saved as an offset, which is applied to all future readings. For instance, if a CO2 sensor reads 10 ppm when exposed to 0 ppm CO2, an offset of "-10 ppm" is stored and applied.
While the terms are often used interchangeably, calibration differs from zero point adjustment. While zero point adjustment enhances sensor accuracy, span calibration is necessary to align the sensor's response curve with a known target gas.
While span calibration is routinely performed at the factory, for cases requiring precise accuracy, it may be conducted in the field or by returning the sensor to the manufacturer.
The advantage of performing span or 2-point calibration lies in its ability to closely match the original factory calibration.
3-Point CO2 Sensor Calibration:
Calibration involves setting points at the lowest, midpoint, and highest gas levels applicable to the product. For CO2 safety alarms, this typically includes calibration at 0.0% CO2, default alarm 1 level, and default alarm 2 level.
CO2 Sensor Calibration Using Fresh Air:
In cases where maximum accuracy is not critical but cost and simplicity are prioritized, some CO2 sensors can be calibrated using fresh air. Instead of calibrating at 0 ppm CO2 using 100% nitrogen, calibration occurs at 400 ppm CO2, representing the average outdoor air level. When calibrated in fresh air, the sensor's software assumes the stable reading as 400 ppm CO2 and stores the difference between this reading and factory calibration as an offset value until the next calibration. This method is ideal for portable sensors or CO2 monitors used for air quality measurement, which can easily be taken outdoors for calibration.
Automatic Background Calibration:
Early CO2 sensors used in buildings faced challenges in calibration, especially wall-mounted units. To address this, Senseair in Sweden developed Automatic Baseline Calibration (ABC). ABC utilizes the principle that in indoor environments, CO2 levels should eventually return to around 400 ppm, matching outdoor air. By storing the lowest CO2 readings taken over time in memory, an offset to 400 ppm can be calculated and applied to actual CO2 readings. ABC calibration offers the advantage of self-calibration over the sensor's lifespan. However, it may not function effectively if the sensor never detects 400 ppm fresh air, such as in continuous occupancy environments like livestock facilities or 24/7 staffed office buildings. ABC calibration is best suited for applications where fresh air CO2 levels can be recorded periodically. Most sensors and products offer the flexibility to enable or disable ABC calibration based on application needs.
Most of our CO2 products utilize non-dispersive infrared (NDIR) carbon dioxide sensors. These sensors measure CO2 levels using an infrared light source and detector. Over time, both the light source and detector degrade, leading to slightly lower CO2 readings, a phenomenon known as "drift" in the industry.
Sensor calibration addresses this drift by exposing the sensor to one or more known gases with specific CO2 concentrations. The difference between the new readings and the original factory-calibrated readings is recorded in EPROM memory. This "offset" is then automatically applied to all subsequent readings, ensuring the sensor remains accurate over time.
Zero Point CO2 Sensor Calibration:
Zero point calibration involves exposing the sensor to 100% nitrogen, which signifies the absence of CO2. This process updates the sensor's "zero point" in its internal memory, compensating for drift over time as the sensor ages. While this method effectively removes deviations from the sensor's zero point, it's not a complete factory calibration, nece ssitating additional steps.
Span CO2 Sensor Calibration:
Also known as 2-point calibration, this procedure is conducted at the lowest and highest gas levels for which the sensor is rated. It typically involves exposing the sensor to 0 ppm CO2 using 100% nitrogen and a calibration gas mixture containing specific concentrations of CO2. This calibration is performed at the factory immediately after sensor manufacturing. The sensor's response to both the absence and highest levels of CO2 is recorded in its memory, ensuring accurate readings across its range.
Once the two calibration points are established, a linear response to gas concentration between these points is assumed, forming a calibration curve. Ideally, gas level readings between the two calibration points should align with this curve. However, some sensors may not exhibit a precise linear response, leading manufacturers to perform 4 or more point calibrations to create a curved response line.
Once the calibration curve is determined, the sensor's memory performs calculations to compute concentrations for every gas level. This calculation could involve a simple slope-intercept for a straight line or a more complex formula, such as the derivative for a curved response.
During span calibration, the zero point adjustment is also stored in the sensor's memory. This adjustment reflects what the sensor reads when exposed to zero calibration gas. The difference between this reading and the actual zero point is saved as an offset, which is applied to all future readings. For instance, if a CO2 sensor reads 10 ppm when exposed to 0 ppm CO2, an offset of "-10 ppm" is stored and applied.
While the terms are often used interchangeably, calibration differs from zero point adjustment. While zero point adjustment enhances sensor accuracy, span calibration is necessary to align the sensor's response curve with a known target gas.
While span calibration is routinely performed at the factory, for cases requiring precise accuracy, it may be conducted in the field or by returning the sensor to the manufacturer.
The advantage of performing span or 2-point calibration lies in its ability to closely match the original factory calibration.
3-Point CO2 Sensor Calibration:
Calibration involves setting points at the lowest, midpoint, and highest gas levels applicable to the product. For CO2 safety alarms, this typically includes calibration at 0.0% CO2, default alarm 1 level, and default alarm 2 level.
CO2 Sensor Calibration Using Fresh Air:
In cases where maximum accuracy is not critical but cost and simplicity are prioritized, some CO2 sensors can be calibrated using fresh air. Instead of calibrating at 0 ppm CO2 using 100% nitrogen, calibration occurs at 400 ppm CO2, representing the average outdoor air level. When calibrated in fresh air, the sensor's software assumes the stable reading as 400 ppm CO2 and stores the difference between this reading and factory calibration as an offset value until the next calibration. This method is ideal for portable sensors or CO2 monitors used for air quality measurement, which can easily be taken outdoors for calibration.
Automatic Background Calibration:
Early CO2 sensors used in buildings faced challenges in calibration, especially wall-mounted units. To address this, Senseair in Sweden developed Automatic Baseline Calibration (ABC). ABC utilizes the principle that in indoor environments, CO2 levels should eventually return to around 400 ppm, matching outdoor air. By storing the lowest CO2 readings taken over time in memory, an offset to 400 ppm can be calculated and applied to actual CO2 readings. ABC calibration offers the advantage of self-calibration over the sensor's lifespan. However, it may not function effectively if the sensor never detects 400 ppm fresh air, such as in continuous occupancy environments like livestock facilities or 24/7 staffed office buildings. ABC calibration is best suited for applications where fresh air CO2 levels can be recorded periodically. Most sensors and products offer the flexibility to enable or disable ABC calibration based on application needs.
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