ACDL function is suitable for residential indoor airquality monitoring. ACDL should not be used for agricultural application such as green house or some places which have to keep high CO2 concentration level. In this case, users have to do 10' MCDL instead of ACDL.
2. Why use ACDL
Virtually all gas sensors are subject to some sort of drift. The degree of drift is partially dependent on the use of quality components and good design. But even with good components and excellent design, a small amount of drift can still occur in the sensor that may ultimately result in the need for a sensor to be recalibrated. Sensor design and components have to do with drift. The primary contributor to sensor drift is the normal and unavoidable aging of the infrared light source within the sensor. The natural drift of the sensor is very gradual at a few ppm per month with the greatest drift occurring in the first few months of operation. This drift can be up or down. ACDL is designed to correct all sensor drift, including aging of the light source.
3. How ACDL works
Outside levels of CO2 are generally very low at around 380 to 420 ppm. Inside buildings people are the major source of CO2. When a building is unoccupied for 4 to 8 hours, CO2 levels will tend to drop to outside levels. For Air Quality Monitoring Application, Sensor remembers the lowest CO2 concentration during the fixed period and assumes this low point is at outside levels. The sensor performs a statistical analysis to see if there have been any small changes in the sensor reading that could be attributable to sensor drift and the correction factor is changed adjust for this drift. As the picture 1 below shows, Sensor #1~#5 with drift became accurate and kept stable through 1st ACDL once in 2 days in houses and offices. It has base on the statistically adjustment.
4. Period of ACDL
ACDL period is 7days or 30days depending on model. First Calibration is done once in 2days or 3days to make the sensor more accurate by compensating the physical effect during delivery or elapsed time effect on storage.