User Manual

ams Datasheet Page 13

[v1-06] 2019-Feb-07 Document Feedback

CCS811 − Detailed Description

Automatic Baseline Correction

The resistance R

of the sensitive layer is the output of the

sensor. However, metal oxide sensors do not give absolute

readings. The resistance R

varies from sensor to sensor

(manufacturing variation), from use-case to use-case, and over

time. To mitigate this problem, the output of the sensor is

normalized: R

is divided by R

. The value of R

is known as the

baseline. R

cannot be determined by a one-time calibration; it

is maintained on-the-fly in software. This process is known as

baseline correction. The air quality is expected to vary in a

typical environment so the minimum time over which a

baseline correction is applied is 24 hours. Automatic baseline

correction is enabled after initial device operation.

Manual Baseline Correction

There is a mechanism within CCS811 to manually save and

restore a previously saved baseline value using the BASELINE

For additional information on manual baseline control please

refer to application note ams AN000370: CCS811 Clean Air

Baseline Save and Restore.