www.sensirion.com

version 1.0 – December 2021

10/22

Figure 9 Process flow for performing a raw signal measurement with the SGP41. For enabling on-chip humidity

compensation, current relative humidity and temperature values have to be supplied as part of the measurement

command.

The SGP41 features an automatic on-chip humidity compensation of both raw signals. The feature remains disabled as long as

default values for both humidity and temperature are sent together with the sgp41_measure_raw_signals command. For

enabling the compensation, the measurement command includes two words (+ respective CRC bytes) where the first word

represents the relative humidity and the second one represents the temperature.

Figure 10 Schematic of the driver and Gas Index Algorithm implementation on a microcontroller.

For best performance in indoor-air-quality use cases, Sensirion recommends processing the (humidity-compensated) raw

signals SRAW_VOC and SRAW_NOX through Sensirion’s powerful Gas Index Algorithm. This algorithm (Figure 10)

Index (Figure 12) scale, respectively, ranging from 1 to 500 index points. In case of the VOC Index, a value of 100 refers to the

average indoor gas composition over the past 24 h. While values between 100 and 500 indicate a deterioration, values between

Algorithm is available on github (see SGP41 product page on Sensirion’s webpage). SGP41 raw signals need to be provided to

the Gas Index Algorithm at a sampling rate of 1 s.

Figure 11 Explanation of the VOC Index scale.