The total volatile organic compounds (TVOC ) concentration in ppb is the sum of hundreds of different VOCs that are constantly changing in the interior.
TVOC can only be measured by analyzing all individual compounds, for example, by gas chromatography and mass spectrometry (GC-MS).
There is no such method to evaluate TVOC concentration using a single metal oxide semiconductor (MOS) sensor.
Sensirion used a different approach for SGP40. The output of the sensor is a number in the range of 0 to 65 535. That is proportional to the logarithm of the resistance of the sensing layer, which is proportional to the VOC concentration.
Sensirion’s VOC Algorithm running on a standalone microcontroller processes the measured values. The algorithm calculates the average value for the last 24h and assigns it VOC Index = 100, and transforms the measured values into a VOC index in the range 0 to 500. Values between 100 and 500 indicate deterioration; values between 0 and 100 inform about improved air quality.
The algorithm triggers the measurement every second. The current consumption from the 3.3V source is only 2.6 mA, even if the heater is permanently switched on.
The SGP40 features an automatic humidity compensation. All you need is to send the sgp40_measure_raw command with current RH and temperature instead of default 50% and 25°C. Sensirion recommends using humidity compensation, especially in dry environments with absolute humidity less than 5g/m3.
Source codes for the SGP40 driver and VOC Algorithm are available on Sensirion’s GitHub.
VOC Index in “Normal” Environment
VOC Index in “Dirty” Environment
VOC Index of 100 continuously adapts to any environment. Therefore, conditions that were previously interpreted as average (VOC Index = 100) are now considered as air quality improvement.
How to Start?
You can also easily connect the kit to an Arduino or Raspberry Pi using the included jumper wires.
The SEK-SVM40 can also serve as a basis for your product. Reference design (PCB + firmware) is available upon request.
SGP40 is ideal for devices where the sensor is used to trigger and regulate a device. For example, air purifiers, air conditioning, kitchen hoods and thermostats (when linked to a ventilation system). Another typical application is air quality monitoring.
If you need more information about Sensirion products, please contact our sales representative SOS electronic for your region or contact us at email@example.com; we will be happy to help you.
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