Nordic Thingy:52 Gas sensor readings

Question

Hello,
We have observed fluctuation in Gas sensor readings from Nordic Thingy:52.
eCo2 and VOC readings are not at all near the calibrated sensor readings.
Tried Nordic Thingy Android app and the Raspberry Pi NodeJs application.
For Co2 sensor we have used co2 mini sensor from co2meter.com it was showing 800 ppm and Nordic Thingy:52 was showing 400 ppm.
 www.co2meter.com/.../co2mini-co2-indoor-air-quality-monitor 
 For VOC we have used Sainsmart TGS2600 sensor which was showing VOC as 10ppb and Nordic Thingy was showing VOC as 25 ppb.
Can someone explain the reason for this difference in sensor readings? 
 Regards,
Hemant

Bjørn Kvaale · Accepted Answer

I just checked up on the CCS811 gas sensor that the Nordic Thingy uses. The CCS811 datasheet says "Please be aware that the CCS811 datasheet recommends a burn-in of 48 hours and a run-in of 20 minutes (you must allow 20 minutes for the sensor to warm up and output valid data) (see datasheet pg 9 Early-Life Use (Burn-In) ). That essentially means that you should run the Nordic Thingy:52 for 48 hours before you see accurate CO2 and VOC readings. After talking with a few colleagues here at Nordic, we believe it is best if you fully charge your Nordic Thingy:52 using a usb cable (remember to keep the power switch on during charging, if the power switch is off the battery is physically disconnected from the Thingy). Then, connect the Thingy to your smartphone via the Thingy app and make sure the Thingy remains connected the entire 48 hours. If the Thingy loses connection to your smartphone, the Thingy will advertise for 180 seconds and then go into sleep mode. If the Thingy goes into sleep mode, then the CO2 and VOC sensor sleeps too... So it might be easiest if you keep your Thingy and your smartphone on you at all times during the 48 hours & make sure that both your Thingy & smartphone have enough charge (if you fully charge the Nordic Thingy, it should be able to last two days if you only enable the gas sensors). Hope that solves your problem! 
 A quick update on CO2 sensor readings with the Thingy: the Thingy does not have an "actual" CO2 sensor, but estimates the CO2 from the TVOC (Total Volatile Organic Compounds) sensor. Hence, the estimated CO2 readings can diverge from a dedicated CO2 sensor.

Nordic Thingy:52 Gas sensor readings

Top Replies