Version 1.1
Stäfa, March 2021

SGP40 – Quick Testing Guide© Copyright Sensirion AG, Switzerland

Confidential1Setup
The goal of this quick testing guide is to enable any customer to verify that their Sensirion SGP40 sensors are
performing according to specifications. Using only common household items we can create an accurate dilution
series of a volatile organic compound (VOC) that will be sufficient to reach this goal.
Required items▪ 2 large bottles (1 l or more)▪ 2 bowls▪ 4 small containers (50–200 ml)▪ Tap water▪ Approximately 200 g of table salt (for keeping the relative humidity constant)▪ 1 teaspoon of ethanol(1) (ca. 40% vol. or more)▪ Either Sensirion SGP40 sensors or SEK-SVM40 EvalKit and Control Center Software (running on any
conventional computer), also see sensirion.com/my-sgp-ek

required time: 2 hours(1) Any hard liquor or rubbing alcohol will do; you can also try some other concentrated VOC source such as nail polish remover, paint thinner or the like© Copyright Sensirion AG, Switzerland

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Step one: salt solution
We first want to prepare a reference solutions for diluting: a saturated salt solution.
▪ Mix 200 g of table salt with 1 l of tap water (room temperature) in one of the bottles▪ Shake bottle well and let it settle. A lot of the salt won't be dissolved and deposit at the bottom. This is yoursalt solution(2) stock.

(2) We use a saturated salt solution because its headspace is non-condensing (ca. 70% relative humidity) and thus more realistic for mimicking indoor climate© Copyright Sensirion AG, Switzerland

Confidential3Step two: high VOC concentration solution
Next, we prepare a high concentration VOC solution as the starting point of the dilution series.
1.
2.
3.

In a bowl, mix 250 ml (1 cup) of the salt solution with 1 teaspoon of ethanol
Dilute it 10:1 in the second bowl: mix two tablespoons of the solution from step 1 with 250 ml of the saltsolution
Dilute it 10:1 once more: in the second bottle, mix two tablespoons of the solution from step 2. with 250 mlof the salt solution (now we have diluted it roughly 100:1)
This is your high concentration solution stock.

You should close the lid of the high concentration solution so that the ethanol does not evaporate and theconcentration remains constant.

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Step three: concentration series
In a next step, we prepare 4 different concentration solutions by diluting our high concentration solution severaltimes. Arrange the 4 small empty containers in front of you.

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Step three: concentration series
Fill the first container exactly halfway(3) with high concentration solution, the rest halfway with salt solution.

Note: Always cover containers when your are not exposing them to sensors so that the VOCs do not evaporate.

1000(3) The absolute amounts are not critical and depend on the size of your containers; just make sure «halfway» is every time precisely the same, and «full» is twice«halfway»© Copyright Sensirion AG, Switzerland

Confidential6Step three: concentration series
Fill the second container with high concentration solution from the stock bottle. Container 3 is now full with halfconcentration solution.

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Step three: concentration series
Fill the third container with half concentration solution from container 2. Then close container 2. Container 3 isnow full with quarter concentration.

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Step three: concentration series
Fill the fourth container with quarter concentration solution from container 3. Then close container 3. Container 4
is now full with 1/8 of the high concentration. We call it the “baseline concentration”.

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9Step three: concentration series
Discard half of the baseline concentration. We now have four different VOC concentration solutions.

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10Step four: training and verification
First we want to train the sensors for the VOC concentration range used in our experiment. Start themeasurement using Sensirion Control Center.
▪ expose(4) the sensors to the baseline concentration (the container with the lowest
concentration) for 60 min▪ expose the sensors to the high concentration for 15 min▪ expose the sensors to the baseline concentration again for 30 min
Your sensors are now trained and are ready for the following verification steps.
▪ expose the sensors to the quarter concentration for 5 min▪ expose the sensors to the half concentration for 5 min▪ expose the sensors to the high concentration for 5 min▪ expose the sensors to the baseline concentration again(4) Expose the sensor for instance as shown in the pictures on the right; you should measure under a lid of sorts so that there is no convection; try to avoid using any
glue in order not to add another VOC source© Copyright Sensirion AG, Switzerland

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11Step five: evaluation
You can now easily assess two key performance indicators of your SGP40 sensors: sensitivity anddevice-to-device variation (in case you have measured several sensors simultaneously).
1.

Sensitivity: read out the difference in raw ADC tick values whenever the concentration is doubled(so going from half to high, or quarter to half concentration). If your sensors behave according tospecifications this difference should be in the range of −710… − 1030 ticks.

2.

Device-to-device variation: in the VOC index output, the different sensors should never be further
apart than 15% (or 15 index points if below 100 index points)© Copyright Sensirion AG, Switzerland

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12Step five: evaluation example
The result should look something like this:1.

Sensitivity: we can read off the differences from quarter to half concentration as 24’239−25’345 = −1016,
and the difference from half to high concentration as 23’590−24’329 = −739 so well within specifications.

quick test: sensitivity
27500
27000

SRAW_Px1

26500
26000

25500

25345

25000

24500

24329

24000
23590

23500

X_DATA
183
368
553
738
923
1108
1293
1478
1663
1848
2033
2218
2403
2588
2774
2959
3144
3329
3514
3699
3884
4069
4254
4439
4624
4809
4994
5179
5364
5549
5734
5919
6104
6290
6475
6660
6845

23000

duration (s)© Copyright Sensirion AG, Switzerland

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13Step five: evaluation example
The result should look something like this:2.

Device-to-device variation: the difference of the two sensors is barely discernible and well within
specifications.

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