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CO in lethal levels


#1

My SCK measures CO levels (600+ ppm) that are life threatening according to the internet: http://en.wikipedia.org/wiki/Carbon_monoxide_poisoning#Signs_and_symptoms

Also my NO2 levels seem to be way of chart: 460+ ppm

In Amsterdam there are more SCKs measuring these crazy high values, but also some that have far more moderate values in the single or double digits…

To me it seems a bug, but I’d like to have some more info on this.
Thnx!


#2

Hi dosch, what you see at the moment in the site is Kohm, not ppm. Those need to be converted to get ppm, and it varies on every sensor. In our priority list, calibration is on the top, and will come with the big update of the platform to come in few months (we are re-designing, re-writing the whole platform)

Another thing is having low cost sensors, which need more care in terms of calibration, and are unpredictable some times. Another big update: pre-calibrated (more expensive) sensors which you can attach to your existing kit via the I2C bus

Tomas


#3

Here the data sheets of all the sensors (working on better documentation):

*CO + NO2
MICS4514
http://www.sgxsensortech.com/site/wp-content/uploads/2013/03/0278_Datasheet-MiCS-4514.pdf

*LUX / Light
BH1730FVC
http://rohmfs.rohm.com/en/products/databook/datasheet/ic/sensor/light/bh1730fvc-e.pdf

*Temp/Hum
HPP828E031

*Mic / Sound
POM-2246P-C33-R
http://www.puiaudio.com/pdf/POM-2246P-C33-R.pdf


#4

thnx! Will have a look at these!


#5

Look what we had from the Air Quality sensor manufacturer:
Calibration for 4514 is more difficult because stability is lower than for 2614 which is the sensor used for outdoor ozone monitoring. After burn-in operation of 2 weeks in electronic and final plastic housing, we recommend multipoint calibration in concentration (depends of the range to cover) at three temp. This calibration is valid for 6 months but depends of environmental conditions and sensor protection.

Important points to bare in mind:

  1. Metal oxide gas sensors have intrinsic drift over time i.e. it is necessary to perform calibration on a regular basis.

  2. Because of spread in baseline resistance, sensitivity, cross-sensitivity, temperature dependency it is not possible to apply same calibration parameters to all the sensors.

  3. This type of sensor is efficient to detect change in concentration but not well adapted to absolute readings because of multiple dependency (T, RH, cross-contaminants).

  4. Using smart algorithm allows indicating useful information like the correlation with CO2 in confined space like offices or buildings (see VZ-87 in attachment).

For absolute readings with high accuracy and repeatability I agree with you that you should use another technology.