Converting to Concentration in Air (parts per million)
The output of the waspmote to the database is a voltage reading with a gain of 7 applied. As CO2 PPM increases, the voltage output drops
Step 1. Determine the baseline voltage reading for 350ppm (EMF1). The datasheet suggests this range lies within 220-490mV but based on real-world observations this range can be much larger. One approximation method of baseline would be to average the upper quartile of readings and assume that is 350ppm - which is a reading of outstanding ventilation for an office building.
Step 2. Take your database reading (EMF2), it must be less than the baseline reading
Step 3. Divide both readings by the gain applied on the sensor, i.e. 7x
Step 4: Apply the equation ΔEMF=(EMF1/GAIN)-(EMF2/GAIN). Multiply by 1000 for value in mV. Result must be positive and between 0-90mV. If not the baseline EMF1 is incorrect.
Step 6: Compare delta EMF to the sensor response diagram below
Measurement of 0.77097v is observed (from our databases in a heavily occupied classroom). An upper quartile average of 0.98616 is averaged over the previous few weeks.