Converting to Concentration of Liquid Petroleum Gases in Air (parts per million)
The output of the waspmote to the database is a voltage reading, as can be seen from the circuit diagram below, this reading is affected by the input voltage, sensor resistance and load resistance.
To convert to ppm, the voltage reading is applied as follows
Step 1. Convert voltage reading to sensor resistance: Rs = ( ( Vcc - Vout ) / Vout ) * Rl
Step 2. Determine sensor resistance at 1800ppm (isobutane) Ro. If there is insufficient data at this stage to do this empirically, begin approximation by using the lower extreme of the expected sensitivity provided in the datasheet ~ 0.68kΩ
Step 3. Normalise against resistance at 1800ppm (isobutane): Rs / Ro(Typical Resistance at 1800ppm (isobutane)
Step 4. Compare normalised result against sensor response diagram:
Measurement of 3.3v is observed (from our databases).