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TIDA-00378: The calculation formula question for TIDA-00378

Mickey Zhang
Genius 12080 points
Part Number: TIDA-00378

Hi team,

The customer refers to TIDA-00378 to measure PM2.5. 

After he installs the TIDA-00378 Firmware, he checks the main.c file. 

He does not know where the calculation formula come and he would like to know if there is the document which

can prove the calculation formula is correct. Please check the attach for the calculation formula.

Would you explain the  calculation formula?

  • 0
    TI__Mastermind 25311 points
    Hi Mickey,

    These formulas are the calibration adjustment step in the software algorithm described in the user guide. The constants in the formulas are derived by comparing data from the sensor to a reference tester which measures PM2.5 and PM10 particles. Other methods such as a look-up table can be used as well to speed up execution.

    Gus Martinez
  • 0 in reply to Gus Martinez
    Prodigy 10 points
    Hi team,
    I didn't find the specific place, still don't quite understand, can you give a picture, thank you
  • 0 in reply to user5170599
    TI__Mastermind 25311 points
    Hi,

    Allow me to elaborate on my previous response.

    As I said before, the formulas are basically the result of a calibration step which is conducted by looking at the output of the TI design and comparing to the output of a reference tester. The calibration steps are as follows:

    - First, the data from the TI design is filtered and the pulse counts are calculated as pictured in Figure 12.
    - Second, the pulse count data from the TI design is plotted against the reference data from the lab instrument (Figure 48) and a linear curve fit is applied (see Figure 48).
    - Third, once the y=mx+b formula for the curve fit is known, a new linear transform function is derived as y = x/m + b/m. This essentially maps the output of the TI design to the output of the reference. This is the part that can also be done with a lookup table.

    Gus Martinez