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TMP007 aboot S0 FOV and the emissivity of the object

Mickey Zhang
Genius 12080 points
Other Parts Discussed in Thread: TMP007, TMP006

Hi Sir,

I have some questions about TMP007.

1.How to get S0? 

The TMP007 Datasheet (SBOS685C) specifies the range of the S0 coefficient register as 0 to 298x10^-15 (section 7.5.11.1).  The TMP007Calibration Guide (SBOU142, section 1.2.1) says "S0 is the material emissivity x the Stefan-Boltzman constant.

The Stefan-Boltzman constant is 5.7x10^-12.  the object emissivity(ε)=0.95, 5.7x10^-12 x 0.95=5.415 x 10^-12> 298x10^-15.

What is the reason？

2.When I knew the emissivity of the object and the FOV , What were they used to do? They have not been used in the back.

How does the FOV affects S0?

Thanks!

  • 0
    TI__Mastermind 35895 points
    S0 should be set based on data collected from TMP007 in your system. The text provides an explanation of why S0 (and the other coefficients) are important, but we do not expect you to measure S0 by an external or even theoretical means.

    S0 is the main coefficient for sensor signal and sensitivity. It describes a linear relationship between thermopile voltage and object temperature. Since a FOV restriction reduces signal received by the TMP007, the S0 is proportional to FOV.

    Ren
  • 0 in reply to Ren Schackmann
    TI__Genius 12080 points
    Thank you very much for your answer. But I see the maximum value of S0 being 298x10^-15 from the datasheet(Table 7. Coefficient Range and Resolution). How to explain this value 298x10^-15？
    I see the same issue from E2E. The link: e2e.ti.com/.../1656320
  • 0 in reply to Mickey Zhang
    TI__Mastermind 35895 points
    This max value for S0 is arbitrary. It doesn't correlate to any theoretical limit in physics, and S0 does not equal emissivity as that linked post assumes.

    In order to give the TMP007 Math Engine enough range to be used in any application, the designers of TMP007 carefully considered the range of coefficient values that we had seen thus far in TMP006 applications. They chose to give all the coefficient registers at least twice the range as what was thought to be necessary. This is why the max values are arbitrary.

    Ren