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Original question:

HDC1080: Influence of pcb-temperature on humidity measurement

HDC2080: Does the Temperature offset adjustment affect the calculation of the relative humidity?

AngelDP
Prodigy 40 points
Part Number: HDC2080

In our application there is no way to avoid a temperature rise, but we are able to compensate it properly in our application. Nevertheless we have the problem, that the relative humidity drops about some percents.

Since we know that the HDC2080 measures the absolute humidity and just calculates the relative humidity our suggestion was to shift the temperature internally in the HDC2080 with the register "Temperature offset adjustment" to get the correct relative humidity. But the effect is the same.

How is the relative Humidity calculate?

  1. Humidity_rel = f(Temperature_RAW, Humidity_absolute_RAW) 
  2. Humidity_rel = f(Temperature_output, Humidity_absolute_output)  with Temperature_output = Temperature_RAW + offset adjustment

If it is the 1): What is the advantage over an offset in the Master CPU like MSP430?

  • 0
    TI__Guru* 91206 points

    Dear AngelIDP -

    The offset register values are applied after measurements and calculations are done, so in your case, you need to characterize and apply offsets for both temp and %RH. 

    The measurement on the %RH side depends on the temperature and the change in (fringe) capacitance of the polymer based on water vapor present and is done in the IC and returns a two byte value which is shifted and concatenated by MCU (like MSP430), which would also then perform the math operation to convert to human readable %RH. 

    Equation 2 on page 18, here: http://www.ti.com/lit/ds/symlink/hdc2080.pdf