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Original question:

HDC3022: difference in response time compared to HDC3020?

HDC3022: Is the response of temperature reading of this sensor as fast as the response to humidity even with the PTFE hood?

Bill Tubbs
Prodigy 10 points
Part Number: HDC3022
Other Parts Discussed in Thread: TMP117,

Tool/software:

in this discussion two years ago, there is some data that shows that the response time of the humidity reading in this sensor with the PTFE hood is only slightly slower than that without the hood.  Could anyone comment on whether the difference in response of the temperature reading would be the same?  I.e. not much different.

  • 0
    TI__Genius 11865 points

    Hi Bill,

    The PTFE filter will not affect the temperature reading response time, only the humidity response time. That is because the temperature sensing element is embedded in the die inside the package body, and heat is transferred through the package body. The filter only slows down humid air from entering the center cavity with the sensing polymer, it does not impact the rest of the package or its thermal coefficients.

    Regards

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 10 points

    Hi Alex.
    Thanks for responding.  That answers my question but I didn't expect that answer!  I assumed the temperature sensor would be in contact with the ambient air.  If the temperature change needs to be conducted through the solid material of the package body then I'm wondering what the response time of that is.  Is the temperature response time in the data sheet or is that information available?  (E.g. Time constant or settling time in seconds/minutes).

  • 0 in reply to Bill Tubbs
    Prodigy 10 points

    Now that I actually check the spec sheet does have the step response time constant for temperature independent of humidity of 2 seconds which is fast.  But this is described as "Response Time (stirred liquid)" which is a surprise.  I had no idea this sensor was for liquids (surely it would soon corrode in a liquid application?).  The response to a change in air temperature would be slower I guess but is not shown.

    The spec also recommends making a cut-out around the sensor to reduce the thermal mass and increase the response time which is a good idea I guess.

    In the absence of any information on the air temp response time I think I'll go with Adafruit's TMP117 which also has 0.1 deg accuracy, no RH sensor (which is not essential) and already has a cut out.

  • +1 in reply to Bill Tubbs
    TI__Genius 11865 points

    Hi Bill,

    The HDC3022 isn't for liquids, the thermal response test is done in a moving oil bath, hence why the spec says "stirred liquid". We test all of our sensors this way for temperature response, although sometimes we publish still air and moving air temperature response. You are correct that for air temperature response, it would be slower (even on a flex PCB), more on the scale of about a minute or so instead of a couple seconds.

    I'm glad you found a solution that will work for you, TMP117 is an excellent device. Please feel free to ask for help on this forum if you have trouble using the TMP117 or are getting unexpected results.

    Regards

    -Alex Thompson