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HDC1080: Internal heater disabled?

Part Number: HDC1080

The datasheet states:

"The heater is an integrated resistive element that can be used to test the sensor or to drive condensation off the sensor."

Question #1:

What reason(s) would there be for disabling the heater? Thermal cycling affecting device lifetime? Reduce power consumption?

Question #2:

If the heater is disabled, how does that affect accuracy?

  • Hi Craig,

    Thank you for your post. 

    Craig Meyers said:

    Question #1:

    What reason(s) would there be for disabling the heater? Thermal cycling affecting device lifetime? Reduce power consumption?

    While the heater is enabled, you will not be able to get accurate results from the HDC1080 device. The heater is really just intended to be run for a short period when condensation occurs to remove condensate from the humidity sensor.

    Craig Meyers said:

    Question #2:

    If the heater is disabled, how does that affect accuracy?

    The device accuracy specification is for with the heater disabled. So in that sense it will not affect the accuracy at all. Instead when you turn on the heater you will see a rise in temperature (heater driving up IC temp), and a drop in relative humidity (moisture being removed from HDC1080). 

    Hopefully my explanation is clear, but please let me know if you have any additional questions. 

    Best Regards,
    Brandon Fisher

  • Brian,

    I'm a little confused about the heater. My understanding is that the heater will operate only prior to a measurement. If disabled, this will not occur. Is the heater on full-time when enabled?

    Thanks,

    Craig

  • Hi Craig,

    You're correct that the heater is not on full-time when enabled for the HDC1080, but when it is enabled the device measurements returned do not accurately reflect the real environmental RH and Humidity.

    It is intended to be run just temporarily to help reduce offset from high humidity conditions. We also recommend increasing your sampling rate while running the heater on the HDC1080 so that the part can more effectively heat the device. 

    Best Regards,
    Brandon Fisher

  • I pulled the excerpt below from the datasheet. We interpreted this to mean we either enable or disable the heater full-time. Right now I measure at 1 sample/sec which I believe is the fastest recommended sampling rate. But we are thinking of reducing to 1 sample every 5 sec. What I'm starting to understand is that we might only want the heater enabled following an outage. We're using this sensor on a board inside the control cabinet up in the top of wind turbines. When the system is down for maintenance we have no idea what the conditions are up-tower. So it makes sense to turn on the heater at startup and then turn it off after some time.

    8.3.3 Heater

    The heater is an integrated resistive element that can be used to test the sensor or to drive condensation off the sensor. The heater can be activated using HEAT, bit 13 in the Configuration Register. The heater helps in reducing the accumulated offset after long exposure at high humidity conditions. Once enabled the heater is turned on only in the measurement mode. To accelerate the temperature increase it is suggested to increase the measurement data rate.

  • Hi Craig,

    You are not the first person to express confusion about the heater operation for this device, we are working on clarifying this for the future.

    I think you have the right plan for your application though. The heater on the HDC1080 will basically begin to heat the sensor slowly over time, reaching thermal equilibrium after x minutes (the amount of time depends on layout, but in my tests with the EVM was around 5-10 minutes). You can increase the equilibrium temperature point (and therefore the effectiveness of the heater) by sampling faster. During normal (heater disabled) operation a 1Hz sampling rate or slower is a safe idea, as it prevents any self-heating from the running of the ADC.

    I think running the heater for a few minutes at start-up is a good compromise for your application, assuming you can tolerate the higher current draw.

    Best Regards,
    Brandon Fisher

  • Thanks for clearing up the confusion.