Author Topic: Are Humidty values displayed for remote and Indoors "calculated" values?  (Read 748 times)

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Offline swb_mct

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With my Indoor/Outdoor weather station, if the remote sensor is sitting indoors by the main interior display unit, the temperature readings are synchronized perfectly to 0.1 Fahrenheit.   The humidly values almost match but are not perfectly synchronized.
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But then if I move both units outside on a 56 degree morning,  the "indoor"  humidity readying is about 15% higher than the "remote" reading.  Again the two sensors are side-by-side, but outdoors.
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Why don't the % values approximately match when both sensors are outside in the cold.  (they match when they are both inside)   Does this mean the displayed values are somehow "calculated" but the assumptions in the formula are wrong if both sensors are outside ?
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I am not a dewpoint or humidity scientist . . so please explain in layman's terms.

« Last Edit: September 24, 2019, 09:14:07 AM by swb_mct »

Offline galfert

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Re: Are Humidty values displayed for remote and Indoors "calculated" values?
« Reply #1 on: September 24, 2019, 09:32:34 AM »
No, humidity is not a calculated value. There is a sensor called a hygrometer that is responsible for the humidity value. Most likely what you are experiencing is that the sensors are not preforming equally due to age and weathering differences. They don't last forever. A hygrometer will perform differently if it is damaged at different humidity ranges. Meaning that at a certain range or level it is okay (like when indoors, because our homes have a climate control systems (air conditioning) and humidity is lower than outside, typically but not always like when you live in very dry desert climate). But the sensor will perform badly when the humity is at a different or higher range level. Usually failing to produce good results when the humidity is higher.

What you experienced is exactly what I would expect also. The indoor sensor is less weathered and capable of reaching a higher humidity level reading. As a hygrometer ages it looses its top end reading potential. So your outdoor sensor needs replacing.
« Last Edit: September 24, 2019, 09:45:29 AM by galfert »
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Offline galfert

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Re: Are Humidty values displayed for remote and Indoors "calculated" values?
« Reply #2 on: September 24, 2019, 09:49:11 AM »
By the way if your humidity sensor (hygrometer) is bad then your dew point reading will be wrong. Dew point is a calculated value using temperature and humidity.
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Offline swb_mct

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Re: Are Humidty values displayed for remote and Indoors "calculated" values?
« Reply #3 on: September 24, 2019, 09:49:31 AM »
The unit is "new".   Could it be the accuracy of new humidity sensors is generally poor on low cost consumer products, but then perhaps are calibrated to match at room temperature to look good "out of the box", but then the dynamic range on 1 sensor is limited by it quality so the calibrations don't match if not at room temperature ?

Offline galfert

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Re: Are Humidty values displayed for remote and Indoors "calculated" values?
« Reply #4 on: September 24, 2019, 09:59:50 AM »
It's new, good, send it back. Get a different brand.

Pick two of these three considerations:
  • Price
  • Quality
  • Service / features


Price    & Quality                = Acurite Atlas
Price    & Service / features = Ambient or Ecowitt (WS-2000 or HP2551 or similar)
Quality & Service / features = Davis VP2
« Last Edit: September 24, 2019, 01:02:13 PM by galfert »
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Offline Old Tele man

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Re: Are Humidty values displayed for remote and Indoors "calculated" values?
« Reply #5 on: September 24, 2019, 12:57:27 PM »
Here's a previous posting about 'how to' check/verify if your RH (and thus dew point) are acceptably accurate: http://www.wxforum.net/index.php?topic=22767.msg219291#msg219291
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