Core Electronics Forum

DHT22 - Humidity vs Relative Humidity

Hi, I have a very quick question around these two products:

  1. DHT22 Temperature and Relative Humidity Sensor Module | 018-DHT22 | Core Electronics Australia
  2. https://core-electronics.com.au/dht22-temperature-and-humidity-sensor.html

Both of these are DHT22. I believe both these are measuring relative humidity. However, since of these is advertised as able to measure ‘relative humidity’ while the other is advertised to measure ‘humidity’ only. Is there any such difference between these two sensors?

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Hi Riddhi,

No difference in measurement abilities, they use the same sensor IC. Humidity measurements are always relative (except in some more esoteric situations). If you’re looking for ‘absolute’ humidity for some reason, you’ll need a sensor that can measure partial pressure of H2O, mass of H2O per volume or similar - though these can be calculated from relative humidity or wet bulb temperature.

The wikipedia article on this is not too bad:

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To be honest, i don’t use them any more. Spent years fiddling with my weather station. The DHT22 series become saturated after 12 months and the humidity becomes unreliable. The temperature is fine as it uses a DS18B20 internally. Do yourself a favour and use a BME280 and set and forget. My 2 cents.

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Thanks for the tip. Any suggestions around weatherproofing the sensor? we were thinking silicon/epoxy.

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Weather proofing a humidity sensor is a bit tricky. It has to be open to the environment to work. If there is an accurite or similar indoor/outdoor Weather station unit is available, check the outdoor unit and follow similar principle.

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I 3D printed a stephensons screen and mounted it in that:
20200802_103806
20200730_220848
20200802_110025

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