How to test relative humidity sensors

In this video, we talk about how you can evaluate a relative humidity sensor by using the atmosphere of a solution saturated with table salt (sodium chloride). The expected humidity at 20C (68F) is 75.5% and 75.3% at 25C (77F).
We test a DHT11 sensor and show that it behaves in line with the expected accuracy of the sensor +/- 5%. Given the frequent deterioration of DHT11 sensors, this is a good method to test sensors routinely and confirm their accuracy.
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[@muhammadammar6413]

Thankyou so much for this awesome video 🤩🤩.. can you please recommend me a humidity sensor for radiosonde. As it goes up in the air upto kms. so a sensor is required which can bear this harsh enviroment.

[@circle4922]

Thanks, Daniel.

[@ScienceinHydroponics]

My pleasure!

[@ross9919]

Thanks for this! Great channel, heard you on Garden Talk, trying to absorb your content before going into my second grow.

[@ScienceinHydroponics]

Awesome! Thank you!

[@Trymon1980]

I should also do this test, my sensor is just an entirely different beast.
I'm using a HYT221. Bought this to have a reference for my Termometers and Hygrometers. While not used in Hydroponics I need good readings for my Guitars. :D
HYT221 has a temperature reading of +/- 0.2C and +/-1.8%
Have to admit that I'm surprised by my Hygrometers. The devices themselve are way cheaper thatn just the sensor but they are luckily very close. Temperature basically spot on and humidity just 1% difference.
But just for fun I will also connect the DHT11 to the Arduino so I can see both sensor readings. Might be very interesting.

[@ScienceinHydroponics]

You can do this test with any humidity sensor. You can tell if any of them are inaccurate in absolute terms.

[@3nertia]

Any experience with the DHT20 temperature/humidity sensor? Supposed to be the update/upgraded version of the DHT11/22

[@ScienceinHydroponics]

They are pretty bad still. They fail quite quickly and they are quite sensitive to high humidity values (fail if you ever get close to the dew point). Their accuracy is also not as indicated. The BME280 is my all time favorite for low cost accurate relative humidity readings.

[@funderspunder8148]

Hey, i had a quick question. The sonsor for my inkbird is covered in a black plastic shell and i notice that the humidity in my tent is lower inside than outside of it when the light is on and they become equal when the light is off. Could this be because my grow light is heating the sensor and causing it to believe that the air temperature is higher?

[@ScienceinHydroponics]

The reason is that the temperature inside your tent is higher, so the relative humidity is lower. Relative humidity only measures the amount of moisture in the air relative to what the maximum amount is, so if you just heat the environment the RH will always go down, even if there is the same amount of water in the air (if the absolute humidity remains constant).

[@canyonlewis6452]

How can I look up a chart showing the relative humidity vs temp for a closed chamber salt water environment?

[@ScienceinHydroponics]

Thanks for commenting. You can search the scientific literature for them. You can use this publication and its references to get you started ( www.researchgate.net/figure/Saturated-salt-solutions-and-its-standard-relative-humidity-value-for-the-measurement_tbl1_238085499 )

[@circle4922]

Good question, Canyon.

[@circle4922]

@@ScienceinHydroponics Hi. This link is broken now.

[@canyonlewis6452]

@@circle4922 you can manually type part of the link in and find the table

[@MausSpaece]

9:13 What sensor(s) would you recommend for monitoring temp/humidity in a hydroponic environment?

[@ScienceinHydroponics]

Thanks for commenting! I would recommend using a BME280 sensor. You can read this post for a deeper comparison between relative humidity sensors (scienceinhydroponics.com/2020/04/the-best-cheap-sensor-setup-for-relative-humidity-in-hydroponic-automation-projects.html).

[@rodgersandrodgers8191]

An interesting video. Thank you. You have told me what you would not recommend, but what relative humidity sensor would you advise me to purchase?

[@ScienceinHydroponics]

I normally recommend the BME280 sensor.

[@GetRealwithMike]

That's humidity, not relative humidity. The DHT22 measures Relative Humidity.

[@vikramdabi3838]

Sir you might be wrong here.

[@ScienceinHydroponics]

I am talking about RH in the video, which is what the DHT22 measures. I don't understand where the source of confusion is but if you let me know maybe I can clarify.