4

I've had a bit of experience with DHT11/DHT22 sensors in a greenhouse environment, and believe that when they get wet they stop working altogether.

Are there any low cost humidity sensors that I can hook up to an Arduino that don't suffer from this problem, or is there a way to protect these sensors from damage when near water? (I'm not talking about immersing them in water - but do expect condensation to get sprayed with water and/or get condensation on them from time-to-time).

Am I correct that the SHTxx sensors are able to withstand this kind of abuse, and that these sensors are about 5-10 times the cost of DHT sensors? (I did not want to spend that much, but if it's the only possibility I might consider it).

dda
  • 1,588
  • 1
  • 12
  • 17
davidgo
  • 175
  • 1
  • 2
  • 6
  • use two temps to calc humidity (wet bulb and dry bulb). that would let a pair of cheap but tough thermocouples measure humidity. a neodymium magnet on an analog dial can also be used with a hall-effect sensor. – dandavis Jun 07 '17 at 08:42
  • 1
    Get a proper enclosure for it. – Gerben Jun 07 '17 at 08:50
  • Adafruit has those sinter metal mesh enclosed humidity sensors: https://www.adafruit.com/product/1298 There is a big difference between (near) 100% humidity and water condensation or sprayed with water. A capacitive soil moisture sensor can be submersed, but it can not measure the air humidity: https://wemakethings.net/chirp/ I suggest to protect humidity sensors with an enclosure as @Gerben wrote (an 'open' enclosure of course) and also use those sinter metal mesh enclosed sensors, and perhaps use a few different types of sensors so hopefully they will not all fail. – Jot Jun 07 '17 at 11:16
  • This HTU21D has a PTFE filter on top of the sensor. Not sure how good they work for water mists. Try checking the data sheet for it. – Gerben Jun 07 '17 at 11:20
  • @dandavis interesting solution Ive not thought of - thank you. Unfortunately I don't think I have the knowledge to pull that off, particularly in my environment with limited airflow (And I don't want to add a fan) – davidgo Jun 07 '17 at 19:29
  • @gerben - can you shed light on what I am looking for with respect if an enclosure? I have not been able find anything for the DHT, and wonder how fine a mesh I would need and how it will impact accuracy. – davidgo Jun 07 '17 at 19:31

1 Answers1

2

2022 UPDATE: After ~5 years since I wrote this answer, I'd like to mention that I don't like BME280 anymore, because of its (1) inaccuracy and (2) requirement to make some non-trivial computations to get real values from sensor's data. If you already got a BME280 and your project requires only approximate values of temperature/humidity, it will work, go ahead. Otherwise, consider using SHT3x!

See also this, this, and especially this one.

Original answer:

I'd consider using Bosch BME280 digital sensor. Although it's a bit expensive, it has very good sensitivity, precision and amazingly fast response for humidity changes (for ex. in my project it detects dry human hand lying in 2" away within a 1-2 seconds).

So its features make possible to put it into an enclosure to avoid direct water contact with water spays and it'll still be very responsive for greenhouse needs, I suppose. Datasheet warns:

Liquids shall not come into direct contact with the device.

Also, I'd use electronic-friendly protective acrylic lacquer (Plasticote 70 for instance) and put two layers to sensor's PCB, avoiding small black tiny vent hole on the chip itself: BME280

UPD: Here's DHT11 with cover removed: DHT11 inside

It might be the easiest and cheapest solution to cover all internal contacts and IC (avoiding humidity sensor's stripes) of DHT11 with Plasticote 70.

finnan
  • 302
  • 1
  • 2
  • 8