Humidity meters and their sensors.

Humidity meters are a useful device to ensure that your home or workplace is kept at a reasonable humidity to avoid problems caused by dampness or extreme dry conditions.
Here's a look at how you can check their accuracy and how they work.
If this video seems a bit rushed it's because the original long video intended for today repeatedly failed to upload.

[OntologicalQuandry]

I used these in my first job making moisture instrumentation in 1999. The sensor needs a higher frequency driving wave at higher humidity to stop polarisation and a much lower frequency at very low humidity. I developed a simple bit of code that smoothly varied the frequency from 10kHz down to 100Hz based on what the sensor was reading, hugely extending the accurate range of the sensor.

[DaPenguin]

Hi Clive, just dropping in to say how useful this video is 4 years later.
I've been researching humidity sensors for a 3D printer filament drying project and was nearly going to pull the trigger on a couple of $8 already in the nice plastic case with the display jobbies, when I remembered I had a few sensors lying around from a previous arduino project. I wondered how they worked, and the words " hygrometer eBay " brought me straight here. I'm fairly certain if I type anything I'm remotely interested in with the word eBay after it I'll end up with result number 1 being a video of yours....

Top quality content as always mate, stay safe during this quarantine, and as always... keep the explosion containment pie dish handy.

[stridermtk]

How the hell do you know these awesome little tidbits like the humidity in a bag trick?
That kind of stuff is awesome to know and I really have to thank you for it.
It's why I subscribe to this channel -infotainment of the highest caliber!

[DrTeddyMMM]

I purchased 10 of these little devices, they were sold as ºC (celsius) only. I wanted to use them mainly for the humidity function. As with everything I get, I take it apart first. I discovered there is a set of solder points inside that will set it to ºF (fahrenheit) temperature readings. Bonus! :)

[Harani]

Very useful video

I bought a pair of these with the sensors on flying leads and put them in a wall mounted box on a cavity wall I've been having damp problems with.

One panel is reading the ambient humidity (and temperature), the other the sensor goes through a hole in the wall so I can measure humidity in the cavity and compare them against each other.

Now I can make sure the two units are calibrated the same.

[flagpoleeip]

put mine through the washing machine. had a significant affect on its accuracy.

[EpicLPer]

Why would anyone need more than 6 of tho... oh wait, you're Clive, never underestimate Clive.

[zorgatron]

I really do appreciate videos like this, Clive. I know it seems like such a simple thing but this is a good unbiased educational video for a product that has worked very well in my life. Thanks for the work you do!

[MrKlyushin]

Thank you for such a great video! I was wondering how those sensors work. I have very poor knowledge of physics but at a amateur level I understood how it works. Thanks a lot!

[azzym]

Clive I thought they were capacitors of which the capacitance varies with humidity. I traced the circuit of one of these and I found this;
There was a CMOS 555 on board of which the frequency varied as a function of the capacitance of the sensor.
I could be wrong perhaps the varying resistance changed the frequency directly. But I remember that the sensor was located where normally a capacitor goes into the 555 oscillator circuit. I built and sold a dozen humidity display plus recorders to a pharmaceutical Co. about 6 years ago.

[DonDegidio]

Nice video and humidity sensor explanation. Great way to test the units. If they were adjustable, wish you would have shown how to bring them closer to the correct reading.

[peterleather]

I never knew that you could check the calibration like that. I have a DHT22 (digital) humidity sensor connected to my Raspberry Pi weather station that I suspect is read way off so could test it with this method. Thanks for the tip!

[XOIIOXOIIO]

Fantastic little thing, I'm ordering one for my server rack right now, I have my own temp sensor I rigged up using a dallas instruments one wire device but something to permanently install will be handy, though without the ability to datalog like mine.

First one I found has a remote sensor, and I figure that will work nicely since I will be able to put it somewhere in the rack if I want to read the temp from somewhere else.

[Marklek]

You can use various salts with their own equilibrium relative humidities. To calibrate a low point at 33%, Magnesium Chloride is an easily accessible salt. You should use kosher salt or canning salt instead of table salt for your Sodium Chloride slurry, though. Common table salt contains anti-caking agents that can throw things off.

[a]

Boveda brand sells salt packs with different humidity settings including a 75% and 33% humidity for calibrating humidity meters...

[grahamrdyer]

Thanks for showing us Clive, I didn't really know how these things work but I'm glad you did this video.

[LPFthings]

Humidity sensors require temperature sensors to get the relative humidity (absolute isn't really used much), you can probably tune the ones that are out by simply tweaking the resistance of the thermistor.

[evilutionltd]

I fitted one of these into a smart Roadster a few months ago. They suffer from leaks and the water turns to vapour and condenses on the main controller PCB for most of the electrics. Monitoring the humidity in the car was an obvious step.

[Seegalgalguntijak]

Last winter, I bought a few of these round analog humidity meters from ebay, because my apartment is always too dry and I was using a humidifyer for the first time. When they arrived, they all showed a different value, so I had to clip open and manually rotate the dial in order to get a somewhat accurate reading (but in fact, I'm happy if it shows me "around 20%" or "around 40%", with the former being almost unbearable for my respiratory system and the latter being the start of where it becomes tolerable.

[TodorTashev]

Wonderful explanation. Thank you so much for sharing. I am also enthusiastic about hygrometers and since they show slightly different values I didn't know which one is correct. Now I know how to check. I'm really excited to try this out.