Humidity meters and their sensors.
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- Опубліковано 7 вер 2024
- 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.
If you enjoy the videos you can help support the channel with a dollar for coffee, cookies and environmental control gadgets at / bigclive
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.
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!
possibly mycology hobby? mycoligists need accurate humidity readings . its commen knowledge for those into mycology . to calibrate an anologue humidity guage, you put it in a bag with salt for upto 75% for high humity upto 99% wrap it in a damp towel for 1 hour and adjust to read 99%
I had it in 10 minutes of Googling. I mean once you have multiple humidity meters, or have ever even been to a store where a bunch of them display different values, the natural question occurs which one is right.
vedasticks
Indeed!
Siana Gearz
Good for you! ;)
Maybe he's a cigar aficionado. They're OCD about their humidors. :)
Maybe cigars! Ask me how I know it 😂
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! :)
Hi @DrTeddyMMM So how did you have them convert Celsius to Fahrenheit? Mine was displayed in Fahrenheit and after battery change it turned into Celsius. I'd really appreciate if you could shed some light. Thanks!
How I didn't see your comment last year when I got some of these and asked Clive how to change it, I don't know. I should have read more comments. LOL But he said the same thing about the solder pads.
did the humidity function work propperly?
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.
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!
Totally agree
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.
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!
Why would anyone need more than 6 of tho... oh wait, you're Clive, never underestimate Clive.
Yeah, it was a group test to see how they compared.
Living room, dining room, kitchen, bedroom, bathroom, basement...
theyre cheap, reason enough to buy at least 5
I bought three of them in white. One for my bedroom, one for my kitchen and one for my fridge.
if you're growing weed...
put mine through the washing machine. had a significant affect on its accuracy.
The washing machine's?
very good.
What kind of washing machine is it? We may be able to help you re-calibrate it, and fix it's accuracy.
+p3rs0n42 Never do your laundry with a non-calibrated washing mashine. Bad things can happen!
+Christian Geiselmann I always recalibrate it before each load, just to be safe!
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.
Thanks for showing us Clive, I didn't really know how these things work but I'm glad you did this video.
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.
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!
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.
You answered every question I had about these units and more. Much appreciated.
Great for homemade humidors, and I know know heaps more about them.
Clive, you're a star.
Great tip about testing. I now know which of my hygrometers to trust. Thank you Clive!
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.
Unlikely. Thermistors are _highly_ nonlinear. The COB has a table programmed into it that compares the resistance of the thermistor to the (nearest) preprogrammed value. At least that’s what should happen theoretically when each unit is calibrated. Granted, there’s not a chance they do that for cheap Chinese hygrometers (they probably use typical values from the thermistor’s manufacturer data sheet), but I don’t see how you can “tweak” the resistance without _decreasing_ the overall accuracy of the unit.
You could, probably, calibrate it this way to be (more) accurate in a specific range of temperatures (for example, around the typical room temperature, refrigerator temperature, or freezer temperature). You’ll still need a highly accurate, certified device as a gauge for that.
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.
I use these in my guitar cases. Thanks for the calibration tips
Thanks for showing us how to test the accuracy i was a bit worried about that and now i have something to help me out!
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.
Man, that is amazing. Humidity cal for cheap meters. Thank you so much for this!
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.
I had an old 480Watt window a/c, so I decided to use the condenser to dry my bedroom.
My humidity sensor Implied 47% humidity at 27.7C/82F. I had it in operation overnight, 5 gallons of water later and the sensor still reads 47% Humidity.
I think my hair is a far better measurement of humidity.
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.
ahey! the first product that you've dismantled that I own, good to see whats inside 'er.
Boveda brand sells salt packs with different humidity settings including a 75% and 33% humidity for calibrating humidity meters...
This video was the simple explanation I was looking for. Thank you!
Thanks big man for another quality video to keep us exciting party folk entertained, this Friday night.
Thank you so much Mr. Clive for this video, me and the wife are looking for new ones for the green houses that dont just crap out in the sunlight and moisture so this is extremely helpful !
you would think a moisture meter would have some protection from the elements but apparently not
Great help to calibrate/check the hygrometer, which turns out to be essential in covid-19 prevention.
That is, keeping a room above 40 %RH and preferable below 50 %RH.
i have a temperature meter in the same package, quite neat to keep an eye on temp inside refridgerator(it has a lead with the sensor on the end) Might get one of these for fun
A great fan of your videos. Please make a video about the humidity sensors that comes with common xh-m452 temperature humidity controller used in egg incubators.
Currently most use this "asair am2120" and it doesn't works for more then 2 weeks.
Every time I look at your channel there's something interesting and timely
Thanks, bigclive! Learnt something new today. AC, not DC for RH sensors. :)
I own a few of these. Great help for tropical plants and exotic animals.
I have these things all through the house,all acceptably accurate. Any discrepancy I just take the average. Very useful little devices.
Excellent video, thanks!
Also, thanks for explaining how to test the accuracy on these things. I have varying different humidity meters around, and I don't know if any of them are correct or not, so I will definitely get them checked.
I really like the HIH-4000. It's a capacitive sensor that does a similar job. The resistive salt based devices age. Capacitive sensors do not. They also output a 0-5v analog signal and don't need to be driven with hard to deal with sine waves. Something to look into...
We build things for grain store monitoring using the HIH 4000 series sensors, been using them for years. Eventually some do go a bit haywire but most of the time it's due to dodgy electrics on a farm that have zapped some part of the circuitry upstream of them.
I got this humitidy meter, but with external long probe model. Later I am going to test its accuracy according to your test.
Thx.
1:49 I'd say the variation in humidity reading is not so much an error in the humidity reading, but rather the calculation it performs based on the temperature. You might mention it later, but I'm commenting in real time; relative humidity is based on the capacity of air to hold water vapor and that changes based on temperature. The meters in the tub are ranging from a low of 18.3C to a high of 19.9C and show a difference in relative humidity of 4%.
I think it comes down to the accuracy of the temperature probes, but there is another 5m7s to this video and I could be totally incorrect.
Great video and great channel. Subbed for sure. Had several of these under cover that drifted due to very fine silica dust (middle east weather). Now I know how and how not to clean these! Most appreciated.
Impedance according to the data sheet is 31.0k@60%RH excited at 1Khz. If these are put in as one leg of a 31.0K "bridge" you can drive them with a 1khz sine wave and then send the output in to a op amp buffer and then rectify it from there. The op amp can have enough gain to compensate for the diode loss and then it can be read directly with a DMM or ADC input. It means ordering expensive 0.1% resistors though and perhaps "balancing" out an offset.
hey Clive your knowledge is immence another ace video top class viewing .Keep it up sir .
BTW most have a small area with 2 solder point that can be shorted for use with Fahrenheit , actually has a C/F denoted on the board
At that price, it would worth ordering 10 and doing the calibration test to cherry pick the most accurate ones. Even the more expensive ones I bought a while back vary several percent from each other when left placed side by side overnight. Great tip about the salt water based calibration. As for distilled water, dehumidifier water makes a good substitute as we use it in the clothes iron, steam cleaner, etc that normal tap water would otherwise leave gunk once evaporated. Going by Amazon, it's surprising how many people fall for the snake oil single-use moisture traps claiming to dehumidify one's home considering they only collect 1-2 litres per refill (which takes several weeks and expensive to buy), compared to 2 to 4 litres per day for a typical electric dehumidifier.
'Dehumidified water'? Let me see that! :-)
+Christian Geiselmann I think this means "water collected from the dehumidifier", which as it has been condensed from water vapour is essentially distilled water.
I have always wanted to know how these worked, thanks.
When they say thin film they actually mean thin film of photoresist on it which is what they use when making microchips. This means the film was put on it when it was part of another 1000 chips on a microchip wafer which are now either 200mm-300mm (8 inch to 12 inch) sized wafers.
I thought that they generally worked as capacitors. I know the ones I've seen have open air separating the plates and the changing humidity in the air changes it dielectric properties, therefore changing the capacitance which can then be measured.
The last humidity meter thing I had was a cheap one which came with a thermometer and a clock in a 3-gauge plastic housing, never worked right, especially after I made the spring pop out... :P
I learned so much in 7 mins thank my good sir..
Thank you. This is of particular relevance to me right now.
WEIRD SENSOR OUTPUT: On a box store portable dehumidifier:
Output is 30% all the time. Exhale on the sensor and humidity spikes to about 90%, then for about 30 seconds, slowly decreases to 80%, then stays constant at 80% for about a minute, then display goes from 80 to 30 or 31% instantly and then stays there forever.
I think something cracked on the sensor (unit is 12 years old), it's open but under high humidity it "conducts" and produces output.
I think the controller has a min display value of 30% no matter how much lower the actual humidity is.
What do you think?
So the million dollar question remains unanswered - did those ones you tested drive the sensors in AC or DC...? :)
On the basis that they are designed for the task and the readings remain stable over time I would guess that they are being run properly.
Great job. Thorough and even authoritative
By the way: You can calibrate the analog ones very easy. Bought a few from china for less than a dollar and they all had a calibration screw in it.
I was struck by the similarity between the hygrometer component and the infamous Cheap Shitty Pink USB Charger From China. Both depend on wires with a very small separation. Presumably the Cheap Shitty Pink USB Charger detects humidity by shorting the USB power to the mains and burning out whatever is plugged into it.
Great video Clive! Very informative, I've always wondered how those cheap devices measured humidity.
One note: The bottom of the line Acurite humidity/ temperature meter I use seems correct for humidity and degrees C in whole numbers. However if I switch temperature display to degrees F it is obvious that it only displays whole numbers in C, because as the degrees change in F they jump 1 or 2 degrees F. The omitted F numbers never show up on the display. Living in the USA and living in higher whole number resolution Fahrenheit , I just do not have a good feel for Centigrade.
if you touch them you can heat them up a bit with the soldering iron while in use until they read right again
If only you made this video 2 months ago clive! I used these little things to make a weather-station and I spent days trying to get it to work correctly, ended up getting the digital sensor modules (DHT modules) and using those instead. It wasn't until later I found that its not very good to drive them using DC.
Just got one as a Christmas gift thinking about putting it in my car
Just subbed to Patreon Clive, keep doing what you're doing mate.
Thanks Clive. Had to find out if these are reliable enough to monitor the humidity for my sneks.
Hi, I have bought two hygrometers. When I do the salt Calibration test they have a difference of 10 between them, one reads 76 the other 86, however when they are out the salt test and in the same spot in my room they read more or less the same? Do you know why this might be? Thanks
I moved down here to Phoenix, Arizona thinking that the humidity would be between 2% and 35%. NOPE!
The humidity during the Summer regularly exceeds 50%! It can get kinda sticky here.
Seems to be as accurate and good as the £15 or so one I got for my cigar humidor.
Always learning something....Thank you!
Interesting... I have heard exactly the same thing, but _without_ using salt results in a humidity of 50% in a sealed container. I never tried this to find out if it is true though.
Those are surprisingly cheap. The Honeywell HumidIcon sensors I use cost about four times as much (about $10 each), and that's for just the sensor itself -- no neat little display, case, PCB, batteries, or anything else.
Thank you for the video. I always wondered how some of these worked. This clarifies and teaches me a lot about them. I wonder how good is their response time and how does their different encasing can affect both the accuracy and response time of it.
Interesting, thanks Clive. Are there other salts you can use that would have different humidity equalisation points? I wonder if the offset you noticed on some of the devices is linear.
Yes there are other salts that can be used, like lithium chloride, but some are very temperature dependent. The plain old sodium chloride test is the simplest.
Boveda brand sells packs with different humidity settings including a 75% and 33% humidity for calibrating humidity meters...
I prefer the digital ones (SHT) from Sensirion. I was using the same method to calibrate my humidor meters.
I got 5 humidity and temperature sensor that use I2C on order.
going to put one out side and one on each floor with 2 1602 lcd display that use I2C also, so it can display all 3 sensors on 1 display each.
then connect to a arduino
because everything is using I2C, it can be put on 1 share line
Would be quite nice to use one of the the 8 pin AtTiny based Arduino compatable boards for that.
I saw a difference in humidity. 75 and 59 moisture. 😉❤️💯👏🥇
Clive, On the polarisation of the sensor from using DC, have you ever tried to measure the resistance of silver loaded conductive paint while it's drying? You could make a video of that but you'd have to do several stripes at hourly intervals before measuring the resistances.
I've often wondered how those work. V cool vid.
It would be great if you could check with an oscilloscope whether these cheap all in one modules correctly use ac on the sensor.
It's interesting how some of these indoor humidity/hygrometer meter/monitors differ in price.. do they all use the same sensors inside?
I thought of using my phone, but found that most newer don't have temperature and humidity sensors.. but there are a few that do: Samsung Galaxy Note 3, AGM X2, Galaxy S4, Motorola Moto X, and the Moto X 2nd Generation.
Useful and interesting video, thank you.
Hi Clive. Is there any chance to reuse the HR202L after getting it wet? Bc I wanna try it into some project and it requires to wash it on a daily basis... in case it's not possible, do you know another idea that could work with it? GREETINGS FROM ARGENTINA!
I'm not sure how well it would last if you got it wet or cleaned it with a detergent. It may lose its accuracy.
How does the BME280 humidity / pressure / temperature sensor work? I have one and it's advertised to be very accurate. I can confirm that it's very fast and that it has a high resolution (which - I'm aware - is not the same as accuracy).
I'm at a loss to understand why my outdoor humidity/temp sensors continually report (all three of them) a +/- 50% lower RH than the RH reported by the Met Office and other official weather organisations. Maybe my devices are rubbish? But why do they all agree?
I think that the temperature sensor is required to have a humidity sensor give a relative humidity percentage, so the inaccuracy of both sensors combined causes the RH% to be off by 5-8%
I don't think these units do relative humidity. They seem to vary dramatically with temperature compared to a real RH unit and more accurately mimic a traditional mechanical humidity meter.
I've just checked by replacing one of the thermistors with a variable resistor, and the humidity reading is affected by the temperature, but at zero or below where you'd expect any humidity to show 99% it doesn't. So not what I'd consider actual RH.
+bigclivedotcom Great idea to check if they're related! That's strange that you got that result though. BTW, I love your videos, thank you for making them!
At some point the work surface got more board marks. 6 years ago it was pristine!
very cool, thank you for showing me this Clive!
Awesome video! Thank you so much.
the zoomed pic of the humidity sensors looks like the ones that used to be fixed to the heads in vhs machines
Hey Clive. I had basic science stuff in school but never really understood the differences between Volts, Watts, Amps etc. Any chance you could do an informational video explaining this like you'd explain it to a 5 year old?
timed this visit to UA-cam quite well!
Hi, I have the same LCD devices. At the shows the constant 10% humidity. Is the sensor defective or does it have to be calibrated? I have already put airtight in a box and with salt. not much has happened.
So,
i) do you know if the above LCD ones suffice? If yes do you know for how long?
ii) Do you know if the only analog one in the video is the correct one, "AC"?
a) Do you know if it's good enough? If yes do you know for how long?
If applying a DC voltage across these sensors polarizes them one way or the other.. could that be used as a cheap way to nudge some of the ones you have their closer to accurate?
I accidentally dropped the sensor in water
It showed 100% at first
Now the humidity is showing 20%
But it is actually 56% inside the incubator
What should i do now
Are these little units resettable? After you bring them to 75%, is there a reset button than allows you to make it read correctly? I could not tell if there was a reset button when you took it apart. Enjoyed your video. Thanks
There's no calibration feature on them.
@@BigClive Thank you for the clarification
Brilliant vdeo. Do you know how long it usually takes for a hygrometer to stabilise, for instance if you move it from one place to another?
Usually just an hour or two.
Dear Mr Clive, if you have the time, could you test the various resistors and pads to figure out how to get the temperature to display in Fahrenheit? I see the LCD does have "F" next to the "C", and this LCD does look purpose made for this hygrometer. I'd love if I could meaningfully read the temperature in the U.S!
I bought 5. Would buy 20 more if they read in °F.
In case you didn't figure this out, the typical examples tend to have a couple of pads labeled c/f and if you jumper them together you get Fahrenheit instead of the default Celsius.
Wow, thanks! Geez those are tiny pads, I didn't even see them before without a magnifying glass. Lowercase 'c/f' to the very right edge of the board, centered vertically.
I've got a humidity sensor for plants with the same board as shown on the photo and a probe for the flower pot, so I can water my plants automatically ... and I corrodet two sensors in about 3 months and the plants were overwatert, really bad idea with DC!
Yeah, I had the same issue with the plant water indicators. They corroded, went high resistance and continually said the soil was dry.
1:21
Middle-left: 75% @ 18.5c
Bottom-right: 75% @ 19.5c
hmm...