Hygrometer Accuracy...

[berty3000]

Hello,

I have had this thermometer and hygrometer, with a digital display, from amazon for some time. The brand is Thermopro. Seems decent, although I've never had anything to compare it to.

As I want to monitor humidity in multiple rooms at once, I have just bought a new system called X-sense, also from amazon. It has a base station and three hygrometers, which communicate readings to an app on my phone using WiFi.

The problem I'm having is the differences being reported by these devices.

At the moment, I have them together in a room - they've been there for at least an hour. The readings are:

Thermopro: 52% RH and 20C

X-sense: 58.4% RH and 19.3C

Now, the blurb for the x sense devices does say 2-3% +/- accuracy, and the x sense ones are apparently calibrated at 25C, with accuracy supposedly varying again outside that... I wouldn't mind if they were apart by 1% or so, but 6% seems a bit much. Can these be trusted?

Does anybody have experience of these devices and brands and know which ones are trustworthy?

I can potentially calibrate the new ones to the digital one. Or if they're just a load of rubbish I'd sooner get my £55 back.

 

[^woody^]

Unless you are conducting scientific experiments under what needs to be controlled conditions, the accuracy of domestic thermo/hydrometers does not really matter.

I have found digital units to be within their tolerances when compared to my professional devices, but with the vast array of makes coming out of China, who knows what you may get.

 

[berty3000]

Unless you are conducting scientific experiments under what needs to be controlled conditions, the accuracy of domestic thermo/hydrometers does not really matter.

I have found digital units to be within their tolerances when compared to my professional devices, but with the vast array of makes coming out of China, who knows what you may get.

But I want to know what the humidity levels are in my house. What would you suggest?

 

[Northman]

It is very easy to do a calibration check on a hygrometer as creating a standard reference is simply a matter of making a saturated salt solution. Thermopro provide instructions here:

https://buythermopro.com/how-to-calibrate-a-hygrometer-hygrometer-calibration/

and a more detailed table is here:

Saturated Salt Solutions - Controlling Air Humidity

A salt solutions can be used maintain a particular value of relative humidity.

www.engineeringtoolbox.com

Takes a while for the units to stabilise, but if you put all them all in the same controlled reference environment you can see how far from the reference value they are, and either adjust them as necessary (if possible) or just make a note of the difference and apply it to any readings. If the unit is well out of its given spec, then you can choose to send it back.

 

[^woody^]

But I want to know what the humidity levels are in my house. What would you suggest?

Just use them. 5% tolerance is not really of any relevance for your purpose ..... unless it's for a grow maybe?

 

[berty3000]

Just use them. 5% tolerance is not really of any relevance for your purpose ..... unless it's for a grow maybe?

LOL!

No, it is more that RH in my house is borderline acceptable. At or just below 60%, despite all my efforts (I've explained this in PIV thread just posted so won't repeat here). Point is, being at 55% or 65% represents an important threshold difference.

 

[berty3000]

It is very easy to do a calibration check on a hygrometer as creating a standard reference is simply a matter of making a saturated salt solution. Thermopro provide instructions here:

https://buythermopro.com/how-to-calibrate-a-hygrometer-hygrometer-calibration/

and a more detailed table is here:

Saturated Salt Solutions - Controlling Air Humidity

A salt solutions can be used maintain a particular value of relative humidity.

www.engineeringtoolbox.com

Takes a while for the units to stabilise, but if you put all them all in the same controlled reference environment you can see how far from the reference value they are, and either adjust them as necessary (if possible) or just make a note of the difference and apply it to any readings. If the unit is well out of its given spec, then you can choose to send it back.

That's brilliant, thanks for sharing it! I may well try this out over the weekend.

As things stand right now, I've had the Thermopro and the three x-sense units together in the same position.

They all now agree that the temperature is 18.9C, so that's good news. It does seem to take a little while for the thermometers on these things to adjust, so probably worth leaving them a few hours in any given place before trusting them. And try to leave them in one position generally.

However, the Thermopro shows 54% RH, whereas the x-sense units all state that it is 58.4%.

Interestingly, the hygrometer on my dehumidifier - which I don't usually place much stock in - agrees with the Thermopro that it is 54%.

So I could calibrate the x sense units down to 54%, or the in between position of 56.2%, or maybe just assume, taking an average between the devices, that they will tend to overestimate by ~2%. As it happens, if they're going to lie I'd rather they do so upwards than downwards.

Other thing is to try this salt test...