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USB hygrometers - any good?

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I've just been reading about these handy USB thermometer/ hygrometers in another thread.


The blurb says the software can automatically alert you when the dewpoint is reached. Very handy for dew control. They are incredibly cheap (<£20) on Ebay.

The blurb states that they are accurate to +/-5% relative humidity. Does anyone know whether this a useful degree of accuracy? Also, has anyone tried one? Are they any good or are they a pile of steaming stuff?


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  • 1 month later...

I got one of these and I'm quite impressed considering how cheap it was

I've already got a USB hub on my mount, so just plugged it into that and away we go! You can even see here the temp start to go up in the obs since I put the PC on


Edited by Euan
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Getting a measure of humidity within 5% would be pretty good under the circumstances - the observatory is not a "constant envirnment room!!!" Firstly you open the "roof" to let the air mix with outside, then you turn on lots of (warm) electro-gizmos and then stand there and breathe warm moist air over everything!!

I reckon these things would give an exellent indication of when you are likely to suffer from dew but they are only ever going to be a "rough" measure as there are so many variables.

Take a look at the graph (for a wet and dry bulb hygrometer - shamelessly nicked from the web!) to see some of the variables and how a tiny change in one can affect the others.

BTW you can make a wet and dry bulb type for the cost of two identical thermometers and a bit of old bandage!!


Edited by Bizibilder
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It looks good. Have you tested it against a 'mechanical' thermometer to see how accurate it is?

16.6c for the USB one and about 16c for the real one

I had to unplug it from a USB hub as it was picking up a few degrees from that. Now it's on an extension cable it seems fine, not bad I suppose

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