Trying to calibrate a wh8040 digital hygrometer

[Shalloy46]

I've just received my wh8040 digital hygrometer from eBay and am trying to calibrate it using the salt test.

For those who do t know this test you fill a bottle cap 3/4 full with salt then add some distilled water to make a slurry. You place this and your hygrometer into a small sealed container or zip lock bag and wait 6-12 hours for it to stabilise. The humidity should be exactly 75%.
I did this with my wireless hygrometer and it was only 1% out which is acceptable.

But while trying to test the wh8040 my readings are all over the place. When I first put the humidity and temp sensor in the RH climbs to over 95% even though my wireless sensor reads around 75%. If I open the lid it drops instantly but climbs again as soon as I close it up. A mate of mine brought one of these and he said it was already calibrated. The calibration only goes 7 % either way and mine seems to be more than 7% out.

No matter what I do the RH just keeps climbing all the time and won't drop much at all.

Any ideas on what could be wrong?

[Shalloy46]

Anyone?

[wheels]

I can only guess that it's faulty.

Phil

[Shalloy46]

Yes but out of the salt test container it seems to behave okay. Even if I take the temp probe out and leave it on the bench next to the container the humidity drops.

Surely someone has one of these and has done the salt test with it and can advise if they had the same issues? I've obtained a refund and brought a new one but now have to wait another four weeks to get it from China.

[RodinBangkok]

I know nothing of this type unit, but in general you may want to check your calibration using a simple wet bulb measurement some info here:

http://www.engineeringtoolbox.com/dry-w ... d_682.html

The air flow around the wet bulb can effect the its temp somewhat, that perhaps may be an issue with the sensor your using, have you asked the manufacturer for a FAQ sheet or calibration procedure.

You may not need to calibrate it just use a wet bulb comparison to see if your close.

[Shalloy46]

Interesting article there RodinBangkok. It was definitely stuffed so I got a refund and ordered a new one. It arrived from China in five days which is a record. This one works much better