Hygrometer help!

[Kermit's shadow]

No.
It is a useful oddity of certain chemicals in saturated solution, that they produce a certain RH in the air above them. In the case of common salt (sodium chloride), the RH in a restricted air space above a saturated water solution is pretty stable at around 75%, irrespective of temperature (almost).

To check any meter, you really need to check at incubation temperature (for a whole variety of reasons), and ideally at incubation RH. Unfortunately, the chemical that produces an RH of around 50% (can't remember exact RH), is, if memory is correct again, magnesium sulphate. Common salt is easy to get.... magnesium sulphate?

The best way to use a salt solution to check an RH meter is to use a small(ish) jar and make a hole in the lid just big enough to take the probe, insert the probe and seal it with tape or similar. Be VERY careful not to get the salt solution on the probe. Put that in the incubator.

I hope that answers your question - your post probably doesn't read as you intended it to, or not to me anyway.

 

[scoopy82]

Sorry I do understand what your saying . . . I'm just trying to work out if there is any way I can use and understand the hygrometers/thermometers that I already have and just work out how far off they are. Sounds like that may just not happen. Anyway - thanks a heap for all your wonderful information, the more i learn the more questions i come up with and the more i ask and the more i learn . . . . and thoroughly enjoy it all!

 

[Kermit's shadow]

Excellent - taxing the little grey cells should always be an enjoyable experience.........

Seriously - a wet-bulb is fool-proof and will not go wrong/drift/go out of calibration. If you can fit one in the incubator, that is what to do.
What you should find is that if you can find and use the "correct" size water tray (aka plant pot saucer/ litter tray/cat food bowl/margarine tub), the Rh will be remarkably constant all year - I know that an 8 inch saucer in my machine will give 48-50% RH come rain come shine for most of the year.

I absolutely would not guarantee it, but you may find that one or both of the meters are useful, but read wrong - you might, just for instance, be able to use one to set and run the machine at a reading on the meter of 60%, which in reality is 50%RH. But that would assume that they are reasonably sensitive, just wrong by 10% in this example. Lots of electronic meters are not at all sensitive though............

 

[scoopy82]

Well guess who is about to hit ebay looking for a wet bulb hygrometer!!!!!!!!!!
I really wanna do this right, so thank you again for steering me in the right direction!
I totally love this forum

 

[Kermit's shadow]

Brinsea sell a tiny one - plenty of people I know use them. Not at all cheap for what they are though (IMO), and presumably available in Oz.

A couple of points about wet-bulbs - if possible use demineralised/deionised/distilled water to keep the wick clean - I have used the same wick for a few years that way and seen no difference in the reading with a new wick when guilt and doubt had me change it. If the wick seems dirty at all, change it.