Hygrometer help!

[scoopy82]

I'm just wondering if there is a difference between humidity and relative humidity? I have 2 digital thermometres/hygrometers in my incubator, I calibrated them both using the salt water method and they both read the same (they were out by 5% so both read 70%), but when I put them in the incubator - they both read very differently! One is at 50% and the other is at 20%. The one that reads 50% has RH written next to the reading so I figured that meant relative humidity where as the other one says nothing. So is there a difference? And which one should i be taking notice of? The one that reads 20% came with my Hovabator and is advertised as being very accurate. I want to get this sorted now before lock down so I can have the right humidity for hatching. Anyone with any idea - your thoughts would be greatly appreciated!

 

[tec27]

Yes they are different.

http://weatherfaqs.org.uk/node/29

http://www.crh.noaa.gov/lmk/soo/docu/humidity.php

 

[scoopy82]

Thanks heaps for that information - I understand the difference now

So going by that which should I be taking more notice of in my incubator?
I'm guessing the absolute humidity, but someone please tell me if this is correct. And considering that the thermometer/hygrometer that came with the bator measures the absolute humidity I think that is the one to go with.

 

[tec27]

I actually had no idea about this topic so i googled it for you and found the above information. Now im freaking out about mine cause i dont know which humidity ive been reading lol. Im going to guess and say absolute humidity. Relative humidity is a measure of the actual amount of water vapor in the air compared to the total amount of vapor that can exist in the air at its current temperature. I dont think that bold would apply to us. I only think that we are measuring the actual amount of water vapor (moisture) in the air, regardless of the air's temperature which is absolute humidity.

 

[scoopy82]

Oh thank you tec27 - your a smart cookie, I was going to google but didn't really know where to start! I think your right though, as the temperature in the bator is suppose to be a constant, i dont think the relative humidity is relevant so to speak lol!
The first time I hatched in my home made bator i only used the RH reader, and wondered why it was so hard to raise it - i ended up with 3rd degree burns to my foot for my efforts but thats a whole other story! Anyway, I callibrated the hygrometer that came with the bator and its only off by 5% so I am going to trust that one

Makes me wonder now too though how many people that have had issues with humidity in the past may have accidently been reading the wrong thing???

 

[tec27]

This is my first time incubating eggs which are due to hatch in the next week. So i have been googling and using this website like crazy to make sure i am doing everything right. For what google told me, humidity isnt a large deal so when i bought my hygrometer i wasnt too picky on which one i bought. However, i have now learned that humidity, maybe not as important as the temperature, is still important. Yes a couple of percentages off wont do a great deal but the correct range in humidity is ideal for a successful hatch. I am glad that you brought this topic to my attention. For my next hatch, i will end up buying a hygrometer that i actually know what it measures (relative or absolute). I had no idea that there were different hygrometers. I definitely do believe that some people were just as "ill informed" as we were on this topic and could have screwed up a potentially good hatch because of it.

 

[Kermit's shadow]

Incubator humidity quoted is essentially always RH - relative humidity - the amount of water that the air holds compared to saturation - which is 100%.
Any meter will always read RH, they may exist, but I have never seen or heard of a cheap absolute humidity meter - they are expensive laboratory instruments, not dime store items. Absolute humidity can also never be a % - a % of what? Absolute humidity is measured in absolute amounts - a weight of water per volume of air for instance, or dew-point, or water vapour pressure.
Electronic humidity meters, unless they are very expensive are very unreliable and very approximate. FAR more accurate to buy a good quality scale and use egg weight loss - a WAY better way to spend the money. Or use a wet-bulb glass thermometer - infallible, unlike electronic meters, and a fraction the price.
If you use salt solution to check a meter, the solution MUST be saturated - loads of crystals sitting in the bottom of the container, undissolved, and the container must be well sealed and the container and meter probe left to settle for as long as it takes to get steady reading - at least an hour I would say.
A correct reading at 75% though, is no guarantee at all that the meter will be correct at any other RH. A correct reading at some temperature other than incubation temperature is also no guarantee that the meter will read correctly in the incubator - the container with salt solution and probe need to be at incubation temperature to check things out - ideally in the incubator.

Unfortunately, absolute faith in cheap electronic wizardry is common, but very often misplaced when it comes to complex and critical things like incubation RH.

RH control is probably MORE important than temperature control - temperature control should be OK if the incubator is well designed, RH control is down to you. An egg has to loose around 12-15% of its weight during incubation - 2% either side and the chicks will struggle, and often fail, to hatch.

 

[scoopy82]

Right - well I'm back to totally confused. So your saying Kermits shadow that RH is always measured as a % and most (however cheap) digital readers display RH. Cos both of mine display a % reading.
My salt solution was certainly saturated, and both were left in an airtight bag for 24 hours. I infact used the same cup of salt solution for both just incase i made the mixture a little different for either.
tec27 - i would never have brought this up either if after calibrating both and being so excited they were both fairly close to 75% and both reading the same, that they read totally different in the bator. I dont know what to do now. I have a very accurate set of digital kitchen scales that measures grams, but I dont think I'm experienced enough to go by that just yet (read I have no experience at all pretty much). I might have to suss out a super accurate hygrometer that isn't a digital one, which of course means spending more money but I'm sure will be worth it in the end. Can anyone reccommend one that can be shipped to Australia???
And the learning curve continues . . .

 

[Kermit's shadow]

Salt solution is salt solution - or certainly so far as we are concerned here for this use.
The only % measure of water content of air that can possibly be quoted is RH - the clue is in the acronym - RELATIVE humidity - relative to saturation, 100%. An absolute measure is exactly that - absolute, not relative and a % is a realtive measure - it is a comparison to 100% - percent - per 100.
Did you check them at 99F? If not - that will almost certainly be the problem. An RH of 100% at around 77F is what you need for incubation - warm that air to 99F and you will have around 50% RH - give or take a little (I have not ploughed through the tables and conversions to calculate it exactly). Any RH at room temperature is a long way from the same RH at incubation temperature.
The problem with humidity is that the commonest measure is RH%, but when it comes to comparing and understanding the relative bit, people get confused. In some ways it would be easier to talk dew-point, but do you really want to get confused? (Dew point is the temperature at which the RH of air with moisture in it, rises to 100% - for incubation conditions, that is around 77F - cool incubator air to around 77F and the Rh is around 100%).

A super-accurate hygrometer is a wet-bulb glass thermometer - costing very little and absolutely will not go wrong. A super accurate scale - J-Scale JS100XV - was about $40-50 the last time I checked.

 

[scoopy82]

Sorry to pick your brains Kermits shadow but if I heated my spare incubator up to 77f and put the salt solution in it, sealed it so it was air tight and then checked the humidity with my digital RH hygrometer are you saying that it should read 100%?

Sorry had to edit as I re-read and realised that at 99f it should not read 100%.