Help with Hygrometer

I know this subject pops up a lot, but what is a good hygrometer? I have an Acu-rite with a probe right now, but here's my story. We have cypress mulch and our screen top 3/4 covered with plexi glass. We heat with a UTH and a heat lamp for ambient temps. We're not sure if the gauge is actually measuring correctly? We can mist the probe directly and the humidity never reads above 47-50... You can see that the mulch is wet and right where the lamp dries it out.. We put the probe on the far wet side and still have 45%.? The tanks glass shows condensation on well over half the tank from the previous days misting and still 45% or so.. It does change readings, but it's hard to believe it is that dry in there?

The Acurite doesn't measure humidity on the probe, the humidity sensor is behind the screen on the box.

The issues with (cheap) digital hygrometers is they measure the micro changes in conductivity caused by the presence of water vapour. The changes are very very small. Many other things can change the reading too, dirt/dust can impede the reading. Even a slight manufacturing error can grossly alter the reading (why they have such a range for accuracy some are 5% +/- some are up to 20% +/- ) Poor solder joints crushed wires can effect the readings. The point is they are very fragile and frail if they are to hold the orginal accuracy.

Good digital hygrometers are too expensive and far to fragile to be used around a snake. (IMO) this leaves good analogue units. They are robust (I have one that ended up in a water bowl over night and is still reading correctly a year later)

What to look for,

1. a METAL face card not a paper one paper swells and warps with water and can prevent the indicator from moving. (all the reptile analogue ones I have seen all are paper cards)

2. a metal spring system (not hair... hair is more accurate, and fragile they do not stand up well)

3. a calibration screw this allows a simple salt test to be done and the unit corrected to accurate again if it is suspect. (google salt test hygrometer)

I have quite a number of ones that fit this criteria, I test them (because I am OCD) every 6 months most are with in 2% or better and very rarely beyond 5%RH off. Cheap and reliable and robust the perfect solution.

something like this one...
http://www.amazon.com/Cheaphumidors-.../dp/B000H69QXE

The down side is they have a magnetic attachment that sucks. I toss the 'magnet' they come with re-glue the steel disk on the back and use a good magnet and have few issues again.

Quote:

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Originally Posted by The Serpent Merchant

The Acurite doesn't measure humidity on the probe, the humidity sensor is behind the screen on the box.

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Well that makes sense... I was honestly thinking it would measure the outside temp at the prob instead of the box, which you keep indoors.. I put the box inside just to check and it is at 56% and climbing.. Sad thing is we also have a Repti- somthing Analog one from Petsmart.. It's reading 75%, who knows how good that one is, others told me it was junk and that's why we went with the Acu-rite... Haha, at least I know it's close to being the right humidity for her.. I kept worrying she would try to shed and it only be 40% I know it's still low for a shed, but better than 43-46% that I thought it was in her tank!

Thanks for the answers Kitedemon too.. I'll look into an Analog one.. I guess we'll wait and see how well the Repti one matches to the acu-rite one while they're both in the tank.

The probe measures the outside temperature, inside the box there is a second temperature sensor (the inside temperature sensor) and the humidity sensor

The problem with the analogue hygrometers from petsmart isn't that they don't work out of the box, but that they quickly stop reading accurately.

Quote:

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Originally Posted by The Serpent Merchant

The probe measures the outside temperature, inside the box there is a second temperature sensor (the inside temperature sensor) and the humidity sensor

The problem with the analogue hygrometers from petsmart isn't that they don't work out of the box, but that they quickly stop reading accurately.

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Well so far the digital is up to 65% and the 1st time in the tank the Analog is up to 75-78% (hard to read)