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bucket949
Stranger

Registered: 04/11/06
Posts: 155
Last seen: 16 years, 8 months
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Digital Hygrometer throwin me a curve ball
#6593324 - 02/21/07 11:04 AM (16 years, 11 months ago) |
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I bought a digital hygrometer/ thermometer yesterday to build my first tit incubator. I bought a nice fish tank heater and have it set at 83 degrees. The water is warm and in the inside walls of my incubator are warm . My thermometer has been saying its 72 degrees in my incubator which seemed wrong since the temp of the room is 70 degrees. I looked on the back of the digi to see if i could reset it or something. I found a switch that said "In" and "Out" it was set "In" I changed it to "out" and my temp was reading at 83 degrees. SO I assume this in and out mean indoor and outdoor but in my case what should it be. The outdoor reading seems more accurate but technically its indoors? ANy ideas?
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creamcorn
mad scientist


Registered: 03/13/06
Posts: 2,962
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Re: Digital Hygrometer throwin me a curve ball [Re: bucket949]
#6593364 - 02/21/07 11:15 AM (16 years, 11 months ago) |
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yes, its indoors and outdoors
the "indoors" setting takes a reading right at the device itself. in that case, you want it inside the TiT
the outdoor setting takes a reading from a temperature probe. it probably came with a piece of wire with a little metal nub at the end that plugs in to the device. the outdoor setting tells you the temp of that little metal nub, wherever you happen to locate it... not necessarily the outdoors. 
handy way to go about it is to run that wire inside the TiT, use the out setting, and you can keep the thermometer/hygrometer on the outside, so you can monitor temps at a glance without opening it up...
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bucket949
Stranger

Registered: 04/11/06
Posts: 155
Last seen: 16 years, 8 months
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Re: Digital Hygrometer throwin me a curve ball [Re: bucket949]
#6593430 - 02/21/07 11:28 AM (16 years, 11 months ago) |
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lol thats exactly what im doing i got the incubator under my desk and the nifty reader on top. I've had the probe in there all night and kept turning the temp up in the water. I hope I didnt cook them. I'm trying to get everything calibrated right now. I added more cold water to the tub and turned the heater down to 82 and i have a fan blowing on it hopefully adding to the waters decrease in temp. God that was a brain fart.
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cappa
Nerd
Registered: 02/12/06
Posts: 854
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Re: Digital Hygrometer throwin me a curve ball [Re: bucket949]
#6593487 - 02/21/07 11:39 AM (16 years, 11 months ago) |
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My experiments with digital hygrometers have shown that they vary GREATLY in their performance. Unless of course it's a HIGH END digital hygrometer. This means 'not available at the local store', unless it's a scientific supply store. Reasons:
1. They use the cheapest of humidity sensors. This usually expresses itself in poor repeatability. Forcing far more samples to be taken from the sensor and then averaged to obtain a reasonable final result. This accounts for a minimum of 1% error. Then add the fact that the cheap sensors are not expected to be highly accuracte anyways. Usually at least 3%+/- off. This +/-3% is what is advertised as the units accuracy. It's the accuracy of the sensor, not the unit.
2. Their supply and reference voltage needs to be what they were calibrated at. This happens for only a brief moment of the battery life cycle. Temperature also effects the accuracy of reference comparison proccess. Their are ways around this but it takes either more components on the board, or a higher end processing IC. Both raise the cost of the device.
3. Their are several formulas for deriving the 'true' rH from a sensor. The more precise you want to get, the more intense that mathematical formula becomes. In other words, you need a faster processing IC and extra memory to handle the complex formula in a timely manner. Again, this translates into higher manufacturing costs. So most companies use the 'basic' formula resulting in poor accuracy and repeatability. A large error occurs usually somehwere in the 2-5% in the math alone.
4. Optimum mycological environments are far from what the units where designed and calibrated for. Add another +/-3%.
5. Saturation. 90% rH will saturate those cheap sensors pretty quickly. So periodically removing them from the terrarrium and lettting them dry out for a few days is advisable. Their are specific proccesses for most of them, but they are out of the scope of this writing.
I've tested just about every electrical humidity sensor that's available to the electrical engineer for the purpose of designing an automated terrarium controller. Their are only a few sensors that are worth using IMO. However, they cost between $25-$75 dollars each, and that's just the sensor.
The good news: Most of the digi's will get you in the ball park though. Just don't expect them to be 'spot-on'.
The better news: Mason's hygrometers are easy and fun to use, and will always be less than 1% off if handled properly.
-------------------- Their are 10 types of people. Those that understand binary, and those who don't. ~Cappa.
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cappa
Nerd
Registered: 02/12/06
Posts: 854
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Re: Digital Hygrometer throwin me a curve ball [Re: cappa]
#6593515 - 02/21/07 11:47 AM (16 years, 11 months ago) |
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I just re-read the post and realized my post isn't exactly on topic. Oh well, food for thought I guess.
-------------------- Their are 10 types of people. Those that understand binary, and those who don't. ~Cappa.
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