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PostPosted: Thu Jan 06, 2011 3:04 pm 
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Superior Bird
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Location: Bendigo
I often get asked to recommend a thermometer for incubator use.

Buying a digital thermometer and expecting it to be correct is a risky business. It is a bit pot luck and whether you pay $2 or $50 there is no guarantee it won't read 0.5 degs too high or too low.

You can pay $2
http://cgi.ebay.com.au/New-Digital-LCD- ... 4aa6e6e951
or $17
http://cgi.ebay.com.au/Home-Brewing-Dig ... 230d1ddad2
for the same thermometer.
The only types of thermometer you can be reasonably certain will be accurate are the little digital medical types.
Image

You should have one of these to use as reference to check your incubator thermometer against. Just fill a sink with water at about 37.7 degsC put both in for 5 mins and compare readings. I say use a sink because with a cup or bowl the water cools too quickly. I actually sit both thermometers in for about 5 mins just to make sure they have time to reach the same temperature as the water. Take several readings and you should be right.
It pays to regularly check your thermometer because batteries do go flat eventually.

Don't change your incubator setting unless you check your thermometer first.

Obviously if you want to use one of these types
Image

that doesn't have have an external sensor on a lead or probe, you can't check this way. Don't worry, the chances of these being accurate enough for incubator work are very slim. Temperature can vary by about a couple of degrees and humidity about 20%.

Image
These are slightly different and have In - Out temperature readout. Designed to sit inside your house and read the Temperature and Humidity inside your house using sensors inside the case exactly like the previous. These ones also have an external sensor you poke outside your window to read outside temperature. If you push the right buttons you can use this outside temperature sensor setting and check it's accuracy using the sink method.
I have had one of these types (not this model/brand) and it was very accurate (pot luck) for a few years but slowly drifted out by 0.2 degs. I picked up on this drifting because it does pay to check regularly because batteries don't last forever.

Checking your thermometer using the above method is fairly easy and just takes 10 mins.
Lots of people on this forum do it so if you are unsure then just ask.
We would all love to be able buy a thermometer off the shelf and be able to trust it completely to be spot on accurate.
You will come across people who who swear by what the thermometer they use, but you should always check the thermometer you buy. They are your chickens so the responsibilty is yours. It isn't hard to do. If it seems to much of a hassle to check your thermometer, I don't have a lot of sympathy.



For those with a bit of electronics knowledge actually correcting your thermometer if it has a resistive type sensor is very easy.
DO NOT ATTEMPT THIS UNLESS YOU COMPLETELY UNDERSTAND WHAT I AM DOING HERE.

If you know your thermometer reads too high or too low then one of the two methods below will likely fix it.
Image
Now I assume the reason the thermometer is giving the incorrect reading is because the resistive sensor is either a tad too high or a tad too low. You should be able to see that in the diagram method 1 is a fix if the sensor resistance is too high and method 2 a fix if the sensor resistance too low.
In other words we are going to correct the thermometer by placing a fairly large resistor in parallel or a fairly small resistor in series with the sensor.

First thing we need to do is work out which method is going to work for us and find the value of the resistor that gets us spot on.

This is how I do it.
First cut the sensor lead, closer to the unit than the sensor, especially if it is going to be used in water.
Inside will be two wires or similar. Strip their ends back. Be generous so it is easy to twist and connect to each other and/or the resistor.

To Determine the method we need to use:
Start by trying method 1. Place a large resistor of about 100K in parallel as shown.
Did the reading move the in direction you wanted it too? If your thermometer was too high before does it now read a lower temp. Similarly if it read too low before does it now read higher.
Don't worry if it moved to little or way too far, did it shift the reading the way you wanted it too? If the answer is yes then this is the method that will work for you. You just need to find the correct resistor value that will get you spot on.

If it didn't move in the right direction you need to try method 2. Start with a resistor of about 100R and see how you go.

A couple of potentiometers would be handy as is a wide range range of resistor values.


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PostPosted: Thu Jan 06, 2011 11:29 pm 
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Proud Rooster
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Denis, well i didn't play around with the wires but you did prompt me to spend the last hour calibrating the 2 I have poking into a hovabator currently. (ones like your second picture, with a long lead and in and out temps.
I used the sink full of water method and compared at various temps between 36 and 38 with my clinical digital thermometer.

Then stuck all three through the hole in the hovabator an equal way down and compared and then also with the lead sensors down near the eggs but the clinical one only about 2inches (as that's as far as it goes without putting whole thing inside and disrupting by opening box).

Resulting in some fine tuning of the thermostat. And on each of my digi thermometers I have written the comparable temperatures e.g. 36.9 = 37.5 etc. They were pretty repeatable.

For the less techo people like me who don't want to fiddle with wires, comparing and making the allowance should be a reasonable method to use.

thanks for prompting me to do this!


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PostPosted: Fri Jan 07, 2011 9:40 am 
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Superior Bird
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What jaffakatie has recommended is spot on. Well done.


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PostPosted: Sun Mar 13, 2011 1:40 pm 
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Showy Hen
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Location: Central Qld near emerald
Denis wrote:

Obviously if you want to use one of these types

that doesn't have have an external sensor on a lead or probe, you can't check this way. Don't worry, the chances of these being accurate enough for incubator work are very slim. Temperature can vary by about a couple of degrees and humidity about 20%.


I read this a few times to make sure i was reading it right as i have a tendency to read things to quickly and not take it in. So i thought i would ask to be completely sure are you saying that this little wall mounted thermometer weather station type things are a waste of space?
I only ask as i am incubating eggs in an incubator for the first time and i am using one of these thermo- hygrometer things as well as an old style thermometer and they are both relatively agreeing on the temp, .1 or .2, difference so i though the hygrometer could be trusted?? Now i am worried.

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PostPosted: Sun Mar 13, 2011 2:07 pm 
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Superior Bird
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Accurate humidity readings aren't important. The most effective way of keeping humidity about right is usually just a matter of keeping water in one channel/container and then maybe adding water to a second channel/container just right at the end when they are actually hatching.


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