# Calibrating thermometer



## jameson_uk (25 Nov 2018)

So I get a temperature controller and now I have a raft of thermometers giving me a 3°C spread.  Most of the ones I use allow you to calibrate them but not sure of the best way.

I see mention of using iced water but will this still be reasonably accurate at 25°C?

Given most are +/- 1°C is it even worth it as I guess two thermometers that read 0°C correctly could be 2°C apart at 25°C??

I do I have a cheap liquid thermometer (no idea what is in it) which I always presumed was more accurate than ant of the digital ones but now I am not sure...


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## Keith GH (26 Nov 2018)

Sounds like a lot of unnecessary expenses.

Over all the years all I ever had was just two basic floating thermometers and in the latter years I bought a stick on the outside of the glass thermometer as well.

Every morning at feeding time I had the best thermometer and it was free, my finger.

Your water will vary depending where you place the thermometer in the tank also depending on your location it will either rise or lower depending on the seasonal temperatures.

Keith


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## jameson_uk (26 Nov 2018)

Keith GH said:


> Sounds like a lot of unnecessary expenses.



Indeed.  I got the basic liquid one with the tank but decided to _upgrade_ to a shiny LCD one.  This looked good so I got one for my second tank (and then noticed they were more than 2.5°C different (which makes me think Juwel's claim of +/- 1°C might not be true...)

Other thermometers have come with other stuff (I have a Seneye that was really bought as a PAR meter but is only really used as a thermometer).  Then I have one with TDS pen which I use for shrimp tank.  I also have one in current heater (although this was an emergency purchase and not something I wanted) and now I have one on the temperature controller (just a safety incase a heater does stick on).

At water changes I use the same thermometer to roughly match water so isn't an issue and my hand tells me the heater is working.  

What I guess I am more interested in is the livestock and just getting a baseline.  Otos for example seem want cooler (21°C-25°C) so just want to make sure that saying 24°C isn't really 27°C


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## Edvet (26 Nov 2018)

jameson_uk said:


> just want to make sure that saying 24°C isn't really 27°C


Only sure way is a themometer that either covers  zero degrees celcius ( metling ice) or 100 degrees celcius (boiling water).
I use a lab themometer if i want to make sure (Lab suplies store) or no themometer.


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## zozo (26 Nov 2018)

jameson_uk said:


> Otos for example seem want cooler (21°C-25°C) so just want to make sure that saying 24°C isn't really 27°C



The million dolar question..  What garanty do we have that the thermometer used to determine this information for us was realy that accurate?
Especialy id it was determined 30 years ago and never reviewed since then with more modern and alledgedly more accurate tools.

Which they are obviously not.. At least how do you know? I got 6 thermometers liquid and digital a few of the same make and non of them give excact same results. Some digitals do, only in a range from 20°C to 25°C, above 25° they start to get lost from eachother, than one says 29° and the other 27°, back down the 23° both give the same again. Reading the factory label all are sold as rather very accurate (obviously commercial bs to make you buy it).

Then it's iniminiminimo to pick me the one that suits me most, only use that one and still don't know zip if it's realy accurate.


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## george29 (26 Nov 2018)

Hi,

Many years ago when designing my own controller and having the same problem in establishing an accurate temperature reference as you are doing, I purchased one of the TropicMarin glass thermometers which seem to be still available but have few outlets, and  Amazon want £50+ for one.

If in the same position today think I would go for one of the Cole Palmer ones which have a variety of glass and digital ones with accuracy specification /prices

Whatever you use you need to test and check them in a large body of well circulated  tank water ( not by a spray bar), letting them settle for a minute before reading;   testing several  in a small glass or jar of water will give false readings as it cools too quickly etc.


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## dw1305 (26 Nov 2018)

Hi all, 





Keith GH said:


> Every morning at feeding time I had the best thermometer and it was free, my finger.


I do the same, put the back of my hand on glass, you can tell instantly whether the tank is  about right, too warm or too cold.  

It doesn't seem like a very effective method, but you can pick up any differences. 

cheers Darrel


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## george29 (26 Nov 2018)

dw1305 said:


> Hi all, I do the same, put the back of my hand on glass, you can tell instantly whether the tank is  about right, too warm or too cold.
> 
> It doesn't seem like a very effective method, but you can pick up any differences.



Agree with DW and Keith  if you have the experience, but , though only suffering one or two heating  failures over the years, having a temperature controller that gives a very loud low / high temperature alarm can be vital ,  they always tend to fail more during the winter nights  ...  when the most heating is needed, plus  you often need an extra louder piezo sounder closer to the bedroom.


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## jameson_uk (10 Dec 2018)

dw1305 said:


> It doesn't seem like a very effective method, but you can pick up any differences



That is it.  I can tell if the tank is warmer or cooler than normal but what I can't tell is whether normal is actually good or not.

None of the inhabitants seem to particularly struggle but I do wonder what effect temperature has.

Going to try and borrow a (hopefully) accurate lab thermometer from a chemistry teacher and use this as a benchmark to calibrate the others.


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## jaypeecee (27 Dec 2018)

I'm not comfortable checking a tank temperature subjectively, i.e. by touch. But I respect those for whom it does the trick. I use a Hanna HI-98501, which has a resolution of 0.1C and accuracy of +/-0.2C from -30C to +120C. Each unit comes with its own calibration certificate. But it will set you back about £45.


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