# Which Thermometers



## KipperSarnie (13 Dec 2016)

Recommendations required for an "Accurate" thermometer I have inaccurate ones comping out of my ears all give different readings.  Testing the same water in the same place, stick on, floating, sinking ones Grrrrrrr!

I wondered about buying a brewing thermometer!


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## ian_m (13 Dec 2016)

After going through I don't know how many digital thermometers, including expensive Juwel digital and cheapy China digital ones I now have one of these.

Apart from occasionally falling off, hasn't have to had batteries replaced, hasn't had water leaked inside and doesn't have a poor display to read. Its temperature reading matches the temperature on my heater thermostat which is handy.




 

https://www.jbl.de/?lang=en&mod=products&func=detail&id=2495


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## zozo (13 Dec 2016)

How do you know what thermometer is accurate? You must have some calibration standard, like one thermometer you trust the most and compair all others to this one. I kinda notice every manufacturer or vendor states their product is accurate, but still it differs with others stating the same..

I even have a few digital thermostats which have a calibration feature and ofcourse function as thermometer at the same time. But here also the accuracy differs when temperature goes up or down. Example i calibrate at 22 degrees and within a scale from 19 to 25 degrees both are pretty close.. But in the summertime during a heatwave the calibration was a few degrees of. The calibrated meter gave 31 degrees the other standerd meter 29 degrees. So the higher temperature the more the toleration.

Not realy a problem  i can not imagine a situation where 2 degrees are life threatening in any situation.

In digital meters working with a heat sensitive resistor (thermistor) usualy ntc 10k ohm for household and hobby use, which all my thermostates and meters use the quality of the resistor gives the toleration. this can vary from 1% to 5%. If you get one with 5% it actualy means from 0 to 5%, so it could be 2 meters can have a difference within 5 degree accuracy.

So regarding electronic meters see those thermistor tolerancy specs. 1 degree (%) tolerancy is pretty accurate.

Never expect a thermometer beeing accurate with the heating from the tank.. All have a bimetalic thermostat, these are the most inaccurate possible.

Tip: If you have digitals using a NTC 10k, these come waterproof actualy pretty cheap. Like 0.60 cents a piece if you buy a lot of 5.  Buy a lot and give them all the same resistor from the same batch with the same tolerance.. 

Oh  Edit.. I bought a set of these a few years ago.. Still working and all are pretty close together. 
http://www.ebay.com/itm/New-Mini-Di...913594?hash=item1a16c1413a:g:mncAAOSwbYZXf4GN


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## KipperSarnie (13 Dec 2016)

zozo said:


> How do you know what thermometer is accurate? You must have some calibration standard, like one thermometer you trust the most and compair all others to this one.



That's the problem I do not know which are accurate, I have no idea!
The tanks concerned I want around 30°c so to be honest a couple of degrees do matter.
Thanks for the link for the NTC 10k but what do you plug them into?  I'm Old & analog!


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## zozo (13 Dec 2016)

Sorry edited it a bit to late..
I bought a set of these a few years ago.. Still working and all are pretty close together.
http://www.ebay.com/itm/New-Mini-Di...913594?hash=item1a16c1413a:g:mncAAOSwbYZXf4GN

Use one set of LR44 cells in a year time or so.. Also come cheap $2.50 for a set of 10 cells..

They use these NTC 10K probes.. And the accuracy is in this probe.. Digitaly it aint rocket science, the electronics give a number to a x resistance at x temp. So if the probe is of different make (tolerance) the display gives a differnet number.

If a few degree do matter, dunno as long as i do not know which is most accurate apperntly it doesn't matter in the range i measured.. As said at the heatwave i had a difference of 2 degrees from 29 to 31 but nothing drastic happened for the time it was alarming high. Oh my Ph penn has a temp sensor and gave a different number don't remember what excactly.. I stopped worrying about it.. 

Still have a difference in the small test tank.. The heater is set to 24 to get a 21 on the hangon and the digital tels me 22.8..


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## mort (13 Dec 2016)

I use a normal glass thermometer and test the accuracy by putting it in a glass of water surrounded by lots of ice. After a few minutes the water will be zero and you can read the difference. It does mean you need to remember that difference. I will say that temperature is less important for me as the heater is set to 20c, so I have a lot of upwards leeway. I do have a simple plug in controller for my reef tank that controls the heater and a fan to cool the tank if need be. It means if the heater fails or sticks on I have warning.


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## AverageWhiteBloke (13 Dec 2016)

The bizarre thing is for some reason I always thought that a glass thermometer would always just work, it was a done deal until you smashed it. Until recently that is, I have a RCS tank in my unheated office which is only heated when I'm in so gets pretty cold this time of year. The tank has been kept at about 19/20 deg so I've been trying to gradually raise the temperature in there up to 24deg as I'm intending moving all the RCS to my tank at home prior to stripping the shrimp tank down for a new project next year. It was heated with a Hydor external but every increase I made seemed to make no difference. The Hydor being 2nd hand when I got it as part of a job lot of other equipment I assumed was giving up so I bought a nano heater to replace it. Next day I went in and the tank was at 15 deg even though it was set at 22. Came to the conclusion that the 25 watt nano heater wasn't up to the job so I dug out an old 100watt heater I had lying around which was physically too big for the tank but better than nothing and the next day was back at 20 deg even though that was set at 22 as well. Strange thing was the tank felt quite warm.to the touch so I took the glass thermometer home and put it into the tank next to another thermometer. 24 deg on my home glass thermometer, 24 degrees on the heater controller, it's a Boyu heater so it lights up the numbers on the control with red for heater on and green for at that temp but the thermometer from the shrimp tank still said 20!
Go figure, I probably bought the nano heater unnecessarily but on the plus side my Hydor is probably still working. Just never thought for one minute it could have been the glass thermometer at fault.


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## zozo (14 Dec 2016)

I use these to control my heaters. 
http://www.banggood.com/DC-12V-50-t...tch-Heat-Cool-Temp-p-933303.html?rmmds=search
The controler itself runs on a 12 volt powersupply, it doesn't need a big one 1 amp is enough.  The sra-12vdc-al relay is rated to 20 Amps at 125VAC. That is rather high, as long as you stay way bellow it, it also handles 220VAC with ease. For me it does for over a year now. I use this one because i still had a set unused and have a 12 volt led setup above the sump. But the same thermostat also comes in a 220VAC rated version. Its fairly the same thermostat build in a housing with a slight stronger relay. 
http://www.banggood.com/220V-Touch-...Switch-Thermostat-p-1047883.html?rmmds=search

Got 2 heaters in the sump total 125 watt.. Both set to 24°C.. The thermostat relay switches 2 powersockets 220VAC where the heaters are pluged in.. The temp probe hangs in the tank.. The other tank i use the same with a DIY 120 watt DC12 volt heater inline.

What is nice about this little thermostat it can be calibrated with a 0.1 accuracy to the thermometer in use and in my case it is set to 22°C..
If it ever fails the heaters are still set to only 24°C.. 

Anyway once it is calibrated to a trustworthy thermometer and the thermostat is placed in a way so the display is in view. Then this is also your thermometer. ¨

Im very satisfied with these thermostats and their calibration option. They work like a charme.


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## darrensp (14 Dec 2016)

I use a similar set u to zozo it is a temperature controller for a vivarium  but it is 240v.

Here is a link to the same one I use however mind was a lot cheaper than this company is selling it for http://m.ebay.co.uk/itm/Temperature...%3Afd4fcd031580a6a4a6a3441fffd6968b%7Ciid%3A4


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## tubamanandy (14 Dec 2016)

I've got a long glass thermometer with mercury (lab grade) - really happy with it but not that practical


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