Stick on thermometers are they any good?

[heshtek]

I purchased a regular glass thermometer the other day and decided to run a test to see whether the stick on thermometer on my fermenter is displaying the correct temperature. The glass thermo that i bought came with some sort of certification saying it was scientifically calibrated and correct.

• The skinny of this story is that the glass thermometer displays a reading which is consistantly 2 degrees Celsius lower than the stick on thermometer on the side of the fermenter. Which one is correct? I am assuming the glass one is more accurate but if that is the case then its incredicble to think that those stick on ones are so far out of whack.
• I should also say that the fermenter that has the stick on thermo on it was purchased second hand. I have no idea how old it is. Am I correct in assuming that these stick on thermometers may become less accurate with time?

If anyone has any explanation about this I would be gratefull for any input.

 

[MHB]

They are generally pretty good, until they get boiling water poured on them a couple of times, then they are scraged...

There are two types of glass lab thermometers, total and partial immersion, it's important to use them the right way or they will disagree by a couple of degrees.
on the back of the thermometer it should tell you what sort it is, usually it will say either : -
"Total Immersion" that means the whole thermometer should be in what you are measuring.
Or "Partial Immersion" or "76mm Immersion" or just have a line around the thermometer, that type should only be stuck into what you are measuring as far as indicated, the rest should be at 20oC.
As the body of the thermometer either heats up or cools down the bore the liquid moves in gets fatter or skinnier so the same amount of liquid can give a different reading, both can be accurate when used correctly but wrong when used the wrong way.

Have a look at your thermometer I wouldn't be surprised if it is fine just used wrong
Mark

 

[verysupple]

Mark brings some good points, but there may be something more fundamental going on. I don't know what environment you FV was in when you did the test, but the wort in the outer region of the FV may actually be at a different temperature to that in the middle. If possible you should compare measurements taken at the same point in space at the same point in time.

Having said that, I wouldn't be at all surprised if the stick on thermometer was a couple of degrees off.

 

[DU99]

it's called tolerance..unless want you to send big $$$ to get really serious.i have one laser,two digitial as seen on MKR..they are all within a degree of each other.

 

[heshtek]

Thanks for the info. I looked at the glass thermometer I bought and it is a total immersion one. I totally immersed it and the results are still the same. I even took readings at the outermost inside part of the fermenter and the middle (they were the same). I suppose like DU99 says its just a tolerance thing. I'm just a newb to home brewing really. I did maybe 10 or so brews back about 7 years ago and are getting back into it. It is my understanding that you want to ferment ales at as lower a temp as possible to avoid certain bad flavours creeping in. Perhaps I need to keep in mind that there may be 2 degree difference in measurements when trying to drop the ferm temp down as low as possible.

 

[yum beer]

It is my understanding that you want to ferment ales at as lower a temp as possible to avoid certain bad flavours creeping in. Perhaps I need to keep in mind that there may be 2 degree difference in measurements when trying to drop the ferm temp down as low as possible.

Perhaps a little more reading to clarify your understanding.

 

[Ducatiboy stu]

Plastic fermenters have an insulating affect. The stick on jobs also tend to read the outside ambient temp. If you outside ambient temp is higher than wort temp the stick-on will read higher.

 

[Rod]

I had a similar problem see my post below


http://aussiehomebrewer.com/topic/79178-a-better-way-to-tell-the-temperature-of-your-fermenter/

my digital thermometer arrived today

stuck the prob onto the fermenter using blue tac

within a couple of minutes the temperature stabilized and gave a reading I thought was correct

checked with a hand held and got agreement

except the digital read to the 1st decimal point

and the handheld dial only read to the degree

happy