Thermometer Calibration

[Electrician_LU_357]

I just bought a miljoco thermometer for my kettle. It has a calibration screw on the back to calibate it, i know water boils at 212 degrees but my thermometer reads 209 degrees. Is this an accurate way to calibrate it? Is there a better way to do this?

 

[passedpawn]

Nope. boil at sea level = 212.

 

[Sawdustguy]

I just bought a miljoco thermometer for my kettle. It has a calibration screw on the back to calibate it, i know water boils at 212 degrees but my thermometer reads 209 degrees. Is this an accurate way to calibrate it? Is there a better way to do this?

The best way to calibrate any thermometer is with an ice bath. An ice bath is exactly 32*. If you know your elevation you can calculate at what temperature your water will boil.

 

[abracadabra]

I bought a calibration (lab) thermometer @ my LHBS for about $5. Who really gives a ---------- if it's accurate at boiling and freezing. You want accuracy at around 150*f and 170*f also accuracy around pitching temp is good depending on how and where you are using it. If it's boiling you can see it, same goes for freezing. You don't need a thermometer for that.

I know the boiling and freezing calibration method is often touted both here and elsewhere on the web. But it's your mash and sparge temps where you want accuracy. So what possible good does being right on the money at boiling get you if you are off 8*f at mashing temp.

Calibrate for the temp you want to hit.

Northern brewer has a lab thermometer for $6.99

 

[sigmund]

Calibrate for the temp you want to hit.

Just how do you propose that be done? What constant do you suggest be used to calibrate a thermometer to 152°?

With freezing and boiling, they are repeatable and can be adjusted for elevation. At least if you test at both extremes and get good readings it's safe to assume that the readings in between will be close.

 

[Sea]

I bought a calibration (lab) thermometer @ my LHBS for about $5. Who really gives a ---------- if it's accurate at boiling and freezing. You want accuracy at around 150*f and 170*f also accuracy around pitching temp is good depending on how and where you are using it. If it's boiling you can see it, same goes for freezing. You don't need a thermometer for that.

I know the boiling and freezing calibration method is often touted both here and elsewhere on the web. But it's your mash and sparge temps where you accuracy. So what possible good does being right on the money at boiling get you if you are off 8*f at mashing temp.

Calibrate for the temp you want to hit.

Northern brewer has a lab thermometer for $6.99

What guarantees that the lab thermo is/will stay accurate?

My thermometers are just resistors, so if they are accurate high and low, it's very unlikely that they are inaccurate in the mid-range.

To the OP: 209 F boiling corresponds to about 1667 ft in elevation, so if you are close to that then your thermo is accurate at boiling. It's also effected by barometric pressure, but if your close, don't worry about it.


.

 

[Ohio-Ed]

What guarantees that the lab thermo is/will stay accurate?

My thermometers are just resistors, so if they are accurate high and low, it's very unlikely that they are inaccurate in the mid-range.

To the OP: 209 F boiling corresponds to about 1667 ft in elevation, so if you are close to that then the thermo is accurate at boiling. It's also effected by barometric pressure, but if your close, don't worry about it.


.

You can check the accuracy of your lab thermometer by checking it in Boiling Water and an Ice Bath...

I bought one and it said my water was boiling at 110c... I returned it.

 

[abracadabra]

Just how do you propose that be done? What constant do you suggest be used to calibrate a thermometer to 152°?

With freezing and boiling, they are repeatable and can be adjusted for elevation. At least if you test at both extremes and get good readings it's safe to assume that the readings in between will be close.

By adjusting the adjustable thermometer so that it's reading and lab themo are equal. at the temp you are trying to hit. Is how I would propose to do it.

Feel free to ASSUME anything you'd like.

Have you ever heard the saying that when you ASSUME you make as A$$ out of U and ME.

 

[david_42]

A solution of ethanol and water boils between 78.2C and 78.3C, depending on the ratio. A very easy process, commonly used in high school chemistry classes.

 

[Rushis]

You can check the accuracy of your lab thermometer by checking it in Boiling Water and an Ice Bath...

I bought one and it said my water was boiling at 110c... I returned it.

Did you account for dissolved solids in your water before returning your thermometer? Colligative properties are a *****

 

[abracadabra]

What guarantees that the lab thermo is/will stay accurate?

My thermometers are just resistors, so if they are accurate high and low, it's very unlikely that they are inaccurate in the mid-range.

.

Are you aware that the resistance of resistors change over time? Are you aware that some resistors are more accurate in the coded value of their resistance than others. I've seen digital thermometers that are accurate at boiling and freezing and off in the ranges in between so it's not only likely but very likely they are off in the ranges in between.

As far as a guarantee goes if I wanted to be anal about it I go drop a couple of thousand $ on calibation thermometer.

 

[Sea]

Are you aware that the resistance of resistors change over time? Are you aware that some resistors are more accurate in the coded value of their resistance than others. I've seen digital thermometers that are accurate at boiling and freezing and off in the ranges in between so it's not only likely but very likely they are off in the ranges in between.

As far as a garantees goes if I wanted to be anal about it I go drop a couple of thousand $ on calibation thermometer.

I am. I'm just saying that a high quality resistance thermo should be accurate enough for homebrewing purposes for many years.

And what's the point of checking a quality thermo with a $6.99 special, when you can't be sure it's right?

 

[Rushis]

What guarantees that the lab thermo is/will stay accurate?

You're correct to question whether a laboratory grade thermometer (sealed mercury or alcohol type) is initially accurate. But once the graduations are made on that thermometer there is absolutely no way it can "drift". The thermal expansion coeffcient of mercury or the appropriate alcohol does not change, consequently a lab thermometer will always be precise.

Just to be sure you can always get an ASTM certified thermometer

 

[sigmund]

By adjusting the adjustable thermometer so that it's reading and lab themo are equal. at the temp you are trying to hit. Is how I would propose to do it.

Feel free to ASSUME anything you'd like.

Have you ever heard the saying that when you ASSUME you make as A$$ out of U and ME.

So, what you are saying is that you bought a lab thermometer that you use for calibrating? How do you know that it's accurate, or did you just assume that since it's called a lab thermometer, it's accurate?

Using an uncalibrated thermometer to calibrate another thermometer doesn't quite cut it.

The assume comment was a tad childish, don't you think? It was funny on The Odd Couple, didn't cut it here.

 

[sigmund]

You're correct to question whether a laboratory grade thermometer (sealed mercury or alcohol type) is initially accurate. But once the graduations are made on that thermometer there is absolutely no way it can "drift". The thermal expansion coeffcient of mercury or the appropriate alcohol does not change, consequently a lab thermometer will always be precise.

If that were the case, then there would never be a need to certify a thermometer. If the graduations are shifted or any number of other production errors occur, the thermometer will be off.

It's safe to say that for the average brewer, a certified thermometer will be good for the life of the thermometer, but an uncertified one should at least be calibrated to ensure it's in the ballpark.

 

[Ohio-Ed]

Obviously thermometers are a great conversation starter...

I was once told that you need need one thermometer or three... If you have three use one of the two that measure closest. Well, I have a drawer full. I think the more you have, the more doubt you end up with. I was sure that when I bought a nist traceable one my problems would be over. Turns out that SOB was off by 10%.

So... while I haven't done it just yet, here is my plan... I have a friend that works at a Lab. They have the ability to VERY accurately set ovens. I'm gonna buy another "Lab" thermo and have him calibrate it in an oven set at 155 degrees. (I won't care what it reads, if it says 160, I'll know that it is really 155). I should then be able to use that to calibrate my other thermometers in/at the most critical range for brewing.

 

[IrregularPulse]

I use my Fluke meter and that's good enough for me

 

[Ohio-Ed]

I use my Fluke meter and that's good enough for me

Yup... wish I had one I trusted and had not been drawn into spiral of distrust. :cross:

 

[Sawdustguy]

Are you aware that the resistance of resistors change over time? Are you aware that some resistors are more accurate in the coded value of their resistance than others. I've seen digital thermometers that are accurate at boiling and freezing and off in the ranges in between so it's not only likely but very likely they are off in the ranges in between.

As far as a guarantee goes if I wanted to be anal about it I go drop a couple of thousand $ on calibation thermometer.

Today, most good metrology labs use Constant Temperature Calibration Baths, accurate to +/- 0.008*C. Here is an example Constant Temperature Calibration Baths.

 

[Ohio-Ed]

Today, most good metrology labs use Constant Temperature Calibration Baths, accurate to +/- 0.008*C. Here is an example Constant Temperature Calibration Baths.

Yep... gonna buy me one of those. That way when I fire up my turkey fryer, I can tell EXACTLY (+/- 0.008C) how much I need to adjust the regulator...

 

[Rushis]

If that were the case, then there would never be a need to certify a thermometer. If the graduations are shifted or any number of other production errors occur, the thermometer will be off.

Same statement, different diction.

Any laboratory grade thermometer will come with ASTM certification from the manufacturer. Considering that a liquid thermometer of this type will never drift, it makes a useful primary standard for calibrating any other temperature measuring device.

 

[MultumInParvo]

Yep... gonna buy me one of those. That way when I fire up my turkey fryer, I can tell EXACTLY (+/- 0.008C) how much I need to adjust the regulator...

You don't already have one?? How do you make beer without knowing the temp to within +-.0008? I bet you rack on the cake too!:fro:

 

[Electrician_LU_357]

Thanks everybody for the input i figured with my elevation I should be at about 209 for boiling which is were im at so i should be pretty close. Still gonna look into getting a certified thermometer to compare to. Thanks again for the help..

 

[Sawdustguy]

Yep... gonna buy me one of those. That way when I fire up my turkey fryer, I can tell EXACTLY (+/- 0.008C) how much I need to adjust the regulator...

I posted that tongue in cheek, but if you could afford one of those would you buy me a Brew Magic System for Christmas?

 

[Ohio-Ed]

I posted that tongue in cheek, but if you could afford one of those would you buy me a Brew Magic System for Christmas?

Guy... After lurking at your posts and lifting ideas from your hardwork I probably owe you a Brew Magic.

I'll run it by the SWMBO and if she agrees, watch your doorstep for that BIG box

 

[mordantly]

I use my Fluke meter and that's good enough for me

K thermocouple?

 

[abracadabra]

Yep... gonna buy me one of those. That way when I fire up my turkey fryer, I can tell EXACTLY (+/- 0.008C) how much I need to adjust the regulator...

!
Thanks for getting my day started with a good laugh!

 

[Sawdustguy]

Guy... After lurking at your posts and lifting ideas from your hardwork I probably owe you a Brew Magic.

I'll run it by the SWMBO and if she agrees, watch your doorstep for that BIG box

Ed,

I would promise you my first born son, but he is married and has kids.

Guy

 

[CrookedChris]

I develop/apply temp sensors for industrial engine controls for a living. I've done A LOT of work crunching temp sensor accuracy data. I'll give this debate my two cents. Take 'em or leave 'em.

Any "lab grade" or NIST traceable temperature measurement device besides a thermometer will drift over time. A mercury or alcohol thermometer is as good as your going to get but even a thermometer has some error. And not all NIST traceable thermometers are created equal. The NIST (ASTM E1 is the actual standard) requirements are defined by the scale and precision of the thermometer.

If you do want to do a calibration and unless you have money that you just need to find a way to get rid of I'd save yourself the money on a NIST device (thermometer or otherwise) and just to a calibration in an ice bath (0 deg C) and/or boiling (using RO water and compensated for altitude).

We have various high accuracy baths in our lab but when we need a quick evaluation of a sensor's performance we use an ice bath. It's quick, easy, and "good enough".

 

[micksmith]

I had a similar problem last year and I had to resort to sending it away to be calibrated properly. I was experiencing all kinds of problems with mine thermometer being just 2 degrees out. Sent mine to Lambda. More info here http://www.lambda-cal.co.uk/temperature_calibration.php on how they do it.