Calibrating thermometers

[slim1836]

How do you calibrate your thermometers? I have three adjustable thermometers
(2 tru-tels) and all show different numbers. :killingpcI don't know which to believe.

I laid the stems on on a hotplate and in the lead pot and get different numbers on each. The difference is 100-150 degrees.:killingpc

I was thinking of putting them in the oven but can I trust the numbers on the oven dial? Would putting them in the oven mess up the cover of the dial?

After a couple of hours I gave up and thought I would get input from the group.

Appreciate all advice.

Slim

[obssd1958]

A glass filled with crushed ice and water above the level of the ice = 32 degrees F once the water temp has stabilized with the ice temp. Give it 10 to 15 minutes.


:-)

[Typecaster]

If you put them in boiling water they should read 212º, so that would at least give an idea how close they are. I would expect that the difference would remain the same over all temperatures for each thermometer.

Whichever one is fathest off is the one I'd experiment with…IIRC, there's a nut that clamps the dial head to the stem on the Tru-Tels. I should think that you'd loosen the nut, rotate the dial so 212º lines up with the pointer, and retighten the nut.

But I'd contact the manufacturer first—I wouldn't be surprised if there isn't a recalibration service offered. I'm not a thermometer doctor, and I don't even play one on TV, so my hypothesis is worth exactly what you paid for it. But you do have spares…

Richard



Richard

[slim1836]

obssd1958,

That won't help as the range of the thermometers are 200-1000 degrees.

Any other suggestions?

Slim

[slim1836]

Typecaster,

I'll give that a try, thanks. Even with that method, IMHO, one would have to calibrate it as soon as the water starts to boil as the temp rises during the process and is not steady.

I would like to calibrate it closer to casting temps if possible, that's why I thought about putting them in the oven. With the oven, I should be able to calibrate all three the same even if the actual temp is not what is shown on the oven dial. Just my 2 cents.

Slim

[slim1836]

OOPS,

Just realized I posted on Reloading Equipment instead of Casting Equipment.

Moderators feel free to move these posts if needed.

Slim

[1hole]

The ONLY standard you have is the boiling water, set one correct for that and you will have done all you can do at home.

Happily, it really won't matter. Set two aside and use ONE. Experimention will soon show the indicated temp for your best casting point. That thermometer will allow you to return to that temp anytime. (Which is, after all, exactly the same as you would have to do anyway.) After you learn the temp you prefer on the one, adjust the others to read the same and you're done.

[slim1836]

1hole,

Thanks for the input, that's the direction I'll probably take.

Slim

[Bent Ramrod]

If you can get pure lead, the melting point is 617 degrees F. That of pure tin is 442 degrees F. You would need to set your heat to a point where enough melt is available to insert your thermometer but enough solid metal is around to establish that you are still at the melting point. Once all is liquefied, the temperature will of course continue to rise. Also, make sure the thermometer probe is not touching the bottom or sides, but is contacting only the liquid.

In the absence of pure materials, there ought to be some melt temperatures of various solders available from manufacturers. If you can secure a couple of these, you can do the same operation. With two temperatures, a straight line can be generated that shows the calibration factor for your thermometer; i.e., how close the actual temp is to the reading.

[mike in co]

the boiling water temp is 212 plus or minus elevation.....

so adjust for elevation and boil water...this should get you a good starting point...

mike in co

[John Boy]

Slim, got $635 to spare?
http://www.teltru.com/p-484-check-temp-calibrator-model-212-setpoint-at-212-degrees-f-single-hole-unit.aspx :holysheep
The accessories will run you another $105

Or if you can find them anymore, Harbor Freight had digital thermometers with K-type probes. IIRC, they are accurate within +/- 2 degrees. Use that as a master thermometer

[geargnasher]

If you can get pure lead, the melting point is 617 degrees F. That of pure tin is 442 degrees F. You would need to set your heat to a point where enough melt is available to insert your thermometer but enough solid metal is around to establish that you are still at the melting point. Once all is liquefied, the temperature will of course continue to rise. Also, make sure the thermometer probe is not touching the bottom or sides, but is contacting only the liquid.

In the absence of pure materials, there ought to be some melt temperatures of various solders available from manufacturers. If you can secure a couple of these, you can do the same operation. With two temperatures, a straight line can be generated that shows the calibration factor for your thermometer; i.e., how close the actual temp is to the reading.

Bingo. I have some 99.99% pure assayed lead that I use for calibrating themometers and PID thermocouples since it is more in the useful range. Calibrating at 212* may not guarantee it will be close at 700*. IIRC pure lead melts at closer to 621.5*, depends on how many decimals you carry when converting. Close enough for a town this size.

Gear

Gear

[mooman76]

Oven temps can vary by 25 degrees or more between kicking on and off not to say they could be off to start with. The boiling water sounds the best to me. At least it will get you close and give you a standard.

[c3d4b2]

the boiling water temp is 212 plus or minus elevation.....

so adjust for elevation and boil water...this should get you a good starting point...


Here is a link

http://wiki.answers.com/Q/How_does_the_elevation_and_air_pressure_affect_the _boiling_point_of_water