Calibrating a Pyrometer at -100¦F 1

[ParcoEngineer]

I need to calibrate a pyrometer for use at sub-zero temperatures. We are considering using a cryogenic liquid with a 1 atm boiling point around -100°F. The plan is to obtain this liquid in a refrigerated vessel and allow it to come to it's boiling temperature, using that as a calibration point. We are looking for +/- 1°F accuracy.

Does this sound like a good method? Has anyone else here performed a low-temperature calibration before? How did you do it? Any suggestions for an appropriate cryogenic liquid?

Thanks in advance for your help.

Rich

 

[isofilm]

Hi ParcoEngineer,

Is this an IR pyrometer?


Best regards,
Daniel L. Thomas, CTO
Novel Concepts, Inc.

http://www.novelconceptsinc.com

 

[ParcoEngineer]

isofilm,

No, it's a Cole-Parmer Digi-Sense thermocouple thermometer.

Rich

 

[isofilm]

Hi ParcoEngineer,

I don’t know if your meter has the capacity for multiple calibration points, if so, you may want to calibrate to 0°C (32°F) (melting point of water) and -78.5°C (-109.3°F) (boiling point of carbon dioxide, dry ice). Both these temperatures are easily achieved.

For the 0°C (32°F) calibration, I use finely crushed ice from a blender (add enough cold water to mix), then I strain the water leaving just the ice (like a snow cone). Leaving the finely crushed ice in the strainer (so the melting water can drain), place the thermocouple deep into the slushed ice, near the bottom of the strainer (but not touching the strainer), so that just melting water flows by the thermocouple. Once the reading reaches equilibrium, set your meter to 0C.

For the -78.5°C (-109.3°F) calibration, I do nearly the same thing except instead of using a blender, I simply pulverize the dry ice in a bag with a hammer. And since the dry ice sublimes, you don’t have to worry about where you put the thermocouple as long as it’s a couple inches deep in the crushed ice.

The reason for the finely crushed ice, is that the bulk ice temperature may be much colder than its melting point, but as the size decreases so does the temperature differential between the bulk and surface temperature of the ice. You will easily demonstrate this fact by measuring the temperature of a fresh-out-of-the-freezer ice cube. Try to find 0°C near the surface of a melting ice cube, good luck.


Best regards,
Daniel L. Thomas, CTO
Novel Concepts, Inc.

http://www.novelconceptsinc.com

 

[ParcoEngineer]

Daniel,

Thank you, I'll try that.

Rich

 

[EdStainless]

The traditional choice is to use a small glass test tube. Put your TC into the tube filled with a liquid (alcohol is nice) making sure that it doesn't touch the sides. Then place the test tube into an ice bath or dry ice bath. This keeps things physicaly cleaner.

Check out the emf curves for your thermocouple first. Some TCs don't like sub-zero service, there are abrupt transitions in their output.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm