Need a temperature standard near 650 deg F

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110112-1259 EST

I need to calibrate a thermocouple somewhere around 650 deg F. I would like a material that can provide an accuracy better than +/-0.5 deg F. Anything in the range of 600 - 700 deg F is probably adequate.

63-37 tin-lead solder, eutectic, is listed at 361.4 deg F. This would be better than nothing but it is a big extrapolation to 650. Also I do not know how precise the alloy content is for commericial solder.

I have searched the Internet to a limited extent.

One interesting reference is
http://cmp.physics.iastate.edu/canfield/course/Calorimetry I.pdf
but has nothing to answer my specific question.

Maybe weressl might have some information.

When I ask this kind of question, then it leads to the question of fundamentally how do you make absolute temperature measurements? These have probably been done for many years with high accuracy, but probably not before 1850.

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GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
looks like boiling point of sulfur is close to your point ... see
nvl.nist.gov/pub/nistpubs/jres/106/1/j61man.pdf but I had to use Google's view as htm for some reason.

Trick to search is "fixed point" temperature ... and I included NIST
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110112-1628 EST

If the averaged noise level is a fractional part of a degree, short time stability (several hours) is also a fractional part of a degree, and I have an accurate reference standard, then why am I dreaming?

Certainly what can be achieved is at least dependent upon what is available as an absolute standard. How is absolute temperature measured with great accuracy?

The boiling point of water is 100.000 deg C at 760.0 MM of mercury. This is a defined standard I believe. Since these values are presented in tabular form down to 700.0 MM of mercury and the change is not linear I assume that instrumentation and techniques exist to allow these measurements to be made. The accuracy is certainly better than 1 part in 10,000 (0.01%), and maybe better than 1 part in 100,000 (0.001%).

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mrickey

Member
How about a thermocouple calibrator?

Omega Block Calibrator

or look at the whole line

Omega Thermocouple Calbrators

TC wire even with Special Limits of Error is stated as approximatly +- 1?C. I assume that is why you are trying to calibrate the TC itself rather than just the data collection device. If you account for the exact error of the TC and DAQ, then +- 0.5?F is not unreasonable. just keep in mind the calibration will be different for every piece of TC wire.
 

ZinskI/E

Member
Location
New Orleans, LA
I have seen a few different TC types (primarily K, J, and E) installed for this temperature range and all seem to perform well. If the issue is checking the TC for calibration against a known value, I would suggest using a steam generator. Using a Mollier chart or table of steam values, an exact temperature for a given pressure at saturation is a reliable standard as far as I'm concerned; certainly within the error of the element, transmitter, or DCS, let alone all three together.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
110113-1039 EST

Thanks to all for the suggestions.

This is an interesting area. Much to be learned.

The NIST paper suggest by GeorgeB is quite important. I have scanned much of it and some conclusions are:

1. Fixed point references can be very accurate. The accuracy will depend upon the purity of the material, and technique of use. For example the uncertainty is listed at 0.7 mK for gallium at 29.7646 deg C. Fixed point cell number Sn 95-1 is 231.928 deg C (449.470 F) with uncertainty 0f 0.36 mK (milli-centigrade). Zinc is 419.527 deg C (787.149 F) with an uncertainty of 1 mK. See section 6.2.2.3 .

2. Pure metal thermocouples of Au/Pt. See section 5.3. Uncertainties of 10 mK or less are mentioned, page 126.

Two Fluke references on Pt thermocouples, these are alloys, not pure metal:
http://www.hartscientific.com/products/5649-5650.htm
http://www.hartscientific.com/products/probes.htm

3. A Pt resistive sensor may be a good solution for a master for us.

I am also interested in whether lead could be used as a fixed point reference for our needs. At one Google location it is listed as -- 600.65 deg K, 327.5 deg C, 621.5 deg F, and 600.61 K, 327.46 C, and 621.43 F.

In my Google searching I found that melting point is used as a means of checking material purity. The following references are a slight digression, but interesting:

http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/MPProcedure.pdf
http://www.thinksrs.com/products/MPA100.htm
http://www.thinksrs.com/downloads/PDFs/Catalog/MPA100c.pdf
http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/DigiMeltVsMelTemp.pdf
http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/MP_CRS.pdf
http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/PvsT_MP.pdf

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