Rockwell Automation 1771-IXHR , D17716.5.80 HIGH RESOL.THERMOCOUPLE - Manual (Page 55)

Thermocouple Restrictions
Appendix C
CĆ2
The negative thermoelement is subject to deterioration above about 871C, but
the thermocouple may be used up to 1000C for short periods.”
“The ASTM Manual [1970] indicates the following restrictions .. at high
temperatures. They should not be used in sulfurous, reducing or alternately
reducing and oxidizing atmospheres unless suitably protected with protecting
tubes. They should not be used in vacuum (at high temperatures) for extended
times, because the Chromium in the positive thermoelement vaporizes out of
solution and alters the calibration. They should also not be used in atmospheres
that promote ”green–rot” corrosion (those with low, but not negligible, oxygen
content).”
“The negative thermoelement, a copper–nickel alloy, is subject to composition
changes under thermal neutron irradiation since the copper is converted to
nickel and zinc.”
“ASTM Standard E230–72 in the Annual Book of ASTM Standards [1972]
specifies that the standard limits of error for the Type E commercial
thermocouples be +/–1.7C between 0 and 316C and +/–1/2 percent between 316
and 871C. Limits of error are not specified for Type E thermocouples below 0C.
Type E thermocouples can also be supplied to meet special limits of error,
which are less than the standard limits of error given above: +/–1.25C between
0 and 316C and +/–3/8 percent between 316 and 871C. The recommended
upper temperature limit for protected thermocouples, 871C, applies to AWG 8
(3.3mm) wire. For smaller wires the recommended upper temperature decreases
to 649C for AWG 14 (1.6mm), 538C for AWG 20 (.8mm) and 427C for AWG
24 or 28 (0.5 or 0.3mm).
J (Iron vs Copper-Nickel <Constantan*>) Type Thermocouple
The J thermocouple “is the least suitable for accurate thermometry because
there are significant nonlinear deviations in the thermoelectric output from
different manufacturers. ... The total and specific types of impurities that occur
in commercial iron change with time, location of primary ores, and methods of
smelting.”
“Type J thermocouples are recommended by the ASTM [1970] for use in the
temperature range from 0 to 760C in vacuum, oxidizing, reducing or inert
atmospheres. If used for extended times above 500C, heavy gage wires are
recommended because the oxidation rate is rapid at elevated temperatures.”
“They should not be used in sulfurous atmospheres above 500C. Because of
potential rusting and embrittlement, they are not recommended for subzero
temperatures. They should not be cycled above 760C even for a short time if
accurate readings below 760C are desired at a later time.”
“The negative thermoelement, a copper–nickel alloy, is subject to substantial
composition changes under thermal neutron irradiation, since copper is
converted to nickel and zinc.”