Rockwell Automation 1771-IXHR , D17716.5.80 HIGH RESOL.THERMOCOUPLE - Manual (Page 57)

Thermocouple Restrictions
Appendix C
CĆ4
alters the calibration. They should also not be used in atmospheres that promote
”green–rot” corrosion (those with low, but not negligible, oxygen content).”
“ASTM Standard E230–72 in the Annual Book of ASTM Standards [1972]
specifies that the standard limits of error for Type K commercial thermocouples
be +/–2.2C between 0 and 277C and +/–3/4 percent between 277 and 1260C.
Limits of error are not specified for the Type K thermocouples below 0C. Type
K thermocouples can also be supplied to meet special limits of error, which are
equal to one half the standard limits of error given above. The recommended
upper temperature limit for protected Type K thermocouples, 1260C, applies for
AWG 8 (3.3mm) wire. For smaller wires it decreases to 1093C for AWG 14
(1.6mm), 982C for AWG 20 (0.8mm), and 871C for AWG 24 or 28 (0.5 or
0.3mm).”
R (Platinum-13% Rhodium vs Platinum) and
S (Platinum-10% Rhodium vs Platinum) Type Thermocouples
“The ASTM manual STP 470 [1970] indicates the following restrictions on the
use of S {and R} type thermocouples at high temperatures: They should not be
used in reducing atmospheres, nor in those containing metallic vapor (such as
lead or zinc), nonmetallic vapors (such as arsenic, phosphorous or sulfur) or
easily reduced oxides, unless suitably protected with nonmetallic protecting
tubes. They should never be inserted directly into a metallic primary tube.”
“The positive thermoelement, platinum–10% rhodium {13% rhodium for R}, is
unstable in a thermal neutron flux because the rhodium converts to palladium.
The negative thermoelement, pure platinum, is relatively stable to neutron
transmutation. However, fast neutron bombardment will cause physical damage,
which will change the thermoelectric voltage unless it is annealed out.”
“The thermoelectric voltages of platinum based thermocouples are sensitive to
their heat treatments. In particular, quenching from high temperatures should be
avoided.”
“ASTM Standard E230–72 in the Annual Book of ASTM Standards [1972]
specifies that the standard limits of error for Type S {and R} commercial
thermocouples be +/–1.4C between 0 and 538C and +/–1/4% between 538 and
1482C. Limits of error are not specified for Type S {or R} thermocouples below
0C. The recommended upper temperature limit for continuous use of protected
thermocouples, 1482C, applies to AWG 24 (0.5mm) wire.
T (Copper vs Copper-Nickel <Constantan*>) Type Thermocouple
“The homogeneity of most Type TP and TN (or EN) thermoelements is
reasonably good. However, the Seebeck coefficient of Type T thermocouples is
moderately small at subzero temperatures (about 5.6uV/K at 20K), being
roughly two–thirds that of Type E thermocouples. This, together with the high
thermal conductivity of Type TP thermoelements, is the major reason why Type