Rockwell Automation 1746-NT4 Series B,D17466.6.1 SLC 500 4-Channel Thermocouple/mV Input Module User Manual - Manual (Page 113)

Publication 1746-UM007C-EN-P - July 2004
Thermocouple Restrictions C-5
“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, 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 (0.8mm) and 427C for
AWG 24 or 28 (0.5 or 0.3mm).”
S and R Type
Thermocouples S (Platinum-10% Rhodium vs. Platinum)
R (Platinum-13% Rhodium vs. Platinum)
“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 suitable 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.”
IMPORTANT
The Constantan element of Type J thermoelements is
not interchangeable with the Constantan element of
Types T or N due to the different ration of copper
and nickel in each.