Rockwell Automation 1746-NT4 Series B,D17466.6.1 SLC 500 4-Channel Thermocouple/mV Input Module User Manual - Manual (Page 112)

Publication 1746-UM007C-EN-P - July 2004
C-4 Thermocouple Restrictions
“Type T thermoelements are not well suited for use in nuclear
environments, since both thermoelements are subject to significant
changes in composition under thermal neutron irradiation. The
copper in the thermoelement is converted to nickel and zinc.”
“Because of the high thermal conductivity of Type TP
thermoelements, special care should be exercised in the use of the
thermocouples to insure that both the measuring and reference
junctions assume the desired temperatures.”
ASTM Standard E230-72 in the Annual Book of ASTM Standards [1972]
specifies that the standard limits of error for Type T commercial
thermocouples be ±2 percent between -101 and -59C, ±0.8C between
-59 and 93C and ±3/4 percent between 93 and 371C. Type T
thermocouples can also be supplied to meet special limits of error,
which are equal to one half the standard limits of error given above
(plus a limit of error of ±1 percent is specified between -184 and
-59C). The recommended upper temperature limit for protected Type
T thermocouples, 371C, applies to AWG 14 (1.6mm) wire. For smaller
wires it decreases to 260C for AWG 20 (0.8mm) and 240C for AWG 24
or 28 (0.5 or 0.3mm).”
E Type Thermocouple (Nickel-Chromium vs. Copper-Nickel <Constantan>)
“Type E thermocouples are recommended by the ASTM Manual [1970]
for use in the temperature range from -250 to 871C in oxidizing or
inert atmospheres. 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 suitable
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).”
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.