Rockwell Automation 1746-NT4 Series B,D17466.6.1 SLC 500 4-Channel Thermocouple/mV Input Module User Manual - Manual (Page 110)

Publication 1746-UM007C-EN-P - July 2004
C-2 Thermocouple Restrictions
“ASTM Standard E230-72 in the Annual Book of ASTM Standards
[1972] specifies that the standard limits of error for Type J commercial
thermocouples be ±2.2C between 0 and 277C and ±3/4 percent
between 277 and 760C. Limits of error are not specified for Type J
thermocouples below 0C or above 760C. Type J thermocouples can
also be supplied to meet special limits of error, which are equal to one
half the limits given above. The recommended upper temperature
limit for protected thermocouples, 760C, applies to AWG 8 (3.3mm)
wire. For smaller wires the recommended upper temperature
decreases to 593C for AWG 14 (1.6mm), and 371C for AWG 24 or 28
(0.5 or 0.3mm).”
K Type Thermocouple (NIckel-Chromium vs. Nickel-Aluminum)
“This type is more resistant to oxidation at elevated temperatures than
the Types E, J or T thermocouples and consequently it finds wide
application at temperatures above 500C.”
“Type K thermocouples may be used at “liquid hydrogen”
temperatures. However, their Seebeck coefficient (about 4uV/K at
20K) is only about one-half of that of E thermocouples. Furthermore,
the thermoelectric homogeneity of KN thermoelements is generally
not quite as good as that of EN thermoelements. Both the KP and the
KN thermoelements do have a relatively low thermal conductivity and
good resistance to corrosion in moist atmospheres at low
temperatures.”
“Type K thermocouples are recommended by the ASTM [1970] for
continuous use at temperatures within the range -250 to 1260C in
oxidizing or inert atmospheres. Both the KP and the KN
thermoelements are subject to oxidation when used in air above
about 850C, but even so, Type K thermocouples may be used at
temperatures up to about 1350C for short periods with only small
changes in calibration.”
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.