Thermocouple Restrictions
B–6
Publication 1794-6.5.7
“Type T thermocouples are recommended by the ASTM [1970] for
use in the temperature range from –184 to 371C in vacuum or in
oxidizing, reducing or inert atmospheres. The recommended upper
temperature limit for continuous service of protected Type T
thermocouples is set at 371C for AWG 14 (1.6mm) thermoelements,
since Type TP thermoelements oxidize rapidly above this
temperature. However, the thermoelectric properties of Type TP
thermoelements are apparently not grossly affected by oxidation
since Roeser and Dahl [1938] observed negligible changes in the
thermoelectric voltage of Nos. 12, 18, and 22 AWG Type TP
thermoelements after heating for 30 hours in air at 500C. At this
temperature the Type TN thermoelements have good resistance to
oxidation and exhibit only small changes in thermal emf with long
exposure in air, as shown by the studies of Dahl [1941].” ...
“Operation of Type T thermocouples in hydrogen atmospheres at
temperatures above about 370C is not recommended since severe
embrittlement of the Type TP thermoelements may occur.”
“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,
+/–.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).
Use this template for your appendices. If it were not for the different
running head, this would be your chapter 4 document.
Содержание 1794-IT8
Страница 1: ...User Manual Thermocouple Millivolt Input Module Cat No 1794 IT8 Allen Bradley ...
Страница 4: ...soc ii Summary of Changes Publication 1794 6 5 7 April 1997 ...
Страница 8: ...Table of Contents iv Publication 1794 6 5 7 ...
Страница 14: ...Overview of FLEX I O and your Thermocouple mV Module 1 4 Publication 1794 6 5 7 ...
Страница 64: ...Specifications A 10 Publication 1794 6 5 7 March 1997 ...