Allen-Bradley CompactBlock LDX 1790D-4T0, Руководство пользователя

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Publication 1790-UM003A-EN-P
Thermocouple Descriptions C-3
The suggested upper temperature limit of 1700°C given in the ASTM
standard [7] for protected type B thermocouples applies to AWG 24 (0.51
mm) wire. This temperature limit applies to thermocouples used in
conventional closed-end protecting tubes and it is intended only as a
rough guide to the user. It does not apply to thermocouples having
compacted mineral oxide insulation.
Type E Thermocouples
This section describes Nickel-Chromium Alloy Versus Copper-Nickel Alloy
thermocouples, known as type E thermocouples. This type, and the other
base-metal types, do not have specific chemical compositions given in
standards; rather, any materials whose emf-temperature relationship
agrees with that of the specified reference table within certain tolerances
can be considered to be a type E thermocouple. The positive
thermoelement, EP, is the same material as KP. The negative
thermoelement, EN, is the same material as TN.
The low-temperature research [8] by members of the NBS Cryogenics
Division showed that type E thermocouples are very useful down to
liquid hydrogen temperatures (n.b.p. about 20.3K) where their Seebeck
coefficient is about 8mV/°C. They may even be used down to liquid
helium temperatures (4.2°K) although their Seebeck coefficient becomes
quite low, only about 2mV/°C at 4K. Both thermoelements of type E
thermocouples have a relatively low thermal conductivity, good resistance
to corrosion in moist atmospheres, and reasonably good homogeneity.
For these three reasons and their relatively high Seebeck coefficients, type
E thermocouples have been recommended [8] as the most useful of the
letter-designated thermocouple types for low-temperature measurements.
For measurements below 20K, the non-letter-designated thermocouple,
KP versus gold-0.07, is recommended. The properties of this
thermocouple have been described by Sparks and Powell [12].
Type E thermocouples also have the largest Seebeck coefficient above
0°C for any of the letter-designated thermocouples. For that reason they
are being used more often whenever environmental conditions permit.
Type E thermocouples are recommended by the ASTM [5] for use in the
temperature range from -200°C to 900°C in oxidizing or inert
atmospheres. If used for extended times in air above 500°C, heavy gauge
wires are recommended because the oxidation rate is rapid at elevated
temperatures. About 50 years ago, Dahl [11] studied the thermoelectric
stability of EP and EN type alloys when heated in air at elevated
temperatures. His work should be consulted for details. More recent
stability data on these alloys in air were reported by Burley et al. [13].
AB Drives