1. Types and characteristics of
common thermocouples
1. K type thermocouple nickel chromium (nickel silicon (nickel
aluminum) thermocouple)K-type thermocouple is a base metal
thermocouple with strong oxidation resistance. It can measure the
medium temperature of 0-1300 ℃, which is suitable for continuous use
in oxidizing and inert gases. Its short-term use temperature is 1200 ℃,
long-term use temperature is 1000 ℃, and its relationship between
thermal potential and temperature is approximately linear, which is the
largest thermocouple at present.However, it is not suitable to be used in
the atmosphere of vacuum, sulfur, carbon and alternate oxidation-
reduction; when the oxygen partial pressure is low, the chromium in the
nickel chromium electrode will be preferentially oxidized, which makes
the thermal potential change greatly, but the metal gas has little effect
on it, so the metal protective tube is mostly used.Disadvantages of K-
type thermocouple: (1) the high temperature thermocouple stability of
thermoelectric potential is worse than that of n-type thermocouple and
precious metal thermocouple, which is often damaged by oxidation at
higher temperature (for example, over 1000 ℃); (2) the short-term
thermal cycle stability is not good in the range of 250-500 ℃, that is, at
the same temperature point, in the process of temperature rise and
temperature drop, the thermoelectric potential indication is different,
2. and the difference can reach 2-3 ℃;(3) The negative electrode will
undergo magnetic transformation in the range of 150-200 ℃, resulting
in the deviation of the graduation value from the graduation table in
the range of room temperature to 230 ℃, especially the time-
independent thermoelectric interference when used in the magnetic
field;(4) In the environment of high flux medium system irradiation for a
long time, the elements such as manganese (MN) and cobalt (CO) in the
negative electrode undergo metamorphosis, which leads to poor
stability and great changes in thermoelectric
potential.http://www.chinathermocouple.com
2S-type thermocouple (Platinum Rhodium 10 platinum thermocouple)
the positive component of the thermocouple is a platinum rhodium
alloy containing 10% rhodium, and the negative electrode is pure
platinum.Its characteristics are: (1) stable thermoelectric performance,
strong oxidation resistance, suitable for continuous use in oxidizing
atmosphere, long-term use temperature up to 1300 ℃, over 1400 ℃,
even in the air, pure platinum wire will recrystallize, so that the grain is
coarse and broken; (2) high accuracy, the highest accuracy level in all
thermocouples, usually used as a standard or measurement of higher
temperature;(3) It has a wide range of application, good uniformity and
interchangeability; (4) the main disadvantages are: the differential
thermoelectric potential is small, so the sensitivity is low; the price is
3. expensive, and the mechanical strength is low, so it is not suitable for
use in reducing atmosphere or with metal
vapor.http://www.tiankangcable.com
3E-type thermocouple (Ni Cr Cu Ni [constantan] thermocouple) E-type
thermocouple is a relatively new product. The positive electrode is Ni Cr
alloy and the negative electrode is Cu Ni alloy (Constantan).Its biggest
characteristic is that in the common thermocouple, its thermal potential
is the largest, that is, the sensitivity is the highest; although its
application scope is not as wide as K-type couple, it is often selected
under the conditions of requiring high sensitivity, low thermal
conductivity and allowing large resistance; the limiting conditions in use
are the same as K-type, but it is not very sensitive to the corrosion with
high humidity atmosphere.http://www.tksiliconerubbercable.com
4N-type thermocouple (Ni Cr Si Ni Si thermocouple)The main
characteristics of the thermocouple are as follows: under 1300 ℃, it has
strong temperature regulation and oxidation resistance, good long-
term stability and short-term thermal cycle recurrence, good nuclear
radiation resistance and low temperature resistance. In addition, in the
range of 400-1300 ℃, the linearity of n-type thermocouple is better
than that of K-type thermocouple. But in the range of low temperature
(- 200-400 ℃), the nonlinear error is large, and the material is
hardProcessing.
4. 5J type thermocouple (iron constantan thermocouple) J type
thermocouple: the positive pole of the thermocouple is pure iron, and
the negative pole is constantan (copper nickel alloy), characterized by
low price,It is applicable to the reduction or inert atmosphere of
vacuum oxidation. The temperature range is from - 200 ℃ to 800 ℃,
but the common temperature is only below 500 ℃, because the
oxidation rate of iron hot electrode is accelerated after exceeding this
temperature. If the wire with coarse wire diameter is used, it can still be
used in high temperature and has a long life. The thermocouple can
resist the corrosion of hydrogen (H2) and carbon monoxide (CO), but it
can'tUse in an atmosphere containing sulfur (s) at high temperature
(e.g. 500 ℃).
6T-type thermocouple (copper copper nickel thermocouple) T-type
thermocouple: the positive electrode of the thermocouple is pure
copper, and the negative electrode is copper nickel alloy (also known as
Constantan). Its main characteristics are as follows:Among the base
metal thermocouples, it has the highest accuracy and good uniformity
of the thermoelectric pole; its service temperature is - 200-350 ℃,
because the copper hot electrode is easy to oxidize and the oxide film is
easy to fall off, so when it is used in the oxidizing atmosphere, it can not
exceed 300 ℃, in the range of - 200-300 ℃, they have relatively high
5. sensitivity. Another feature of the copper constantan thermocouple is
its low priceThe cheapest one of several styling products.
7R-type thermocouple (platinum rhodium 13 platinum thermocouple)
the positive electrode of the thermocouple is a platinum rhodium alloy
containing 13% and the negative electrode is pure platinum. Compared
with S-type thermocouple, its potential rate is about 15% higher and
other properties are almost the same. This thermocouple is used most
in Japanese industry as a high temperature thermocouple, but less in
China.
