A Thermocouple consist of two electrical conductors of dissimilar material connected at one end (the hot junction), the two free ands are connected to the measuring instrument via a reference junction (the cold junction). The connection of the these two materials provides an electromotive force (emf).
The thermoelectric voltage produced depends on the materials of the thermocouple wires and the temperature difference between the hot junction and the cold junction.
To measure temperature accurately the cold junction tempereture should be kept constant, If a local reference junction is not available, the thermocouple is extended by means of extension or compensating cable to a reference junction of known temperature (most indicators incorporate a cold junction compensation circuit). Thermocouple can be supplied with or without a protective sheath.
In addition to thermocouples in accordance with the JIS, ANSI, BS and DIN, such as K, J, E, T, R, S, B, types, we also furnish various types of special thermocouple iincluding Tungsten Rhenium and Nicrosil - Nisil combinations, etc.
The type E thermocouple is suitable for use at temperatures up to 1650oF (900oC) in a vacuum, inert, mildly oxidizing or reducing atmosphere. At cryogeenic temperatures, the thermocouple is not subject to corrosion. This thermocouple has the highest EMF output per degree of all commonly used thermocouples.
The type J may be used, exposed or unexposed, where there is a dificiency of free oxygen. For cleanlines and longer life, a protecting tube is recommended. Since JP (iron) wire will oxidize rapidly at temperatures over 1000F (5400C), it is recommended that larger gauge wires be used to compensate. Maximum recommended operating temperature is 1400oC (760oC)
Due to its reliability and acuracy, Type K is used extensively at tempeatures up to 2300oF (1260oC). It's goog practice to protect this type of thermocouple with a suitable metal or ceramic protecting tube, especially in reducing atmostpheres. In oxidizing atmostphere, such as electric furnaces, tube protection is not always nessesary when other condition are suitable; however, it is recommended for cleanlines and general mechanical protection. Type K will generally outlast Type J because JP (iron) wire rapididly oxidizes, especially at higher temperatures.
This nikel-based thermocouple alloy is used primaily at high temperatures up to 2300o (1260oC). While not a direct replacement for Type K, Type N provides better resistance to oxidation at high temperature and longer life in application where sulfur is present. It also outperforms Type K in K's aging range.
This thermocouple can be used in either oxidising or reducing atmospheres, though for longer life, a protecting tube is recommended. Because of its stability at lower temperatures, this is a superior thermocouple for q wide variety of applications in low and cryogenic temperatures. It's recommended operating range is -330° to 660°F (-200 to 350°C), but it can be used to -425°F (-269°C) (boiling helium).
Maximum recommended operating temperature for Type S or R is 2640°F (1450oC); Type B is recommended for use at high as 3100°F (1700°C). These thermocouple are easily contaminated. Reducing atmospheres are particularly damaging to the calibaration. Noble metal thermocouples should always be protected with a gas-tight ceramic tube, a secondary tube of porcelain, and a silicon carbide or metal outer tube as condition require.
TSMIFLEX is a trade name of SOKITECH'S sheathed thermocouple that is composed of a fine gauged metal sheath in which high purity MgO powder is tightly compacted around thermoelement wires.
M. I. Cable was first developed to meet the requirement for a fire-resistant cable, free of flammab;e materials, that would neither cause nor promote a fire. Because of its unique contrucyions M. I. Cable will continue to work effectively during a fire. It generally resists to install and provides extremely compact, neat surface wiring, yet its durable enough for direct burial.
By virture of its integrated structure composed of thermoelement wires, insulating material and a protection tube, SMIFLEX has very quick response to temperature changes.
With its tightly compacted from SMIFLEX has high mechanical strength and pliability up to bending radius equal to 2 times of the sheath O. D.
Excellent resistance to Heat, Corrosion and Pressure:
As high purity MgO powder is tightly compacted in a heat resistant metal tube, SMIFLEX is highly gas-tight, no corrosion from surrounding atmospheres and withstands high pressures up to 500kg/m2.
From very fine gauge of 1.0mm to 12,7mm in O.D. and up to 300 meters in length are available. Thermoelement wires of 2-pairs and 3-pairs are also available.
From cryogenic -200oC to high temperature +1,200oC can be measured.
Thermoelement wires are welded together directly at hot end of sheath to form a hot junction. Not recommended for type T annd R due to wide difference in melting points between composed metals and alloying compatibility. To overcome such a difficulty, apatented special junction is made on request. Quick response and suitable at high temperature and pressure but not recommended for use in hostile, vibrating and noise generating field.
Thermoelement wires are welded together to from a bare hot junction by protruding from the sheath. Quickest response and can detect even a slight temperature change instantaneously, but not durable for long time in corrosive, high temperature and high pressure atmospheres. Care must be exercised to prevent from moisture ingress at low temperature or during storage.