Simple Temperature Sensor Type K

• Customized: Customized
• Certification: RoHS, ISO9001, CE
• Brand: Ohmalloy
• Display Type: Ohmalloy
• Transport Package: Cusotmized
• Specification: 0.2MM
• Model NO.: KK
• Trademark: OHMALLOY
• Origin: China
• HS Code: 9025900090
• Production Capacity: 50000PC/Month

Product Description

Types

Certain combinations of alloys have become popular as industry standards. Selection of the combination is driven by cost, availability, convenience, melting point, chemical properties, stability, and output. Different types are best suited for different applications. They are usually selected on the basis of the temperature range and sensitivity needed. Thermocouples with low sensitivities (B, R, and S types) have correspondingly lower resolutions. Other selection criteria include the chemical inertness of the thermocouple material, and whether it is magnetic or not. Standard thermocouple types are listed below with the positive electrode (assuming ) first, followed by the negative electrode.

Nickel alloy thermocouples

Characteristic functions for thermocouples that reach intermediate temperatures, as covered by nickel alloy thermocouple types E,J,K,M,N,T. Also shown are the noble metal alloy type P, and the pure noble metal combinations gold-platinum and platinum-palladium.

Type E

Type E (chromel - constantan) has a high output (68 µV/°C) which makes it well suited to cryogenic use. Additionally, it is non-magnetic. Wide range is −50 °C to +740 °C and Narrow range is −110 °C to +140 °C.

Type J

Type J (iron - constantan) has a more restricted range (−40 °C to +750 °C) than type K, but higher sensitivity of about 50 µV/°C.[2] The Curie point of the iron (770 °C)causes a smooth change in the characteristic, which determines the upper temperature limit.

Type K

Type K (chromel - alumel) is the most common general purpose thermocouple with a sensitivity of approximately 41 µV/°C.[10] It is inexpensive, and a wide variety of probes are available in its −200 °C to +1350 °C range (−330 °F to +2460 °F). Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics may vary considerably between samples. One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is that they undergo a deviation in output when the material reaches its Curie point; this occurs for type K thermocouples at around 185 °C.
They operate very well in oxidizing atmospheres. If, however, a mostly reducing atmosphere (such as hydrogen with a small amount of oxygen) comes into contact with the wires, the chromium in the chromel alloy oxidizes. This reduces the emf output and the thermocouple reads low. This phenomenon is known as green rot, due to the color of the affected alloy. Although not always distinctively green, the chromel wire will develop a mottled silvery skin and become magnetic. An easy way to check for this problem is to see if the two wires are magnetic. (Normally, chromel is non-magnetic.)
Hydrogen in the atmosphere is the usual cause of green rot. At high temperatures, it can diffuse through solid metals or an intact metal thermowell. Even the sheath of a magnesium oxide insulated thermocouple will not keep the hydrogen out (http://ohmalloy.en.made-in-china.com)

Type N

Type N (Nicrosil - Nisil) thermocouples are suitable for use between −270 °C and +1300 °C owing to its stability and oxidation resistance. Sensitivity is about 39 µV/°C at 900 °C, slightly lower compared to type K.
Designed at the Defence Science and Technology Organisation (DSTO) of Australia, by Noel A. Burley, type N thermocouples overcome the three principal characteristic types and causes of thermoelectric instability in the standard base-metal thermoelement materials:

1.            
2. A short-term cyclic change in thermal EMF on heating in the temperature range ca. 250-650 °C, which occurs in types K, J, T, and E thermocouples. This kind of EMF instability is associated with structural changes such as magnetic short range order in the metallurgical composition.
3. A time-independent perturbation in thermal EMF in specific temperature ranges. This is due to composition-dependent magnetic transformations that perturb the thermal EMFs in type K thermocouples in the range ca. 25-225 °C, and in type J above 730 °C.

The Nicrosil and Nisil thermocouple alloys show greatly enhanced thermoelectric stability relative to the other standard base-metal thermocouple alloys because their compositions substantially reduce the thermoelectric instabilities described above. This is achieved primarily by increasing component solute concentrations (chromium and silicon) in a base of nickel above those required to cause a transition from internal to external modes of oxidation, and by selecting solutes (silicon and magnesium) that preferentially oxidize to form a diffusion-barrier, and hence oxidation-inhibiting films.

Type T

Type T (copper - constantan) thermocouples are suited for measurements in the −200 to 350 °C range. Often used as a differential measurement since only copper wire touches the probes. Since both conductors are non-magnetic, there is no Curie point and thus no abrupt change in characteristics. Type T thermocouples have a sensitivity of about 43 µV/°C. Note that copper has a much higher thermal conductivity than the alloys generally used in thermocouple constructions, and so it is necessary to exercise extra care with thermally anchoring type T thermocouples.

Platinum/rhodium alloy thermocouples

Characteristic functions for high temperature thermocouple types, showing Pt/Rh, W/Re, Pt/Mo, and Ir/Rh alloy thermocouples. Also shown is the Pt-Pd pure metal thermocouple.
Types B, R, and S thermocouples use platinum or a platinum/rhodium alloy for each conductor. These are among the most stable thermocouples, but have lower sensitivity than other types, approximately 10 µV/°C. Type B, R, and S thermocouples are usually used only for high temperature measurements due to their high cost and low sensitivity.

Type B

Type B thermocouples (Pt/Rh 70%/30% - Pt/Rh 94%/6%, by weight) are suited for use at up to 1800 °C. Type B thermocouples produce the same output at 0 °C and 42 °C, limiting their use below about 50 °C. The emf function has a minimum around 21 °C, meaning that cold junction compensation is easily performed since the compensation voltage is essentially a constant for a reference at typical room temperatures.

Type R

Type R thermocouples (Pt/Rh 87%/13% - Pt, by weight) are used up to 1600 °C.

Type S

Type S thermocouples (Pt/Rh 90%/10% - Pt, by weight), similar to type R, are used up to 1600 °C. Before the introduction of the International Temperature Scale of 1990 (ITS-90), precision type S thermocouples were used as the practical standard thermometers for the range of 630 °C to 1064 °C, based on an interpolation between the freezing points of antimony,silver, and gold. Starting with ITS-90, platinum resistance thermometers have taken over this range as standard thermometers.