Ohmalloy Material Co., Ltd.  

Product Name: Simple Temperature Sensor Type K Model NO.: KK Display Type: Ohmalloy Brand: Ohmalloy Certification: RoHS, ISO9001, CE Customized: Customized Trademark: OHMALLOY Transport Package: Cusotmized Specification: 0.2MM Origin: China HS Code: 9025900090 Product Description TypesCertain 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 Stypes) have correspondingly lower resolutions. Other selection criteria include the chemicalinertnessof the thermocouple material, and whether it ismagneticor not. Standard thermocouple types are listed below with the positiveelectrode(assuming) first, followed by the negative electrode.Nickel alloy thermocouplesCharacteristic 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 EType E(chromel-constantan) has ahigh output (68 µV/°C) which makes it well suited tocryogenicuse. Additionally, it is non-magnetic. Wide range is −50 °C to +740 °C and Narrow range is −110 °C to +140 °C.Type JType J(iron-constantan) has amore restricted range (−40 °C to +750 °C) than type K, but higher sensitivity of about 50 µV/°C.[2]TheCurie pointof the iron (770 °C)causes asmooth change in the characteristic, which determines the upper temperature limit.Type KType K(chromel-alumel) is the most common general purpose thermocouple with asensitivity of approximately 41 µV/°C.[10]It is inexpensive, and awide variety of probes are available in its −200 °C to +1350 °C range (−330 °F to +2460 °F). Type Kwas specified at atime whenmetallurgywas less advanced than it is today, and consequently characteristics may vary considerably between samples. One of the constituent metals,nickel, is magnetic; acharacteristic of thermocouples made with magnetic material is that they undergo adeviation in output when the material reaches itsCurie point; this occurs for type Kthermocouples at around 185 °C.They operate very well in oxidizing atmospheres. If, however, amostly reducing atmosphere (such as hydrogen with asmall 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 asgreen rot, due to the color of the affected alloy. Although not always distinctively green, the chromel wire will develop amottled 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 amagnesium oxide insulated thermocouple will not keep the hydrogen out (http://www.transcat.com/calibration-resources/application-notes/thermocouples/)Type NType 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 theDefence Science and Technology Organisation(DSTO) of Australia, by Noel A. Burley, type Nthermocouples overcome the three principal characteristic types and causes of thermoelectric instability in the standard base-metal thermoelement materials: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 Ethermocouples. This kind of EMF instability is associated with structural changes such as magnetic short range order in the metallurgical composition.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 Kthermocouples in the range ca. 25-225 °C, and in type Jabove 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 abase of nickel above those required to cause atransition from internal to external modes of oxidation, and by selecting solutes (silicon and magnesium) that preferentially oxidize to form adiffusion-barrier, and hence oxidation-inhibiting films.Type TType T(copper-constantan) thermocouples are suited for measurements in the −200 to 350 °C range. Often used as adifferential measurement since only copper wire touches the probes. Since both conductors are non-magnetic, there is noCurie pointand thus no abrupt change in characteristics. Type Tthermocouples have asensitivity of about 43 µV/°C. Note that copper has amuch higherthermal conductivitythan the alloys generally used in thermocouple constructions, and so it is necessary to exercise extra care with thermally anchoring type Tthermocouples.Platinum/rhodium alloy thermocouplesCharacteristic 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 Sthermocouples useplatinumor aplatinum/rhodiumalloy 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 Sthermocouples are usually used only for high temperature measurements due to their high cost and low sensitivity.Type BType Bthermocouples (Pt/Rh 70%/30% -Pt/Rh 94%/6%, by weight) are suited for use at up to 1800 °C. Type Bthermocouples produce the same output at 0°C and 42 °C, limiting their use below about 50 °C. The emf function has aminimum around 21 °C, meaning that cold junction compensation is easily performed since the compensation voltage is essentially aconstant for areference at typical room temperatures.Type RType Rthermocouples (Pt/Rh 87%/13% -Pt, by weight) are used up to 1600 °C.Type SType Sthermocouples (Pt/Rh 90%/10% -Pt, by weight), similar to type R, are used up to 1600 °C. Before the introduction of theInternational Temperature Scale of 1990(ITS-90), precision type Sthermocouples were used as the practical standard thermometers for the range of 630 °C to 1064 °C, based on an interpolation between the freezing points ofantimony,silver, andgold. Starting with ITS-90,platinum resistance thermometershave taken over this range as standard thermometers.