Constantan alloy

These devices have a disk (e.g. constantan alloy) on which the sample and reference pans rest on symmetrically placed platforms. Thermocouple wire (e g. chromel alloy) Is welded to the underside of each platform. The chromel-constantan junctions make up the differential thermocouple junctions with the constantan disk acting as one leg of the thermocouple pair. 

A thermocouple consists of wires of two dissimilar metals (e.g., constantan alloy and copper) connected in series at soldered or welded junctions. A many-junction thermocouple is called a thermopile (Fig. 2.7). AYhen adjacent junctions are placed in thermal contact with bodies of different temperatures, an electric potential develops that is a function of the two temperatures. 

Temperature measurement. The most commonly used metliod of temperature detection in the HRE-2 is the thermocouple measurement of vessel and pipe wall temperatures the couples arc spot-welded directly to the wall and then covered with insulation. When faster response is desired, thermocouples are spring-loaded into thin thermowells. Chromel-Alumel wire is generally used because its resistance to corrosive attack by moisture is better than that of iron-constantan alloys. 

Not all elements of the industrial thermocouple need to be wine. For example, if a copper pipe contains a flowing fluid whose temperature is to be measured, a constantan wine attached to the pipe will form a T, or copper—constantan, thermocouple. Such arrangements ate difficult to caUbrate and requite full understanding of the possible inherent problems. For example, is the copper pipe fully annealed Homogeneous Pure, or an alloy Many ingenious solutions to specific measurement problems ate given in Reference 6. 

Thermocouples of platinum with an alloy of platinum and 10 per cent, of rhodium or iridium are used at higher temperatures, and of copper and constantan at lower temperatures. 

To measure temperatures not exceeding 800 °C, one should use thermocouples made from copper and constantan (the latter is an alloy of 45-60% copper, 40-55% nickel, and 0-1.4% manganese it usually also contains about 0.1% carbon), Alumel (an alloy of 95% nickel, 2 % aluminium, 2% manganese, and 1% silicon), and Chromel (90% nickel and 10% chromium), or iron and constantan. Platinum-platinum/rhodium thermocouples are generally used for measuring high temperatures (up to 1600 °C). 

An iron-constantan thermocouple (constantan is an alloy of copper and nickel) is calibrated by inserting its junction in boiling water and measuring a voltage V = 5.27 mV, and then inserting the junction in silver chloride at its melting point and measuring V = 24.88 mV. 

For moderate and for low temperatures iron-constantan (an alloy of 60 per cent, copper with 40 per cent, nickel) is generally used. 

This couple gives an e.m.f. of about - millivolt per 1° C. For high temperatures, above the melting point of constantan, Le Chatelier s pyrometer is used. It is a thermocouple consisting of pure platinum and an alloy of platinum containing 10 per cent, of rhodium. 

For general work at higher temperatures, several different types of couples are employed in this country. Up to 360°C. for extreme precision or to 500°C. for a precision of 5 to 10°C. the couple may consist of one wire of copper and the other wire of constantan. Iron-constantan or nichrome-constantan may be employed for technical processes below 900°C. For operation below 1,100°C. special patented alloys of chromium and nickel and of aluminum and nickel, chromel-alumek or nichrome-alumel are very satisfactory even for continuous service. For the temperature range 300 to 1,500°C. the Le Chatelier couple should be employed. This couple consists of one wire of platinum and the other wire an alloy containing 90 per cent platinum and 10 per cent rhodium. Other alloys and metals may be employed for special work but the above combinations are sufficient for almost all technical processes carried on in the temperature range 0 to 1,500°C. No satisfactory couple has been developed for operation much above 1,500°C. 

EN or TN A copper-nickel alloy, constantan Cupron,4 Advance/ Thermokanthal JNr ... 

This copper-nickel alloy is the same for both EN and TN, often referred to as Adams constantan or, sometimes, con-stantan. 

This copper-nickel alloy is used in JN. It is similar to, but not always interchangeable with, EN and N. By SAMA specifications, this substance is often referred to as SAMA constantan, but it is also loosely called constantan. 

Cupronickels contain from 15 to 20 per cent of nickel, the remainder being copper. They can be cold-worked for example they can be cold-rolled from I inch down to 0-05 inch without annealing being necessary. They have been extensively used for bullet jackets. The 2 5 Ni, 75 Cu alloy used in coinage has already been mentioned. A 30 Ni, 70 Cu alloy is used for condenser tubes. Another useful alloy, sometimes known as constantan, has 40 Ni and 60 Cu. Owing to its high electrical resistance and low resistance temperature coefficient it is used for standard electrical resistances. 

Monel metal Constantan Nichrome Manganin Wood s alloy Rose s alloy... 

Constantan /kon-stan-tan/ (Trademark) A copper-nickel (cupronickel) alloy containing 45% nickel. It has a high electrical resistivity and very low temperature coefficient of resistance and is therefore used in thermocouples and resistors. 

In power compensated DSC the small size of the individual sample and reference holders makes for rapid response. The temperature sensors are platinum (Pt) resistive elements. The individual furnaces are made of Pt/Rh alloy. It is important that the thermal characteristics of the sample and reference assemblies be matched precisely. The maximum operating temperature is limited to about 750 °C. High temperature DSC measurements (750-1600°C) are made by heat flux instruments using thermocouples of Pt and Pt/Rh alloys. The thermocouples often incorporate a plate to support the crucible. The use of precious metal thermocouples is at the expense of a small signal strength. Both chromel/alumel and chromel/constantan are used in heat flux DSC equipment for measurements at temperatures to about 750 °C. Multiple thermocouple assemblies offer the possibility of an increased sensitivity - recently a 20-junction Au/Au-Pd thermocouple assembly has been developed. Thermocouples of W and W/Re are used in DTA equipment for measurements above 1600°C. The operating temperature is the predominant feature which determines the design and the materials used in the con-... 

There are two main types of DSC instrumentation, heat-flux DSC and power-compensated DSC. A schematic of a commercial heat-flux DSC is presented in Figure 16.19. In a heat-flux instrument, the same furnace heats both the sample and the reference. In heat-flux DSC, the temperature is changed in a linear manner, while the differential heat flow into the sample and reference is measured. The sample and reference pans sit on the heated thermoelectric disk, made of a Cu/Ni alloy (constantan). The differential heat flow to the sample and reference is monitored by area thermocouples attached to the bottom of the sample and reference positions on the thermoelectric disk. The differential heat flow into the pans is directly proportional to the difference in the thermocouple signals. The sample temperature is measured by the alumel/chromel thermocouple under the sample position. This temperature is an estimated sample temperature because the thermocouple is not inserted into the sample itself. The accuracy of this temperature will depend on the TC of the sample and its container, the heating rate, and other factors. As shown in Figure 16.19, the sample and reference pans both have lids and the reference pan is an empty pan. A schematic of a power-compensated DSC is presented in Figure 16.20. The major difference in power-compensated DSC... 

Constantan kan(t)-ston- tan [ft. the fact that its resistance remains constant under change of temperature] (1903) n. An alloy containing about 55% copper and 45% nickel and having a low thermal coefficient of resistivity. Its main use in the plastics industry is in thermocouple wire with either iron or cooper as the mating element. Iron-constantan, Type J, and chromel-alumel. Type K, are widely used to sense temperatures in plastics-processing equipment. 

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