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Chromel-constantan thermocouple

All the samples were further purifred by removing dust particles through 0.2 pm Millipore filter and sealed in fused silica cells or P x cells. The sample cell was embedded in a specially designed home-made cryostat or furnace. The temperatures were measured with a chromel-constantan thermocouple closely attached to a cell. The accuracy of the temperature control is within 0.1 K. The thermocouples were prepared at Chemical Thermodynamics Laboratory, Osaka University. [Pg.188]

A Ni(lll) single crystal, oriented to within 0.2° of the (111) plane, is mounted on a manipulator which rotates it 360° around an axis parallel to its surface and translates it in three mutually perpendicular directions while maintaining the ultrahigh vacuum conditions in the main chamber. The crystal can be cooled to 8 K by contact with a liquid He reservoir and can be heated to 1400 K. A chromel-constantan thermocouple is spot-welded to the crystal for temperature measurements. The procedure for cleaning the crystal by Ar ion sputtering, oxidation and reduction has been discussed previously (ref. 5). [Pg.54]

The operating temperature range is typically 100 -1000 K using samples of area 30-50 mm and thickness 0.01-0.3 mm. The temperature resolution is 0.0025 K for T< 770 K and 0.025 K for r> 770 K. The sample holder is purged with a dry inert gas. Alumel-chromel or chromel-constantan thermocouples of 0.002 mm diameter are placed in a paper frame and soldered to metal samples to measure. Polymers are dissolved in an organic solvent and the solution is spread on a thin metal... [Pg.144]

Type E thermocouples are often referred to as chromel-constantan thermocouples. They are regarded as more stable than Type K, therefore often used where a higher degree of accuracy is required. [Pg.156]

Thermopower measurements used the differential technique [48,49] two isolated copper blocks were alternately heated with the sample mounted between the copper blocks with pressure contacts. The heating current was accurately controlled by computer. The temperature difference between the two copper blocks was measured by a chromel-constantan thermocouple and did not exceed 0.5 K for each thermal cycle. The voltage difference across the sample was averaged for one complete cycle. Any temperature difference between sample and thermocouple was less than 10% of the temperature gradient across the sample the thermometry was carefully calibrated for the entire temperature range (5 K < T < 300 K). The absolute thermopower of the sample was obtained from the absolute scale for lead [48,49]. [Pg.28]

Temperature measurements ranging from 760 to 1760°C are made usiag iron—constantan or chromel—alumel thermocouples and optical or surface pyrometers. Temperature measuriag devices are placed ia multiple locations and protected to allow replacement without iaciaerator shutdown (see... [Pg.55]

Calvet and Persoz (29) have discussed at length the question of the sensitivity of the Calvet calorimeter in terms of the number of thermocouples used, the cross section and the length of the wires, and the thermoelectric power of the couples. On the basis of this analysis, the micro-calorimetric elements are designed to operate near maximum sensitivity. The present-day version of a Tian-Calvet microcalorimetric element, which has been presented in Fig. 2, contains approximately 500 chromel-to-constantan thermocouples. The microcalorimeter, now commercially available, in which two of these elements are placed (Fig. 3) may be used from room temperature up to 200°C. [Pg.200]

Calvet and Guillaud (S3) noted in 1965 that in order to increase the sensitivity of a heat-flow microcalorimeter, thermoelectric elements with a high factor of merit must be used. (The factor of merit / is defined by the relation / = e2/pc, where e is the thermoelectric power of the element, p its electrical resistivity, and c its thermal conductivity.) They remarked that the factor of merit of thermoelements constructed with semiconductors (doped bismuth tellurides usually) is approximately 19 times greater than the factor of merit of chromel-to-constantan thermocouples. They described a Calvet-type microcalorimeter in which 195 semiconducting thermoelements were used instead of the usual thermoelectric pile. [Pg.201]

Fig. 1.45.1. Artist s view of a DSC cell in Tzero technology as used in modulated DSC (MDSC) processes. 1, Sample and reference table made from one piece of constantan 2, chromel thermocouples directly connected to the constantan tables 3, Tzero sensor from chromel-constantan in the middle between sample and reference table (TA Instruments, New Castle, DE, USA... Fig. 1.45.1. Artist s view of a DSC cell in Tzero technology as used in modulated DSC (MDSC) processes. 1, Sample and reference table made from one piece of constantan 2, chromel thermocouples directly connected to the constantan tables 3, Tzero sensor from chromel-constantan in the middle between sample and reference table (TA Instruments, New Castle, DE, USA...
Thermocouples are based on the thermoelectric Seebeck effect, which generates a voltage at the junction between two metallic conductors, which depends on temperature [13]. Thus, in the measuring circuit, two junctions are created, namely, a sensitive (or hot) junction at the point where temperature has to be measured and a nonsensitive (cold) junction, kept at a constant known temperature, where the voltage established between the conductors can be easily measured [19]. Different typologies of thermocouples exist for application in a wide range of conditions they essentially differ by the materials, the most common being J (iron/constantan), K (chromel/alumel), T (copper/constantan), and E (chromel/constantan). [Pg.33]

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. [Pg.40]

Two principal DSC designs are commercially available—power compensated DSC and heat flux DSC. The two instruments provide the same information but are fundamentally different. Power-compensated DSCs heat the sample and reference material in separate furnaces while their temperatures are kept equal to one another (Fig. IB). The difference in power required to compensate for equal temperature readings in both sample and reference pans are recorded as a function of sample temperature. Heat flux DSCs measure the difference in heat flow into the sample and reference, as the temperature is changed. The differential heat flow to the sample and reference is monitored by chromel/ constantan area thermocouples (Fig. IC). ... [Pg.394]

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-... [Pg.69]

The measurement and control of the temperature of experimental apparatus in cryogenic environments has been widely explored p]. Problems in such measurement and control by thermoelectric and thermal resistance effects are receiving constant attention. However, the application of Chromel-P vs. constantan thermocouples to cryogenic temperature measurement and control has not become widespread. The reason for this limited usage is not clear, especially since the sensitivity and potential 2. 3] fQj. his thermocouple system are higher than for the more popular copper vs. constantan thermocouple system. Furthermore, the use of low-thermal-conductivity Chromel-P P] wire, instead of copper wire, would reduce heat leaks into cryogenic systems. [Pg.437]

The temperatures are determined with a thermocouple such as Chromel-Constantan calibrated at three temperatures the boiling point of water and the melting points of lead and antimony. [Pg.195]

In heat-flux DSC, the difference in heat flow into the sample and reference is measured while the sample temperature is changed at a constant rate. Both sample and reference are heated by a single heating unit. Heat flows into both the sample and reference material via an electrically heated constantan thermoelectric disk, as shown in Figure 31-12. Small aluminum sample and reference pans sit on raised platforms on the constantan disk." Heat is transferred through the disks and up into the material via the two pans. The dififerential heat flow to the sample and reference is monitored by Chromel-constantan area thermocouples formed by the junction between the constantan platform and Chromel disks attached to the underside of the platforms. The differential heat flow into the two pans is directly proportional to the difference in the outputs of the two thermocouple junctions. The sample temperature is estimated by the Chromel-alumel junction under the sample disk. [Pg.986]

Sample, constantan disk, reference, furnace, chromel disks, chromel-alumel thermocouples... [Pg.194]

Modules 910,2910, and2920 The TA Instruments Q series DSCs evolved from their 910,2910, and 2920 modules. The DSC 910,2910, and 2920 cells use a thermoelectric heat leak made of constantan (a copper/nickel alloy) as noted in Hg. 2.2. The sample and reference pans sit on raised platforms or pods with the constantan disk at their base. The temperature sensors are disk-shaped chromel/constantan area thermocouples and chromel/alumel thermocouples. The thermocouple disk sensors sit on the underside of each platform. The AT output from the sample and reference thermocouples is fed into an amplifier to increase their signal strength. The heating block is made of silver for good thermal conductivity and also provides some reflectivity for any emissive heat. [Pg.22]

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). [Pg.27]

This instrument utilises a silver block chamber with an external heater. The chamber contains a constantan disc with raised platforms for the sample and reference containers. The temperature difference between sample and reference is monitored by area thermocouples formed by the constantan disc and chromel wafers under the platforms. Amplification and electronic compensation of the differential temperature signal provides a linear calorimetric response over a wide temperature range. The theory of this instrument is discussed by Lee and Levy 6). Other available examples of... [Pg.113]

Thermocouples Temperature measurements using thermocouples are based on the discovery by Seebeck in 1821 that an electric current flows in a continuous circuit of two different metallic wires if the two junctions are at different temperatures. The thermocouple may be represented diagrammatically as shown in Fig. 8-63. There A and B are the two metals, and I) and T2 are the temperatures of the junctions. Let 7) and T2 be the reference junction (cold junction) and the measuring junction, respectively. If the thermoelectric current i flows in the direction indicated in Fig. 8-63, metal A is customarily referred to as thermoelectrically positive to metal B. Metal pairs used for thermocouples include platinum-rhodium (the most popular and accurate), chromel-alumel, copper-constantan, and iron-constantan. The thermal emf is a measure of the difference in temperature between T2 and Ij. In control systems the reference junction is usually located at the emf-measuring device. The reference junction may be held at constant temperature such as in an ice bath or a thermostated oven, or it may be at ambient temperature but electrically compen-... [Pg.56]

Type-E Thermocouples (Chromel vs. Constantan) [4]. These are nonmagnetic and have a high sensitivity (68 pV/ C), which makes them well-suited to cryogenic use. [Pg.625]


See other pages where Chromel-constantan thermocouple is mentioned: [Pg.1161]    [Pg.22]    [Pg.334]    [Pg.28]    [Pg.197]    [Pg.1161]    [Pg.22]    [Pg.334]    [Pg.28]    [Pg.197]    [Pg.617]    [Pg.567]    [Pg.72]    [Pg.308]    [Pg.349]    [Pg.901]    [Pg.439]    [Pg.539]    [Pg.1826]    [Pg.91]    [Pg.66]    [Pg.126]    [Pg.1026]    [Pg.179]   
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