Constantan thermocouple

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. 

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. 

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. 

Unfortunately, the thermoelectric power vanishes when temperature tends to zero pairs as the classic Cu/constantan thermocouples show very low sensitivity below 10 K (see Fig. 9.2). 

The liquid-liquid phase equilibria measurements under ambient pressure and temperature (288.2 K) were carried out using an apparatus of a 300 ml glass cell. The temperature of the cell was controlled by a water jacket and measured with a copper-constantan thermocouple and was estimated to be accurate within + 0.1 K. A series of liquid-liquid equilibria measurements were performed by changing the composition of the mixture. 

BL TEMPKRATURF- Thermocouples are the most commonly used temperature sensing devices. The two dissimilar wires produce a millivolt signal that varies with the hot-junction temperature. Iron-constantan thermocouples are commonly used over the 0 to 1300°F temperature range. 

The temperature of the reaction vessel was measured with an iron-constantan thermocouple and controlled at 3 K. The pyrolysis experiments were performed at temperatures of 575, 625, 675, 725, 775, 825 and 925 K. The steam gasification experiments were carried out at temperatures of 825, 875, 925, 975, 1025, 1075, 1125, 1175 and 1225 K (Demirbas, unpublished work). 

In order to determine the temperature profile across the melted zone of each run, a separate, identical run is carried out under the exactly same conditions. The reproduceability of the experimental runs was checked by comparing the separation results of both runs. A copper-constantan thermocouple is situated in the casted sample by inserting it during the casting, to measure the temperature of the melted zone while it is passing the thermocouple. 

The heating regimen is developed using a KAYE validator or equivalent and copper-constantan thermocouples. The determination of the load cold spot is achieved by actual experiments. A microbiological challenge test was performed to verify the sterilization conditions. Biological indicators... 

The most common thermocouple type used in a laboratory situation is the Type J iron/constantan thermocouple. Low cost, high thermopower, and a use-... 

For temperature control runs it is necessary to run the conveyor in the dwell mode of operation—i.e., the carrier is transported to a fixed location, centered between the plaques in the cell, at which point a liquid nitrogen line is remotely attached to the carrier (Figure 10). The rate of nitrogen flow, hence the cooling rate, is controlled by copper-constantan thermocouples in the carriers which are connected to temperature controllers outside the irradiation cell. 

The formulation was intensively mixed for 15 s in a cylindrical vessel of 9.5 cm diameter and 10 cm height. A copper-constantan thermocouple was centered, and the signal continuously monitored. Figure 5.16 shows adiabatic temperature rise curves for different catalyst concentrations. The adiabatic temperature rise was estimated as 155°C. 

X-ray diffractometry was performed, by methods described in a companion paper (8), between 80 and 600 K at ambient pressure on thin solid wafers cut from the prepared samples. Mounted with high temperature cement on relatively massive metal backing plates, these wafers could be maintained at temperatures constant to within 3 K, as measured by either a platinum thermometer or a copper-constantan thermocouple. The... 

The error limits of an iron-constantan thermocouple manufactured to meet the "special" limits of ISA. 

The dynamics of heating in the initiation region was studied with the help of a copper-constantan thermocouple mounted on the heater surface (not shown in Fig. 2). The results of the measurements are presented in Fig. 3 (the arrow indicates the instant of switching on the pulse heater). Whatever the pulse energy, no reaction burst is observed in nonirradiated samples after switching on the heater (Fig. 3, solid curve). In the preirradiated CB + Cl2 system,... 

Fig. 2.31 A simple diagram of a copper-constantan thermocouple.This illustration is from The Temperature Handbook 989 by Omega Engineering, Inc. All rights reserved. Reproduced with the permission of Omega Engineering, Inc., Stamford, CT 06907...

Junction 2. The connection of the constantan thermocouple wire to the copper wire of the volt meter. 

Problem A copper-constantan thermocouple is in an inert-gas stream at 350 K adjacent to a blackbody surface at 900 K. The heat transfer coefficient from the gas to the thermocouple is 25 W/(m2K). Estimate the temperature of the bare thermocouple, (e = 0.15 for copper-constantan.)... 

Thermocouples, or thermal junctions, or thermoelectric thermometers have two intermetallic junctions between two different metals (or semimetals, or semiconductors) A, B in a loop (Fig. 10.21). When these two junctions are held at different temperatures (T i, and T2), then a potential difference A Vis set up this is the Seebeck98 effect. For instance, for a Cu-constantan thermocouple, with T2 = 300 K and T, 273.15 K, AV = 1.0715 mV. Its converse is the Peltier99 effect If a current at a fixed voltage is applied in a loop like in Fig. 10.21, then a temperature difference AT can be maintained (thermoelectric heaters and coolers). The Seebeck effect arises because, before the junctions are made, the two metals have different Fermi levels after the junctions are made, electrons will flow from the higher-level metal to the lower-level metal, until a single Fermi level results across the junction. 

---