Thermocouple, iron-constantan

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experiments were carried out at temperatures of 825, 875, 925, 975, 1025, 1075, 1125, 1175 and 1225 K (Demirbas, unpublished work). 

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

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

Fig. 2.33 An iron-constantan thermocouple using an isothermal block and an ice bath. This illustration is from The Temperature Handbook 1989 by Omega Engineering, Inc. All rights reserved. Reproduced with the permission of Omega Engineering, Inc., Stamford, CT 06907...

Iron-Constantan thermocouples, which had been calibrated against an N.B.S.-standardized platinum resistance thermometer, measured both the sample temperature and the difference in temperature between sample and reference tubes. The thermocouple wires were embedded in magnesia and electrically insulated from their Inconel sheaths. The signal of the thermocouple in the sample tube could be determined either by a recording potentiometer or by a manual potentiometer and null meter. 

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. 

The pyrolysis unit consisted of an insulated 316 stainless steel preheater tube (1.3 cm i.d. X 50 cm length) which extended 1 in. into a 316 stainless steel fixed bed tubular reactor (2.5 cm i.d. x 46 cm length), which was heated by a cylindrical block heater. Two type J (iron-constantan) thermocouple probes were used to both monitor the internal catalyst bed temperature and maintain a consistent reactor wall temperature in combination with a temperature controller, A syringe pump, condenser, vacuum adapter, receiving flask, nitrogen cylinder, and gas collection system were connected as shown in Fig uTe 2. The reactor midsection was packed with 40 g of activated alumina, which was held in place by a circular stainless steel screen. The preheater and reactor were operated at 180-190 and 450 C, respectively. The entire process remained at normal atmospheric pressure throughout the mn. 

The temperature is registered by an iron-constantan thermocouple located in the metal support plate 4. The instrument gives the opportunity of measuring the intensity of emitted light vs. temperature from room temperature up to 300°C. Izothermal as well as various heating rate experiments can be carried out with the precision of the temperature control of il°C. 

The thermocouple built into the Harrick Model HVC-DRP cell is attached to the outside surface of the sample post at a point below the sample cup (as shown in Figure 1). In order to get a more accurate reading of the actual sample temperature, an auxiliary thermocouple (not shown in Figure 1) was epoxied into a fitting that attached to a third port in the base of the cell. The section of this auxiliary (iron/constantan) thermocouple inside the cell was strapped to the gas exit tube that runs from the upper portion of the sample post to the gas exit port, after which the tip end was bent into a small semicircle so that the tip of the thermocouple could be positioned at the surface of the powdered specimen in the sample cup. The built-in thermocouple was used as the control thermocouple, but its temperature setting was adjusted to give the desired temperature at the sample surface as measured by the auxiliary thermocouple. All temperatures reported in this paper were those measured by the auxiliary thermocouple. 

The circuit consisted of a stabilized voltage supply, KFKI type P-13-1RK, and the conductivity cell that was connected with the electrometer in series. The lower limit of the SEA type 6-ATCC-5 electrometer sensitivity was 10"13 amp. The variations in the output current were displayed on a Graphispot, type GR4VAD recorder. The sample was warmed by two different methods, both essentially spontaneous. The sample was either exposed to the surrounding air or left to warm slowly inside of the metal block that was cooled to liquid nitrogen temperature before the measurement. The sample temperature was measured by recording the thermo e.m.f. vs. time of an iron constantan thermocouple put in the middle of the opened sample. The temperature was measured to a 5° accuracy. 

PROCEDURE. A three-junction iron-constantan thermocouple was calibrated against the freezing points of sodium, lithium, tin, lead, and zinc to 0.05 C. and inserted into the stainless steel protection tube shown in Figure 1. 

The remaining 45 cm of IT is wrapped with glass tape and 1.6A/ft nichrome wire (Pelican) to form a stem heater, SH. The temperature of the stem heater is measured by a second, identical, iron-constantan thermocouple, SS. This heater is powered by a variable AC powerstat (lOB, Superior Electric Company, Bristol, CN, USA). The entire stem heater is wrapped with a layer of glass tape. The oven-end of IT is coupled to a reducing union, RU (ZRU1.5,... 

Nernst, Koref, and Lindematm (1910) described an aneroid drop calorimeter for the measurement of specific heat capacities. Figure 7.14 shows the design of this instrument. The entire system is located in isothermal surroundings such as melting ice. Of particular interest is the measurement of the temperature change of the calorimeter substance by means of 10 iron-constantan thermocouples mounted between the calorimeter substance and the isothermal Ud. 

When certain materials are bonded together, electrons tend to transfer from one to the other. This is called the Volta effect. If two such materials are joined together with two junctions at the same temperature, the plus Volta emf at one junction will be balanced by a minus emf at the other and no current will flow. However, if the two junctions have different temperatures, a current will flow from one junction to the other. This is called the Seebeck effect, and is the basis of the thermocouple. Figure 11.1 (a) shows a thermocouple with a small voltmeter in series with two thermocouple wires (iron and 60 Cu-40 Ni constantan). The emf will be proportional to (T2 - Tj). Figure 11.1 (6) gives the calibration curve for an iron-constantan couple. Thermocouples are used to measure very high (furnace) temperatures, and when the upper range of an iron-constantan thermocouple is reached, a platinum-rhodiiun couple [also shown in Fig. 11.1(6)] may be employed. 

Iron-constantan thermocouple tables, 15-1 to 9 Irradiance of the sun, 14-18 Isoelectric point, amino acids, 7-1 to 2 Isotopes, summary of properties, 11-56 to 253 Isotopic abundance, 1-14 to 17,11-56 to 253 ITS-90... 

Temperature-Measuring Devices—A removable iron-constantan thermocouple with a sensitive pyrometer, or other suitable temperature-indicating device, located centrally near the bottom portion of the furnace and arranged to measure the temperature of the furnace so that the performance tests specified in Section 7 can be obtained. It is desirable to protect the temperature-indicating device with a quartz or thin metal sheath when a molten bath is used. 

Note 7—In use at the high temperature of the test, iron-constantan thermocouples oxidize and their calibration curves change. 

The iron-Constantan thermocouple is used most widely in industrial applications. The copper-Constantan thermocouple is used widely in industrial and laboratory thermometry. 

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