Thermocouples fabrication

When accuracy greater than the tolerances in Table 16.9 is required, the wires must be calibrated. Normally, this requires comparison calibration of sample thermocouples taken from each spool to account for spool variability. Typically, two thermocouples—one fabricated from the beginning and the other from the end of the spool—are calibrated to determine an average calibration for the entire spool. If the deviation between the two calibrations is not within the required uncertainty, a third thermocouple fabricated from the center of the spool should be used. If the results are still unsatisfactory, then each thermocouple should be calibrated individually, or a different spool should be used. 

In addition to aerospace uses, sihca fibers can be twisted into sewing threads and yams for weaving into fabrics. These fabrics are used extensively for heat-resistant clothing, flame curtains for furnace openings, thermocouple protection, and electrical insulation. The cloth can also be used to encapsulate other fibers to produce flexible sheets. 

Two alloys containing tungsten are commercially available. The first, containing about 3 wt % rhenium, is used for heating filaments. The rhenium contributes improved resistance to thermal and mechanical shock. The second alloy contains about 25 wt % rhenium. This latter alloy is sold as sheet, rod, and heavy wire and may be fabricated for various uses. An important use of these rhenium alloys is in the constmction of thermocouples. Various combinations, 3 wt % Re—97 wt % W, or 25 wt % Re—75 wt % W, are usehil for measurement of temperatures to 2500°C (see Temperaturemeasurement). 

High Temperature. The low coefficient of thermal expansion and high thermal conductivity of sihcon carbide bestow it with excellent thermal shock resistance. Combined with its outstanding corrosion resistance, it is used in heat-transfer components such as recuperator tubes, and furnace components such as thermocouple protection tubes, cmcibles, and burner components. Sihcon carbide is being used for prototype automotive gas turbine engine components such as transition ducts, combustor baffles, and pilot combustor support (145). It is also being used in the fabrication of rotors, vanes, vortex, and combustor. 

The single cell thus fabricated was placed in a single chamber station as illustrated in Fig. 2. A humidified mixture of methane and oxygen was supplied to the station so that both electrode compartments were exposed to the same composition of methane and oxygen. For the measurement of the cell temperature, a thermocouple (TC) was placed approximately 4 mm away from the cathode site. For the evaluation of the fuel-cell performance, Ft wires and Inconel gauzes were used as the output terminals and electrical collectors, respectively. 

Fabrication was done by photolithography and deep reactive ion etching (DRIB). The catalyst was inserted by sputtering. Such a prepared microstructure was sealed with a Pyrex cover. The bonded micro device was placed on a heating block containing four cartridge heaters. Five thermocouples monitored temperature on the back side. A stainless-steel clamp compressed the device with graphite sheets. 

Photolysis Procedure. The solvent-cleaned Kevlar-29 fabric swatch (2.5 cm x 18 cm) was placed around the outside quartz tube inside the photolysis chamber, which was subsequently evacuated, before - - 02 (99%) was introduced to 0.2 atm. The photolysis chamber was preheated to the specified photooxidation temperature, before the Hg-Xe lamp was turned on. The temperature, which was held constant in the chamber by adjusting the air flow around the lamp, was monitored by a thermocouple placed next to the fabric sample inside the chamber. After the photooxidation had continued for the specified... 

Thermopiles are considered temperature sensors and are fabricated incorporating a number of thermocouples. Each thermocouple is formed by a couple of different materials (Metall-Metal2, Metal-Semiconductor, Semiconductor-Semiconductor) and responds to a temperature difference localized between the two junctions (cold junction and warm junction ), see fig. 11. One of the two junctions can be considered the reference one. 

In another report, a microthermocouple (Ni-Ag) was fabricated on-chip for temperature measurement (see Figure 7.45). The thermocouple metals were fabricated using electrodeless deposition. This thermal measurement method was used to monitor an acid-base neutralization reaction and an enzymatic reaction, [271],... 

FIGURE 7.45 Schematic showing the procedure used for the microfabrication of a thermocouple. The thermocouple, which consists of intersecting Ni and Ag metal lines, is fabricated by electrodeless metal deposition as masked by the PDMS channels [271]. Reprinted with permission from the American Chemical Society. 

Light Exposures. Silk fabric samples, 0.25 m x 0.17 m, were mounted in Atlas Electric Devices aluminum sample holders according to AATCC Test Method 16E-1982 (7). An Atlas Ci-35 Weather-Ometer xenon-arc was used on continuous light cycle. Exposures were conducted at an irradiance of 0.35 W/m2 measured at 340 nm and the irradiance was monitored and controlled automatically. Borosilicate inner and outer filters were used to simulate the solar spectrum. The relative humidity was maintained at 65% and the black panel temperature was 50°C. The actual fabric temperature during the irradiation was measured, using small thermocouples threaded into the fabric, and was found to be 35 C. Control samples for these tests were kept in the dark at 35°C and 65% RH for the same time period as the illuminated samples. 

Three experimental units each with different experimental focus were designed, fabricated and delivered to NASA Langley. The first unit contains four passive and four active films samples to be exposed to combined atomic oxygen and vacuum UV. The second unit contains 11 passive and four active samples to be exposed only to vacuum UV (see Fig. 2). The third unit has two passive samples with different thicknesses of protective aluminum layers to be exposed to atomic oxygen and vacuum UV. All passive samples will be characterized, both in terms of chemical and physical properties, after the mission and compared with pre-exposure characterization to determine the effects of the space environmental exposure. Thin foil-type thermocouples are attached and logged underneath the samples to measure actual temperatures experienced. By recording the temperature it will be possible to correlate the deflection properties with temperature conditions of the active samples. 

Figure 4 shows a schematic diagram of an ultrahigh vacuum (5 x 10 ° Torr) apparatus that integrates LEED, XPS, TPD, LEISS, and electrochemistiy (EC). The base pressure of the chamber is 5 x 10" Torr. The sample is mounted on a probe, a tube fabricated out of stainless steel, at the top of the chamber. The probe allows experiments to be performed at very low temperatures for example, the probe is filled with hquid nitrogen for experiments at 77 K. The sample can also be heated resistively (up to 1500 K) via copper wires attached to the sample for still higher temperatures, an electron beam from a tungsten wire located behind the sample is employed. Temperature is monitored via a ReAV-Re thermocouple. 

CO temperature in cleaning vessel was not consistent and was hotter at the top than at the bottom Insufficient heating of CO entering vessel. Poor positioning of extractor control thermocouple Designed, fabricated and installed temperature controlled water bath with heat exchanger and repositioned thermocouples... 

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