Thermocouples reproducibility

Fig. 3. Cross section of the side view of a typical EXAFS in situ cell (A) main body made of stainless steel (B) beryllium windows (C) convection baffles (D) gas inlet (E) liquid inlet (F) gas and liquid outlet (G) cooling jackets (J) thermocouple [reproduced from Dalla Betta et al. (29), with the permission of the American Institute of Physics].

Fig. 12. Metal dewar liquid nitrogen cell. (A) Nitrogen fill, (B) nitrogen vent, (C) liquid nitrogen, (D) main pump out, (E) detachable tail section, (F) sample, (G) aluminum foils, (H) Mylar window, and (I) thermocouple. Reproduced from Herber and Hazony (87) with permission.

Fig. 1.38 A micro-heater assembly for a DAC (1) anvils, (2) gasket, (3) platinum wires, (4) alumina cement, (5) mica, (6) high-temperature adhesive, (7) thermocouples . (Reproduced with permission from Kluwer Academic Publishers.)...

Fig. 6.13 Temperatures in the y-z plane at locations, PI, P2, Dl, D2, D3, Cl, C2 and C3 at the holding time of 0.18 ks, and calculated isothermal contours under constant current discharge conditions, with nits in K. The values within parentheses were the temperatures measured by the thermocouples. Reproduced with permission from [33]. Copyright 2003, Elsevier...

Figure 4 Apparatus for column electrophoresis. 1, Separation column 2, anode compartment 3, foam at the platinum anode 4, cathode compartment 5, molten zinc cathode 6, fused salt bath 7, stirrer 8 and 9, thermocouples. (Reproduced with permission from Ljublimov V and Lunden A (1966) Zeitschrift fur Naturforschung 2Aa 1592-1956.)...

Great care is needed in the design of autoclaves and sterilization cycles because of the requirement for the presence of moisture. The autoclave must be loaded to allow complete steam penetration to occur in all parts of the load before timing of the sterilization cycle commences. The time required for complete penetration, the so-called heat-up time, varies with different autoclave constmction and different types of loads and packaging materials. The time may not exceed specific limits in order to guarantee reproducibility and, for porous loads, saturated steam. The volume of each container has a considerable effect on the heatup time whenever fluids are sterilized. Thermocouples led into the chamber through a special connector are often employed to determine heatup times and peak temperatures. The pressure is refleved at the end of each sterilization cycle. Either vented containers must be used or... 

Measurement of the hotness or coldness of a body or fluid is commonplace in the process industries. Temperature-measuring devices utilize systems with properties that vaiy with temperature in a simple, reproducible manner and thus can be cahbrated against known references (sometimes called secondaiy thermometers). The three dominant measurement devices used in automatic control are thermocouples, resistance thermometers, and pyrometers and are applicable over different temperature regimes. 

The international temperature scale is based upon the assignment of temperatures to a relatively small number of fixed points , conditions where three phases, or two phases at a specified pressure, are in equilibrium, and thus are required by the Gibbs phase rule to be at constant temperature. Different types of thermometers (for example, He vapor pressure thermometers, platinum resistance thermometers, platinum/rhodium thermocouples, blackbody radiators) and interpolation equations have been developed to reproduce temperatures between the fixed points and to generate temperature scales that are continuous through the intersections at the fixed points. 

The ITS-90 scale is designed to give temperatures T90 that do not differ from the Kelvin Thermodynamic Scale by more than the uncertainties associated with the measurement of the fixed points on the date of adoption of ITS-90 (January 1, 1990), to extend the low-temperature range previously covered by EPT-76, and to replace the high-temperature thermocouple measurements of IPTS-68 with platinum resistance thermometry. The result is a scale that has better agreement with thermodynamic temperatures, and much better continuity, reproducibility, and accuracy than all previous international scales. 

The burning of a column of delay composition takes place by the passage of a reaction front along the column. The temperature profile of this reaction front can be measured by the use of suitable thermocouples and recording instruments. By analysing the shape of the front it can be shown that the reaction is a solid/solid reaction initiated by thermal conduction of heat through the unreacted material. It follows that to obtain reproducible reaction rates there must be (1) constant amount of solid to solid contact and (2) constant thermal conductivity. 

Figure 2 Schematic diagram of a 100-mL UV-autoclave. a = gas and sampling valve, b = thermocouple, c = quartz window, d = Teflon O-rings, e = autoclave lid, f = rupture disc, g = valve and pressure gauge, h gaskets, i = autoclave body, k = glass insert, 1 = temperature control, m stirring bar. (Pmax 300 bar, Tmax = 150 °C) (Reproduced with permission from Ref. 7. Copyright 1983 Elsevier Sequoia.)...

Figure 1. Labyrinth air flow calorimeter. Cross section A - A shows the measuring channel with four samples and the two outer insulating labyrinth channels. Cross section B - B shows one of the two piles of thermocouples which are placed at the channel inlet and the outlet to record the air temperature difference. (Reproduced with permission from ref. 10. Copyright 1989 De Gruyter.)...

Figure 10.4 Adiabatic high-temperature calorimeter [15], 1 Calorimeter proper 2 Silver guard 3 Silver shield 4 Shield heater 5 Thermocouple sleeve 6 Silica glass container 7 Sample 8 Calorimeter heater 9 Pt resistance thermometer 10 Silica ring spacer 11 Type S thermocouple 12 Guardheater 13 Removable bottom. Reproduced by permission of F. Grpnvold.

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. 

Figure 3.3 Side- and top-view of the in situ infrared autoclave. A IR window B Turbine rotor C Reagent addition D Thermocouple E Opening between upper and lower chamber F Electrical heaters C Kalrez O-rings (from Ref [6], reproduced by permission of Elsevier).

It is also possible to use a single thermocouple at different positions in multiple mns. This requires careful control of autoclave temperature to reduce error caused by run-to-mn variation. Repeat studies are required to establish reproducible cold points and temperature profiles of the liquid in the container. The profile point having the lowest temperature or lowest Fq is designated as the cold spot. 

Figure 3.3 Sonoelectrochemical cell used for electrosynthesis and voltammetric studies. 1, Sonic horn 2, transducer 3, to control unit of sonic horn 4, graphite counter electrode 5, argon inlet for degassing 6, Pyrex reservoir 7, platinum-disk macro- or microelectrode 8, copper cooling coil connected to the thermostatted water bath 9, titanium tip 10, platinum resistance thermocouple 11, SCE reference. (From Ref. 557, reproduced with permission.)...

Most low-temperature engineering temperature measurements are made with metallic resistance thermometers, nonmetallic resistance thermometers, or thermocouples. In the selection of a thermometer for a specific application one must consider such factors as absolute accuracy, reproducibility, sensitivity, heat capacity, self-heating, heat conduction, stability, simplicity and convenience of operation, ruggedness, and cost. Other characteristics may be of importance in certain applications. 

Testing. Studies of the catalytic activity and selectivity were conducted in a tubular unit reactor. Since this is a reactor consisting of a catalyst-packed tube of dimensions identical with those of a single tube inside a large-scale reactor, it becomes possible to reproduce the industrial conditions A thermocouple was placed in the catalyst bed, A detailed description of the experimental procedure has been presented elsewhere [4]. The tube was packed with two layers of catalyst (0.6 dm3 each). The total bed length was about 2.65 m. The feed was o-xylene of purity 98.4 wt.%. The air flow rate was 3.5 m3(STP)/h. The calcined catalyst samples were tested under conditions of continuous operation over a period of a couple of weeks during this period the concentration of o-xylene was varied from 20 to 70 g/m3(STP). 

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...

Many other temperature sensors are in use. One which is convenient and reproducible is a bifilar, annealed platinum resistance thermometer. Here the resistance R and absolute temperature T are related by the expression R-Ro(l+aT+ bT2 + cT3), where R0 a, b, c, are constants which must be established by calibration. Quite commonly two-junction thermocouples are used as thermometers these produce an emf E... 

The checkers monitored the internal temperature of the reaction mixture via thermocouple using an immersion well. The checkers observed that accurate temperature control is essential to obtain the reported yields reproducibly. 

Calculated RON values corresponded to engine values of debutanized reformate samples (25 samples) with a standard deviation of 0.55 RON units, which is close to the accuracy of engine measurements. By carrying out a number of repeated test runs, the reproducibility taken as the standard deviation for the measured reformate and hydrogen yields were determined as 0.25 and 0.02 wt%, respectively, and 0.25 units for RON. In order to achieve this a detailed calibration of the GC system was carried out, and the reactor thermocouples, the hydrogen mass flow controllers and naphtha feed pumps were thoroughly calibrated between each test run. 

Thermometers, or thermocouples, whatever their nature, must be standardised over the whole range of temperature for which they are to be used. This may be done by comparison with an instrument which has already been standardised, or by the actual determination of temperatures which are accurately known and easily reproducible. For this purpose the thermometer is immersed in a bath in which some process is going on, which takes place at a constant and known temperature, such, for example, as the melting or boiling of a pure substance, or the... 

---