Differential thermometer

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A technique for observing the temperature, direction, and magnitude of thermally induced transitions in a material by heating/cooling a sample and comparing its temperature with that of an inert reference material under similar conditions. Differential Thermometer... 

Thermometer Scale Correction. An NBS thermometer was used for the adiabatic jacket and a Beckmann differential thermometer for the calorimeter water. The Beckmann thermometer was calibrated against the NBS thermometer. Corrections were made to the initial and final temperatures recorded on the Beckmann thermometer. 

In a certain experiment, cylindrical samples of diameter 5 cm and length 10 cm are used. The two thermocouples in each sample are placed 3 cm apart. After initial transients, the electric heater is observed to draw 0.4 A at 110 V, and both differential thermometers read a temperature difference of 15°C. Determine the. thermal conductivity of the sample. 

Elevations of boiling points and depressions of freezing points, which will be discussed later, are usually quite small for solutions of typical concentrations. They can be measured, however, with specially constructed differential thermometers that measure small temperature changes accurately to the nearest 0.001°C. 

The first historical calorimeters of this type were manually-operated (see Figure 6). Person, in 1849 decided to cancel die temperature difference Ts - TV which he could measure by means of a double-bulb differential thermometer. For this puipose, he made use of a second, external, water bath, at a higher or lower temperature, in which he could partly immerse the water thermostat surrounding the system. He adjusted the depth of immersion by means of the crank visible in the drawing. He called his set-up a cancelled heat-loss calorimeter [21]. This is the first known active adiabatic calorimeter. 

The simplest and, despite its several drawbacks, the most widely used type of control is the on/off control system. An example is a contact thermometer, which closes or opens a heater circuit. The designation on/off means that the controller output, or the manipulated variable (electric current) is either fully on or completely off. To avoid oscillations around the setpoint, the real on/off controller has built into it, a small interval on either side of the setpoint, within which the controller does not respond, and which is called the differential gap or deadzone. When the controlled variable moves outside the deadzone, the manipulated variable is set either on or off. This is illustrated in Fig. 2.30. Such shifts from the set point are known as offset. 

Stiction, in mercury thermometers, 24 465 Stiff differential equation, 25 285 Stiffness loss, in fatigue, 16 187-188 of fibers, 11 181, 182 Stiffness values, of paper, 18-101 Stilbene(s), 25 181... 

Several techniques are available for thermal conductivity measurements, in the steady state technique a steady state thermal gradient is established with a known heat source and efficient heat sink. Since heat losses accompany this non-equilibrium measurement the thermal gradient is kept small and thus carefully calibrated thermometers and heat source must be used. A differential thermocouple technique and ac methods have been used. Wire connections to the sample can represent a perturbation to the measurement. Techniques with pulsed heat sources (including laser pulses) have been used in these cases the dynamic response interpretation is more complicated. 

Figure 3.1 Analytical working curve for a self-indexed luminescent thermometer based on the ratio between the measured excimer (E, 475 nm) and monomer (M, 375 nm) emission bands of l,3-b/s(l-pyrenyl)propane in [C4Cjpyr][Tf2Nj. The optical thermometer is perfectly reversible in the temperature range shown and highly precise, with the measured uncertainties in the ratio (1 /1 ) falling well within the symbol dimensions. The dashed curve represents the temperature uncertainty predicted from explicit differentiation of a sigmoidal fit to the calibration profile 5T = 0T/0R 5R where R = I /Iu- (Reprinted from Baker, G.A., Baker, S.N., and McCleskey, T.M., Chem. Commun., 2932-2933, 2003. Copyright 2003 Royal Society of Chemistry. With permission.)...

The heating element is connected to a 110-volt line through a rheostat (such as a 140-ohm, 3-ampere resistor), and the temperature is adjusted with the aid of two thermometers (7 and 7V), a reasonable differential, depending upon the materials to be distilled, being allowed. 

AT Actual temperature differential may vary considerably from design cooling range throughout the seasons and process campaigns. The reader is recommended to periodically determine actual AT using a thermometer. 

Design temperatures, operator guesses, and actual operating temperature differentials almost never correspond. Representatives should always carry a pocket thermometer with them (accurate to 0.2°F/0.rC) and carry out an actual measurement during the survey. A difference of 1.0°C between actual and estimated temperatures can eventually produce a considerable difference in estimated annual chemical costs. Again, it is necessary to qualify the temperature differentials for seasonal variations. 

The most accurate measurements of the CMB spectrum to date have come from the Far InfraRed Absolute Spectrophotometer (FIRAS) on the COsmic Background Explorer (COBE) (Boggess et al., 1992). In contradiction to its name, FIRAS was a fully differential spectrograph that only measured the difference between the sky and an internal reference source that was very nearly a blackbody. Figure 9.2 shows the interferograms observed by FIRAS for the sky and for the external calibrator (XC) at three different temperatures, all taken with the internal calibrator (IC) at 2.759 K. Data from the entire FIRAS dataset show that the rms deviation from a blackbody is only 50 parts per million of the peak Iv of the blackbody (Fixsen et al., 1996) and a recalibration of the thermometers on the external calibrator yield a blackbody temperature of... 

Here, the heat evolved on adsorption increases the temperature of the sample and its container (usually a copper cylinder). The heat is prevented from flowing to the peripheral shield (the surroundings ) by an appropriate control of the shield temperature. Thus, the shield is usually maintained at the same temperature as the sample container by the use of a differential thermocouple and a heat coil - as indicated in Figure 3.14. The temperature rise is measured by means of a resistance thermometer attached to the sample container. 

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