Thermometric devices

Boiling-point apparatus. The mercury thermometer can be replaced by a resistance thermometer or other direct-reading thermometric device. 

In this section, the design and operation of familiar liquid thermometers, thermocouples, platinum resistance thermometers, thermistors, and optical pyrometers are discussed in detail. Briefer descriptions are also given of a variety of special thermometric devices such as quartz thermometers, germanium resistance thermometers, and sihcon-diode thermometers. 

Special Liquid Thermometers. For low temperatures, one can use several kinds of liquid-in-glass thermometers. Toluene thermometers may be used down to — 95°C, and pentane thermometers will operate as low as — 130°C. However, it is usually more convenient, as well as more accurate, to use thermometric devices of other types, especially thermocouples or resistance thermometers. 

Other Thermometric Devices. The vapor pressure of a pure liquid or solid is a physical property sensitive to temperature and thus suitable for use as a thermometer. The use of a liquid-nitrogen vapor-pressure thermometer is suggested for the range 64 to 78 K in Exp. 47. At very low temperatures (1 to 4.2 K), the vapor pressure of liquid helium can be used. 

Temperature Several instruments are available that provide continuous measurement of temperature—for example, thermocouples, thermometers, thermopiles, and resistance thermometric devices. 

A very wide range of thermometric devices has been developed for the measurement of cryogenic temperatures. Thermometry between 4 K and room temperature is dealt with under Cryogenic Process Engineering, in this article, we discuss thermometry in the temperatore range below 4 K. The principal thermometers and their approximate ranges of useful apphcation are shown in Table III. 

Thermometers—Calibrated liquid-in-glass thermometers of suitable range with subdivisions and maximum scale error of 0.1 C (0.2 F) or any other thermometric device of equal accuracy, precision and sensitivity shall be used. Thermometers shall conform to the requirements of Specification E 1. 

A2.2.1 Use liquid-in-glass thermometers with an accuracy after correction of 0.02 C or better, calibrated by a laboratory meeting the requirements of ISO 9000 or ISO 25, and carrying certificates confirming that the calibration is traceable to a national standard. As an alternative, use thermometric devices such as platinum resistance thermometers, of equal or better accuracy, with the same certification requirements. 

A2.2.2.2 Other thermometric devices, if used, will also require periodic recalibration. Keep records of all re-calibration. 

A2.2.4 When in use, immerse the thermometric device to the same depth as when it was fully calibrated. For example, if a liquid-in-glass thermometer was calibrated at the normal total immersion condition, it shall be immersed to the top of the mercury column with the remainder of the stem and the expansion volume at the uppermost end exposed to room temperature and pressure. In practice, this means that the top of the mercury column shall be within a length equiva-... 

Thermometers—C alibrated liquid-in-glass thermometers (see Table X4.2) of an accuracy after correction of 0.04 F (0.02 C) can be used or any other thermometric device of equal accuracy. ASTM Kinematic Viscosity Thermometers 47F and 47C are suitable for the most commonly used temperature of 140T (60 C). 

Thermometric devices based on the measurement of the heat effects of a specific chemical reaction or adsorption which involve the analyte. Examples of this group are the so-called catalytic sensors. The devices based on measuring optothermal effects can alternatively be included in this group. 

The principle of the dispersive prism or diffractive grating spectrometer can be readily extended to the infrared and even to the far infrared. However the photographic plate for the recording and measurement of the spectrum is not available here. Early devices for sensing infrared radiation consisted of sensitive thermometric devices called bolometers. Bolometers do not form images and hence a spectrum must be recorded by sequentially displacing the bolometer to measure the intensity of radiation at different wavelengths. 

A liquid flow microcalorimeter, the thermal activity monitor (TAM), is commercially available from ThermoMetric (formerly LKB/Bofors). This instrument consists of two glass or steel ampules with a volume of 3 to 4 cm3 (25 cm3 ampule available with a single detector), placed in a heat sink block. Recently, an injection-titration sample vessel was developed which acts as a microreactor. This vessel is provided with flow-in, flow-out, and titration lines, with a stirring device. The isothermal temperature around the heat sink is maintained by a controlled water bath. Each vessel holder, containing an ampoule, is in direct contact with a thermopile array, and the two arrays are joined in series so that their output voltages subtract. The two pairs of thermopile arrays are oppositely connected to obtain a differential output,... 

A comparison has been made between small scale test results and a field trial at a 17-ton scale for a solid compound [217]. The test results from a very sensitive calorimeter (Thermal Activity Monitor from ThermoMetric, Sweden) were substituted in a model, and the self-heating situation in bulk containers was predicted. The large-scale trial was carried out in a steel rectangular container lined with polyethylene. A control device was used to keep the container at a temperature of 40 to 45°C. Several thermocouples enabled monitoring of the temperature as a function of time in different places in the large container. 

The establishment of the International Temperature Scale has required that the thermodynamic temperatures of the fixed points be determined with as much accuracy as possible. For this purpose a device was needed that measures essentially the thermodynamic temperature and does not depend on any particular thermometric substance. On the other... 

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

In the recent past, multianalyte determination has found increased applications, i.e. specific and multiple reactions favor a system that allows the specific determination of each reaction, using the same principal measurement methods, detectors and conditions. In keeping with this idea, a flow injection thermometric method based on an enzyme reaction and an integrated sensor device was proposed for the determination of multiple analytes. In principle the technique relies on the specificity of enzyme catalysis and the universality of... 

Based on the plethora of applications of thermistor/thermopile based devices, it can be concluded that the field of thermometric sensing offers several avenues of progress in materials science, process monitoring, process control, molecular level detection, characterization of biocatalysts, hybrid sensing and multisensing devices, as well as in telemedicine and other areas of biomedical analysis. 

Although thermistor devices involving the use of immobilized enzymes or antibodies for a number of clinically relevant substances have been described (Table 22), their practical use is at present limited to a few research laboratories. Thermometric enzyme linked immunosorbent assays are being routinely employed in monitoring the production of monoclonal antibodies. A broad application is restricted by the low sample throughput and the high equipment costs. 

The air in Galileo s device was the thermometric substance, and its expansion or contraction depended upon changes in atmospheric pressure as well as temperature. Because of this, it is more properly called a barothermoscope, although its dependence on barometric fluctuations was not recognized until after the invention of the barometer in 1643 (Roller, 1960, pp. 12—13). Galileo also fitted his barothermoscope with a scale marking off degrees at pleasure, but he made no attempt to base the scale on standard temperatures that were reproducible. 

The product of PV for a low-density gas is said to be a thermometric property in that to each value of FV there corresponds only a single value of temperature. The ideal gas thermometer is not convenient to use. however, because of both its mechanical construction (see Fig. 1.4-3) and the manipulation required to make a measurement. Therefore, common thermometers make use of thermometric properties of other materials—for example, the single-valued relation between temperature and the specific volume of liquid mercury (Problem 1.2) or the electrical resistance of platinum wire. There are two steps in the construction of thermometers based on these other thermometric propenies first, fabrication of the device, such as sealing liquid mercury in an otherwise evacuated tube and second, the calibration of the thermometric indi-... 

Test strips, which are available for the determination of about ten low-molecular mass substances (metabolites, drugs, and electrolytes) and eight enzymes [356], can be considered as precursors of optoelectronic biosensors. Efficient optoelectronic sensors based on immobilized dyes have been devised for the determination of glucose, urea, penicillin, and human serum albumin [357]. Other approaches use immobilized luciferase or horseradish peroxidase to assay ATP or NADH or, when coupled with oxidases, to measure uric acid or cholesterol. These principles have not yet been generally accepted for use in routine analysis. Thermistor devices involving immobilized enzymes or antibodies for a number of clinically relevant substances have also been described. Thermometric enzyme linked immunosorbent assays are being routinely employed for monitoring the production of monoclonal antibodies. 

In addition to these defining and secondary temperature standards, a thermocouple wire (SRM 733, a silver-28 at.% gold alloy) has been certified, which serves to compare manufactured wire to standard reference thermocouple tables between 4 and 273 K. SRM 767, a superconductive thermometric fixed-point device, provides temperature calibration in the range 0.5 to 7.2 K This device incorporates five high-purity elements (lead, indium, aluminum, zinc, and cadmium) in long, thin cylinders whose superconductive transition temperatures are certified to be reproducible within 1 mK. 

Work is in progress on modifying the existing superconductive thermometric fixed-point device to extend the range to both lower and higher temperatures. Another thermocouple wire (SRM 1967, platinum) will soon be available. This platinum wire, referred to in the thermometry literature as Pt-67, will take the place of Pt-27, which was the standard referred to until 1973. 

Thermoelectric-, pyroelectric-, and thermoconductivity-based devices are other representatives of thermometric gas sensors (Korotcenkov 2011). In particular the thermal conductivity technique for detecting gas is suitable for the measurement of high (vol. %) concentrations of binary gas mixes. The heated sensing element is exposed to the sample and the reference element is enclosed in a sealed compartment (see Fig. 1.14). If the thermal conductivity of the sample gas is higher than that of the reference, then the temperature of the sensing element decreases. The higher their thermal conductivity, the lower the concentration which can be measured (Table 1.14). Power loss of a single filament thermistor by heat conduction via the ambient gas can be expressed as... 

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