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1、Experiment 4 Calibration of Temperature SensorsI.Objective:The purposes of this experiment are to: (1) acquaint you with common thermometry instruments, (2) impart a fundamental understanding of the physical principles that underpin these devices, and (3) point out the respective advantages and disa
2、dvantages that these instruments offer. II.Apparatus3 ” Floppy Diskette (Supplied by the student.) Personal Computer Running LabView Keithley 2000 6 Digit Multimeter Equipped with 2000-SCAN MUX Card Julabo F12-MD PID Temperature-Controlled Bath Type-J 0.250” Dia. Sheathed Thermocouple Omega GJ QSS-1
3、4G-12 Type-J 0.0625” Dia. Sheathed Thermocouple Omega GJ QSS-116G-12 Type-T 0.250” Dia. Sheathed Thermocouple Omega GT QSS-14G-12 Type-T 0.0625” Dia. Sheathed Thermocouple Omega GT QSS-116G-12 Industrial Thermistor Omega ON-970-44006 (10 k 25 C) Industrial Resistance Temperaure Detector (RTD) Rosemo
4、unt 563792 1, S/N 0693603 Precision Mercury Thermometer (NIST Certified) Omega GT-3554Y (-1-100 C +/- 0.1 C) Standard Alcohol Laboratory Thermometer Fisher 14-997III.Introduction:Thermometry is an essential element in many industrial processes. For example, when extruding polymers such as polyethyle
5、ne, the extruder is partitioned into several thermal zones. The temperature of each zone must be maintained within strict limits. If for instance, the temperature in any zone is too great, then the polymer will burn and carbon will be deposited on the interior walls of the extruder. This carbon is n
6、early impossible to remove and it has an unfortunate tendency to break-off when the extruder is in operation. These chunks of carbon contaminate the end product. The product is subsequently sent to a landfill because it can be neither sold nor recycled. Clearly, control relies upon accurate measurem
7、ent of the operating temperatures. Thermometers:These devices are the oldest thermometry instruments and their use is well known. Two thermometers are used in this experiment. One should be familiar with the standard alcohol thermometer. The precision thermometer uses mercury and it has been calibra
8、ted at NIST. Thermocouples:These devices consist of two dissimilar metals that are joined at the ends. When these junctions are held at different temperatures, a thermoelectric potential difference exists. This is called the Seebeck effect and one may measure the thermoelectric potential ( or electr
9、omotive force, emf) to infer temperature junction temperatures. The potential, temperature range, and sensitivities of thermocouples depend upon the combinations of wire used. The Type-T thermocouples employ copper and constantan and the Type-J thermocouples employ iron and constantan. Thermoelectri
10、c potentials are typically small (mV). A calibration relation e.g., formula or table, relates temperature to thermoelectric potential. The NIST (formerly NBS) thermocouple tables comprise standard calibrations for the most popular thermocouple types. The accuracy of these tables is approximately +/-
11、 2 degrees C. Please refer to the introductory section of Experiment 3 for more complete information on thermocouples.Resistance Temperature Detectors (RTD):These devices use the property that the electrical resistance of materials varies with temperature. RTDs typically consist of a platinum wire e
12、nclosed within a sheath. The Callendar-Van Duesen calibration equation, , (1) )(01. 0() 1)(01. 0()(01. 0() 1)(01. 0()()()()(300CTCTCTCTCTRRR relates wire resistance to temperature. The symbols , , , and represent calibration 0R constants. The factory-determined values of these constants are stamped
13、on the metal tag attached to the RTD used in this laboratory. Record these constants and the serial number of the RTD in your lab notebook. Note that the constant is used only when the measurement temperature is below 0 C, i.e., . The manufacturer reports the accuracy of CT0 when 0 Eqn. (1) to be 0.
14、06 C over the range from 0 to 100 C when their calibration coefficients are used. The calibration constants of the RTD are NIST (National Institute for Standards and Technology) traceable. This implies that the RTD was calibrated against internationally accepted temperature standards. Thermistors: T
15、hese devices also use the property that the electrical resistance of materials varies with temperature. In contrast to RTDs, thermistors are made of semiconductor materials. Unlike metals, the temperature-resistance dependence of semiconductor materials is strongly non-linear. Consequently among the
16、rmometry instruments, thermistors generally have the greatest sensitivity, but their useful range is comparatively small. The calibration equation are typically of the form .(2)3lnln)(1RCRBAKTJulabo F-12MD Constant Temperature Bath:The following diagrams and instructions are exerpted from the Julabo manual.Operating controls and functional elements1a2 357481
