Resonance thermometers

Electrical effects. Electrical methods are convenient because an electrical signal can be easily processed. Resistance thermometers (including thermistors) and thermocouples are the most widely used. Other electrical methods include noise thermometers using the Johnson noise as a temperature indicator resonant-frequency thermometers, which rely on the temperature dependence of the resonant frequency of a medium, including nuclear quadrupole resonance thermometers, ultrasonic thermometers, and quartz thermometers and semiconductor-diode thermometers, where the relation between temperature and junction voltage at constant current is used. 

In a resonant-frequency thermometer, the resonance frequency of the medium serves as the temperature indicator. Included in this category are nuclear quadrupole resonance thermometers, quartz thermometers, and ultrasonic thermometers. These thermometers usually... 

Nuclear quadrupole resonance thermometers [83] can be used between 20 and 400 K. In the ultralow temperature range below 1 K, a direct measurement of temperature is feasible by using the spectrometer to measure the intensity ratio of magnetic resonance lines [84]. A precision and accuracy of 1 mK can be achieved. However, these thermometers are quite expensive and are therefore used most often as transfer standards... 

Resonance Thermometers. Two resonance phenomena, nuclear quad-rupole resonance (NQR) and nuclear magnetic resonance (NMR), can be utilized to measure low temperatures. NQR provides usable temperature sensitivity in the range from approximately 20 to 500 K. Accuracies on the order of 1 mK are possible near 77 K. Accuracies on the order of 1 mK can be achieved using an NMR thermometer at temperatures above 50 K. 

Yokagawa Electric Works has developed a thermometer based on the nuclear quadmpole resonance of potassium chlorate, usable over the range from —184 to 125°C. This thermometer makes use of the fundamental properties of the absorption frequency of the Cl nucleus, and its caUbration is itself a constant of nature. 

Filled-system thermometer Rotameter Bourdon tube Lever Magnetic resonance analysis (MRA)... 

Quartz Crystal Thermometer. The temperature coefficient of the resonant frequency of quartz (14-20 MHz), using the piezoelectric effect, is a function of temperature (1 kHz per degree). In the temperature range -80°C to 230°C, an electronically controlled quartz crystal thermometer can be accurate to 0.02°C and has a sensitivity of 10 microdegrees centigrade in temperature difference measurements. 

Fig. 1. 249.9-GHz FIR-ESR spectrometer. A, 9-T magnet and sweep coils B, phase-locked 250-GHz source C, 100-MHz master oscillator D, Schottky diode detector E, resonator and modulator coils F, 250-GHz quasioptical waveguide G, power supply for main coil (100 A) H, current ramp control for main magnet I, power supply for sweep coil (50 A) J, OC spectrometer controller K, lock-in amp for signal L, field modulator and lock-in reference M, Fabry-Perot tuning screw N, vapor-cooled leads for main solenoid O, vapor-cooled leads for sweep coil P, He bath level indicator Q, He transfer tube R, bath temperature thermometer S, " He blow-off valves. [From Lynch et al. (1988), by permission of the AIP.]...

Quartz crystals have been used as thermometers in calorimetry relatively recently. Their use is based on the fact that the resonance frequency of the quartz crystal cut in a certain orientation to the axis of its crystal structure depends on temperature, whereby the temperature dependence is high and almost linear. 

After protons, C is the most widely detected nucleus in NMR. Proton cross-polarization and decoupling are usually applied to increase the S/N, and these types of experiment can result in substantial sample heating. Many forms of C-based NMR thermometers have been proposed. The first such system was based on the cis-trans conformational equilibrium of furfural, with the linewidths of carbon-3 and the aldehyde carbon being temperature-dependent. There are many disadvantages of linewidth-based measurements, and subsequent developments concentrated almost wholely on temperature-dependent C chemical shifts. The first such system utilized a temperature-dependent lanthanide-induced pseudocontact shift in a complex of acetone-de and ytterbium(III)1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octadionate (Yb (fod)3). The 6co of the acetone-dg, measured with respect to a CS2 standard, was almost linearly dependent on 1 / T with a small quadratic term over a range 200-315 K. If a small amount of protonated acetone was added, then the proton resonance, measured with respect to the protons of TMS, was also found to be temperature dependent ... 

GC Campbell, RC Crosby, JF Haw. 13C chemical shifts which obey the curie law in CP/MAS NMR spectra. The first CP/MAS NMR chemical-shift thermometer. J Magn Reson 69 191-195, 1986. 

B Wehrle, F Aguilar-Parrilla, H-H Limbach. A novel 15N chemical-shift NMR thermometer for magic angle spinning experiments. J Magn Reson 87 584-591, 1990. 

Another resonant-frequency thermometer is the quartz crystal resonator (Benjaminson and Rowland, 1972), which, if the crystal is properly cut, is quite linear from about 190 to 525 K. Although this thermometer has excellent resolution, it does exhibit hysteresis and drift. The principle of quartz crystal thermometry is based on the temperature dependence of the piezoelectric resonant frequency of a quartz crystal wafer of a given dimension. The angle of cut of the quartz crystal is selected to give as nearly a linear and yet sensitive correspondence between resonant frequency and temperature as possible. This angle of cut is referred to as an LC (linear coefficient) cut. The temperature sensitivity of the quartz crystal thermometer is about 1000 Hz/°C. 

Other Thermometers. Among the many other types of thermometers, we will briefly discuss the following bimetallic thermometers, noise thermometers, resonant-frequency thermometers, and semiconductor diode thermometers... 

For a quartz thermometer, the resonant frequency of a quartz crystal resonator is strongly related to the temperature variation. With high resolution, the temperature change can be directly determined from the frequency change of a quartz crystal thermometer. A quartz thermometer developed for use between -80 and 250°C [85] has a resolution of 0.1 mK. If used at the same temperature, a comparable precision can be achieved. However, with temperature cycling, hysteresis can reduce its repeatability. An accuracy of 0.05°C can be achieved with calibration. Nevertheless the temperature resolution for the quartz resonator is found to be less accurate at lower temperatures Over the temperature range from 4.2 to 400 K, the temperature resolution with the resonant frequency change for a YS cut quartz crystal thermometer drops from 1 kHz/K at 300 K to 80 Hz/K at 4.2 K [86]. 

A. Ohte and H. Iwaoka, A New Nuclear Quadrupole Resonance Standard Thermometer, in Temperature Its Measurement and Control in Science and Industry, vol. 5, pt. 2, pp. 1173-1180, American Institute of Physics, New York, 1982. 

A. Bielecki, D.P. Burum, Temperature dependence of ° Pb MAS spectra of solid lead nitrate. An accurate, sensitive thermometer for variable-temperature MAS, J. Magn. Reson. All6 (1995) 215-220. 

C.P. Grey, A.K. Cheetham, C.M. Dobson, Temperature-dependent solid-state Sn-MAS NMR of Nd2Sn20y, Sm2Su207, and Yi 8Smo.2Sn207. Three sensitive chemical-shift thermometers,. Magn. Reson. 101 (1993) 299—306. 

Finally, two other temperature-measuring devices are the quartz crystal thermometer, incorporating a quartz crystal whose resonance frequency is temperature dependent, and optical pyrometers, which are useful above about 1300 K to measure the radiant intensity... 

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