Thermal measuring and testing – Temperature measurement – By a vibratory effect
Patent
1990-05-07
1992-06-23
Yasich, Daniel M.
Thermal measuring and testing
Temperature measurement
By a vibratory effect
367 48, G01K 1122
Patent
active
051237504
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to a gas thermometer and, more particularly, to a gas thermometer with a hermetically sealed case and a phase measuring circuit.
BACKGROUND
A gas thermometer of this kind is described in German Patent Disclosure Document 30 31 678, HIRT. It serves for the direct measurement of the temperature of hot fluids. To protect the sound generator and the sound receivers against high temperatures the latter are disposed at a comparatively great distance from the actual area of measurement, and to exclude the influence of the sliding temperature transition between the measuring range at high temperature and the sound-generator/sound-receiver range held at lower temperature the two reflector walls are provided, disposed in the measurement area at a distance apart in the direction of propagation of the sound. By measuring the phase shift of the portions of the sound field reflected by these two reflector walls a working signal is then obtained which, under otherwise unchanged measuring conditions, depends only on the temperature of the volume of gas situated between the reflector walls.
In the known measuring system this constitutes a nonreleasable component of the container in which the hot fluid that is to be measured is situated.
THE INVENTION
The present invention provides an improved gas thermometer which is a portable, independent apparatus which can be moved from one point of use to another point of use like a normal thermometer.
In the gas thermometer according to the invention there is a hermetic case in which the reflector walls form part of the case walls. A working gas, which can be especially selected with a view to the particular use of the gas thermometer, is enclosed in the case interior.
The hermeticity of the case does not simply permit the use of a working gas especially suited to temperature measurement in a particular temperature range; since a good acoustical isolation from external noise is also provided, the temperature measurement can be performed with low sound amplitudes, and this is again an advantage as regards low radiation of the sound of the gas thermometer to the exterior.
According to a further feature of the invention it is brought about that, even at high temperatures, the working gas does not enter into any chemical reactions with the material from which the case is made. If krypton or xenon is used as the working gas, there is additionally a poor thermal conduction in the gas column situated between the measuring end and the generator/receiver end of the gas thermometer. Furthermore, in noble gases the velocity of sound is largely independent of pressure, so that the gas thermometer has a great temperature range with high accuracy, without the need for correction of the measurement due to the pressure-dependence of the velocity of sound, or for taking precautions at the apparatus to keep the pressure of the working gas constant.
According to further features of the invention, it is brought about that, even at extremely high temperature differences, the pressure inside the case of the gas thermometer remains substantially constant, so that even at these very great temperature differences no corrections of the results of the measurement are necessary.
According to further features of the invention, undesirable consequences of sound reflections at the ends of the sound channels which are adjacent to the sound generator or a sound receiver are mitigated. Secondary waves reflected at these channel ends would otherwise possibly superimpose themselves on the main wave used for the measurement and falsify its phasing. In a gas thermometer featuring sound absorbers, however, the ends of the measuring channels are terminated by an acoustical sink. The sound receivers in the system serve as pure detectors of pressure variations.
An embodiment with 2 folded sound channels is advantageous for its particularly good isolation of the two sound channel sections returning from the reflector walls. The small inside dimension of the sound channels in compa
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patent: 3595082 (1971-07-01), Miller et al.
patent: 4215582 (1980-08-01), Akita et al.
patent: 4655992 (1987-04-01), McKnight et al.
patent: 4762425 (1988-08-01), Shakkottai et al.
patent: 4848923 (1989-07-01), Ziegler et al.
Behlen Horst
Ziegler Horst
Heraeus Sensor GmbH
Yasich Daniel M.
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