Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-05-11
1990-11-13
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
25022717, 25023110, 374161, G02F 101, H01J 4014, G01K 1100
Patent
active
049703854
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an optical temperature measuring device and more particularly, a temperature measuring device capable of measuring temperature by using photoelastic effect.
PRIOR ART
Various temperature measuring devices have been well known. The most popular one uses a thermocouple as its sensor. The temperature measuring device using a thermocouple is used in those cases where temperature at a remote place must be measured. The thermocouple is low in cost and easy to handle, and moreover can make high accuracy temperature measurements. It is, however, interfered by electromagnetic wave because thermoelectro-motive force generated between two different metals is very small. Therefore, the temperature measuring device which uses the thermocouple cannot be used in high electric or magnetic fields, for example.
The conventional temperature measuring device which can be used in high electric or magnetic fields measure temperature by using a change of an energy gap of a semiconductor. If the energy gap changes, the edge of the absorption spectrum changes. This change can be detected as the change of transmission of LE light which has peak spectrum near the edge of the absorption spectrum. This temperature measuring device uses light as signals transmission media. This temperature measuring device can be used in high electric or magnetic fields. However, the temperature measuring device is extremely low in sensitivity because the change of the energy gap of the semiconductor depending on temperature is small. It is therefore impossible for this temperature measuring device to measure a slight change of temperature.
As described above, the conventional optical temperature measuring devices could not measure temperature with high accuracy because they were low in temperature sensitivity.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide an optical temperature measuring device which is simple in construction and capable of measuring temperature with high accuracy even in high electric or magnetic field.
A temperature measuring device according to the present invention comprises a thermal expansion photoelastic cell including a photoelastic element and a stress generating means which are closely contacted with each other for yielding anisotropic stress in a photoelastic element in response to ambient temperature because the stress generating means is quite different in thermal expansion coefficient from the photoelastic element; a means for making linearly polarized light which is entered into the photoelastic element of the thermal expansion photoelastic cell; a means for detecting phase difference between two polarized light components passed through the photoelastic element, which are, for example, one component polarized in a stress direction or largest stress direction, and the other one polarized in a direction perpendicular to the above stress direction thereof; and a means for converting the detected phase difference into a temperature and displaying the converted temperature.
When the temperature measuring device is arranged as described above, stress in the photoelastic element changes according to changing ambient temperature. Stress thus generated in the photoelastic element also changes accordingly. This stress has anisotropy. When anisotropic stress is yielded in the photoelastic element, the photoelastic element has birefringence (or anisotropy of refraction) depending upon the stress. The degree of this birefringence in the photoelastic element can be detected phase difference between two orthogonal polarized components passed through the photoelastic element, which are one component polarized in a stress direction or largest stress direction thereof and the other component polarized in a direction perpendicular to the stress direction thereof. The system for detecting this phase difference may be wellknown. When materials of the photoelastic element and the stress generating means are selected in such a way that large
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Optics Letters; W. Eickhoff; 1981 (Jan. 15), vol. 6, No. 4, p. 204, "Temperature Sensing by Mode-Made Inference in Birefringent Optical Fibers".
Tatsuno Kyoichi
Watanabe Ikuo
Kabushiki Kaisha Toshiba
Messinger Michael
Nelms David C.
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