Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-05-10
2001-11-20
Bruce, David V. (Department: 2889)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S221000, C250S559390
Reexamination Certificate
active
06320199
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a process for improving the reliability of operation of optical gas sensors.
BACKGROUND OF THE INVENTION
Optical gas sensors usually have one or more radiation sources, which emit suitable radiation over a measured section, wherein the resulting measuring beams pass through the measured section containing the gas to be measured once or several times, and the intensity of the measuring beams weakened by the optical absorption of the gas to be measured is measured by means of one or more radiation detectors. The residual, measured radiation intensity of a gas-specific wavelength or gas-specific wavelengths is an indicator of the concentration of the measured gas.
Such a measuring device is described, e.g., in DE 197 13 928 C1.
The infrared absorption is characteristic for the measurement of the concentrations of many gases, e.g., hydrocarbons (e.g., methane), and it is therefore particularly preferred for the measurement.
A problem arises in the prior-art optical gas sensors from the fact that the optical measured section must be as readily accessible as possible to the gas to be measured in order for a measured signal representative of the current gas concentration at the site of the measurement to be able to be obtained possibly without a time delay.
Since the measured section is usually limited by optical elements, such as windows, mirrors or lenses or is provided with such elements, these elements are also exposed to interfering environmental effects, e.g., rain, snow, dust, aerosols or contaminants in the same manner at the site of the measurement, besides the gases to be measured. These environmental effects lead to disturbances or weakening of the measuring beam and ultimately of the measured signal sent by the radiation detectors.
When the measuring beam is weakened beyond a certain extent, the concentration of the gas to be measured cannot be measured any longer, so that the measuring unit with the radiation detectors will send more or less abruptly an interference signal in this case, especially an electric interference signal in the form of a constant current intensity.
SUMMARY AND OBJECTS OF THE INVENTION
The object of the present invention is to provide a process for optical gas sensors that increases the reliability of operation in the case of increasing interferences of the measuring beam due to environmental effects.
According to the invention, a process is provided for improving the reliability of operation of optical gas sensors with at least one radiation source and at least one radiation detector. The measured signals sent by the radiation detector, of which there is at least one, are first compared with a first stored reference value, so that
when the first stored reference value (D
1
) is exceeded by the measured signals (D) sent by the radiation detector the corresponding measured values are sent by the gas sensor, and
when the first stored reference value (D
1
) does not exceed the measured signals (D) sent by the radiation detector, the measured signals (D) are compared with a second stored reference value (D
2
), so that
when the second stored reference value (D
2
) is exceeded by the measured signals (D) sent by the radiation detector, the measured signals are compared with a third stored reference value (K), and
when the third stored reference value (K) does not exceed the measured signals (D) sent by the radiation detector, the corresponding measured values are sent by the gas sensor, and
when the third stored reference value (K) is exceeded by the measured signals (D) sent by the radiation detector, the first warning signals are sent by the gas sensor and,
when the second stored reference value (D
2
) is not exceeded by the measured signals (D) sent by the radiation detector, the second warning signals are sent by the gas sensor.
The process may also compare the measured signals sent by the radiation detector with the stored reference value or stored reference values (D
1
, D
2
, K) at preset, adjustable time intervals.
The warning signals may be sent by means of a constant current, a digital signal, an optical display and/or by means of an acoustic warning means. The first and second warning signals and/or the third warning signals may be sent by the gas sensor in the form of a constant current. The first and second warning signals and/or the measured values may be interrupted at preset, adjustable time intervals.
The third stored reference value (K) preferably corresponds to a characteristic concentration critical for the gas to be measured, especially to the concentration of the gas that is the maximum allowable concentration at the workplace or to the concentration of the gas in a gas mixture, which concentration is critical for an explosion limit. When the second stored reference value (D
2
) is overshot and the third stored reference value (K) is at the same time not exceeded by the measured signals (D) sent by the radiation detector, additional third warning signals are preferably sent by the gas sensor.
One essential advantage of the process according to the present invention is, especially in the case of toxic or explosive gases to be measured, that the readiness of the gas sensor to measure, which may be vitally important, is increased, combined with the timely warning of a limited operating state, during which the user or users of the gas sensor are protected from toxic damage and machines and units located in the environment are protected from explosion damage, because critical gas concentrations continue to be measured and displayed.
It shall be mentioned in connection with the design of the process according to the present invention that it is described in the patent claims and in the description of the exemplary embodiment such that the measured signals increase with increasing degree of contamination, so that defined stored reference values for the degree of contamination are reached quasi from below and are optionally exceeded with increasing degree of contamination.
The optical measured signals received by the radiation detector, of which there is at least one, do, of course, become weaker in practice with increasing degree of contamination, so that the process according to the present invention should be considered in this case to be complementary and equivalent to the text of the patent claims as written, i.e., e.g., such that when the measured signal drops below the first stored reference value according to this text, the measured signals are compared with a second stored reference value, so that when the measured signals sent by the radiation detector, of which there is at least one, also drops below the second stored reference value, warning signals are sent by the gas sensor. However, when the measured signal drops only below the first stored reference value, but not below the second stored reference value, it is compared with a third stored reference value, which is, in general, an indicator of a critical gas concentration: depending on whether or not this indicator of a critical gas concentration is exceeded, measured values are sent (for a critical gas concentration when the measured signal exceeds the indicator) or first warning signals are sent (when the indicator for a critical gas concentration is not exceeded).
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
REFERENCES:
patent: 5969623 (1999-10-01), Fleury et al.
patent: 6096560 (2000-08-01), Scripca et al.
patent: 197 13 928 C1 (1998-04-01), None
Fassian Bernd
Kessel Robert
Wahlbrink Gunter
Bruce David V.
Drager Sicherheitstechnik GmbH
McGlew and Tuttle , P.C.
Song Hoon K.
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