CA2029317A1 - Flame detection - Google Patents
Flame detectionInfo
- Publication number
- CA2029317A1 CA2029317A1 CA002029317A CA2029317A CA2029317A1 CA 2029317 A1 CA2029317 A1 CA 2029317A1 CA 002029317 A CA002029317 A CA 002029317A CA 2029317 A CA2029317 A CA 2029317A CA 2029317 A1 CA2029317 A1 CA 2029317A1
- Authority
- CA
- Canada
- Prior art keywords
- radiation
- wavelength
- flame
- level
- value
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000001514 detection method Methods 0.000 title claims description 7
- 230000005855 radiation Effects 0.000 claims abstract description 50
- 238000002485 combustion reaction Methods 0.000 claims abstract description 6
- 238000000034 method Methods 0.000 claims description 12
- 239000000523 sample Substances 0.000 claims description 8
- 230000003287 optical effect Effects 0.000 claims description 6
- 238000012544 monitoring process Methods 0.000 abstract description 2
- 239000003086 colorant Substances 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N5/00—Systems for controlling combustion
- F23N5/02—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium
- F23N5/08—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using light-sensitive elements
- F23N5/082—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using light-sensitive elements using electronic means
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B17/00—Fire alarms; Alarms responsive to explosion
- G08B17/12—Actuation by presence of radiation or particles, e.g. of infrared radiation or of ions
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2223/00—Signal processing; Details thereof
- F23N2223/20—Opto-coupler
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2227/00—Ignition or checking
- F23N2227/28—Ignition circuits
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2229/00—Flame sensors
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2231/00—Fail safe
- F23N2231/20—Warning devices
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2241/00—Applications
- F23N2241/20—Gas turbines
Landscapes
- Engineering & Computer Science (AREA)
- Business, Economics & Management (AREA)
- Emergency Management (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
ABSTRACT OF THE INVENTION
The presence or absence of a flame in an engine combustion chamber is detected by monitoring the level of radiation at two different wavelengths. One wavelength is between 470nm and 530nm whereas the other wavelength is about 670nm. The ratio of the level of radiation at one wavelength to that at the longer wavelength is measured.
When the ratio is between about 0.1 and 1.0, this indicates the presence of a flame. When the ratio is outside this range this indicates absence of a flame and causes a signal to be supplied to an igniter control unit.
The presence or absence of a flame in an engine combustion chamber is detected by monitoring the level of radiation at two different wavelengths. One wavelength is between 470nm and 530nm whereas the other wavelength is about 670nm. The ratio of the level of radiation at one wavelength to that at the longer wavelength is measured.
When the ratio is between about 0.1 and 1.0, this indicates the presence of a flame. When the ratio is outside this range this indicates absence of a flame and causes a signal to be supplied to an igniter control unit.
Description
- FLA~E DETECTIO~I
Background of the Invention :~
This invention relates to flame detection.
In gas-turbine engines it is desirable to know whether or not a flame is present in the combustion chamber or afterburner. The presence of a flame can be detected by monitoring when optical radiation of a particular wavelength is greater than a predetermined -~ -background level. The problem with this, is that hot parts of the engine casing will also emit optical ~ ~
radiation a part of which will be at the wavelength being ~ ~-monitored. Stray radiation from the sun can also, in some cases, enter the engine and give rise to a spurious indication of the presence of a flame.
Brief Summàry of the Invention It is an object of the present invention to provide a method and apparatus for flame detection which is less susceptible to false indication.
....
Background of the Invention :~
This invention relates to flame detection.
In gas-turbine engines it is desirable to know whether or not a flame is present in the combustion chamber or afterburner. The presence of a flame can be detected by monitoring when optical radiation of a particular wavelength is greater than a predetermined -~ -background level. The problem with this, is that hot parts of the engine casing will also emit optical ~ ~
radiation a part of which will be at the wavelength being ~ ~-monitored. Stray radiation from the sun can also, in some cases, enter the engine and give rise to a spurious indication of the presence of a flame.
Brief Summàry of the Invention It is an object of the present invention to provide a method and apparatus for flame detection which is less susceptible to false indication.
....
According to one aspect of the present invention there is provided a method of flame detection including the steps of comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the presence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and less than a second, higher value.
According to another aspect of the present invention there is provided a method of flame detection including the steps of comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.
The method may include the step of supplying an output to an ignition unit in response to the indication of the absence of a flame.
The one wavelength may be between about 470nm and about 530nm, the longer wavelength being about 670nm. The first value may be about 0.1 and the second value about 1Ø
. .
.. .. ... .
.:
.: ., .. . ,. :
;:: : . . .
-2 ~
According to another aspect of the present invention there is provided apparatus for carrying out a ~ ~;
method according to the above one or other aspect of the present invention. ~ - ;
According to a further aspect of the present invention there is provided apparatus for detecting the presence of a flame including means for comparing the ~: ;
level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the presence of a flame when the ratio of ..
the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and :~
less than a second, higher value. :~
.
According to yet another aspect of the present inventon there is provided apparatus for detecting the :~
absence of a flame including means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the absence of a flame when the ratio of the :level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.
-' 7 The indication may be provided on a display.
The apparatus may include an optical probe arranged to view a combustion zone, a fibre-optic cable arranged to supply radiation from the probe to a dichroic beam splitter, and the beam splitter being arranged to split the radiation from the probe into wavelengths including the one wavelength and into wavelengths including the longer wavelength. The apparatus may include a first photodiode arranged to provide an electrical output representative of the level of radiation at the one wavelength and a second photodiode arranged to provide an electrical output representative of the level of radiation at the longer wavelength.
Flame detector apparatus for a gas-turbine engine and its method of operation will now be described, by way of example, with reference to the accompanying drawing.
Brief Description of the Drawings Figure 1 shows the apparatus schematically; and Figure 2 is a graph illustrating spectral intensity of a radiant source at three different temperatures.
_ 5 _ ~ 3-i ~
With reference first to Figure 1, the apparatus includes an optical probe 1 mounted on the casing 2 of a gas-turbine engine 3 to view optical radiation within the combustion chamber or zone 4. The probe 1 supplies the received radiation via a fibre-optic cable 5 to a dichroic beam splitter 6. The beam splitter 6 divides the radiation passed via the cable 5 into two component wavelengths. Radiation within a wavelength band located between about 470nm and 530nm, that is with a colour between blue and green is passed to a first photodiode 7.
The wavelength band may be of any width and may be located anywhere within this blue to green part of the spectrum according to the availability of the dichroic beam splitter and the response o~ the photodiode 7. The other output of the dichroic beam splitter 6 comprises radiation in a band of substantially the same width as that passed to the photodiode 7 but is of longer wavelength being centred around 670nm, that is, it is of red colour. This radiation is supplied to a second photodiode 8.
The outputs of the two photodiodes 7 and 8 are supplied to a comparator 10 which produces an output indicative of the ratio of the levels of radiation at the two different wavelengths bands. The output of the comparator 10 is supplied to a unit 11 which detects when the ratio is greater than a first value of 0.1 and less than a second value of 1.0~
. .
- - 6 - 2~2~
When the ratio lies between the two values, the unit 11 provides an output to a display 12 which gives an indication of the presence of a flame. An output could be provided to other utilization means 13, such as an igniter control unit which causes energization of an igniter when the absence of flame is detected.
The average flame colour temperature Tc in a gas-turbine combustion chamber is around ~800K, whereas the engine casing may be at about lOOOK and that of the sun about 6000K. The wavelength at which the maxima of emitted radiation occurs is given by Wien's Displacement Law: ~ max = 2897.9/Tc micron.
With reference now to Figure 2, it can be seen that, at any temperature, some radiation is emitted at all wavelengths but that the proportion emitted at any selected wavelength will depend on how close that wavelength is to the maxima. More particularly, for the three different colours: blue (470nm), green (527nm) and red (670nm), the radiation emitted by the sun will be at 99% that of the maxima, 99% of maxima and of 83% of maxima respectively. For a flame at 1800K these values for the three colours will be 1.3%, 4% and 20% respectively. For a body, such as the engine casing at lOOOK the values will be 2 X 10 , 1.5 X 10 and 4 X 10 . If the level in the blue-green range :is compared with that of red radiation, . ~.
- 7 - ~ 3 ~rJ
this gives, approximately, for the sun, a value greater than l; for a flame, a value less than 1 but greater than 0.1; and for the casing, a value of less than 0.1.
Thus, by determining whether the relative values of the radiant intensity at the different wavelengths are :
greater or less than 1 and greater or less than 0.1, it is possible to determine whether the radiation is from a flame, the sun or the engine casing. -It will be appreciated that the invention is not confined to engine applications ~ut could be useful in other applications, especially where the flame probe can receive sunlight, such as in flame stacks.
-'~ ~ . . :
-:
::
'~
~ : ~
' ~'~', '''`' ' " ' ' . `
'. ~ ' ' '' ' . ' ' ' ' " ''``. ` ' `
According to another aspect of the present invention there is provided a method of flame detection including the steps of comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.
The method may include the step of supplying an output to an ignition unit in response to the indication of the absence of a flame.
The one wavelength may be between about 470nm and about 530nm, the longer wavelength being about 670nm. The first value may be about 0.1 and the second value about 1Ø
. .
.. .. ... .
.:
.: ., .. . ,. :
;:: : . . .
-2 ~
According to another aspect of the present invention there is provided apparatus for carrying out a ~ ~;
method according to the above one or other aspect of the present invention. ~ - ;
According to a further aspect of the present invention there is provided apparatus for detecting the presence of a flame including means for comparing the ~: ;
level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the presence of a flame when the ratio of ..
the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and :~
less than a second, higher value. :~
.
According to yet another aspect of the present inventon there is provided apparatus for detecting the :~
absence of a flame including means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the absence of a flame when the ratio of the :level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.
-' 7 The indication may be provided on a display.
The apparatus may include an optical probe arranged to view a combustion zone, a fibre-optic cable arranged to supply radiation from the probe to a dichroic beam splitter, and the beam splitter being arranged to split the radiation from the probe into wavelengths including the one wavelength and into wavelengths including the longer wavelength. The apparatus may include a first photodiode arranged to provide an electrical output representative of the level of radiation at the one wavelength and a second photodiode arranged to provide an electrical output representative of the level of radiation at the longer wavelength.
Flame detector apparatus for a gas-turbine engine and its method of operation will now be described, by way of example, with reference to the accompanying drawing.
Brief Description of the Drawings Figure 1 shows the apparatus schematically; and Figure 2 is a graph illustrating spectral intensity of a radiant source at three different temperatures.
_ 5 _ ~ 3-i ~
With reference first to Figure 1, the apparatus includes an optical probe 1 mounted on the casing 2 of a gas-turbine engine 3 to view optical radiation within the combustion chamber or zone 4. The probe 1 supplies the received radiation via a fibre-optic cable 5 to a dichroic beam splitter 6. The beam splitter 6 divides the radiation passed via the cable 5 into two component wavelengths. Radiation within a wavelength band located between about 470nm and 530nm, that is with a colour between blue and green is passed to a first photodiode 7.
The wavelength band may be of any width and may be located anywhere within this blue to green part of the spectrum according to the availability of the dichroic beam splitter and the response o~ the photodiode 7. The other output of the dichroic beam splitter 6 comprises radiation in a band of substantially the same width as that passed to the photodiode 7 but is of longer wavelength being centred around 670nm, that is, it is of red colour. This radiation is supplied to a second photodiode 8.
The outputs of the two photodiodes 7 and 8 are supplied to a comparator 10 which produces an output indicative of the ratio of the levels of radiation at the two different wavelengths bands. The output of the comparator 10 is supplied to a unit 11 which detects when the ratio is greater than a first value of 0.1 and less than a second value of 1.0~
. .
- - 6 - 2~2~
When the ratio lies between the two values, the unit 11 provides an output to a display 12 which gives an indication of the presence of a flame. An output could be provided to other utilization means 13, such as an igniter control unit which causes energization of an igniter when the absence of flame is detected.
The average flame colour temperature Tc in a gas-turbine combustion chamber is around ~800K, whereas the engine casing may be at about lOOOK and that of the sun about 6000K. The wavelength at which the maxima of emitted radiation occurs is given by Wien's Displacement Law: ~ max = 2897.9/Tc micron.
With reference now to Figure 2, it can be seen that, at any temperature, some radiation is emitted at all wavelengths but that the proportion emitted at any selected wavelength will depend on how close that wavelength is to the maxima. More particularly, for the three different colours: blue (470nm), green (527nm) and red (670nm), the radiation emitted by the sun will be at 99% that of the maxima, 99% of maxima and of 83% of maxima respectively. For a flame at 1800K these values for the three colours will be 1.3%, 4% and 20% respectively. For a body, such as the engine casing at lOOOK the values will be 2 X 10 , 1.5 X 10 and 4 X 10 . If the level in the blue-green range :is compared with that of red radiation, . ~.
- 7 - ~ 3 ~rJ
this gives, approximately, for the sun, a value greater than l; for a flame, a value less than 1 but greater than 0.1; and for the casing, a value of less than 0.1.
Thus, by determining whether the relative values of the radiant intensity at the different wavelengths are :
greater or less than 1 and greater or less than 0.1, it is possible to determine whether the radiation is from a flame, the sun or the engine casing. -It will be appreciated that the invention is not confined to engine applications ~ut could be useful in other applications, especially where the flame probe can receive sunlight, such as in flame stacks.
-'~ ~ . . :
-:
::
'~
~ : ~
' ~'~', '''`' ' " ' ' . `
'. ~ ' ' '' ' . ' ' ' ' " ''``. ` ' `
Claims (11)
1. A method of flame detection comprising the steps of: comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the presence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and less than a second, higher value.
2. A method according to Claim 1, wherein said one wavelength is between about 470nm and 530nm and said longer wavelength is about 670nm.
3. A method according to Claim 1, wherein said first value is about 0.1 and said second value is about 1Ø
4. A method of flame detection comprising the steps of: comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.
5. A method according to Claim 4, wherein said one wavelength is between about 470nm and 530nm and said longer wavelength is about 670nm.
6. A method according to Claim 4, wherein said first value is about 0.1 and said second value is about 1Ø
7. Apparatus for detecting the presence of a flame comprising means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the presence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is greater than a first value and less than a second, higher value.
8. Apparatus according to Claim 7, including a display, wherein said indication is provided on the display.
9. Apparatus for detecting the absence of a flame comprising means for comparing the level of radiation at one wavelength with the level of radiation at a longer wavelength, and means for providing an indication of the absence of a flame when the ratio of the level of radiation at the one wavelength to that at the longer wavelength is less than a first value or greater than a second, higher value.
10. Apparatus according to Claim 9, including an igniter control unit, wherein the means for providing an indication of the absence of a flame provides an output signal to the igniter control unit.
11. Apparatus for detecting a flame comprising: an optical probe mounted to view a combustion zone; a dichroic beam splitter; a fibre-optic cable, the cable supplying radiation from the probe to the beam splitter; first and second photodiodes; means supplying radiation between about 470nm and 530nm from the beam splitter to the first photodiode so that the first photodiode provides a first electrical output in accordance therewith; means supplying radiation at about 670nm to the second photodiode so that the second photodiode provides a second electrical output in accordance therewith; a comparator for comparing the first and second electrical outputs, said comparator providing an output indicative of the presence of a flame when the ratio of the level of radiation supplied to the first photodiode to that supplied to the second photodiode is between about 0.1 and 1.0, and said comparator providing an output indicative of the absence of a flame when the ratio of the level of radiation supplied to the first photodiode to that supplied to the second photodiode is outside the range 0.1 to 1Ø
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8925460 | 1989-11-10 | ||
| GB898925460A GB8925460D0 (en) | 1989-11-10 | 1989-11-10 | Flame detection |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2029317A1 true CA2029317A1 (en) | 1991-05-11 |
Family
ID=10666096
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002029317A Abandoned CA2029317A1 (en) | 1989-11-10 | 1990-11-05 | Flame detection |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPH03170821A (en) |
| CA (1) | CA2029317A1 (en) |
| DE (1) | DE4035324A1 (en) |
| FR (1) | FR2654509A1 (en) |
| GB (2) | GB8925460D0 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6071114A (en) * | 1996-06-19 | 2000-06-06 | Meggitt Avionics, Inc. | Method and apparatus for characterizing a combustion flame |
| DE19710206A1 (en) * | 1997-03-12 | 1998-09-17 | Siemens Ag | Method and device for combustion analysis and flame monitoring in a combustion chamber |
| IT1314125B1 (en) * | 1999-12-13 | 2002-12-04 | Imit Spa | COMBUSTION CONTROL DEVICE. |
| DE10101457A1 (en) * | 2001-01-10 | 2002-07-18 | Infineon Technologies Ag | Detection of electromagnetic radiation using two or more optoelectronic semiconductor sensors combined such that the desired output response is obtained |
| DE10118628C1 (en) * | 2001-04-12 | 2002-12-05 | Aeg Infrarot Module Gmbh | Detecting spectrally selective infrared radiator involves acquiring broadband image and image in sub-band of broadband image in immediate succession using infrared detector |
| GB2421788A (en) * | 2004-12-21 | 2006-07-05 | Rolls Royce Plc | Fire warning system |
| DE102006036563A1 (en) * | 2006-08-04 | 2008-02-07 | Siemens Building Technologies Hvac Products Gmbh | Monitoring combustion processes in one location by fast oxygen sensor |
| RU2495270C1 (en) * | 2012-05-23 | 2013-10-10 | Федеральное государственное унитарное предприятие "Центральный институт авиационного моторостроения имени П.И. Баранова" | Method of definition of supersonic ramjet fuel mix combustion efficiency |
| EP3825611A1 (en) * | 2019-11-20 | 2021-05-26 | Siemens Aktiengesellschaft | Flame detection system |
| CN110986037A (en) * | 2019-12-20 | 2020-04-10 | 张学昌 | Method for improving boiler combustion thermal efficiency by adopting light energy conversion |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4051375A (en) * | 1976-01-02 | 1977-09-27 | Combustion Engineering, Inc. | Discriminating flame detector |
| US4156816A (en) * | 1976-09-01 | 1979-05-29 | Telefonaktiebolaget L M Ericsson | Optical fire-detector |
| US4101767A (en) * | 1977-05-20 | 1978-07-18 | Sensors, Inc. | Discriminating fire sensor |
| GB2030288B (en) * | 1978-09-06 | 1982-04-28 | Nohmi Bosai Kogyo Co Ltd | Photo-electric fire detectors |
| US4220857A (en) * | 1978-11-01 | 1980-09-02 | Systron-Donner Corporation | Optical flame and explosion detection system and method |
| US4701624A (en) * | 1985-10-31 | 1987-10-20 | Santa Barbara Research Center | Fire sensor system utilizing optical fibers for remote sensing |
| GB8607373D0 (en) * | 1986-03-25 | 1986-04-30 | Airoil Flaregas Ltd | Flame condition monitoring |
-
1989
- 1989-11-10 GB GB898925460A patent/GB8925460D0/en active Pending
-
1990
- 1990-11-02 GB GB9023820A patent/GB2239090A/en not_active Withdrawn
- 1990-11-02 JP JP2295545A patent/JPH03170821A/en active Pending
- 1990-11-05 CA CA002029317A patent/CA2029317A1/en not_active Abandoned
- 1990-11-07 DE DE4035324A patent/DE4035324A1/en not_active Withdrawn
- 1990-11-09 FR FR9014123A patent/FR2654509A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB2239090A (en) | 1991-06-19 |
| FR2654509A1 (en) | 1991-05-17 |
| JPH03170821A (en) | 1991-07-24 |
| GB9023820D0 (en) | 1990-12-12 |
| GB8925460D0 (en) | 1989-12-28 |
| DE4035324A1 (en) | 1991-05-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |