EP0267568B1 - Protective resistor circuitry for limiting current at X-ray generators - Google Patents
Protective resistor circuitry for limiting current at X-ray generators Download PDFInfo
- Publication number
- EP0267568B1 EP0267568B1 EP87116532A EP87116532A EP0267568B1 EP 0267568 B1 EP0267568 B1 EP 0267568B1 EP 87116532 A EP87116532 A EP 87116532A EP 87116532 A EP87116532 A EP 87116532A EP 0267568 B1 EP0267568 B1 EP 0267568B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- protective resistor
- circuit arrangement
- ray
- voltage
- cable
- 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.)
- Expired - Lifetime
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05G—X-RAY TECHNIQUE
- H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
- H05G1/08—Electrical details
- H05G1/26—Measuring, controlling or protecting
- H05G1/54—Protecting or lifetime prediction
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05G—X-RAY TECHNIQUE
- H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
- H05G1/02—Constructional details
- H05G1/04—Mounting the X-ray tube within a closed housing
- H05G1/06—X-ray tube and at least part of the power supply apparatus being mounted within the same housing
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05G—X-RAY TECHNIQUE
- H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
- H05G1/08—Electrical details
Definitions
- the invention relates to a circuit arrangement for limiting the current of an X-ray emitter with a protective resistor connected to or in the X-ray emitter in the power supply line.
- the X-ray tube is the X-ray tube arranged in a housing and provided with the connections necessary for operation for the electrical and the coolant supply.
- Protective resistors of this type which are usually located together with the high-voltage generator and other switching and control devices in an apparatus called an X-ray generator, are required in order to limit the short-circuit current occurring in the event of a flashover in the tube.
- the energy stored in the charging capacitor of the high-voltage generator would appear fully on the tube without a protective resistor, and this could be destroyed at the first flashover or be spectrally contaminated by eruption-like melting at the anode.
- German patent specification 610 555 it has therefore already been proposed to install a protective resistor in the introduction of the high-voltage cable into the X-ray emitter. Because of the necessary enlargement of the cable entry and the need to dissipate the power dissipation occurring in the protective resistor, it is stated in the aforementioned German patent, however, to design the cable core of the cable leading from the high-voltage generator to the X-ray source as a high-resistance resistor.
- the present invention has for its object to arrange the protective resistor for X-ray tubes so that the tube current is safely limited in the event of a rollover, both for X-ray tubes with high-voltage anode and for those with high-voltage cathode and grounded anode.
- the protective resistor can be a purely ohmic resistor or a low-capacitance, complex resistor in the form of an RL element. In the latter case, the inductive and ohmic values are expediently chosen so that the aperiodic limit case is observed.
- the inductor is constructed from a plurality of inductors connected in series, preferably in the form of disk windings. The partial inductances can also be tuned to different frequency ranges with ferrite cores, so that the total inductance is effective over a wide frequency range.
- the protective resistor within the emitter can be connected in series with the anode of the X-ray tube which is at high voltage and can be cooled with it. This allows a particularly high-resistance and thus space-saving design of the protective resistor.
- FIGS. 1 and 2 exemplary embodiments of the circuit arrangement according to the invention are shown schematically in FIGS. 1 and 2.
- FIG. 1 shows an X-ray emitter RS, in the housing G of which the actual X-ray tube RR of the end window type is arranged.
- the high voltage of the order of magnitude between 20 and 100 kV required for the operation of the X-ray emitter RS is generated in the high-voltage generator HE and supplied to the X-ray emitter RS via a high-voltage cable HK up to 10 m long.
- a radiator-side cable end connector or plug HV which is inserted into the high-voltage socket HB of the X-ray emitter RS, is used to connect the high-voltage cable HK.
- a protective resistor S is connected inside the X-ray emitter RS in series with the high-voltage-fed anode A and in its cooling water circuit. This makes it possible to design the protective resistor S with high resistance and thus to save space.
- Another possible circuit is to divide the protective resistor into two partial resistors, with a protective resistor S '- as was previously the case - arranged in the high-voltage generator HE and the other part S - as shown - in the X-ray emitter.
- the protective resistor located in the X-ray emitter RS can then be designed such that it mainly limits the discharge current surge of the cable capacitance C.
- FIG. 2 shows an embodiment with a so-called side window tube RR in the X-ray emitter RS with a grounded and cooled anode A and a heated and high-voltage cathode K.
- the high voltage generated in the high voltage generator HE is here also supplied via the high voltage cable HK with distributed cable capacity C to the high voltage socket HB of the X-ray emitter RS.
- the heating current of the directly heated cathode K is provided via two high-voltage conductors of the high-voltage cable HK.
- the heating circuit is very low-resistance, approx. 1 to 3 ohms, so that a high-resistance protective resistor cannot be arranged directly in the X-ray emitter RS.
- the protective resistor S is installed in the radiator-side end connection HV of the high-voltage cable HK, together with an isolating transformer TT for electrical isolation.
- the isolating transformer TT is designed as a heating transformer HT. If you choose the operating frequency of the heating transformer HT in the order of 100 to 300 kHz, it can be built so small that it is to be accommodated in the cable end connection HV together with the protective resistor S. In this embodiment too, the protective resistor S can be divided into two partial resistors S and S ', as already described for FIG.
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- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Toxicology (AREA)
- X-Ray Techniques (AREA)
Description
Die Erfindung bezieht sich auf eine Schaltungsanordnung zur Strombegrenzung eines Röntgenstrahlers mit einem am oder im Röntgenstrahler in die Stromversorgungsleitung geschalteten Schutzwiderstand. Als Röntgenstrahler wird die in einem Gehäuse angeordnete und mit den zum Betrieb notwendigen Anschlüssen für die elektrische und die Kühlmittelversorgung versehene Röntgenröhre bezeichnet.The invention relates to a circuit arrangement for limiting the current of an X-ray emitter with a protective resistor connected to or in the X-ray emitter in the power supply line. The X-ray tube is the X-ray tube arranged in a housing and provided with the connections necessary for operation for the electrical and the coolant supply.
Derartige Schutzwiderstände, die sich üblicherweise zusammen mit dem Hochspannungserzeuger und anderen Schalt- und Steuereinrichtungen in einem Röntgengenerator genannten Gerät befinden, sind erforderlich, um den bei einem Überschlag in der Röhre auftretenden Kurzschlußstrom zu begrenzen. Die im Ladekondensator des Hochspannungserzeugers gespeicherte Energie würde ohne Schutzwiderstand voll an der Röhre auftreten, und diese könnte bereits beim ersten Überschlag zerstört oder durch eine eruptionsartige Ausschmelzung an der Anode spektral verunreinigt werden.Protective resistors of this type, which are usually located together with the high-voltage generator and other switching and control devices in an apparatus called an X-ray generator, are required in order to limit the short-circuit current occurring in the event of a flashover in the tube. The energy stored in the charging capacitor of the high-voltage generator would appear fully on the tube without a protective resistor, and this could be destroyed at the first flashover or be spectrally contaminated by eruption-like melting at the anode.
Es hat sich herausgestellt, daß bei höheren Spannungen, etwa ab 50 kV, die in der Kabelkapazität des Hochspannungskabels zwischen Röntgenstrahler und Hochspannungserzeuger gespeicherte Energie nicht mehr vernachlässigt werden kann. Besonders kritisch wird der Betrieb bei Spannungen um 100 kV. Hier kann bereits bei unvorsichtiger Betriebsweise durch die in einem z. B. 5 m langen Hochspannungskabel gespeicherte elektrische Energie bei einem einzigen Durchschlag zur Zerstörung der Röntgenröhre führen.It has been found that at higher voltages, for example from 50 kV, the energy stored in the cable capacity of the high-voltage cable between the X-ray emitter and the high-voltage generator can no longer be neglected. Operation becomes particularly critical at voltages around 100 kV. Here can already with careless operation by the z. B. 5 m long high-voltage cable stored electrical energy with a single breakdown to destroy the X-ray tube.
In der deutschen Patentschrift 610 555 wurde daher schon vorgeschlagen, einen Schutzwiderstand in die Einführung des Hochspannungskabels in den Röntgenstrahler einzubauen. Wegen der dadurch notwendigen Vergrößerung der Kabeleinführung und der Notwendigkeit zum Abführen der im Schutzwiderstand auftretenden Verlustleistung ist in der genannten deutschen Patentschrift demgegenüber angegeben, die Kabelseele des vom Hochspannungserzeuger zum Röntgenstrahler führenden Kabels als hochohmigen Widerstand auszubilden.In German patent specification 610 555 it has therefore already been proposed to install a protective resistor in the introduction of the high-voltage cable into the X-ray emitter. Because of the necessary enlargement of the cable entry and the need to dissipate the power dissipation occurring in the protective resistor, it is stated in the aforementioned German patent, however, to design the cable core of the cable leading from the high-voltage generator to the X-ray source as a high-resistance resistor.
Der vorliegenden Erfindung liegt die Aufgabe zugrunde, den Schutzwiderstand für Röntgenröhren so anzuordnen, daß der Röhrenstrom im Überschlagfalle sicher begrenzt wird, und zwar sowohl für Röntgenröhren mit auf Hochspannung liegender Anode als auch für solche mit auf Hochspannung liegender Kathode und geerdeter Anode.The present invention has for its object to arrange the protective resistor for X-ray tubes so that the tube current is safely limited in the event of a rollover, both for X-ray tubes with high-voltage anode and for those with high-voltage cathode and grounded anode.
Erfindungsgemäß wird diese Aufgabe mit den in den Ansprüchen 1 und 2 angegebenen Maßnahmen gelöst.According to the invention, this object is achieved with the measures specified in claims 1 and 2.
Der Schutzwiderstand kann ein rein ohmscher Widerstand oder ein kapazitätsarmer komplexer Widerstand in Form eines RL-Gliedes sein. Im letzteren Falle werden die induktiven und ohmschen Werte zweckmäßigerweise so gewählt, daß der aperiodische Grenzfall eingehalten wird. In einer bevorzugten Ausführungsform wird dabei die Induktivität aus mehreren in Reihe geschalteten Induktivitäten, vorzugsweise in Form von Scheibenwicklungen, aufgebaut. Die Teilinduktivitäten können ferner mit Ferritkernen unterschiedliche Frequenzbereiche abgestimmt sein, so daß die Gesamtinduktivität über einen weiten Frequenzbereich wirksam ist.The protective resistor can be a purely ohmic resistor or a low-capacitance, complex resistor in the form of an RL element. In the latter case, the inductive and ohmic values are expediently chosen so that the aperiodic limit case is observed. In a preferred embodiment, the inductor is constructed from a plurality of inductors connected in series, preferably in the form of disk windings. The partial inductances can also be tuned to different frequency ranges with ferrite cores, so that the total inductance is effective over a wide frequency range.
Wird der Schutzwiderstand in den strahlerseitigen Kabelendanschluß oder Stecker des Hochspannungskabels eingebaut, werden Änderungen an bereits betriebenen Röntgenstrahlern nicht notwendig.If the protective resistor is installed in the radiator end connection or plug of the high-voltage cable, changes to already operated X-ray radiators are not necessary.
Bei Röntgenstrahlern mit Endfensterröhre kann der Schutzwiderstand innerhalb des Strahlers in Reihe mit der auf Hochspannung liegenden Anode der Röntgenröhre geschaltet und mit dieser gekühlt werden. Dies läßt eine besonders hochohmige und damit platzsparende Ausführung des Schutzwiderstandes zu.In the case of X-ray emitters with end window tubes, the protective resistor within the emitter can be connected in series with the anode of the X-ray tube which is at high voltage and can be cooled with it. This allows a particularly high-resistance and thus space-saving design of the protective resistor.
Bei Röntgenstrahlern mit Seitfensterröhren mit geerdeter Anode ist im strahlerseitigen Kabelanschluß eine galvanische Trennung in Form eines Trenntransformators vorzusehen. Dieser kann auch als Heiztransformator für die Röhrenheizung ausgebildet werden.In the case of X-ray emitters with side window tubes with a grounded anode, electrical isolation in the form of an isolating transformer must be provided in the cable connection on the emitter side. This can also be designed as a heating transformer for tube heating.
Zur Erläuterung der Erfindung sind in den Figuren 1 und 2 Ausführungsbeispiele der erfindungsgemäßen Schaltungsanordnung schematisch dargestellt.To explain the invention, exemplary embodiments of the circuit arrangement according to the invention are shown schematically in FIGS. 1 and 2.
Es zeigen
- Figur 1 eine Schaltungsanordnung mit in den Röntgenstrahler eingebautem Schutzwiderstand,
- Figur 2 eine Schaltungsanordnung mit in den strahlerseitigen Kabelendanschluß eingebautem Schutzwiderstand.
- FIG. 1 shows a circuit arrangement with a protective resistor built into the X-ray emitter,
- 2 shows a circuit arrangement with a protective resistor built into the radiator-side cable end connection.
Figur 1 zeigt einen Röntgenstrahler RS, in dessen Gehäuse G die eigentliche Röntgenröhre RR vom Endfenstertyp angeordnet ist. Die von der mittels des Heiztransformators HT geheizten Kathode K austretenden Elektronen treffen auf die auf Hochspannung liegende Anode A. Die dabei entstehende Röntgenstrahlung R tritt durch das Endfenster F nach außen. Da die Anode A gekühlt werden muß, ist sie in einem Kühlwasserkreislauf W im Röntgenstrahler angeordnet.FIG. 1 shows an X-ray emitter RS, in the housing G of which the actual X-ray tube RR of the end window type is arranged. The electrons emerging from the cathode K, which is heated by means of the heating transformer HT, hit the anode A which is at high voltage. Since the anode A has to be cooled, it is arranged in a cooling water circuit W in the X-ray source.
Die zu dem Betrieb des Röntgenstrahlers RS erforderliche Hochspannung in der Größenordnung zwischen 20 und 100 kV wird in dem Hochspannungserzeuger HE erzeugt und über ein bis zu 10 m langes Hochspannungskabel HK dem Röntgenstrahler RS zugeführt. Zwischen der Hochspannung führenden Leitung im Hochspannungskabel HK und seinem geerdeten Mantel besteht die verteilte Kabelkapazität C. Zum Anschluß des Hochspannungskabels HK dient ein strahlerseitiger Kabelendanschluß oder -stecker HV, der in die Hochspannungsbuchse HB des Röntgenstrahlers RS eingeführt ist.The high voltage of the order of magnitude between 20 and 100 kV required for the operation of the X-ray emitter RS is generated in the high-voltage generator HE and supplied to the X-ray emitter RS via a high-voltage cable HK up to 10 m long. There is a distributed cable capacity C between the high-voltage line in the high-voltage cable HK and its grounded sheath. A radiator-side cable end connector or plug HV, which is inserted into the high-voltage socket HB of the X-ray emitter RS, is used to connect the high-voltage cable HK.
Zur Begrenzung des Kurzschlußstroms bei einem in der Röhre auftretenden Überschlag zwischen Kathode und Anode ist ein Schutzwiderstand S im Innern des Röntgenstrahlers RS in Reihe mit der hochspannungsgespeisten Anode A und in deren Kühlwasserkreislauf geschaltet. Damit ist es möglich, den Schutzwiderstand S hochohmig und damit raumsparend auszuführen.To limit the short-circuit current in the event of a flashover between the cathode and anode in the tube, a protective resistor S is connected inside the X-ray emitter RS in series with the high-voltage-fed anode A and in its cooling water circuit. This makes it possible to design the protective resistor S with high resistance and thus to save space.
Eine andere Schaltungsmöglichkeit besteht darin, den Schutzwiderstand in zwei Teilwiderstände aufzuteilen, wobei ein Schutzwiderstand S' - wie bisher üblich - im Hochspannungserzeuger HE angeordnet ist und der andere Teil S - wie gezeigt - im Röntgenstrahler. Der im Röntgenstrahler RS befindliche Schutzwiderstand kann dann so ausgelegt werden, daß er hauptsächlich den Entladestromstoß der Kabelkapazität C begrenzt.Another possible circuit is to divide the protective resistor into two partial resistors, with a protective resistor S '- as was previously the case - arranged in the high-voltage generator HE and the other part S - as shown - in the X-ray emitter. The protective resistor located in the X-ray emitter RS can then be designed such that it mainly limits the discharge current surge of the cable capacitance C.
Figur 2 zeigt eine Ausführung mit einer sogenannten Seitfensterröhre RR im Röntgenstrahler RS mit einer geerdeten und gekühlten Anode A und einer geheizten und auf Hochspannung liegenden Kathode K.FIG. 2 shows an embodiment with a so-called side window tube RR in the X-ray emitter RS with a grounded and cooled anode A and a heated and high-voltage cathode K.
Die in dem Hochspannungserzeuger HE erzeugte Hochspannung wird auch hier über das Hochspannungskabel HK mit verteilter Kabelkapazität C der Hochspannungsbuchse HB des Röntgenstrahlers RS zugeführt. Die Heizstromversorgung der direkt geheizten Kathode K erfolgt über zwei auf Hochspannung liegende Leiter des Hochspannungskabels HK. Der Heizkreis ist sehr niederohmig, ca. 1 bis 3 Ohm, so daß ein hochohmiger Schutzwiderstand direkt in dem Röntgenstrahler RS nicht angeordnet werden kann. Um eine wirksame Strombegrenzung im Überschlagsfall zu erhalten, ist hier der Schutzwiderstand S in den strahlerseitigen Endanschluß HV des Hochspannungskabels HK eingebaut, zusammen mit einem Trenntransformator TT zur galvanischen Trennung. In einer bevorzugten Ausführungsform ist der Trenntransformator TT als Heiztransformator HT ausgebildet. Wählt man die Betriebsfrequenz des Heiztransformators HT in der Größenordnung zwischen 100 und 300 kHz, so kann dieser so klein gebaut werden, daß er in dem Kabelendanschluß HV zusammen mit dem Schutzwiderstand S unterzubringen ist. Auch bei dieser Ausführung kann der Schutzwiderstand S in zwei Teilwiderstände S und S' aufgeteilt werden, wie bereits zu Figur 1 beschrieben.The high voltage generated in the high voltage generator HE is here also supplied via the high voltage cable HK with distributed cable capacity C to the high voltage socket HB of the X-ray emitter RS. The heating current of the directly heated cathode K is provided via two high-voltage conductors of the high-voltage cable HK. The heating circuit is very low-resistance, approx. 1 to 3 ohms, so that a high-resistance protective resistor cannot be arranged directly in the X-ray emitter RS. In order to obtain an effective current limitation in the event of a flashover, the protective resistor S is installed in the radiator-side end connection HV of the high-voltage cable HK, together with an isolating transformer TT for electrical isolation. In a preferred embodiment, the isolating transformer TT is designed as a heating transformer HT. If you choose the operating frequency of the heating transformer HT in the order of 100 to 300 kHz, it can be built so small that it is to be accommodated in the cable end connection HV together with the protective resistor S. In this embodiment too, the protective resistor S can be divided into two partial resistors S and S ', as already described for FIG.
Claims (6)
- Circuit arrangement for the current limitation of an X-ray source with a protective resistor connected into the current supply line in or at the X-ray source, characterized in that the high-resistance protective resistor (S) is connected into the coolant circuit (W) for the anode (A) lying at high voltage.
- Circuit arrangement for the current limitation of an X-ray source with a protective resistor connected into the current supply line at or in the X-ray source, characterized in that for X-ray sources (RS) with X-ray tubes (RR) of the side-window type with earthed anode (A) the protective resistor (S) together with a separating transformer (TT, HT) is installed into the cable end terminal (HV) of the high-voltage cable (HK), whereby the protective resistor (S) bridges the separating transformer.
- Circuit arrangement according to claim 2, characterized in that the operating frequency of the separating transformer (TT, HT) lies between 100 and 300 kHz.
- Circuit arrangement according to one of claims 1 to 3, characterized in that the protective resistor has an inductive and an ohmic portion, whereby the two portions are designed such that the aperiodic limiting case is maintained.
- Circuit arrangement according to claim 4, characterized in that the inductance consists of several series-connected partial inductances, preferably in the form of disc windings.
- Circuit arrangement according to claim 5, characterized in that the partial inductances have ferrite cores with different frequency ranges.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19863639088 DE3639088A1 (en) | 1986-11-14 | 1986-11-14 | CIRCUIT ARRANGEMENT WITH A PROTECTIVE RESISTOR FOR CURRENT LIMITATION IN X-RAY EMISSIONERS |
| DE3639088 | 1986-11-14 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| EP0267568A2 EP0267568A2 (en) | 1988-05-18 |
| EP0267568A3 EP0267568A3 (en) | 1989-12-06 |
| EP0267568B1 true EP0267568B1 (en) | 1994-02-09 |
Family
ID=6314029
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP87116532A Expired - Lifetime EP0267568B1 (en) | 1986-11-14 | 1987-11-09 | Protective resistor circuitry for limiting current at X-ray generators |
Country Status (2)
| Country | Link |
|---|---|
| EP (1) | EP0267568B1 (en) |
| DE (2) | DE3639088A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE8807359U1 (en) * | 1988-06-06 | 1989-10-12 | Siemens Ag, 1000 Berlin Und 8000 Muenchen, De | |
| DE3929402A1 (en) * | 1989-09-05 | 1991-03-07 | Philips Patentverwaltung | X-RAY DEVICE |
| US5008912A (en) * | 1989-10-05 | 1991-04-16 | General Electric Company | X-ray tube high voltage cable transient suppression |
| US5107187A (en) * | 1990-12-06 | 1992-04-21 | Maxwell Laboratories, Inc. | High voltage protection resistor |
| US5229743A (en) * | 1990-12-06 | 1993-07-20 | Maxwell Laboratories, Inc. | High voltage protection resistor |
| US5132999A (en) * | 1991-01-30 | 1992-07-21 | General Electric Company | Inductive x-ray tube high voltage transient suppression |
| US5159618A (en) * | 1991-05-22 | 1992-10-27 | General Electric Company | X-ray tube enclosure with resistive coating |
| US5347571A (en) * | 1992-10-06 | 1994-09-13 | Picker International, Inc. | X-ray tube arc suppressor |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE393871C (en) * | 1921-08-09 | 1924-04-16 | C H F Mueller Spezialfabrik Fu | Device for damping overvoltage waves in X-ray systems with resistors connected to the supply line |
| DE610555C (en) * | 1933-01-24 | 1935-03-14 | Siemens Reiniger Werke Akt Ges | Device containing high-voltage cables for the operation of discharge tubes |
| US3588510A (en) * | 1968-04-22 | 1971-06-28 | Picker Corp | X-ray tube protective circuit including thermionic discharge means connected in series with the x-ray tube |
| US3683191A (en) * | 1970-05-18 | 1972-08-08 | Machlett Lab Inc | Modulator system |
| FR2513061A1 (en) * | 1981-06-12 | 1983-03-18 | Thomson Csf | X-RAY TUBE MULTIPLE CATHODE POLARIZATION DEVICE AND RADIOGENIC SOURCE COMPRISING SUCH A DEVICE |
| FR2579401B1 (en) * | 1985-03-22 | 1987-05-15 | Thomson Cgr | HIGH VOLTAGE GENERATOR ASSEMBLY AND RADIOGENIC DEVICE |
-
1986
- 1986-11-14 DE DE19863639088 patent/DE3639088A1/en not_active Withdrawn
-
1987
- 1987-11-09 EP EP87116532A patent/EP0267568B1/en not_active Expired - Lifetime
- 1987-11-09 DE DE87116532T patent/DE3789047D1/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DE3639088A1 (en) | 1988-05-26 |
| DE3789047D1 (en) | 1994-03-24 |
| EP0267568A2 (en) | 1988-05-18 |
| EP0267568A3 (en) | 1989-12-06 |
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