DE3308555C1

DE3308555C1 - Apparatus for automatically measuring the leakage rate of a vessel

Info

Publication number: DE3308555C1
Application number: DE19833308555
Authority: DE
Inventors: Heinz-Dieter 6980 Wertheim/Main Bürger
Original assignee: CIT Alcatel GmbH
Current assignee: CIT Alcatel GmbH
Priority date: 1983-03-10
Filing date: 1983-03-10
Publication date: 1984-07-19

Abstract

The invention relates to an apparatus for measuring the leakage rate of a vessel which has tracer gas flowing round it on the outside and is connected to a mass spectrometer analysis cell which is sensitive to tracer gas and to a high vacuum pump via a valve. Before the valve is opened, the vessel is pre-evacuated to a pressure acceptable for the analysis cell. According to the invention, a pressure-controlled control device (9) is provided which opens the valve (4) if the pressure in the vessel drops below a limit value and closes it again and reduces the limit value by a fixed amount in the direction of higher vacuum if, after the valve has been opened, the rate of the pressure rise exceeds a fixed threshold value or a predetermined limit pressure in the analysis cell (1) is exceeded in the direction of lower vacuum. <IMAGE>

Description

Die Betriebsweise der Vorrichtung ist die folgende: Zu Beginn eines Meßzyklus ist die Vorvakuumpumpe 7 über das Dreiwegeventil 6 unmittelbar an den Prüfbehälter angeschlossen, um ihn auf einen vorgegebenen Grenzwert, beispielsweise 6 10-2 Millibar zu evakuieren. Ist dieser Wert erreicht, dann wird das Dreiwegeventil 6 umgeschaltet und vom Steuerglied 9 das Ventil 4 geöffnet. Der angegebene Druck ist zwar auf die Dauer für die Analysezelle nicht akzeptabel, kann aber kurzfristig toleriert werden, da die Gefährdung des Heizfadens von einem langsam ablaufenden Vorgang, der Oxydation, abhängt. Bei nicht zu großem Behälter und geringer Leckrate sinkt der Druck im Behälter durch die Wirkung der Hochvakuumpumpe 5 und der Vorpumpe 7 schnell auf Werte unterhalb 10-4 Millibar ab. Die Messung kann dann erfolgreich beendet werden. Liegt jedoch ein größerer Behälter vor, dann kann der gefährliche Druck in der Analysezelle länger als zulässig an- The operation of the device is as follows: At the beginning of a The measuring cycle is the backing pump 7 via the three-way valve 6 directly to the Test container connected to it to a predetermined limit value, for example 6 evacuate 10-2 millibars. When this value is reached, the three-way valve 6 switched over and the valve 4 opened by the control member 9. The specified pressure is not acceptable in the long run for the analysis cell, but it can be short-term be tolerated, as the hazard to the filament from a slowly running Process, the oxidation, depends. If the container is not too large and the leak rate is low the pressure in the container drops due to the action of the high vacuum pump 5 and the backing pump 7 quickly drops to values below 10-4 millibars. The measurement can then be successful be terminated. However, if there is a larger container, then the dangerous one Pressure in the analysis cell longer than permissible

dauern, was verhindert werden muß. Zu diesem Zweck ist das Steuerglied 9, das beispielsweise einen Mikroprozessor enthält, so ausgestaltet, daß es das Ventil 4 wieder sperrt, wenn nach einer vorgegebenen Zeit der im Meßgerät 8 ermittelte Druckwert nicht unter einen Wert von z. B. 5 10-3 Millibar abgesunken ist. Gleichzeitig wird der Schwellwert für das Wiedereinschalten um einen bestimmten Betrag zu niedrigeren Drücken hin verstellt. Wird der nun neu eingestellte Druck im Behälter erreicht, dann wird das Ventil 4 erneut geöffnet, und es wird erneut geprüft, ob nach einer gewissen Zeit der Druck im Behälter auf einen hinreichend niedrigen Wert absinkt. Ist dies nicht der Fall, entweder aufgrund des großen Prüflingsvolumens oder aufgrund von dessen Leckrate, dann wird derselbe Vorgang erneut wiederholt, und es wird die Schwelle, bei der das Ventil 4 erneut einschalten soll, nochmals heruntergesetzt. Der Vorgang kann öfter wiederholt werden.take what must be prevented. The control link is for this purpose 9, which contains, for example, a microprocessor, designed so that it Valve 4 blocks again when the one determined in measuring device 8 after a predetermined time Pressure value not below a value of z. B. 5 10-3 millibars has dropped. Simultaneously the threshold value for switching on again is reduced by a certain amount Pressing adjusted. If the newly set pressure is reached in the container, then the valve 4 is opened again, and it is checked again whether after a a certain time the pressure in the container drops to a sufficiently low value. If this is not the case, either due to the large sample volume or due to of its leak rate, then the same process is repeated again and it becomes the The threshold at which the valve 4 is to switch on again is reduced again. The process can be repeated several times.

Das Schließen des Ventils 4 kann auch abhängig vom Druck in der Analysezelle 1 gesteuert werden, und zwar dann, wenn der Druck in der Analysezelle z. B. über 10-4 mbar ansteigt. Auch dann wird der Grenzwert des Behälterdrucks bei dem das Ventil wieder geöffnet wird, um einen festen Betrag in Richtung auf höheres Vakuum verstellt. Die Steuerung kann alternativ oder ergänzend zu der Steuerung abhängig vom Behälterdruck vorgesehen werden, wobei im letzteren Fall nur verhindert wird, daß die Ausschaltungsautomatik des Heizstroms anspricht und damit die Messung gänzlich unmöglich wird. The closing of the valve 4 can also depend on the pressure in the analysis cell 1 can be controlled, namely when the pressure in the analysis cell z. B. over 10-4 mbar increases. Even then, the limit value of the tank pressure at which the Valve opens again by a fixed amount towards higher vacuum adjusted. The control can be an alternative or a supplement to the control can be provided by the tank pressure, in the latter case only preventing that the automatic switch-off of the heating current responds and thus the measurement completely becomes impossible.

Man erkennt also, daß eine Messung nur bei einem den Meßbereich der Analysezelle übersteigenden Leckratenwert nicht zum Erfolg führt. Die Größe des Prüfbehälters sowie dessen Gasrate spielen nur eine Rolle für die Anzahl der Schließzyklen des Ventils 4, ehe eine gültige Messung zustandekommt. So it can be seen that a measurement is only possible when the measuring range of the Leak rate value exceeding the analysis cell does not lead to success. The size of the The test container and its gas rate only play a role in the number of closing cycles of valve 4 before a valid measurement is made.

Ein wesentlicher Vor.teil der erfindungsgemäßen Vorrichtung liegt darin, daß ein billiges Ventil mit einer einfachen Auf-Zu-Ansteuerung verwendet werden kann. Auch kann aufgrund der Schnelligkeit der Messung dieser Vorrichtung mit mehreren Prüfbehälteranschlüssen versehen sein, die zyklisch nacheinander auf die Analysezelle durchgeschaltet werden. Selbst wenn Behälter sehr unterschiedlicher Volumen an den einzelnen Anschlüssen liegen, stellt sich die Vorrichtung selbsttätig darauf ein und führt die Messung in der kürzestmöglichen Zeit durch, ohne daß die Sicherheitsautomatik für die Ausschaltung des Heizstroms in der Analysezelle anspricht. A significant Vor.teil the device according to the invention is in using an inexpensive valve with a simple on-off control can be. Also, due to the rapidity of the measurement, this device be provided with several test tank connections, which are cyclically one after the other the analysis cell can be switched through. Even if the containers are very different Volume are at the individual connections, the device is automatically and carries out the measurement in the shortest possible time without the Automatic safety system for switching off the heating current in the analysis cell responds.

Die verschiedenen Grenzwerte, die nacheinander im Steuerglied 9 wirksam werden, lassen sich bei der Verwendung eines Mikroprozessors in dessen Speicher einschreiben. Die Umsteuerung des Dreiwegeventils 6 erfolgt vorzugsweise auch durch das Steuerglied 9, so daß nach einem von außen gegebenen Startbefehl alle Schalt- und Meßvorgänge automatisch ablaufen. The various limit values that take effect one after the other in the control element 9 can be stored in its memory when using a microprocessor enroll. The reversal of the three-way valve 6 is preferably also carried out by the control member 9, so that after an externally given start command, all switching and measurement processes run automatically.

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Claims

Claim: Device for the automatic measurement of the leak rate a container around which a tracer gas flows and a valve to a tracer gas sensitive mass spectrometer analysis cell and a high vacuum pump is connected, the valve opening when the container is driven by a forevacuum pump is evacuated to an acceptable limit pressure for the analysis cell, characterized in that that the valve (4) is assigned a pressure-controlled control member (9); the the Valve closes again and the limit pressure by a fixed amount in the direction adjusted to a higher vacuum if the speed after opening the valve the pressure increase in the direction of a higher vacuum falls below a fixed threshold value or a predetermined limit pressure in the analysis cell (1) in the direction of the weaker Vacuum is exceeded.

The invention relates to a device for automatic Measurement of the leak rate of a container according to the preamble of the claim.

Leak rate measurements in which a tracer gas washes around the outside Container connected to a mass spectrometer arialysis cell are known for example from the magazine "Vakuumtechnik", Issue 8, 1980, pages 232 to 245.

In such devices, for example, helium is used in a mass spectrometer analysis cell detected having an ion source with a filament. The filament, mostly made of tungsten, may only be heated if the pressure in the analysis cell is longer Operation is below 10-4 millibars, otherwise the filament will burn out or a disruptive development of secondary ions occurs.

In order to meet this requirement, the actual leak measurement is carried out the test item or container is evacuated with the aid of a foreline pump to a value that there is no risk of opening the valve between the container and the analysis cell as well as the high vacuum pump. In addition, the analysis cells are better known of this type Devices equipped with an automatic safety system that controls the heating current of the Releases mass spectrometer depending on the pressure measurement in the analysis cell. In this context it is from a prospectus from Leybold-Heraeus HV 150 / H-L / 5.1.1./0210/04.72 known to use a safety valve that the analysis cell automatically safeguards against ingress of air.

The measurement of leak rates with such a device is manually controlled Often times, the way of working is complicated and tedious. A specialist must one after the other the backing pump switch on and disconnect and open and close the measuring valve. He must before that Wait until the measuring valve is opened until it is harmless to the filament of the analysis cell Pressure has set in the container and he must close this valve again immediately, if he determines that the leakage rate or the gas rate in the container is so great that the limit pressure cannot be reliably maintained.

The limit pressure at which the measuring valve is opened could in itself be set a little higher (in Meaning a worse vacuum) than the pressure, to which the analysis cell may be exposed in continuous operation, since the filament of the Analysis cell can withstand a higher pressure for a short time, and since this higher pressure degraded after a short time by the high vacuum pump assigned to the analysis cell will. Of course, this dismantling time depends on the size of the test container and on the other hand from its leak rate and its gas rate. At least the latter two but are often completely unknown at the beginning of the measurement.

This poses a problem when the measurement process is automated should, and leads to the fact that the limit pressure is set so low with automatic measurement must be that in no case an impermissible operating condition in the analysis cell entry. The time required for pre-evacuation is then very long.

The object of the invention is therefore to provide an automatic device for measuring the leak rate of a container according to the preamble of the claim indicate that for both large and small containers as well as for containers with a very different gas rate and the length of time for the pre-evacuation shortened as far as possible without endangering the filament of the analysis cell.

This task is carried out in the characterizing part of the claim contained measures resolved.

The invention is described below on the basis of a preferred exemplary embodiment explained in more detail with the aid of the drawing, which schematically shows such a device shows.

The device according to the figure has a mass spectrometer analysis cell 1, which is connected to a cold trap 2. A test container is via a connector 3 connected to the device. Located between the connection 3 and the cold trap 2 an on-off valve 4, which acts as a measuring valve and in the open state Test connection 3 connects to the analysis cell 1. Next to the cold trap 2 is a High vacuum pump 5 and a backing pump 7 connected to this via a three-way valve 6. The three-way valve 6 optionally connects the backing pump with the high vacuum pump 5 or with connection 3 for the test container. Finally there is a pressure gauge 10 is provided for measuring the pressure in the analysis cell and a control element 9, that of the pressure gauges 8 and 10, the information relating to the pressure in the test container or is supplied to the analysis cell and to be described further below Way the on-off valve 4 opens and closes.