Industrial vacuum leak detection with intelligent gas leak detectors: Not just a mass spectrometer

Abstract

In recent years, the requirements for reliability and lifetime of industrial components have increased significantly. This is due both to customer requirements and the Total Quality philosophy that has been much more widely introduced. This development has had an impact especially on industrial leak detection, since this is one of the non-destructive testing techniques that has been at a rather low level both regarding the involved technologies and the training of personnel. Modern leak detectors that use test gases, especially helium, for testing components and systems have addressed these needs. In a most important first step, as early as 20 years ago, helium leak detectors did away with liquid nitrogen traps by introducing counter flow technology. This, together with the replacement of manual valves by electromagnetic ones controlled by a microprocessor, enabled operation by relatively unskilled persons in industrial processes. In the years that followed, efforts concentrated on lowering the detection limit and the helium signal response time of the new method. The introduction of dry pumping systems (required by the semiconductor industry) was an additional challenge to be mastered parallel to those efforts. With the latest instruments, and this is the major concern of this article, operation under industrial conditions was optimized, now also focusing on background signal handling, which is mandatory for a quick pump-down of large vessels (up to 100 liters of volume) and unambiguous detection of leaks under contamination conditions. Reaching the leak rate range below 1 × 10-9mbarl/s within a few minutes when pumping a 100 liter vessel is one of the specifications to be achieved. Several 1000?ppm of ambient helium background or contamination of elastomer gaskets may not produce long waiting times with no value added. It is not surprising that alongside new pumping technologies software is an increasingly important part of modern leak detectors. There are ways of dealing with signal instabilities to increase the detection limit for leak rates, it is possible to reduce the effect of water vapor desorption on the pump-down time for large volume vessels without LN2, there are more and more sophisticated ways of “ZERO” functions and non-linearity compensations for high total pressure operation. These developments are explained and demonstrated with some examples of modern leak detectors recently introduced into the market.