Bl Technology Limited

Peter E Marshall

Francis R Piper

John F Wilson

David J Bray

Iain H Murdoch

Peter E Johnson

A leak detector has a gas probe 1 for sensing signal gas escaping from an enclosure containing that gas at a pressure slightly in excess of ambient surrounded by a curtain of barrier gas. The reading of a gas analyzer such as a mass spectrometer depends on the height of the probe from the surface. A height sensor is attached to the leak detector and a programmable amplifier 6 contains information on the characteristic curve of the gas sensor. An output signal from the programmable amplifier compensates for the height of the probe from the surface being detected. The speed of the leak detector can be corrected for in the same way.

Detecting leaks

A leak detector comprises a detector head which is to be scanned across a surface to detect a signal gas eminating from the surface. The opposite side of the surface from the head is supplied with a signal gas under pressure so that signal gas passes through leaks in the surface. Detection of signal gas by the head should then constitute detection of a leak. A curtain 1 of barrier gas is provided around a sample inlet 2 to protect the inlet from spurious signal gas. Orifices 36 provide narrow high velocity jets 38 which impinge on the surface S within curtain 1 and break up jets such as 34 of signal gas which escape under the curtain 1 without allowing the signal gas to reach the sample inlet.

The leak detector comprises an annular chamber 11 which leads to a circumferential orifice 14 which in turn leads to an annular duct 21 which is symmetrical about the axis of the detector. Barrier gas is fed to the annular chamber 11, for example from an annular chamber 18 and emerges from the opening 20 to form a substantially laminar flow. Leaks are detected by means of a signal gas within an enclosure at a pressure slightly in excess of ambient, and the signal gas is detected from leaks via a probe 2 which is connected for example to a mass spectrometer. The curtain 1 is stable and enables uneven surfaces to be tracked.

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Stratford-on-Avon, United Kingdom

Peter E Marshall