Fasteners and Sealing
Measuring leaks
The standard IEC 60068-2-17Qk method 3 for leak measurement applies to a ‘short-term leak’. Connector hermeticity is usually tested by spraying helium onto the connector and measuring the quantity of helium traversing it. This test detects ‘leaking’ connectors without measuring the real long-term leak value. If the threshold is established at 1E-8mbar.l/s (as at Fischer Connectors), the test can effectively identify connectors unsuitable for vacuum applications. Lower thresholds (1E-9mbar.l/s or 1E-10mbar.l/s) are irrelevant because the diffusion leak through O-rings inevitably reaches higher values after several minutes. Although the diffusion effect depends on numerous factors, a value of 1.5E-7mbar.l/s (air) for standard-size connectors can be given as a ‘medium- and long-term leak value’ (equivalent to a leak of 4E-7mbar.l/s for helium).
Fig. 4. Fischer Connectors offers a wide variety of hermetically sealed connectors which consistently prove to be totally reliable in even the most demanding environments.
Fig. 3. After a minimum test period of 10 seconds, leaking connectors can be identified using the helium spray standard IEC 60068-2-17Qk method 3. However, the real measure for ‘long-term leaks’ cannot be quantified.
Connector sealing techniques
Fischer Connectors’ hermetically sealed products have several independent sealing barriers – including panel, block and interface seals – designed to control the connector’s performance precisely according to requirements. Panel seals, joining the connector housing to the panel or equipment housing, have large cross-sections contributing to hermeticity.
Genuine PEM® ®
All Fischer Connectors’ standard hermetically sealed connectors feature a Viton panel seal. Block seals ensure long- term hermeticity. Combining sealing gasket and advanced polymer compound minimises permeation and optimizes reliability over a wide temperature range. Interface seals protect the interface between two connectors, preventing water or harmful particles from entering the connection where male and female contacts mate. Sealing is a highly complex science and designing a totally
reliable seal necessitates expertly combining mechanical design, materials science, surface science and fluid behaviour. Selecting the right connector and seals depends on thoroughly analysing the operating environment and determining specific application requirements. ●
Enter 40 or ✔ at
www.engineerlive.com/ede
Christophe Boillat is Product Quality Manager at Fischer Connectors SA, Saint-Prex, Switzerland.
www.fischerconnectors.com
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