Instrumentation • Electronics
1) External sealing which is achieved through a protective device such as a flexible boot. 2) Internal sealing which is using some combination of O-rings or potting material. Some applications only require protection against dust
or splashing liquid. They can use an unsealed connector with a flexible protective boot. When not in use, an unmated connector can be sealed with a protective cap. Using protective caps and boots (Fig. 2) is often a cost-effective solution to prevent mud, dirt and other foreign matter from deterioration, shorting or otherwise damaging contacts and connector locking mechanisms. In addition, mechanical damage caused by impact on hard surfaces can be minimized by using covers and boots. Applications that require exposure to
Fig. 2. Caps and flexible boots, represent a cost- effective solution to protect interconnections from environmental conditions.
environmental factors like pressure, vacuum, liquids or steam demand a greater degree of sealing than provided by caps and boots. The connector needs to be designed intrinsically sealed (Fig. 3). Elastomer O-rings are one of the most common mechanical gaskets used in
connector technology (a, b and d in Fig. 3). They are designed to be seated in a groove and compressed between two parts – for example between two mating connectors, between a connector and its mounting surface (typically a chassis-panel), or between a cable and its attached connector. O-rings create a seal at the interface. The sealing technique generally applied to the contacts of
a panel mounted connector utilizes various potting materials (c in Fig. 3) such as epoxy resin, rubber compounds, or for the highest levels of impermeability, glass. Sealing this area of the connector guarantees that no fluid or other contaminant will enter an enclosure through the connector even when the connector is unmated. These sealing methods can achieve reliable and
economical sealing performance for different types of pressure such as under water at depths in excess of 100m or ultra vacuum with leakage rates below 10-8
mbar·l/s. There are
greater levels of performance available by implementing specialised techniques and materials. Fischer Connectors design centre can provide assistance to customers with such special requirements. Customised product developments can be proposed, combining hermeticity with high strength mechanical design. This initial assessment will allow selecting the most
adequate connector using the adapted sealing technology. However, the design process does not come to an end here. The connector alone does not guarantee that the sealing specifications will be met. It is time to evaluate the interaction between the connector and the product where it will be integrated (panel and/or cable).
Installation a critical step
In addition to the design, the installation of the panel mounted connectors also plays an important role in sealing. Efficient panel sealing can only be achieved if the contact
surface is correctly prepared. No excessive torque should be involved to mount the connector, which generally implies the
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Fig. 3. Section of a panel mounted receptacle showing internal sealing barriers a: Panel seal, b + c: Sealing of block, d: Interface seal.
surface flatness to be <0.05 mm. Following the O-ring shape of the seal, circular machining grooves will contribute to improve the contact between the two surfaces. And finally, the edges of the panel cut should be clean and free from burrs.
Cable assemblies for optimal sealing
Cable seal is one of the assembly solutions designed for optimal sealing to prevent ingress of liquids into the connector along the cable. Cable sheath material and quality strongly affects long
term behaviour and reliability of the plug seal. The grommet type seal acts through compression by tightening the connector back nut. Soft cable materials may relax over time resulting in a
potential loss of sealing efficiency and/or loosening of back nut. Trials are always recommended to determine the right grommet size. Careful selection of cable diameter and shape is also
essential. Some cable qualities show poor cross-sectional circularity. This can also have negative impact on short and long term sealing reliability. Sometimes selection of a smaller cable seal size can help to overcome this problem. Through an adequate match of cable and seal, IP rating
up to IP68 or even IP69K for a limited period of time, can be achieved. Fischer Connectors recommends potting and
overmoulding the plug back-end for the highest reliability of long term sealing in demanding applications. This offers a strong hermetic link between cable and connector even in applications subject to intense mechanical stress. Fischer Connectors is continuously developing customer specific solutions for potting and overmoulding. The new Fischer UltiMate™ for instance (Fig. 5), with its
highly performing epoxy potting and overmoulding designed for harsh environment, offers an excellent sealing IP68/69K even unmated. After defining the complete interconnect solution
(connector, panel interface and cable assembly) according to the sealing level required by the application, it is critical to verify that the selected solution fulfills these requirements.
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