Interconnect for harsh environments
Connectivity is a key determinant of overall system reliability - and in harsh environments even more so. An understanding of connector types that provide the highest reliability in environmental extremes is an important consideration for designers.
There are many different concerns to be taken into account when designing a system, and which of these will affect the required specifications of interconnect products used within that design when heat or cold, motion or fluids can all contribute to impeding the flow of data or power. Key environmental factors can include: ingress prevention against water or other fluids, dust or gas, extremes of temperature, humidity levels, pressure, including water submersion at depth, physical impact, ruggedness and lifetime reliability/secure mating, shielding from electro-magnetic interference (EMI) or electro-magnetic discharge (ESD), or exposure to high levels of ultra-violet and other types of radiation.
Typical markets that require high levels of protection from the environment are energy production, such as in the oil and gas industries as well as the growing number of renewable energy installations, aerospace, defence, including marine applications, railway and transportation, in addition to chemical industries and also medical applications. The good news is that there are a wide range of suppliers such as Amphenol, Delphi, FCI, Glenair, Harwin, Molex, Samtec and TE Connectivity, among others, which offer interconnect products and technologies for harsh environments.
There is no ultimate heavy-duty, hermetically sealed ‘super connector’ that can also handle high levels of vibration or the extremes of temperature, or at least there are none available that come without an extraordinarily high price tag. This means that an engineer will need to carefully examine the stresses to be borne in a particular target application - a connector may be placed on a rooftop or buried in the ground, for example - and choose the right combination of protective features to select the right harsh-environment device.
There are several connectivity aspects to be considered to tackle these environmental challenges, including the overall design and the contacts, housing and seals. Fundamentally, the contacts are the key element in any connector - they carry the power and the signal for the system. To work in many different environments, many types of materials including metals, plastics, rubber and ceramics will be used in device construction to achieve a positive interconnect and also to meet environmental challenges. Internal connector components will likely vary in material for reasons of performance and cost, while external elements, such as shells and inserts, are often metal and can be aluminum, stainless steel, brass, titanium, or even composite materials.
In terms of protection against water penetration and dust contamination, the Ingress Protection (IP) rating system is used to assign a value to components and equipment. The typical IP standard rating for an industrial harsh-environment connector is IP67, where ‘6’ indicates no ingress of dust and ‘7’ indicates no ingress of water in harmful quantities with immersion up to 1m depth in water along with other defined conditions of pressure and time.
One example of an IP67-rated device that is designed for rugged and harsh environment applications is Molex’s MX120G space-saving connector system, which is a sealed and highly compact wire-to-wire and wire-to-board interconnect family that delivers optimal performance in wet, high-vibration and wide-operating-temperature (-40 to +105°C) conditions.
Figure 1 – Molex MX120G space-saving connectors
Typical applications for the connector system include transportation vehicles such as buses or agricultural or recreational vehicles; industrial such as in construction or marine equipment or oil and gas installations; splash-proof medical equipment; and exterior LED lighting applications such as traffic or overhead street lights. A more reliable and less expensive solution than pre-crimped wire-seal alternatives, the MX120G wire-to-wire and wire-to-board receptacles feature a single-piece pre-assembly comprised of a high-temperature connector housing, a male silicone seal and a seal cap for strain relief - pre-assembled and ready for easy crimp insertion. Silicone seals are reliable in most applications that are exposed to water or other common fluids, and are more durable and able to withstand higher temperatures than ordinary Nitrile-rubber seals. The seal-cap provides strain relief for the seal interface, enabling easy insertion of crimped wires directly into the connector.
In addition, the family’s high-vibration resistance - up to 10G acceleration - secures mating in high-vibration environments and applications. The connector’s built-in positive locking feature also ensures robust terminal retention, while preventing any accidental terminal back out. Its twist-lock design ensures proper terminal alignment of the header contacts with those of the female receptacle, thus eliminating the need for any fasteners.
When it comes to housings, although many plastic-bodied connector designs are sufficiently robust for many automotive and similar vehicle applications, they are not always heavy duty enough for more industrial environments such as use in railways or in exposed locations. In these types of applications, metal-bodied connectors such as Amphenol’s ‘heavy|mate’ brand range is one solution. Although designed as a heavy-duty connector, the heavy|mate connector, shown in figure 2, is also a good example of a modular hybrid connector solution. The connector is designed to be mechanically robust, vibration proof, corrosion resistant and impervious to the ingress of dust and moisture. It is targeted at industrial applications, including the more demanding end of the transportation market, but also in heavy machinery and the type of robotics equipment that are commonly found in car assembly plants.
The basic connector format is a wire-to-panel design, but also offers a metal panel connector housing, a metal cable connector shroud and metal locking levers, all of which contribute to a highly robust design that provides secure and vibration-resistant connector mating. Corrosion resistance is achieved with different case coatings to meet various performance specifications and, where other parts can exhibit surface peeling and rivet corrosion after 100-hour salt spray tests, its highly resistant coating can protect against much more extreme conditions.
Figure 2 – Amphenol heavy|mate modular metal connector
Of course not all applications will require the same level of environmental protection, so where it is not necessary it can make some sense to choose a lower specification. The IP67 version of the heavy|mate connector saves cost with a more compact design that uses potted rivets and a collar to avoid sealing movement while still maintaining a compatible panel cut. As well as sealing, the design also addresses EMC requirements with a special housing that incorporates shielding plates and collars.
The modular nature of the heavy|mate connector design provides frames that accommodate either 2, 3, 5 or 7 modules and allows for hybrid connectivity, supporting multiple-pin power or control connections at high voltage (up to 1000V) and high current (up to 240A) as well as signal interconnections including fibre-optic, RJ45 and CAN-Bus type connectors. Available contact technologies include machined contacts or lower-cost stamped contacts based on a vibration-proof double-crimp design using a quality bronze material combined with partial plating for lower cost. High power contacts are provided by using the company’s Radsok-technology, which enables high current in a small diameter by providing a large contact surface.
Also designed for industrial applications, the Amphenol Socapex RJF series allows the use of Ethernet connectivity in harsh environments such as in robotics and industrial process control. Implementing the company’s patented RJstop technology, the RJF connectors allow the use of a standard RJ45 cord set in a metallic plug, which is sealed to IP68 against dust and fluids and offering resistance to shock and vibration.
For outdoor and rooftop applications such as communications towers for example, the Amphe-Lite connector series (figure 3) is aimed at communications equipment manufacturers that require robust performance in terms of signal, power, RF and fibre-optic interconnect. The circular composite connectors are also ideal for manufacturing process control and medical equipment. A key feature of the series is its EMI shielding capability – implementing EMI grounding fingers and conductive finishes – and exceeding the requirements of the MIL-DTL-38999 (series III) standard for defence and aerospace applications. A non-magnetic variant of the series is also available for a wide array of applications.
Figure 3 – Amphe-Lite connectors
Aimed at panel and I/O applications is Samtec’s AccliMate range of connector systems. All tested to IP68 for dust and water, the range includes bayonet and threaded circular types as well as a space-saving rectangular design that provides maximum density for low-profile 1U applications. The bayonet sealed circular types are available in three standard shell sizes and come in metal, over-moulded plastic or field-terminated plastic housings. The threaded sealed circular connectors feature a rugged construction and are suitable for Ethernet, USB and mini-USB interconnectivity. Designers can easily choose from thousands of permutations comprising shell size, material, pin-out and contact size among other characteristics via the company’s online ‘Solutionator’ selection tool.
In summary, whether the application demands protection from fluids, extremes of temperature, high vibration or shielding against EMI, or some combination of the above, selecting the right connector that meets the demands of the specific target environment can mean significantly reduced electrical faults, less down time and lower maintenance costs.
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