November 13, 2012
By Gary E. Brown
SEA CON/Brantner & Associates Inc.
SEA CON has been working on many projects with the principle aim of reducing various key parameters, such as size and weight, of electrical and optical connectors for extreme environments, without major compromises on performance. This technology is not limited to underwater applications but also applies to those in tactical and support environments, including airborne, surface shipping, and field applications subject to extreme operating conditions. SEA CON’s Gary E. Brown discusses the drivers behind shrinking extreme environment connectors and the technology innovations that have resulted. You can read the complete white paper online.
There are many factors driving the reduction of size and weight of electrical and optical connectors for extreme environments. Most of these are driven by particular and unique customer requirements, although many are a result of a considered opinion of potential customer requirements.
Specific examples of these requirements are:
- Smaller host vehicles. As ROV, AUV, or other systems greatly reduce in size or experience a reduction in available space due to increased vehicle complexity, the impact, both in size and weight of the connection elements of that system, become more significant. There is a need to not only reduce individual connection sizes but also minimize the number of connections for reliability reasons.
- Diver Systems. The expectation that we’d see a reduction in diver or manned systems in favor of unmanned systems and operations has so far not occurred to the extent predicted, but there is still a strong emphasis on weight reduction or increased density of electrical or optical functionality — but not necessarily smaller equipment, as too small may prove too difficult for manual operation.
- Swimmer or marine-mammal-deployable systems. Similar to diver systems but with a specific emphasis on not only small size but small mass and weight, as well as simple operation.
- Low-profile surveillance systems. Required to be hidden or undetectable, EMI-compliant, low mass, non-metal, etc., but still operational in extreme environments, including deep water, sub-surface, or buried.
- Underwater lighting and security. With the increasing emphasis on underwater lighting and security systems, smaller and lower cost connection systems assist with the economic viability of large-scale operations and systems.
- Lower cost and smaller Vessel-Of-Opportunity (VOOP). Similarly with an emphasis on cost reduction, which can focus on the use of vehicles or vessels of opportunity rather than specialized and more expensive ocean-going vessels.
- Small-bore modular arrays. An example of a single application, in that a combination of the reasons above requires a slim-line, small-bore modular array system, with net result requiring increased complexity but reduction in size and weight in water or air as part of an automatic deployable system.
The key to achieving a reduction in size and/or weight, without significant technical compromise, is to offer a variety of choice of what we call enabling-technology that can facilitate the future concepts, viabilities, and practicalities of strategic system planning and implementation.
The most basic form of dry-mateable and wet-pluggable connectors is based on very simple rubber-molded technology that has been around for many decades. It has only been recently that even the functionality offered by these, the most basic underwater connector types, has been able to be significantly increased as well as reduced in size.
Reduction in connector size can be achieved by several means. However it is important to understand the parameters that have the most significant impact on size. Below are the many factors that must be taken into consideration when designing a smaller, lighter connector.
Voltage rating is defined by the quality of insulation between each of the current-carrying conductors and the external environment. Insulators have different properties and are defined by their dielectric strength and measured as insulation resistance. Miniaturization requires an effective reduction in conductor spacing and insulation dimensions, with the consequent use of high dielectric properties to insulate materials.
The current rating of a conductor is defined by its cross-sectional area. One of the greatest impacts on miniaturization is the ability to meet a reduction in conductor cross-sectional area. However the primary impact of this is a reduction in the steady state operating current and, hence, a balance is required to ensure the connector is suitably designed, rated, and tested for a useful steady-state current.
The development of smaller contacts that can be efficiently and economically produced is an important consideration in conjunction with the development of the required production tooling and handling procedures as part of the production cycle.
Wasted Space and Material
In traditional connectors, there is a lot of wasted space and material. The miniaturization process requires removing all excess materials. The large areas of material are the result of O-ring grooves, retaining ring grooves, and key/keyway requirements. Several techniques were adopted to meet this requirement, enabling connectors to be produced that were not economically achievable 15 years ago.
Traditionally the industry has based O-ring selection on published charts and handbooks, but the reality of miniaturization spurred the customization of a series of O-rings and tools to provide the required sealing. There were significant challenges in adapting the theoretical modeling of the new seals but these were overcome to meet the practicalities of repeatable, high-quality, and high-quantity production.
New CNC active tools allowed the repeatable production of new concept key/keyways that enabled significant reduction on metal shell size.
The retaining mechanism needed to be smaller than anything commercially available. New tools and materials enabled viable alternatives that offered more space to maximize the insert face diameter, thus allowing higher contact densities.
Minimal Wall Thickness
All wall thicknesses have been reduced to their absolute minimum. Material choices have helped in this area. As an example, titanium was chosen as the material for the shells so that wall sections could be thin and still retain strength for the design pressure ratings with the required 50% Factor of Safety in all calculations and computer models. Other materials can be used, but the choice of material does affect the mated pressure rating.
Aft End Technology
One of the major hurdles to overcome was the wire termination and cable area. One method was to load the inserts into the shells from the rear for easier termination and assembly. Rear-loading was necessary to properly handle the small wires. These wires are as small as #28 AWG and some customer designs have required solid-core wire. Reverse loading eliminates large service loops in the wire and minimizes the size of the termination and overmold.
Proper mating sequence is essential to ensure that the pins and the connectors are not damaged during engagement. It is important to take this into account for the smaller connectors, and this can work against size reduction, so new methodologies were required.
As for the reduction in weight, the availability of new metallic and non-metallic materials has brought about other advances in connector design not related directly to achieving miniaturization. As it turns out, connector changes will tend towards miniaturization rather than the other way around, but some material changes have tended to also produce a reduction in connector weight underwater. Typical changes have been the use of titanium, which is lightweight, strong, and less dense (but expensive). It is the main alternative material in use; however, research and development for alternative materials that are less expensive is ongoing. Additionally, the use of non-metals eliminates any cathodic de-lamination issues. These materials, including PEEK, GRE, Delrin, and Acetal, are very light and buoyant, can be used underwater, and are non-magnetic.