The classic circular connector design is available with a wide range of materials, coupling mechanisms, and protection levels to reliably serve applications that operate in harsh environments. 

Power, signal, and high-speed data are essential to the nervous system of modern electronics, and secure interconnect coupling mechanisms are critical to the reliability and integrity of their transmission. In our increasingly data-driven society, the demand for these essential requirements is infiltrating nearly every market and application environment, including harsh-environments such as those encountered in every transportation segment.

circular connectors for transportation vehicles

Several factors in harsh environments can jeopardize connector couplings and disrupt operation. The integrity of power, signal, and digital data transmissions can be disrupted by vibration, shock, extreme temperatures and pressures, and the ingress of dust, dirt, and liquids ranging from humidity to splashing water and chemicals. Extreme conditions can also affect operators’ ability to complete normally simple actions, like coupling the circular connectors that are a stalwart choice for vehicles.

Circular connectors are extensively employed in a variety of applications in the transportation market and other harsh environments. These connectors are available in a wide range of configurations and coupling mechanisms, many of which help ensure the reliable transmission of power, signal, and high-speed data even under the influence of hazards including vibration, shock, the ingress of dust and water, extreme temperatures, high pressure, and radiation.

How Various Hazards Affect Connector Couplings 

Extreme Temperature and Pressure: Extreme variations in temperature or pressure can cause rapid material expansion and contraction. The coupling mechanisms of connectors deployed in applications exposed to these hazards must be designed to withstand their effects in order to prevent environmental ingress that could lead to short circuits or outright failure. Transportation industry applications such as construction and agricultural equipment, railway equipment, and heavy-duty trucks must operate in a wide range of climate extremes, so the connectors in these machines must be able to endure high heat as well as frigid cold.

Ingress: Ingress can result when connectors are exposed to dust, dirt, sand, splashing water, rain, flooding, submersion, chemical cleaning agents, and oil. Circular connectors sealed against liquid ingress and the infiltration of foreign object debris must remain tightly mated — even under pressure — to ensure reliable operation. Ingress can short-circuit interior contacts, causing random equipment behavior and intermittent or total failure. The materials used to make these connectors, including shells, seals, and insulators, must be impervious to ingress and their construction must be rugged.

Long-term resistance to chemical, water, and humidity exposure is often critical in industrial control applications. For instance, in semiconductor fabrication plants, many chemicals and a lot of water are used to implant, etch, and wash wafers. In these areas, connector couplings have to be more than just airtight to prevent ingress. Connectors employed in underwater applications also require reliable coupling mechanisms to maintain impervious seals. Circular connectors with military-grade threaded circular couplings serve both types of applications.

ITT Cannon CA Threaded Series circular connector

Based on the MIL-C-5015 standard, ITT Cannon’s CA Threaded Series circular metal connectors serve harsh-environment commercial, military, industrial, and heavy vehicle applications around the globe.

Shock and Vibration: Vibration is characterized by continuous sine waves and can negatively affect the lifespan and reliability of interconnects. Vibration that is undetectable without specialized equipment may be detrimental to connections over time. Shock, on the other hand, constitutes extreme forces caused by sudden acceleration or deceleration. Shock can be especially hard on connectors. The primary difference between vibration and shock is the frequency and amplitude.

Vibration can be introduced through uneven driving surfaces and other simple, seemingly innocuous factors. The engines in industrial, transportation, military, and aerospace equipment are frequently subjected to shock and vibration. The connector components employed in such applications must be engineered to remain tightly mated despite high shock and vibration to protect the contacts at the heart of every connector. If a coupling becomes just a bit loose in these environments, it can potentially damage the interior contacts, as even slight movement under vibration can quickly destroy components. A locking coupling system will keep the halves tightly mated under constant vibration and reliably prevent both movement and ingress.

Radiation: UV radiation exposure is common in avionics and other aerospace equipment and can cause plastics to deteriorate.

Leading Connector Coupling Methods for Harsh Environments 

Threaded Couplings: Threaded couplings are highly reliable. However, threads can be tedious to mate because the exact stop position can be difficult to determine. If you twist too far, you risk stripping threads. If you don’t tighten the coupling enough, it can loosen and lose resistance to shock, vibration, or ingress. Without an obvious end position, torque testing may be required.

ITT Cannon MKJ Series connectors

ITT Cannon’s MKJ Series connectors, including the MKJ5 Triple-Start Ratchet Connector (left) and MKJ1 Double-Start Connectors (right) are 52% smaller and 71% lighter than standard military-grade connectors but deliver comparable high-reliability performance in harsh environments.

If torquing is not required, multi-start threaded coupling systems can offer the security of a standard threaded coupling while being both quicker and easier to mate. Regular threaded couplings have one starting point, whereas triple-start threaded couplings have three starting points. The angle of the threads in triple-start threaded couplings requires fewer total turns to reach the endpoint. Double-start threaded couplings have similar features, with slightly more bite, and cover even more turning distance than triple-start couplings. Several suppliers’ threaded connectors also have an indicator (e.g., a line or dot) on the mating shell to provide visual confirmation of full mating. However, when precise torquing is required, especially in tight spaces, as is often the case in transportation applications, it can be difficult to use a tool on threaded couplings. In those cases, bayonet-style couplings might be the answer.

Bayonet-Style Couplings: Unlike threaded couplings, bayonet couplings have a tangible end position. Many also offer sensory confirmation of proper mating. Some bayonet-style couplings are spring-loaded and provide audible and tactile feedback when they click into position; some are marked to provide visual confirmation of positive locking; and some combine visual, audible, and tactile confirmation features for utmost assurance of secure mating.

ITT Cannon’s CA Bayonet connectors require only a 120° turn to quickly and securely lock the connectors against harsh conditions.

Like threaded couplings, bayonet-style couplings also provide secure connections that reliably withstand shock, vibration, and ingress. They require only a firm grasp and turn to mate. Some models can take longer to mate than threaded couplings, especially if a great deal of hand pressure is required to depress the internal spring in the bayonet coupling.

A bayonet-style coupling mechanism (left) and a diagram (right) revealing its internal spring structure both before (top) and after mating (bottom). (Left and right images courtesy of IaianF per CC BY 2.5, with contrast adjusted in the left image.)

Clip-Lock Couplings: Clip locks, or secure push-pull-style couplings, are another positive-locking mechanism for circular connectors. Clip-lock couplings have a small latching system that securely clips the push-pull style connectors into place and often have a convenient indicator, such as a line or a dot, where the internal latch on one half of the mating pair mounts behind a ledge on the other half to establish a secure connection. Clip-lock couplings also provide positive feedback installers can both see and feel upon locking, and perform well in harsh environments. In addition, clip locks don’t require as much room to grasp, mount, and mate as other coupling styles, which makes them ideal for tightly packed panels that are low on space. The clip-lock design also enables a good physical grasp and even makes one-handed push-in and release from a fixed in-panel connector possible, as simply pushing down on the clip will release the internal lock. Clip-lock connectors are well-suited for use in transportation, commercial aerospace, missile systems, munitions, and medical diagnostic and monitoring equipment.

ITT Cannon’s versatile MKJ Clip-Lock Miniature Circular Connectors are small, lightweight, robust, and competitively priced and repurpose a clip-lock latching system originally designed for the automotive industry.

Breakaway Couplings: Versatility is prized almost as much as high performance and reliability in mission-critical harsh-environment applications. In many military applications, and especially soldier-worn applications like field communications equipment, connections must be lightweight, frustration-free, high-performance, and secure, but also capable of quick disconnect to avoid cable snags and entanglements that hinder soldiers’ movement and, in extreme cases, could even be a matter of life or death. Breakaway-style couplings offer secure, positive latching under normal-use conditions but, if a cable gets caught on something and the specified amount of pull-force is reached, break away (i.e., unmate) without damaging the connector, contacts, or device. Breakaway connectors can also offer adjustable versatility. ITT Cannon’s breakaway coupling, for instance, utilizes a canted retention spring design that allows users to adjust the pull-force at which the connector will break away from its mate, as well as establishes environmental protection by pulling the projecting “nose” within one mating half into an O-ring seal in the other to prevent the ingress of fluid or dust. Some suppliers also offer breakaway connectors that can be fully locked when necessary.

ITT Cannon’s miniature, circular MKJ4 Breakaway connectors enable quick and easy mating and unmating and exhibit rugged resistance against hazards including high temperatures, vibration, shock, submersion, and chemicals. MKJ Connectors are also roughly half the size and weight of traditional 38999 layouts with size 22 contacts.

Low-Cost, Lightweight Couplings: Durability is less important in some harsh-environment applications than others. In these instances, robust but lightweight plastic couplings offer suitable mating features. Medical environments, for instance, may require lightweight, wearable, breakaway couplings that are impervious to fluids and low-cost enough that they can be used as disposables. Plastic-shell breakaway connectors are ideal for applications like these. Ultimately, designers must weigh the various hazards that exist in the intended operating environment to select a circular connector that can perform under the type of stress it will be exposed to. A wide range of circular products exist to serve every need.

Visit ITT Cannon online.

Like this article? Check out our other Harsh Environment, Heavy Duty, and high-reliability articles, our Transportation Market Page, and our 2021 and 2020 Article Archives.

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