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Making the Right Connections in Tough Environments

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Source : Mouser Electronics

We all know the story about chains and weakest links. But this mechanical analogy also applies to signal chains in electronics. In fact, the mechanical aspects remain relevant in this context, as the weakest link – especially in harsh environments – may well be the connector. This is especially true where the application demands rugged components, for example in transportation, mining and many industrial applications. Many signal chains in these systems form part of safety-critical systems where any failure is almost certainly serious, and often fatal.

Connectors form an integral part of many designs, carrying a variety of signals including power, digital data and analog signals. Connectors also enable connection of subsystems, sensors, actuators and more.

When specifying connectors, it is relatively easy to pick the toughest available – which often results in over-specification that increases size, weight and cost. In this article, we’ll look at the environmental conditions that cause failure and the various types of connector available for deployment in harsh environments.

Dust and Moisture: The Enemies of Reliability

Something getting inside a connector, such as dust, moisture or another contaminant, is a very common source of failure. This can be as a result of adverse weather conditions or even from activities such as maintenance or cleaning. Corrosion is often the result of cleaning chemicals or surfactants getting inside the connector, which can degrade signals and/or lead to premature failure.

Humidity is another possible source of failure, as condensation is often formed when a system is moved from one temperature to another. The condensation can also cause corrosion and/or partial or full short-circuits – leading to intermittent operation or total failure.

Solid matter such as dust or other dirt can build up, creating an insulating layer over the conductors. If this is not removed an intermittent connection is the most likely result, although overheating is also possible within connectors carrying power.

To define how well connectors (and other sealed assemblies such as cases) can withstand ingress, the IEC’s IP standard, IEC 605029, was created. This is now in common use and has a simple arrangement where the first digit denotes protection against solid objects and the second digit indicates the protection against liquids. The full list of codes/ratings is shown in the table below.

IP67 is a common rating found on many enclosures and connectors. Through the use of seals and grommets, IP67 means the housing is entirely dustproof and can withstand temporary immersion in water. In many cases, several seals are uses so that if one fails, the device retains its protection level.

1st digit Protection against solid objects 2nd digit Protection against liquids
0 Not protected 0 Not protected
1 Protected against objects >50mm 1 Protected against drips
2 Protected against objects >12.5mm 2 Protected against drips if the housing is bent at an angle of 15°
3 Protected against objects >2.5mm 3 Protected against spray water
4 Protected against objects >1.0mm 4 Protected against splash water
5 Dust-protected 4K Protected against splash water at increased pressure
6 Dust-tight 5 Protected against water jet
6 Protected against strong water jet
6K Protected against strong water jet at increased pressure
7 Protected against the effects of temporary submersion in water
8 Protected against the effects of permanent submersion in water
9K Protected against water during high-pressure/steam cleaning

Table 1: IEC 605029 ratings for ingress protection. (Source: https://www.mouser.co.za/applications/ingress-protection-matters/)

A second often-used system for defining ingress protection is from the National Electrical Manufacturers Association (NEMA) in the USA. Many connectors and enclosures will include both IP and NEMA ratings in their product data.

Temperature, Shock and Vibration

Temperature can be extreme in many industrial applications, especially in mining where very high temperatures are experienced during drilling. The application of a high temperature can, in itself, be a possible cause of failure and this situation is exacerbated if the temperature often cycles from high to low – or vice versa.

In outdoor installations, ice is often a challenge in winter. Any water inside the connector will freeze as temperatures drop, and this will put significant pressure on the housing and contacts. Ice can also form on the cables, adding weight, which is another source of increased strain.

If specifying connectors for use in high-temperature environments, a connector with an appropriate temperature range must be specified. Molex’s LC2 metallic optical connectors are ideal for high-temperature applications that require the high data available with fiber optics. Their metal body allows them to be rated up to 150°C.

MRXACI022(Fig1)

Impact and vibration can cause physical damage to connectors, which can lead to failure of the connections or simple mechanical failure. Bodies built from metal tend to be stronger and can withstand impact better. However, thermoplastics are better at resisting corrosion and are also flame- and chemical-resistant. Metal housings (if earthed) also provide protection against electrostatic discharge (ESD) and electromagnetic interference (EMI), which can be a challenge. Which material is chosen will depend on the hazards likely to be present in any given application.

Even if any force is not applied directly to the housing, forces applied to the cable can also be a source of damage. For this reason many connectors provide strain relief as standard – or at least as an option.

Vibration is another source of potential early failure and connectors designed for use in harsh, high-vibration environments are often qualified to MIL-STD-202 or similar. One product that is IP67 rated, has an operating temperature range of -65°C to +175°C, and can cope with high levels of vibration is TE Connectivity’s CeeLok FAS-T Gigabit Ethernet connectors.

MRXACI022(Fig2)

Connector Selection Advice

The very first step is to be sure that you fully understand the application and, in particular, the environmental conditions and stresses to which it will be exposed. Without over-engineering, you should plan for the worst-case conditions to limit the chances of premature failure.

Some applications will require standards to be met – these could be for the environment (ingress protection), for safety (such as isolation) or for correct operation (for example in the case of data communications). The manufacturer’s datasheet or selection charts are good places to check that all of the necessary certification is in place – saving you time and cost in obtaining approvals of the end equipment.

Checking that the electrical needs can be met (voltage capability, current handling, bandwidth, etc.) can also be done via the datasheet. Mechanical requirements such as strain relief and latching/locking mechanisms are sometimes standard and can be added by a suffix on the part number. Again, this will be explained on the datasheet, along with all other available features and options.

Datasheets will often contain reliability data and describe the testing that has been done to meet certain standards, such as MIL-STD-202. Many tests ensure product reliability using techniques such as highly accelerated life tests (HALTs) to accurately simulate real-world conditions in a far shorter time.

If you are tempted to specify the highest level of every parameter, in excess of what you really need, you will spend more money than you should and likely end up with a solution that is larger and heavier than you want, making your product uncompetitive.

Summary

Often, connectors are an afterthought in the design process. However, their impact on the design and potential to cause failure mean they must be considered as important as any other element of the system. There is a huge range of options available so, if you need guidance, the technical support team at Mouser is available to guide you to the best option for your application.

To learn more, visit www.mouser.com

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