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Design News, January 2013

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Electronics & Test O-ring Materials Operating Temp Range Petroleum / Fuel Ketones Wear Resistance Radiation Resistance NR G F Buna-N (Nitrile) -35 - 250°F (-37 - 121°C) R EPDM -60 - 320°F (-51 - 160°C) NR R G F Silicone -65 - 450°F (-54 - 232°C) NR NR P G FPM (Viton) -15 - 400°F (-26 - 204°C) R NR G P r = recommended, Nr = Not recommended, G = Good, F = Fair, P = Poor Table B 6 Insulator Materials Operating Temp Range Dielectric Strength* Radiation Resistance PEEK -85 - 392°F (-65 - 200°C) 18 kv/mm 10⁹ Rad PTFE -85 - 320°F (-65 - 160°C) 20 kv/mm 10⁴ Rad PBT -85 - 275°F (-65 - 135°C) 17-30 kv/mm 108 Rad *IAW IEC 60243-1 Table C the manufacturer's IP rating (more information about IP ratings can be found at www.iec.ch). Most of the IP designations have specific conditions, but the IP68 rating may be defined differently by each manufacturer. When looking for a connector with an IP68 sealing rating, inquire as to exactly how the manufacturer's IP68 rating is measured. A system being submerged at 2m for 24 hours has a different impact on the connector than if it were submerged at 120m for 24 hours, but both situations can be defined as an IP68 rating. For a vacuum application, you may need a product that's sealed to a greater level than what's defined by the traditional IP ratings. These are defined as hermetic (airtight) sealed products. 5 Materials: What does the connector housing material need to be? Can it be plastic? Can it be metal? Select the material wisely as this may impact reliability, weight, and cost. Brass connectors with nickel/chrome plating are traditionally more wear-resistant and have longer lifecycles than many other materials. If weight is an issue, aluminum connectors may be an option. Consider plastics for limited reuse and disposable applications. If you are considering plastic, you must adequately test to confirm that it will withstand the end use application. If used in medical applications, make sure your connector will withstand the sterilization processes used by the end customer. For aggressively corrosive environments or some food industry applications, stainless steel may be required. Don't sacrifice reliability for cost when deciding what material you select. At this point, you should also review the operating temperature of the insulating materials used in the connectors you are evaluating. This includes contact insulators, potting materials, and O-rings. Tables B and C can guide you in your selection process. Reliability Needs: Now that you've investigated the electrical, termination, sealing, and material requirements, it's time to take a look at the frequency your user will connect and disconnect the device over its lifetime. If you require a high number of mating cycles, consider a connector with 5,000 to 10,000-plus mating cycles. This is especially important if a failed electrical connection can put lives at risk, such as in the medical or military environments. Another requirement to look at is whether your connector will be able to stay stable in harsh and extreme environments. Many connectors, for example, work well indoors, but they will lose their performance when they are used under extreme outdoor conditions. It's important to ensure that your connector is suited for use under these conditions when necessary. 7 Miniaturization: There have been some advances in miniaturization recently, and you should take advantage of it when possible. It's possible to design in one connector today for an application that would have needed two or three only a year ago, but you must be careful. Look closely at the details of each connector, since those details become more important as the voltage and current increase. Compare models for pin size, number of pins, and functionality. Miniature connectors are nice packages that fit in small places, but only a few can carry power and signal. These small connectors are extremely difficult to terminate. Hence, the miniature plugs and receptacles are often sold pre-wired to maintain reliability. 8 Raw Cables and Assemblies: Once you've identified your connector, it's time to define the raw cable and the cable assembly. With connectors continually getting smaller, it's becoming easier to inadvertently spec a small connector that won't work with the larger cable you would like to use.You'll have to look at both the cable and the connector together to make sure they are compatible. Design News | jaNuary 2013 | www.d esign n ews.com –48–

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