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.
Table B
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.
MiniaturizationThere 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.
I have to agree. Having spent over 15 years providing technical support for products in industrial environments, connection issues were by far the most prevalent. This is not the area to take shortcuts. Connector design, fabrication, backshell, wire gage and level of sealing are all important to get right.
A poorly soldered connection to a wire is certainly a potential for failure, far moreso if there is not a good degree of strain relief. My experience with soldering is that if it is done right, the solder does not wick up the strands more than the conductor diameter. Greater wicking indicates that too much heat was applied to the connection and to the wire. But the most important part is indeed the strain relief that prevents flexing at the connector pin. No question about that.
For my early years in the industry I ran the Service Department for an agricultural equipment manufacturer. The environment was hostile, to say the least, but I quickly found that nearly all of the failures were switches, potentiometers and connectors. Semiconductors rarely failed, but anything electromechanical was bound to be damaged by vibration or user input. Not only were connectors an issue, but providing strain relief on cables without damaging the cable under vibration was an issue too. Connectors became such a problem that we decided to do without them at one point and used terminal strips. This wasn't an installation friendly approach, of course, but it did solve the problem.
When I played in a band connectors were always the first component to fail, too. Smoking was still legal in Chicago Blues clubs back then, and a layer of brown goo accumulated on all connectors. Switched 1/4" connectors were the worst with the switch contacts quickly failing with a layer of cigarette goop. Line Out and Insert connectors typically had this type of connector, so the quick stage fix was always to shove a loop back cable in the offending channel and see if this fixed the problem.
I also found that MTA connectors used as interconnects would fracture solder joints on circuit boards during thermal cycling. This happened quite a few times on newer Fender amps (why many musicians favor point to point wiring). The solder will expand and contract at much greater rates than the steel pins in the connector during thermal cycling and eventually the solder joint fractures around the connector pins. Later when I worked at an appliance controls company the same thing was happening to our oven controls and my stage experience paid off in finding a solution.
I think for the average assembler the crimp connections are much more reliable. They probably don't need replaced as often. Also, what is the most common failure mode in a soldered pin connection? I would guess that wire breakage where the solder wicked up into the wire. If so, the wire would have to be shortened in that case too.
How in the world is a crimp on pin connector field repairable? REplacing a damaged pin would require cutting of the crimped on pin, making that wire in the cable too short to use. When I was an application/support engineer I would solder the crimp pins on for those 28 and 36 pin MS connectors with the individually inserted pins. The result was that I could replace a damaged pin in just a few minutes instead of needing to fight with stores for 2 hours to get a replacement cable assembly.
It is certainly true that connector choice can break a product and render it totally user unfriendly.
As I design CNC machinery, I just want a connector that is already attached to the type of wire I need. So, I end up looking over countless catalogs for the perfect option. Often I end up having to build the harness myself. I am truly tired of doing that. All I need is a DB9 with 18 awg wire, shielded, twisted pair, 6 feet long. Is that so hard to manufacture?
Anyway, price is also a concern. With proprietary connectors, you often end up stuck with one vendor.
I've encountered numerous failures of the large rectangular modular connectors offered by LappUSA, Weidmuller, Harting to name a few that do not stand up to real use. This year I've personally witnessed four different incidents where the connectors permitted water to enter.
Going to higher ratings than are strictly necessary is sometimes necessary to get the protection desired.
IP69K is a high pressure high temperature environment that better represents industrial food processors. IP67 sensors were simply not holding up.
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