It’s often the little things in life that seem to cause the biggest problems, and it’s no different in design engineering. That small detail, that one piece of the puzzle that was overlooked or underappreciated, can cause the largest project to grind to a halt, resulting in missed deadlines, expensive rush charges and contractual delay fines.
From an overlooked stress concentration in the hull plating on a Liberty ship to the aero-elastic flutter of the original Tacoma Narrows Bridge, miscalculating small details has led to very public disasters. Similarly, small errors have led to the failure of innumerable projects and untold amounts of wasted money. The lesson? The same attention and design diligence that goes into planning for large design challenges is needed in smaller projects, as well.
An area where personal experience has shown this to be the case is in the seemingly innocuous area of pressure or vacuum bulkhead wiring penetrations. Over the course of their careers, design and test engineers in many fields will likely encounter a pressure or vacuum penetration design challenge. In applications such as vacuum systems, manufacturing equipment, process monitoring, fluid-filled devices, and pressurized equipment, penetrations are needed to get power, electrical signal or optical feeds into and/or out of sealed enclosures.
Over the years, it has been our experience that missteps often occur when engineers:
- Underestimate the importance of the feedthrough in their final design or product;
- Overestimate their ability to build something in-house;
- Overestimate the ease of finding the right feedthrough solution;
- Underestimate the lead time that will be involved when they find a vendor
When these missteps occur, designers can end up with delays, expenses and embarrassment that a little preplanning could have eliminated.
There are some situations in which the application is straightforward, and an off-the-shelf feedthrough may suffice. But there are other design, material or envelope considerations that require a customized solution. For example, if an existing bulkhead already has NPT penetrations, a matching feedthrough should be sourced to eliminate drilling and rethreading the penetration.
Often, a design may require more wires than can fit in an off-the-shelf feedthrough. Rather than adding another penetration or enlarging the existing penetration (if either option is even feasible), a feedthrough can be designed to precisely match the customer’s conductor requirements within the existing envelope.
Following are some examples all design engineers can learn from—applications in which either judicious preplanning or custom feedthrough design kept a project on track.
SPACE SIMULATION
With the increase in space exploration and commercial space ventures, space simulation testing has become a necessity for many companies. Testing typically requires multiple penetrations for power and signal cabling in vacuum chambers of all sizes where hermetic sealing is essential. For years, companies have been getting by with connector-to-connector or connector-to-solder cup feedthroughs that don’t provide complete, wired, and connectorized solutions, therefore requiring excessive time to install and adding potentially problematic connections. Often, twisted and shielded wire pairs are needed to eliminate electromagnetic noise in the data and control signals passing through the feedthroughs. As there are no off-the-shelf feedthroughs for twisted shielded pairs available, a custom solution was required to enable the needed testing without forcing a redesign of the vacuum chamber.
MAGNETIC BEARINGS ON FLYWHEELS
The application of flywheels as energy storing devices has been around for centuries, but interesting new applications of this age-old technology have been integrated into our power grid on both large and small scales, including UPS power backup systems to bridge the time between a power outage and backup generator activation, leveling the power in the grid, and flywheel farms for storing energy from solar and wind installations for use in off-peak hours.
The use of magnetic bearings and vacuums to maximize the efficiency of these flywheel systems has greatly improved their utility, but also made them dependent on wire feedthroughs to provide a means of delivering the power and signal feeds required for these precision systems to run safely without loss of vacuum. With flywheels weighing upwards of 100 pounds and running at 15,000 RPM, the need for constant monitoring is essential and provided by use of numerous Hall-effect sensors and their corresponding wire feedthroughs.
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