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Choosing the right switch for the job: a guide to switch selection in mission-critical devices

When it comes to the performance of mission-critical devices, such as medical products or factory equipment, it’s no secret that accuracy and reliability are key success factors. Whether it’s an automatic external defibrillator (AED) for a heart attack victim or a pressure transmitter in a chemical processing plant, lives can be at stake if these devices fail to function properly. While the end product gets most of the credit for high performance, very rarely do people think about what goes into these devices and how they are created in the first place.

 

Fortunately, there are teams of dedicated design engineers who evaluate the best components for each device — from the nuts and bolts that hold them together to the high-performance materials that are durable enough to withstand challenging environments. However, this is no easy feat, and there are many factors that come into play when designing mission-critical devices. Given a host of design variables and the seemingly infinite material choices available, selection can be extremely complicated, costly, and time-consuming.

 

To guide the selection process, designers should keep five considerations in mind when choosing the best possible components for the job: performance requirements, size, customization, the environment in which they operate, and production factors.

 

Performance requirements

One of the primary factors in choosing components such as switches is the required performance and reliability level of the end application. There is a significant difference between the needs of consumer products, such as electric toothbrushes, and medical applications, such as electro-surgery instruments. These differences in performance requirements need to be understood and matched to the appropriate components for the end product to function correctly and reliably. Consider the switch used to actuate an AED, for example. The ability to prevent oxidation of the switch contacts is critical because this product may sit in a building for years. However, the switch has to reliably conduct a low-level signal when the button is actuated.

 

Similarly, components used on utility meters need to withstand the challenge of potentially harsh outdoor environments. Tamper switches used to detect cover removal also need to resist contact oxidation because they may also remain untouched for years but still need to reliably send a signal to the utility if a customer attempts to tamper with the meter. Another example is elevator buttons, which need to withstand up to 5 million cycles and be robust enough to handle the impact from a variety of passengers. These are just a few scenarios that help illustrate the importance of understanding performance requirements early in the design process.

 

 

Components such as switches used for elevator buttons need to be able to handle impact and perform reliably for millions of cycles.

 

Size

Component size and footprint is another key factor that must be considered in the design process. From industrial products to medical devices, there are a number of factors, including increased product functionality and features, putting pressure on designers to reduce component size. The emergence of connected devices driven by trends such as Industry 4.0, mHealth, and connected care requires the addition of communication components, such as antennas, transceivers, and related circuitry, and puts more pressure on traditional components, such as switches, to reduce their footprint on the circuit board. For the growing market of medical wearables, such as health trackers, cardiac monitors, and wearable drug delivery devices, the addition of flex circuits on the PCB is critical to save space. Components such as electromechanical switches need to be able to push the boundary on footprint and overall height to free up valuable real estate on either traditional circuit boards or flex circuits.

 

Customization

With a massive number of suppliers and an even bigger catalog of commercial off-the-shelf components, sometimes it’s just a matter of finding the right fit. However, most design involves some form of personalization to provide the exact performance required. Although customizing components sounds expensive and difficult, many suppliers are willing to make modifications to existing products to save time, cost, and complications for designers and engineers. Customization may range from simply modifying the size and features of a standard component to integrating the component into a complete module or sub-assembly. Features such as lighting, graphics, and snap-in mounting are also typical customization options. A good supplier will take the time to understand the requirements of the application and make recommendations around the best way to integrate their component. The supplier is a partner who can be used to determine a realistic timeline and budget and should also provide insights into how they plan to test and troubleshoot any non-standard features.

 

Environment

From blood, body fluids, and the harsh sterilization chemicals used in a hospital to exposure to high heat or rain in an outdoor plant or worksite, mission-critical devices need to hold up in a wide range of tough conditions. As a result, corrosion resistance is one of the most important factors when narrowing down the appropriate components in mission-critical devices. In addition, components need to be robust and have the ability to handle impact in certain environments, such as in a busy emergency room where equipment is moved around quickly and personnel don’t always have the time to be gentle or use equipment as recommended. Smoke detectors must be able to operate reliably in the high-sulfur-dioxide environments typical during a fire. The relays and voltage regulators used in power transmission equipment must be able to withstand the outdoor environment of a typical sub-station.

 

Designing durable components that can handle physical and environmental impact allows the equipment to work reliably for years, even in challenging situations. Environmental specifications can restrict these choices, so it’s best to determine early on if this will limit your choice of components. Be sure to work with manufacturers to meet specific needs.

 

 

Corrosion resistance and reliability are requirements for switches used on mission-critical devices such as electro-surgery instruments.

 

Production factors

Geographical concerns may seem low on the list of things to consider, but location shouldn’t be dismissed in the design phase. With a host of supply chain variables, as well as an OEM’s ability to communicate with the supplier’s engineering team during the design and development process, there are some real benefits to working with a supplier in close proximity. Global suppliers with locations in the region where the end product is manufactured can better understand the advantages and limitations of various product offerings as well as get specific in-person recommendations regarding the best way to integrate the component into the end device.

 

Designing for the assembly process used on the end application is another key concern. Whether the final assembly process is manual or automatic, components need to be designed with the appropriate assembly method in mind in order to include features that can increase assembly efficiency and reduce potential for quality issues.

 

Although selecting the right component is no easy feat, it’s a critical task to ensure that mission-critical devices function properly. Component selection affects a device’s usability, durability, longevity, and safety and can significantly contribute to the product’s overall success as well as the perception of quality that the market has about the end product. By keeping these five considerations in mind, design engineers can streamline the component selection process, reduce the risk of costly and dangerous mistakes, and, most importantly, create a positive experience for the end user.

 

Mike Bolduc is Global Marketing Manager at C&K, where he is responsible for leading market strategy and global growth efforts for the industrial and medical business segments. Mike has an engineering and business background and over 25 years of diversified experience in the automotive, semiconductor, HVAC, aerospace, industrial, and medical industries working for large global corporations such as Texas Instruments and Stanley Black & Decker.

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