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Enter the small world

Enter the small world

"Let's get small," said comedian Steve Martin. Designers of relays and switches have heeded that call for many years, and the trend continues unabated. A quick survey finds smaller and smaller components-all part of the quest to free up board real estate.

Take the mature technology of general-purpose relays, for example. The evolution to smaller and smaller sizes is being driven by OEM design engineers striving to reduce the size of their products. They are also demanding lower costs wherever possible, says Dave Fleak, business unit manager for Tyco Electronics' SCHRACK relay operation. "Although we are not seeing any quantum leaps in technology, improvements in processes and materials are allowing us to work towards these goals," he says.

Reducing size along one dimension can sometimes result in an increase in size along another. Tyco Product Engineer Harold Leipold points to the recently introduced PB series relay. Its overall footprint is smaller than previous designs, but it is also taller. If overhead clearance is no problem, then a customer can save quite a bit on the footprint (40%) with a cost reduction to boot.

New plastics with improved arc tracking index (arcing potential over a surface), temperature and flame ratings, and improved dielectrics and surge voltage are allowing for reductions in material thickness and clearances between internal relay parts. Leipold says this is particularly important in ensuring safety in white goods (appliances) sold in Europe. That market's environmental rules are also driving the use of metal contact materials in relays and switches to benign alloys without cadmium. "However, when changing contact materials, designers have to make sure the contact force is correct," he warns. Also, spring properties with temperature extremes have to be predictable. Here again, engineers can minimize cost by designing contacts to eliminate the need for a separate return spring, for example, cutting parts count and assembly complexity (see figure).

Other manufacturers are working to reduce the size of their relays. Omron Electronics (Schaumburg, IL) just added two low signal relays, the G6J and G6L, to its lineup. These come in at only 5.1-mm wide (the G6J) and 4.0-mm high (the G6L), allowing more features in a given board space or reduced height for stacking boards (see figure). Product Specialist Terry Harmon notes that LCP material contributes to the durability of the components, and allows both to meet UL 1950 Basic Insulation requirements at 125V. The G6J also withstands a 2.5-kV surge between coil and contacts. The devices feature lower power consumption and are targeted for telecom office uses, computer racks, and devices where space is tight, such as smoke detectors.

Arnold Offner, INTERFACE product manager at Phoenix Contact (Harrisburg, PA) says that while relays have become smaller and use less energy, designs are also more adaptable to both industrial and consumer requirements-obviating the need for PLCs in many applications. An example is Phoenix' rail-mounted PLC-RELAY single-relay terminal block. It comes in a 6-mm thin package with modularity, bridging, status indication via LED, and expansion potential. Vital to the thin package's versatility is the internal molded lead frame structure-with just two lead frame configurations the company produces more than 130 variations in both electromechanical and solid-state relay types (see figure).

The lead frame facilitates automated pick-and-place assembly and testing of components-all contained within the block, all fabricated in one machine-cutting end user costs. Such manufacturing control also avoids assembly and hook-up errors in the field. Different relay packages can be accommodated-from 5 to 125V dc for ex-ample-within the same basic housing. The lead frame's adaptability is important for critical time-to-market, Offner says. "We can make changes in four weeks, going from design through component changes to test" to develop new variants.

An added benefit of lower power consumption of modern relays is that the stored energy in the coil is reduced. When power is off, the resulting reverse voltage (inductive kickback) is lower-resulting in less of a damaging spike within the application.

Virtual success. Similar to relay technologies, advances in switches hinge on materials and design changes. Bill Agnatovech, design engineering manager for ITT Industries, Cannon (C&K; Watertown, MA) stresses the importance of design tools in switch design today. He notes that for the past several years the company has developed smaller and smaller switches, using its core technologies of insert- and overmolding in conjunction with the latest engineering resins. "However, in recent years the popularity and ever-decreasing size of hand-held devices, and the reduction in product life cycles, coupled with the need for reduced development cycle time, has driven us to focus on virtual prototyping-using software to develop our initial prototypes," says Agnatovech. "We use the latest 3D modeling software (Pro/ENGINEER); finite element software to perform stress analysis; a motion-software package to analyze forces and interactions between components, such as interference checks; and most recently, a mold-flow analysis package to determine whether or not the thin walls of these miniature switches can be filled during the molding process."

While such concept and design tools have not completely eliminated building prototype molds, engineers have reduced the iterative trial-and-error process to ensure that when steel is cut the design meets requirements.

Recent examples to emerge from this process are the latest detector switches in the C&K line (see figure), which detect an object for activation. The switches are all suited for low current applications and range from large to micro-miniature types, with various actuation positions, surface- and slot-mountings, and different length and connector configurations.

E-Switch's latest snap-action switches are also miniature types. John Benson, VP of sales and marketing, says that in smaller applications many customers want to save space by surface mounting switches to PC boards. This arrangement requires that the forces impacted on the solder joint be minimized. Thus, switches need "soft" actuation and low forces. "The key is the switch's interface with the moving object whose position is being detected, such as a can in a vending machine or a piece of paper in a copier," says Benson. To reduce forces, adequate actuator overtravel (past the open or closed contact position) can be provided along with features such as rollers at the end of the actuator to disperse force and obviate jamming.

By clever design with modern tools and materials, engineers are indeed "getting small" when it comes to the size of switch and relay components.


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