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Reed Components Expertly Handle Automatic Seat Positioning and Reclining

Tue, 03/01/2011 - 10:23am
John Beigel, Consultant for MEDER electronic Holding, www.meder.com
John_BeigelThe reed switch sensor and its sister component, the reed relay, continue to find increased use in applications taking advantage of their unique characteristics. These characteristics include: 

• Hermetically sealed reed switch
• Ultra small packaging
• Rugged packaging
• Excellent in all tough, moist, dirty environments
• Capable of operating from -55°C to 200°C
• Best isolation of all the switching technologies: >1012 ohms
• Dielectric strength >4000 V
• Switching up to 100 W
• Switching voltages up to 1000 V
• Switching currents up to 1 A
• Carrying currents 3 A and pulsed up to 5 A
• Capable of RF switching and carrying DC up to 20 GHz

With this large set of unique features, it is easy to see why reed switch technology is not decreasing, but on the contrary, growing rapidly in many areas, with several new applications every day.

Due to the previously mentioned characteristics, reed switches are a great choice for use in the design of the many new features of automatic chair and seat recliners, whether in an automobile seat or one’s ‘easy chair’ at home. In fact, seat designers often prefer to use reed switch sensors. One specific benefit of the reed sensor is that it has the ability to sense a position within less than 1 mm (0.040”) accurately. It also has the ability to count rotations of a small motor. The reed can then send the counts to an integrated circuit, which easily keeps track of the number of rotations. Then, the rotations can be translated to linear distance so that any number of exact positions (i.e., “favorites”) can be stored and programmed for later retrieval.

ec1103mc103Figure2Almost Endless Features
The features of recliners in the home appear to be endless: they can rock; they can recline with multiple staging points; they can swivel 360°; they can massage at multiple speeds; they can lift; they can supply heat to the cushions and they can even cool -- all while providing the most comfortable seat in the house. With all these features, it is rather easy to understand why insomniacs use them for sleeping, and nursing mothers use them to soothe their babies. When designing these features, you need to consider how you are going to turn them on and off, either manually or automatically. In general, we are moving away from doing things manually, and many automatic/reclining seats now rely on wireless remote controls to activate the various switches that run the chairs’ features and functions. Here the reed relay receives the wireless RF frequency and sends it to the integrated circuit. There, actions are initiated to operate other power reed relays carrying out the given tasks.

In chairs that have a cool-down mode, moisture will be generated and will need to be stored. For this function, a liquid level reed sensor would be the perfect component to alert the user when the moisture storage is full and needs to be emptied.

Many of the new automatic reclining chairs at home are now battery-operated, which places an additional burden on the electrical components used, as they must be very frugal with their power consumption. Here, the reed sensor separates itself from the rest of the technology. The reed sensor draws zero power when not in use. So days, weeks, and months can go by with the reed sensor never drawing any power. Then, when called to action, it will activate and carry out its job function using minimal power. The latching reed relay also uses minimal power in carrying out its switching function, with only a single 2 ms pulse needed for activation, and another 2 ms pulse needed for deactivation. There is no additional power draw, thus the switching function is carried out with minimal draw from the battery current.

Flammability and Effects from Spills Are Not Issues
The switching for reed sensors and reed relays takes place in a glass encapsulated, hermetically sealed reed switch, so any arcing is well contained from the outside environment. With the additional over-molded packaging, flammability is never a concern.

Seats, whether in an automobile or our favorite room in the home, are vulnerable to spills from coffee and an assortment of other drinks/liquids. Many of these liquids are acidic and will affect most electronics or electromechanical components they contact. Since the reed sensors are hermetically sealed and packaged in rugged, environmentally safe, high strength thermoset plastic, they are an excellent choice to use in seats susceptible to liquid spillage. Being hermetically sealed insures the reed sensor will never be influenced in a negative way by inadvertent liquid spills and/or dirty, dusty, moist environments. On the contrary, electromechanical switches/sensors are quite vulnerable in these environments and situations.

Summary
With the fast growing need for mechanization in our daily lives, the electronic world is taking over. The microprocessors and computers on a chip supply all the memory and logic to carry out almost all functions. However, these chips need input from the ‘real world’. They need to have sensing information fed into them before they can carry out their tasks. Reed sensors are the best option for supplying the chips with this critical information.

Also, the computers and microprocessors cannot directly drive actions. The desired functions and features of automatic seats and recliners need components that can switch and carry the power effectively and efficiently. Reed relays are the best option for this, and are therefore an integral component of the technology in these seats.

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