Instrumentation • Electronics
Auto seat positioning/reclining handled by reed technology
John Beigel outlines the reasons why the use reed switch technology is still growing.
T
he reed switch sensor and its sister component, the reed relay, continue to find increased usage in applications taking advantage of their unique characteristics. With a set of 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. These features include:
l Hermetically sealed reed switch. l Ultra small packaging. l Rugged packaging. l Excellent in all tough, moist, dirty environments. l Capable of operating from -55°C to 200°C. l Best isolation of all the switching technologies >1012 ohms. l Dielectric strength >4000 volts. l Switching up to 100 watts. l Switching voltages up to 1000 volts l Switching currents up to 1 amp l Carrying currents 3 amps and pulsed up to 5 amps. l Capable of radio frequency switching and carrying DC up to 20 GHz..
Monitoring and controlling the motion
Due to the above-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-in) 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 (ie, ‘favourites’) can be stored and programmed for later retrieval.
Almost 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 whole 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.
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. l
Enter 29 or ✔ at
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Fig. 1. Reed switches are a great choice for use in the design of the many new features of automatic chair and seat recliners. Plus inset: The reed sensor is that it has the ability to sense a position within less than 1 mm.
John Beigel, a consultant for MEDER electronic is based in Singen, Germany.
www.meder.com
www.engineerlive.com 29
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