A washer door that can be opened without the machine braking to a complete stop. A copy machine that runs while a user looks behind an access panel. A furnace that operates while a homeowner changes the filter. All are red-flag situations.
Safety agencies require that such machines have a shutoff actuated by a primary circuit device. An electronic circuit that can stop or disable the machine won't do the job. To paraphrase the regulators, "When the door opens, a switch behind the door must shut the machine off."
New regulations, such as UL #1950, demand that position-sensing switches be included on access doors, panels, and interlocks, and that they:
Carry a primary load, sometimes 10 to 15 amperes or more.
Have a contact gap of at least 3 mm.
Break on two contacts for added reliability.
Agencies including CSA, TUV, VDE, and SEMKO have similar requirements.
Cherry Electrical Products has developed a line of small interrupt switches that still meet the 3-mm requirement. These devices interrupt one to three parallel circuits with a design that breaks on two contacts.
The first contact is the "make" to establish the circuit; the second creates the "break." When the circuit is broken, it is interrupted at both contacts, creating the 3-mm gap.
The most recent addition to this line, the F85 switch, breaks three separate circuits with two contacts that gap to 8 mm, while one circuit "make" is delayed. It can control current levels of 0.1 to 16A at 250V ac. The smallest family member, the DD Series, meets UL#1950 and comes in a standard snap-switch package.
Cherry Electrical Products, 3600 Sunset Ave., Waukegan, IL 60087, (708) 360-3483, FAX (708) 360-3566.
Upside-down relay solves surface-mount problems
Surface-mount technology (SMT) has increased electronic-manufacturing efficiency by enabling producers to significantly reduce product size. It involves mounting components to both the top and bottom surfaces of pc boards. Unfortunately, the harsh reflow solder process of surface mounting has caused problems for larger components, such as relays.
In the past, most surface-mount relays mimicked their thru-hole cousins, but with the addition of "L"-shaped leads. However, these tall relays "shadowed" other components in infrared reflow soldering systems. The result: slower soldering, which slowed down manufacturing and productivity. Also, the relay's rigid leads wouldn't flex with the board, resulting in failed solder joints.
Omron Electronics' G6S relay for SMT applications overcomes such problems. In addition to high-temperature plastics that maintain the integrity of the relay after high-temperature reflow soldering, the designers virtually turned the relay upside down to improve its SMT performance.
With the upside-down design, the leads begin at the top instead of the bottom. The longer leads more effectively absorb IR heat and transfer the heat to the solder pad, resulting in a much faster and complete solder reflow. The longer leads also feature multiple bends, which flex along with the pc board during excessive temperature transitions and rugged handling.
The heat transfer also allows manufacturers to mount components closer because the solder reflow no longer solely depends on direct illumination from the IR source. Collectively, the new design provides for a more reliable solder bond and higher manufacturing productivity, report Omron engineers.
Omron Electronics, Inc., 1 East Commerce Dr., Schaumburg, IL 60173, (708) 843-7900, FAX (708) 843-7787.
Low-current membrane switching aids automotive design
Automotive low-current membrane switching is here. Combining the functions of low-current switching technologies with the flexibility of silicone rubber first-surface materials, Lucas Body Systems can produce low-current membrane switches that occupy one third the package depth of standard switch packages.
Although low-current (typically defined as less than 50 milliamps) switches have been in use for some time in various industries, automotive switching has been historically high-current. This resulted from the simplicity of connecting vehicle electrical power to a peripheral device (such as a power-seat motor) via a high-current switch.
However, in today's vehicles' complex electrical architectures, the number of driven devices has increased, their diagnostics and control have become much more critical, and available electrical power is at a premium. Low-current membrane switches grant a vehicle designer the latitude to incorporate as many--or as few--switches as needed--without disturbing the master vehicle architecture, rerouting electrical power, or making styling or tactile changes.
The low-current switch elements are encapsulated in domed sheets to seal them from environmental damage. Solid silicone-rubber switch tops actuate the domed elements. A substrate of solid or flexible circuit material provides a base for various types of illumination, adds structural rigidity where required, and provides an area for local electronics for power, control, or multiplexing.
The "sandwich" of these elements comprises an extremely thin package, even with the full range of customer actuation requirements. Nearly any type of switch can be encapsulated, including momentary-push, latching-push, single-rocker, and full-rocker devices.
Lucas Body Systems, 14241 Fenton Rd., Fenton, MI 48430, (810) 750-7510, FAX (810) 750-7540.
Circuit breakers double as switches
Need a switchable circuit breaker that combines circuit protection and on/off switching in a single, compact package? Previous version of such a device offered circuit protection, but with only a push-to-reset button. The new W28S Series circuit breakers from Siemens Electromechanical Components' Potter & Brumfield Products Div. eliminate the reset step.
Switchable circuit breakers in the past typically didn't offer the low cost and compact size demanded by such applications as multiple-outlet power strips. The W28S rocker actuator easily moves from the "on" to the "off" position. When the device trips, the breaker's rocker moves to an intermediate position.
The W28S occupies about the same space as a conventional twist-cap fuseholder, and is available in ratings of 3 to 15 amps. The device is designed to be prewired in the front of a panel, then snapped into place. No additional mounting hardware is required for most panel thicknesses. It suits industrial, medical, and consumer applications.
Siemens Electromechanical Components, Inc., 200 S. Richland Creek Dr., Princeton, IN 47671, (812) 386-1000, FAX (812) 386-2072.
Tiny device combines relays, optocoupler
Aromat Corp.'s AQW series photoMOS relays combine two separate circuits in an 8-pin SOP package about three quarters the size of the two standard 6-pin DIPs separate circuits formerly required.
The circuits can be two relays, or one relay plus one optocoupler. The new combined devices enable PCMCIA card (also called PC card) manufacturers to increase circuit handling capabilities, or to combine more than one function on a card. Example: a fax/modem and Ethernet LAN connection on one PCMCIA card.
The NAiS-brand relays come in the smallest footprint (9.37 x 4.4 mm) and lowest profile (2.1 mm) solid-state relay package available today, say Aromat officials. In addition to the size advantage, AQW relays offer excellent on-resistance stability, low leakage current, and high sensitivity.
Aromat Corp., 629 Central Ave., New Providence, NJ 07974, (908) 464-3550, FAX (908) 464-8513.
Sealed switch survives soldering
C&K Components' KT Series miniature tactile key switches feature a proprietary seal technology that enables the devices to survive fully automatic soldering and cleaning, even the high temperatures of the latest convective-infrared-reflow techniques. The seal also prevents flux- and solvent-cleaning solutions from entering the contacts during cleaning.
The switches' modular design permits easy customization. Options include thru-hole, wave-soldered, or surface-mount terminal styles; right or vertical mounting styles; actuation force from 150 to 500 grams; and flush or extended, hard or soft actuators. Parallel manufacturing based on DFM (design for manufacturing) and flexible automation permit short runs of customized configurations.
Because of their mechanical feedback features (tactile feel and audible click), low cost, low profile, and mounting options, these switches meet audio, medical, test equipment, modem, and remote-car-alarm specifications.
C&K Components, Inc., 57 Stanley Ave., Watertown, MA 02172, (617) 926-6400, FAX (617) 926-6846.