Switches & Switching Devices
Pushing Appliance Industry Buttons

By David Simpson, Contributing Editor

Tried and true switch and switching technology continues to have a place in the appliance industry. After all, products such as thermostats and standard push-button switches have long proved themselves to be reliable and low cost, and they are readily available. At the same time, though, appliance engineering needs change.

One area of change is the increasing use of digital technology in appliances. "There's been a big changeover to digital appliances," points out Mike O'Brien, switches marketing manager at Omron Electronics, LLC, (Schaumburg, IL, U.S.). "Digital appliances require switches for extremely low loads and high levels of operations."

Yas Sasao, director of the Alps Electric (USA), Inc., business unit in San Jose, CA, U.S. observes that the adoption rate of digital technology varies from region to region, with Asia and Europe farther along than the U.S. He notes that about 80 percent of washers in Japan use microprocessors and membrane switches, a much higher percentage than in the U.S., although digital is still growing there.

In ovens and ranges, he points out, digital controls provide more accurate temperatures. "But the U.S. consumer is not so concerned with this," Mr. Sasao says. "They are more price sensitive and not as impressed with digital advantages as, for instance, are European consumers. Some appliance companies may consider presenting traditional controls on the outside, but incorporating digital on the inside."

Overall, many suppliers are seeing a mix of requirements from customers. "On user interfaces, appliance companies demand everything from the traditional switches with tactile feel to solid-state switching applications," observes Doug Williams, business unit manager at Marquardt Switches, Inc. (Cazenovia, NY, U.S.). "They have the flexibility to select not only what solves their switch needs, but also what addresses the look and feel they want to achieve. Internal switch systems incorporate more sensors and integration as appliance companies work to optimize performance while minimizing costs."

Achieving the Optimum

How does an appliance company achieve the optimum switch solution? "We have been able to provide savings to customers by being involved in the process early, while at the same time, providing unique solutions to meeting aesthetic requirements," says Al Hollenbeck, technical director, Poly-Flex Circuits (Cranston, RI, U.S.). "But many times customers provide us with completed drawings, where it is too late to integrate new ideas or make modest changes to improve design-for-manufacturing, therefore, lowering the cost."

It is also important to focus on electrical load and discuss it in detail. Steve Hugener, marketing manager at Cherry Electrical Products (Pleasant Prairie, WI, U.S.) points out that occasionally, appliance companies design a switch based solely on its catalog ratings. "For example, it might seem reasonable to assume that a switch rated at 10 A maximum should also work fine at 50 mA, but this is not always the case," he explains. "Switch manufacturers can help steer OEMs around those potential pitfalls.

"The nuances of switch performance can also result in a lot of pain for OEMs that drive their sourcing through reverse auctions or similar processes," Mr. Hugener continues. "Switches often appear to be easily cross-referenced commodities, but subtle differences between manufacturers' products can make the difference between success and failure in the customer's application."

John Cotton, sales manager of Saia-Burgess USA, Inc. (Vernon Hills, IL, U.S.), advises that when selecting a switch, an appliance company should know the current and voltage the switch is being asked to make and break. "Silver and silver-cad contacts are the materials of choice for 1 A, 2 A, 5 A, and 10 A," Mr. Cotton explains. "Gold contracts rated for 0.1 A @ 125 V a.c. are required for dry-circuit switching. Too often we find people overlooking the need for gold contacts in dry-circuit switching applications."

Because of today's greater focus on energy conservation, temperature control is especially important in some appliance applications. As a result, Ron Buchanan, executive vice president of Madison Company (Brandford, CT, U.S.), says his company is seeing higher levels of interest in thermocouple and RTD designs for commercial appliances. One approach his company takes is to add a temperature sensor into a liquid-level switch design. "That would be either a thermocouple or an RTD sensor," he says. "The advantage of the 'combo' switch is that the appliance can now monitor two conditions, and the mounting design/hardware cost is reduced from two devices to one combo device."

While customization may be the ideal way to optimize a switch, this is not always a practical avenue for smaller manufacturers. "These [manufacturers] have historically been forced to use standard products or pay huge R&D costs for custom products," says Mr. Williams of Marquardt. "Being a local supplier to companies on a global basis means we can utilize local design resources to develop a solution and then tap into our global manufacturing base to manufacture their products at a competitive cost. We have embraced design and manufacturing principles like JIT and One Piece Flow that allow for customization on a smaller scale."

In some cases, arriving at the optimum switch solution means going beyond the switch itself and offering value-added services, such as switch assemblies. For instance, Toneluck Micro (Hong Kong, China) reports that it previously sold a microswitch to a water heater manufacturer in Europe. The appliance producer then assembled the microswitch into a complete pressure switch. Today, Toneluck makes the microswitch, builds the complete pressure switch, and calibrates it according to the appliance producer's specifications. This approach reportedly brings total cost down 30 percent by integrating all of these assembly processes.

Another application was a project with GE Consumer & Industrial (Louisville, KY, U.S.). Initially, Toneluck Micro provided just the microswitch for one of the control modules used in a washing product. However, the supplier also had capabilities in tooling and plastic parts. After assessing these capabilities, GE decided it wanted the supplier to build the whole module with the microswitch assembled rather than supplying the switch alone to a sub-contractor for assembly. The sub-contractor had to buy other plastic parts from another injection house. Toneluck Micro's tool engineers worked closely with GE's design and manufacturing experts, and the result reportedly gave better value and savings since fewer parties were involved.

Increasing Safety Standards

A high level of customer safety continues to be a goal in switches. "In years past, the major emphasis of manufacturers was to provide products to consumers that would be considered safe if the various types of protection devices incorporated into an application would function if the end application was in a fault condition," says Brandon L. Wehl, president and CEO of Portage Electric Products Inc. (North Canton, OH, U.S.). "Basically, you were more interested in keeping the entire application from causing other problems for the consumer rather than protecting the consumer from themselves. Today, dual-function protection devices are now being used in many applications to not only protect the application in a fault or misuse situation, but they also protect consumers, who believe they can fix whatever is wrong."

One such device is a self-hold thermal control. These incorporate some type of resistive heat source along with the functionality of a thermal-control-switching device to provide an extra level of consumer protection. With Portage's Model J(S) Series, should the device function due to a fault condition or misuse by the end user, then the thermal control portion of the switching device effectively opens the electrical circuit, turning off the power to the application. The resistive heat source is energized, creating enough heat to prevent the thermal control portion of the switching device from automatically closing and turning the power on to the application. The only way to reset the device is to interrupt the power from the source or pull the plug from the electrical outlet. Once the power has been interrupted, the resistive heat source no longer provides heat and permits the entire device to cool prior to resetting.

"This type of dual-function device is especially good for food blenders and food processors," Mr. Wehl says. "By adding a second level of protection, you now are able to protect the consumer, who might try to rectify the problem while the main power switch is still on or the device is plugged into an electrical outlet."

One interesting development informs consumers that a particular safety device is included in their appliances. This is taking place in kettles that include control systems provided by Strix Ltd. (Ronaldsway, Isle of Man, UK). Packaging for kettles from Birming-ham-based Team International carry a hologram label in a prominent position. The hologram indicates that a Strix control system, which complies with British and international safety standards, is included. The hologram is said to be very difficult to duplicate and distribution of the label is controlled by the switch company so only authorized manufacturers can use them. The label is said to be a response to counterfeit or illegal controls.

Many manufacturers strive to meet not just regional, but worldwide test requirements for switches. Amr Khalil, product specialist at Aromat Corporation (New Providence, NJ, U.S.) adds that there has been a greater push to meet European test requirements such as VDE and TUV ratings. His company and parent company Matsushita Electric Works have invested a significant amount of effort to meet these standards. Now, all switches provided by Matsushita Electric Works and its subsidiaries are certified to worldwide standards, including UL, CSA, VDE, TUV, and SEMKO.

One potentially useful standards development is that UL and VDE have agreed to adopt a harmonized standard for switches, and UL has established clear phase-outs for existing UL 1054 standards, about 10 years in the future. Mr. Hugener of Cherry observes: "Over the years, the differences in UL and VDE standards have contributed to some divergence of Cherry's product lines, with certain switches ideal for U.S. applications and other switches ideal for European applications. The upcoming harmonization should enable us to converge these products and offer more globally standardized switches."

Also on the standards front, there is a new version of a regulation, valid in Europe, which describes safety requirements for appliances and their components. "Under this regulation, called EN 60335-1, the appliance industry will be confronted with much sharper regulations concerning flammability of switches, tested by a glow-wire test," observes Anton Hartmann, sales manager of Switches & Controls for Cherry GmbH (Auerbach/Opf, Germany). "Our D4 series does have a recently introduced material that already fulfills the new rules that become effective in 2008. Designing in switches that meet the standards now helps our customers prevent headaches in the future."

Touch Solutions

In touch-panel applications, Marty Hedrich, president and CEO of Monopanel Technologies, Inc. (West Allis, WI, U.S.) reports that the requirements for tactile feel continue. This, he says, is achieved through the use of metal domes or other means of achieving a firm response to switch closure. This would include the use of discrete switches underneath an overlay.

"The improvements in performance, size, and price make it more attractive to embed LEDs in flex membrane switches and achieve the economics and features of both tactile and visual feedback of switch closure," Mr. Hedrich says. For harsh environments, his company's Endura product line uses a patented membrane switch that can be operated through .031 thick aluminum and up to .060 thick polycarbonate. It is specified for such products as commercial washers and dryers, scales, gas dispensing equipment, and other applications with harsh and abusive environments.

One alternative to membrane and mechanical keypad offerings uses piezo technology. Barantec, Inc. (Clifton, NJ, U.S.), a subsidiary of the Baran Group, reports that its patented technology is rugged, with no moving parts to ensure a zero-failure rate. A unit is a totally sealed one-piece construction, allowing it to operate in harsh environments and in high-usage areas. The switch is behind a metal layer. The piezo switch measures force - the actual deflection of the metal. It is not a capacitive switch, which senses a finger on the metal but does not work as well when someone is using gloves.

One principle behind the Baran piezo technology is the assembly of all the necessary components into a single unit (the module), thus eliminating the need for handling every component for each push point manufactured. "Understand that the module is the technology behind all of our products," says Ayal Vogel, president of Barantec. "This makes it very universal and gives the industrial designers the ability to make sexy products without sacrificing any durability. In addition, our switches are non-mechanical and do not require any power. With these switches, the appliance industry benefits from easy cleaning, lower service costs, and reduced maintenance."

Switches and Sensing

Sensors are playing a larger role in appliance switching. Energy efficiency, water conservation, and system performance are driving the increased need to provide feedback for advanced control algorithms, says Mr. Williams of Marquardt Switches. "We have expanded our technology base to include sensor solutions to provide flow, turbidity, pressure, vibration, and other key measurement input," he notes.

One development for vacuum cleaners is an Automatic Speed Adjuster (ASA) from Kurz U.S.A. L.L.C. (Sarasota, FL, U.S.). This monitors vacuum cleaner suction power based on the type of surface being cleaned. Thus, there is less power when vacuuming carpets and more power when vacuuming hard floors, enabling users to clean hard-to-get, deeply embedded dirt in small cracks and gaps. "The ASA consists of a pressure switch mounted on an electronic control," explains Heinz Kutschera, president of Kurz. "It's being used by such companies as Miele, Electrolux, and BSH Bosch und Siemens Hausgeräte."

Therm-O-Disc, Inc., (Mansfield, OH, U.S.) has taken its knowledge of temperature switching and applied it to liquid-level sensing and flow sensing. "Our level sensor uses one or more thermocouples to sense level, and we have developed a flow sensor using a specially packaged thermistor and some proprietary software," says Martin Leslie, product manager. "The effect of both technologies is that we can sense level or flow rate with no moving parts."

The company has also developed products that combine its bimetal thermostats and packaged thermistor probes into one package "to bring added value to customers," Mr. Leslie notes. "We are also in development of a polymer-based product that, instead of switching in response to temperature, switches in response to certain vapor in the air, hence providing a vapor sensor to our customers. All three items are proven technologies right now. We plan to be selling actual products based on these technologies in the near future."

Whether it is new technologies like these or tried-and-true solutions, look to your suppliers to show you how to push the right switch buttons for your appliances.