Design trends add value to controls & sensors

Merging technologies, standardized packages and vendor partnership ease OEM’s search for DFM solutions. Choosing controls and sensors for your products isn’t an apple vs. orange proposition. Trends in R&D are providing integrated, high-tech solutions for what were once considered low-tech requirements.

Say yours is a low-end, thermostatically controlled appliance. Suppliers are working on offering you cost-efficient, solid-state sensors, replacing inexpensive, but reliable bimetal thermostats.

If your products are mid- to high-end, you can expect trends that will not only affect the marketability of your line, but the very way you do business with your suppliers.

Electromechanical or electronic?

Electronic controls may displace electromechanical ones in higher-rangeĀ appliances, but some suppliers are staking their business on the needs of their low end OEM customers.

Improvements in electromechanical controls come in the manufacturing process,” says Tim Andrews, general manager of Corox Appliance Controls, Mansfield, Ohio. “What we try to introduce in our controls are better materials-plastics that allow you to reach higher temperatures for less cost.

“Our niche is temperature controls. We’ve made smaller infinite switches, allowing a lot of design freedom in the layout of range front backguards. Only three of us in the country make infinite switches for range tops.”

Gary Miller, vice president of research and development for Elmwood Sensors, Pawtucket, R.I., agrees about the importance of serving an OEM’s special needs. His company specializes in thermostats for appliances ranging from coffeemakers to dryers and ranges.

Miller says the need for greater setpoint precision will split the thermostat market into solid-state and bimetal.

The small-appliance market needs a low-cost thermocontrol to justify a product’s $15 price,” Miller continues. They need a component that costs 15 cents or less.

“Another factor that favors the bimetal thermostat is it doesn’t consume energy. It reacts to the heat generated by the appliance. It’s also simple to install and repair.”

Miller acknowledges, however, that as larger appliances go with microprocessor controls, solid-state will start creeping down into the mid-range. Elmwood is preparing to become a player in that arena.

Narrowing the gap

Eaton Corp.’s Controls Division, Carol Stream, Ill., is working to narrow the gap between electronic and electromechanical controls. The company has developed a nickel-wire oven-temperature sensor which it says is more cost effective than what has previously been used in electronic oven thermostats.

The sensor is rated for temperatures between 150 OF and 950 OF, and has a +/- 3 percent temperature change tolerance up to 600 0 and +/- 4 percent to 950 OF.

“The future of electronics is based on an evolutionary process that will go through electronic enhancements of current electromechanical technology,” says Bob Ochoa, national sales manager.

“A good example is what we’ve done with pressure switches in clothes washers. The pressure switch continues to be the sensing device to control water-level in a wash load, but we have a couple units out there that interface with electronics.

“One uses eddy current technology, where you have a non-contact environment within the sensor but you still have the diaphragm to take the actual waterlevel reading. This gives an electronic signal output to the machine that controls other functions, including water valve and timer.”

National Controls Corp., West Chicago, Ill., is taking a similar tack with its line of level controls. Its goal, according to Bob Fabro, sales manager, is to incorporate thermostatic, timing and level control into one electronic unit.

“You may eventually have one controller, and all you’ll have to do is change software,” Fabro predicts. Standard packages

Suppliers contacted by AM agree that standardization is key to the economical replacement of mechanical sensors by solid-state devices.

“We offer the appliance manufacturer a reasonably low-cost, effective means of temperature sensing using an interchangeable mounting,” says Jim Holbrook, director of marketing for ThermO-Disc, Mansfield, Ohio.

“If a manufacturer wants to change their line of dryers from electromechanical to electronic, they don’t have to retool all the drums. They can mount our control package right into the existing space. “

Dan Slocum, business manager for the Phoenix-based Opto Sensor and Commodity Products Division of Motorola, says he is seeing more application-specific packaging for sensors.

“We foresee some highly automatable basic structures that can be flexibly designed into application-specific packaging,” e concludes.

Another company capitalizing on the standardization angle is Appliance Control Technology (ACT), Addison, Ill. According to Bob Vandusen, vice president of marketing, an electromechanical timer in a dishwasher isn’t much different from one used in a clothes washer, a microwave or a range.

“We put all this common circuitry into an application-specific IC, which takes components off the board, improves our costs and increases our throughput, ” Vandusen explains. “That results in lower cost for the appliance manufacturer.” Systems integrators

The economical application of electronic controls and sensors will be greatly enhanced by the trend toward control/sensor integration. Sensor and control manufacturers agree that a closer working relationship between them is necessary to achieve the level of electronic integration they’re targeting.

ACT intends to expand the functions of its basic electronic control, which it considers to be closer to an electromechanical timer, by interfacing it with sensors. Vandusen says ACT will be able to replace electromechanical controls with a sensor that would not only sense water level, but turn off the fill valve as well.

Robertshaw, Richmond, Va, manufactures electronic controls for gas and electric ranges, as well as forĀ refrigerators. Mike Harenchar, vice president of marketing, emphasizes that electronic controls must add value to a product, not just cost.

“They have to do more than say ‘door is ajar, ” he says. “Combine a self-clean control and a deluxe electromechanical The sense to cook potatoes correctly

It takes more than a sense of time and temperature to cook consistently good potatoes-especially if you want to do it automatically. According to Norm Burk, project manager at the American Gas Association Laboratories in Cleveland, the secret lies in high-temperature humidity sensing.

Burk has been working on a way to automate the cooking process so that doneness can be controlled precisely. This could mean a lot to future airline passengers. One company that prepares food en masse for the airlines is interested in automation.

“Right now their process is controlled through time and temperature,” Burk says. If you cook two different-size roasts by the same time and temperature parameters, you get different degrees of doneness.

“As food cooks, moisture is given off . If we can relate (calibrate) the amount of moisture given off and sense changes in that, we can better sense when it is done.”

Although moisture sensors are already used in some microwave ovens, the challenge is to adapt these sensors to convection ranges. Burk says the burning of natural gas in ranges results in the release of moisture, which affects humidity sampling.

Results of his work with these sensors are promising, however.

“We cooked a bunch of potatoes, a couple at a time, that were almost the same size and weight,” he recounts. “First we cooked some potatoes with the moisture sensor controlling the cook cycle. We also monitored the temperature with thermocouples in the potatoes and timed the cycles. The potatoes turned out quite good.

“We tried to duplicate this with the same size potatoes, only this time, we programmed the process by temperature alone, then by temperature and time alone. They didn’t come out as well. “

Burk says it will be a while before high-temperature humidity sensing is adaptable to gas-convection ovens. The effects of extraneous elements have yet to be conquered. F] DFM teams work out sensible sensor solutions

Many of today’s standardized control and sensor solutions are the result of DFM partnerships between OEMs and suppliers. Domer Schubert, business development manager for the Micro Switch Division of Honeywell, Freeport, In., cites the microwave oven as a perfect example.

“When that industry was first formed,” he recalls, “the initial designs didn’t account for how the interlock switches would fit into the latches in the doors. In those days, electromechanical switches had different types of external actuating levers. Finding places to put these switches resulted in a lot of non-standard, high-cost products.

“As that industry matured, we developed a value-added product whereby instead of bolting the switches in place with nuts, screws and washers, they now snap in place on a plastic bracket. The levers were eliminated because the switches can be positioned for actuation directly by the latching mechanism.”

Terry Wellman, product manager for solid-state sensors at Micro Switch, tells about the design challenge provided by a shaft-rotation counter used for a water-fill control circuit.

“It was very difficult to get a sensor mounted close enough to the shaft to pick up a magnetic rotation, ” she says. “The solution was a magnetic-position sensor, which we mounted on a piece of custom-flex circuitry and snapped over the posts. It got the sensor out where it needed to be and it’s a reliable assembly.” Microsensors for appliances: Good things in small packages

There are something like 100 sensing technologies for which there are 10,000 different applications, says Robert Powers, executive director of the Edison Sensor Technology Center in Cleveland. Powers keeps his facilities busy just exploring the chemical and biochemical worlds.

The Edison Center’s purpose is to develop core sensor technologies and invite businesses in many industries to take the R&D ball and run with it.

According to Dr. Powers, much of the technology they’ve developed holds a lot of promise for pioneering appliance manufacturers, particularly with regard to gas sensors.

“Gas sensors used to be fairly large, bulky and expensive and required a lot of power due to their need to operate at high temperatures,” Powers explains’ “Now they’ve shrunk to a size where they require only a few milliwatts of power. And now you can make thousands of them at a time, relatively inexpensively.”

This new generation of sensors is microfabricated. Powers explains that as sensors get smaller, they not only exhibit lower power requirements, but better control and response times, as well.

They are also easy to customize. The basic sensor body can be used to make a host of different types of sensors.

“By taking the same basic construction and putting an organic membrane on it instead of an oxide, you can make the device sensitive to oxidizing gases like chlorine,” Powers continues. “Ninety- nine percent of the sensor’s manufacture is similar. The difference is in what you do to tweak it.”

Which developments hold the most promise for the appliance industry?

  • As part of a range-control system, a sensor could indicate whether gas is on or off or whether the ignitor had ignited.
  • A CO sensor could show if gas weren’t burning completely, or if the unit were putting out too much carbon monoxide.
  • As part of an HVAC system, gas detectors could automatically increase air flow when someone lights a cigarette.

In a similar vein, a “human comfort sensor” has been developed to react as a human would to temperature humidity, radiation and air flow, adjusting the HVAC system for comfort.

  • Corrosion sensors could indicate corrosive conditions in washers and dryers. They could also be used in furnace controls, says Powers, especially high-efficiency gas furnaces which condense out water.
  • Sensors could monitor the bath condition in a high-speed electrogalvanizing line. They could also be used for continuous on-line analysis of chemical processes for finishing appliance parts or electrocoating.

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