Electronics Assembly Knowledge, Vision & Wisdom
Sealed Membrane Switch Mystery
Sealed Membrane Switch Mystery
A factory was building membrane switches but all the switches from units in Denver failed. What was unusual about Denver?
Mysteries of Science
Dr. Gilleo
Mysteries of Science by Dr. Ken Gilleo
Dr. Gilleo is a chemist, inventor and general problem solver. Ken has been tracking industrial forensics and collecting case histories for decades. These cases are taken from the vast world of industry and commercial enterprise.

Check out Dr. Gilleo's eBook, 100 Mysteries Solved by Science. We hope you enjoy these case histories. You need not be an engineer or scientist to understand the problems and appreciate the solutions.
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A factory in Wisconsin was building membrane switches for a new over the counter microwave oven. The first switch design was an unexpected disaster as all the switches failed during testing. Steam from boiling pots on the stove below condensed inside the switches, circuitry inside the switches shorted out as silver ink formed dendrites due to electro-migration

The switch was changed with a new sealed switch design. Two months later another problem surfaced with the sealed switches. Some switches were just too hard to activate. The microwave ovens with the problem were replaced and the units were returned for testing. The switches were tested but the switch actuation force was normal in the test lab in Wisconsin.

Then a surprise, all complaints were from Denver. 

So what was unusual about Denver?

Here's the rest of the story.

Cooking can take longer in Denver since boiling water in Denver isn't as hot as in most other places. Water boils at 202 F instead of 212 F, so it takes 17 minutes to cook a hard-boiled egg.

The mile-high city has lower air pressure because of the higher altitude. If Denver has lower atmospheric pressure, what else does this affect? How about a sealed oven switch? The switches were sealed at normal atmospheric pressure in Wisconsin. When they traveled to Denver, the air sealed inside the switch is at a higher pressure.

The switches expanded and were hard to push. The problem was eventually solved by sealing all but one small corner of the switch that served as a vent hole.

Great scientific solution!
Henry ochoa Fortich
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