Ask The Search Engineer 25576

Hey, Search Engineer: Do you know how a Slinky(R) is made? I need to make a similar part out of a brass material.-Richard in Los Angeles

Dear Richard: You're not working with Dean Kamen, are ya? Slinkies^(R) are just flat wound springs, similar to retaining rings or wave springs made by companies like Smalley Steel Ring. They take a round wire (steel, bronze, and Be-Cu) and flatten it to size, then wind it. Maybe they'd be willing to make them for you out of bronze. For more details, the Slinky patent reveals all (US patent 2,415,012).

Mr. Search Engineer, Sir: I'm looking for an electronic fluid level sensor for my design, but my boss is pretty miserly. He's making me stick to a budget of less than five bucks. I was thinking of a float with a magnet attached to a shaft that activates a Hall sensor. But I'm concerned that I will have a corrosion problem, since the device will be subjected to unfiltered water and a max temperature of 100C.-Ron in Phoenix

Dear Ron: We describe this type of design problem as overconstrained. If you decide to go your route, you should take a look at any late-model automotive master cylinder. (You know those Scrooge-like auto engineers!) The float and the plastic tube the cylinder rides in do not corrode and are suitable for underhood temperatures (125C). Alternatively, Motorola makes an electric field imaging device that generates and detects loading of an electric field. This type of device could be used for liquid-level detection as long as the container is non-metallic. The liquid will change the electric field absorption for the electrodes. For finer resolution, analog outputs can be used to interpolate the level between the electrodes.

Greetings, Search Engineer: In one of our designs we use aluminum extrusions that are black anodized to obtain required optical characteristics. However, we find that the parts are fading to a brownish color after exposure to fluorescent light. How can we keep our black parts black?-K.K. in R&D

Dear K.K.: Have you talked to Mick Jagger? Because, bottom line, you got one big problem. Anodizing can fade extremely fast under fluorescent light. The solution to retain the color is to seal the parts. Keep in mind, though, that the seal is softer than the anodized surface. Check out more pointers at www.finishing.com.

Konichiwa, Search Engineer: I work for a manufacturer of plastic film capacitors and am working with the makers of digital tariff meters for auto rickshaws. They're having a problem with RF noise generated in the engine, which interferes with the functioning of a microprocessor in the meter. What capacitor should be used for suppressing the noise?-Tom in Tokyo

Dear Tom: You, me, we all got EMI problems! Your best bet is to attenuate the RF noise at the source. Try using resistor suppression ignition wires and/or resistor spark plugs in the engine.

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