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Bench Talk for Design Engineers

Bench Talk


Bench Talk for Design Engineers | The Official Blog of Mouser Electronics

Your Mileage (and Other Things) May Vary Barry Manz


The practice of taking liberties with performance specifications to show a product in its best light is obviously nothing new in the electronics industry, and many others as well. If you’re old enough to remember, the output of stereo amplifiers and receivers was rated as “peak power”, which is typically five or six times higher than RMS power, but for the anointed it certainly makes the amplifier appear to be a real powerhouse. The output power of RF power transistors is even today sometimes specified at a single frequency where it’s highest, even though it falls off below and above it. And so on.

So when Volkswagen took this to a new level by gaming the testing regime to deliver the exceptional fuel economy numbers of their “TDI” diesel powered vehicles, who should be surprised? After all, unless you’re in need of massive low-end torque, fuel economy is the biggest and perhaps only incentive to buy a diesel. As emissions standards are getting tougher and the EPA is trying harder than ever to provide real-world fuel economy numbers for buyers, this may be the death knell for the diesel in America.

Of course, it’s possible to find loopholes in any set of requirements, especially if the holes are as wide as the tunnel. For example, in Europe tests are conducted with everything turned off that’s not necessary to run the vehicle–air conditioning, lights, heated windows, heated seat, radio, etc. they can even make the car lighter by removing roof rails and, incredibly, the passenger-side mirror as well. To be fair, VW is not the only company caught fudging fuel economy numbers, and as Mitsubishi’s latest admissions and Hyundai/Kia’s earlier ones can attest, and all carmakers take steps to ensure that the ratings they provide to the EPA are the best possible. They can drain all the gasoline but a gallon or so from test vehicle, remove all optional equipment, use a lightweight driver, run the test in ideal weather conditions, ramp up the engine speed as slowly as possible to reduce engine RPM, and overinflate tire pressure.

But these are the only instances of specsmanship in the auto industry. As I’ve been a car fan since I could first wield a wrench and afford subscriptions to enthusiast magazines, I’ve seen numerous examples. For example, until very recently manufacturers stated the horsepower of turbocharged four-cylinder and other high-compression engines without mentioning the fact that it can only be achieved using premium fuel. And you’d still be hard-pressed to find this information in the brochure of any model or on manufacturer Web sites, which if present at all are found in the fine print. So unless you’re willing to cough up the extra money for premium, the actual horsepower will be less, sometimes significantly so.

There’s also the issue of acceleration, either 0 to 60 mph or quarter-mile times, which most people probably don’t care about but plenty of others do. It’s safe to say that unless you’re a professional driver you’ll never be able to achieve those numbers no matter how you try. Sure, the published numbers shown in car magazines are great for making comparisons between models of the same type, but not much else. I’m sure these aren’t the only examples of auto industry specsmanship, so as always: caveat emptor.

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Barry Manz is president of Manz Communications, Inc., a technical media relations agency he founded in 1987. He has since worked with more than 100 companies in the RF and microwave, defense, test and measurement, semiconductor, embedded systems, lightwave, and other markets. Barry writes articles for print and online trade publications, as well as white papers, application notes, symposium papers, technical references guides, and Web content. He is also a contributing editor for the Journal of Electronic Defense, editor of Military Microwave Digest, co-founder of MilCOTS Digest magazine, and was editor in chief of Microwaves & RF magazine.

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