Letters 10/21/2010

Oct. 21, 2010
Letters 10/21/2010

A little bit of everything
Readers add their two cents on a variety of subjects. One leaps to the defense of safety expert Lanny Berke while another fills us in on the background of OFDM. And the August winner of the “World’s Smartest Design Engineer” competition lets us know what the Game does for him.

And the winner was . . .
I started playing the game, the “World’s Smartest Design Engineer” (www.smartestengineer.com), simply to check my knowledge and understanding of the engineering topics. I felt comfortable with several of the categories, but quickly found that my knowledge was greatly lacking in others. So, I have found the Game to be not only challenging and entertaining, but also educational. My knowledge of hydraulics and motion control, especially, has increased immensely due to research on the Web to find the answers to the questions in those categories. I’ll continue playing, learning more things along the way, and I’ll also try to catch the players ahead of me. -- James Melton, August winner of the WSDE

Cut Berke some slack
I am amazed at the constant stream of letters criticizing Lanny Berke and his monthly column, “Berke on Safety.” His comments and suggestions are meant to keep manufacturers out of the courts or to help them defend themselves when they do end up in court. You may not like what Mr. Berke suggests you do to minimize your chances of being successfully sued, but he is only trying to help. Some of his examples may seem farfetched or frivolous, but you will spend just as much time preparing to defend a case you consider “frivolous” as for a “serious” one.

I try to educate our new hires by saying anyone can sue us over anything. The real question is: “Can we successfully defend ourselves when we are sued?” Manufacturers can be sued for products behaving exactly as they expected them to. Unfortunately, consumers will get hurt using products, sometimes through their own fault, sometimes because of lack of adequate instructions or warnings, improper safeguards, or unsafe design. Nevertheless, they can sue either way.
Pay heed to Mr. Berke’s comments. They may save you and your company a lot of time and money. I base this opinion on 20 years helping to handle our corporation’s product liability. When we are sued, I do the fact-finding, work with our lawyers, attend the deposition, get deposed, and if necessary, go to court.  -- Willard Sickles

OFDM background
I really appreciated the article on OFDM PLC (“Your Next Network Connection Could be a Powerline,“ Aug. 26 issue). You will probably hear from lots of old EEs about this. Perhaps you are aware that OFDM (though not known by that acronym) goes back a long way. The first commercial use I am aware of was the Collins Radio Kineplex system of the 1950s. The armed forces lifted this principle in the 60s, modified the protocols for star network topology, and called it (TActical Data Information Link) TADIL A or Link 11. It was ideally suited to typical high-frequency radio paths with selective fading and intersymbol interference.

The elegance of OFDM arises from the frequency domain character of “square” pulses of sinusoidal energy. The power spectrum has the form of the sin(f)/f function where there is a maximum at the frequency f0, and periodic zeros at frequencies f0 ± 1/ts, where ts is the time duration of the square pulse. Further, the ideal linear filter for such a pulse is an ideal resonator that integrates signal (and noise) energy for exactly ts seconds, measures the amplitude at t = ts, and dumps or quenches the resonator and integrates during a subsequent symbol. Thus, phase modulated tones (in Kineplex) spaced at frequency intervals of 1/ts and sampled at time intervals of ts are indeed orthogonal because at that instant the energy from all other signal tones is zero. That, of course, is the ideal case of perfect synchronization and no intersymbol multipath interference. One can take this idea and stack (encode) any number of bits of information into each symbol that signal-to-noise will let you get away with. In those days, coding theory was still in its infancy and error detection/correction was practical to implement.

During the mid-1980s while at SRI, I was approached by a Japanese manufacturer of medical electronic-monitoring equipment that proposed a method of central monitoring of ambulatory patients. OFDM came immediately to mind because of its ability to ignore harmonically related interference by synchronizing the signal to the power-line phase. At very low frequencies, the frequency spectrum of energy on a power line is dominated by sharp spikes at precisely 50 or 60-Hz intervals well up into the VLF regime, say, 30 kHz. It seemed that a patient wandering about his or her hospital room or home could wear a small inductively coupled transmitter that could be “picked-up” by the house wiring and received/decoded at a nursing station. I am not aware that anything was done with the idea, but it is not surprising that OFDM with a power-frequency symbol rate eventually found its way into PLC.  --  John MeLoy

Power for the turbines
I was just reading your editorial asking how much power windmills use (“How much power does it take to run a wind turbine,” Aug. 10 issue) and was wondering the same thing when I saw a huge wind farm in Indiana. It was an amazing sight. Giant wind turbines from horizon to horizon and most of the wind turbines were turning, at least on the way to Chicago.

But on the way home, most were not turning, so I stopped and checked one out up close. The things are huge. But on to the reason for my e-mail. Even though the wind turbine was not turning, the transformer was really humming. I could also hear a hydraulic motor/pump unit running and it got me wondering the same question you posed.

The other thing I noticed is that there was no above-ground power grid anywhere in sight. All the wind turbines must be connected by underground conductors which had to cost a fortune to install.
The sight of the wind farm in Indiana is an “out-of-this-world” experience. And people quote all sorts of a large numbers about the power they generate. I want to believe, but no matter how hard I try, I still have my concerns.  -- Jock Stucki

Stick to the engineering
Regarding the article on power and energy (“Power to the People,” Aug. 12), I am concerned about the implicit bias within the text. The big-named but small-minded Center for Energy Policy and the Environment at the Manhattan Institute have well-known, conservative, big-business biases. Their energy-related estimates are only useful as Big Business talking points and should not pollute a technical magazine’s attempts at an article. Stick to what you know, and what we want to know, and stay out of politics.  --  Phil Cassista

As the analysis you mention is cited by Robert Bryce and is based on published operating figures for existing wind and solar-plant installations, I would consider it a valid talking point in a technical publication for engineers who design these devices. It is another way to measure the efficiency of their designs. The wind and solar industry have been remarkably silent on the validity of these values, nor can we find any values they have supplied. As Machine Design Editor Leland Teschler stated in a recent editorial, “Wind boosters open themselves up to skepticism about their industry’s viability when they don’t disclose real figures about the power their turbines generate and consume.” The same is also true for PV plants. — Robert Repas

© 2010 Penton Media, Inc.

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