Author: badengineer

Normally I am all in favor of, and like, the way that the skeptical community tests some of the unlikely claims of companies and individuals who are trying to sell a product or service to the gullible public. The approach usually has some scientific rigor that easily exposes the flaws, or the hype. Some things, however, can be discounted with just a little engineering common sense.

Take the ADE 651 bomb detector, for instance. This is a device that is currently being used in Iraq and other conflict areas for detecting explosives. It consists of a belt-mounted box and a hand held unit from which a rod protrudes. The rod is free to move horizontally and point to guns and explosives. If this sounds a bit like dowsing, you’re right. But forget about that for a moment. Let’s look at this without preconceived notions, but rather with some engineering common sense.

First, the control module. Into this are fed cards programmer for specific explosive types. Okay, then we need scanning circuitry in the box and a chip or barcode or magnetic strip on the card. The BBC, on a similar unit, found the box to be empty and the cards to have RFID tags similar to the security tags on a CD package. Whether this kind of tag would be enough to change settings is questionable, but even if it could, an empty box can’t read it. First red flag.

Now the hand unit. The rod swings freely with the slightest movement of the operator’s hand. No engineer worth his salt would design a product where the primary indicator is sensitive to how the user holds the thing. Imagine if your GPS were to tell you to turn left one day and the next day tells you to turn right, just because you have a passenger or because it is raining. Second red flag.

Closely following that are the instructions which state that the user must be relaxed and in a good state of mind before using the unit. This is something you will never see in engineering requirements or specifications. Third red flag.

Finally, let’s look at the power source. Oh, wait, there isn’t one! The instructions say that the operator must shuffle his feet to build up the static electricity to operate the device. Even if this could be done reliably, this would only build up a charge in the person. Without a discharge path there is no current and no power. Final (huge) red flag.

So even if you didn’t know that dowsing is a crock, would you buy any of these to protect yourself and others? Of course not. But who is to blame here, the slimy manufacturer or the credulous purchaser? If this was a harmless dowsing rod that entertains a fringe group of believers, I’d say the latter. But people are dying because of these things so I think both are responsible. And even if we say that the buyers were well meaning but ignorant, we would have to question how they could possibly be in that position and not have the sense that almost everything we carry around these days at least needs a battery.

So no scientific testing was really required here. Just some good engineering common sense shows these things to be what they really are: a fraud.

More here: http://en.wikipedia.org/wiki/ADE_651 and here.

Many good engineers pride themselves on their ability to do quick “back of the envelope” calculations that are accurate enough to be used as the basis for some expedient decisions. The ability to do this stems from experience, where rules of thumb and instinct about the numbers are cultivated, and from good engineering fundamentals which provide the engineer with the tools to develop the right approach and process to do the calculation, even if it is a new problem.

What can be difficult is knowing when and how to question yourself.

I recently came upon a paper (fortunately of limited distribution) where the approach, process and calculations were correct, but all the conversions from metric to English were wrong. Seems that 2.45 was used instead of 2.54 for conversion from centimeters to inches. Though it looked like a case of transposition, in fact the author said that he always thought the conversion was the former. And there lies the potential pitfall to the engineer — assuming he is correct because he always did it that way.

It’s not that I am advocating second-guessing yourself all the time, but rather that periodically we all can use a quick check on some of our fundamental constants, rules of thumb, and calculations methods to both shore up our memories and correct bad habits.

It is sort of like the driving tests that this country doesn’t periodically give to established drivers. I was in a car with a middle-aged driver who tailgated, didn’t use signals, and cut people off. When I tried to bring this to his attention (while making sure my seatbelt was on), he replied that he had been driving for thirty years. Yes, I thought, but you’ve been driving badly for all those years. His experience didn’t change the fact that he was dangerous driver.

If we have bad habits in our engineering calculations or processes, they need to be caught and corrected before they become part of our experience and thus “correct” in our minds. As engineers we need to understand the limitations of our human minds (especially, I am sorry to say, as we age) and bolster our memories with the tools of our trade such as handbooks and structured calculation processes. Though it may cost a bit in terms of pride, it shouldn’t. As far as I can see, no engineer should be faulted — by herself or anybody else — for checking their work. And while you’re at it, you might want to check those handbooks and spreadsheets too. Nothing is sacrosanct where good engineering is required, and the guys that wrote that handbook may have had some bad habits too.

What do you think? Have you ever found yourself using the wrong value, equations, or process out of habit? How often do you go back to examine your fundamentals? Drop us a comment.

I made some comments earlier about anecdotes of engineers not accepting the theory of evolution and natural selection (link) and that got me thinking about the engineering process that is, or closely resembles, evolution.

There is a reason we don’t see a half-crocodile, half-duck (the famous crocoduck) in nature – because those two species had a common ancestor millions of years ago and at that point they parted ways and evolved independently into the current two species.  This is analogous to why we don’t see the tail of a Sopwith Camel on an F-16.  They both have tails, but the design of aircraft has evolved over the years so the F-16 has a tail that is appropriate for itself, not some older airplane.

And engineering does the same kind of testing before accepting a new feature or process, just like nature.  A random change in nature is tested by the environment and if beneficial to the individuals, it is more likely to be retained (a greater percentage of the population survive and breed if they have the change) for future generations and slowly the change becomes part of the species.  In engineering, many designs start from a previous, successful design and add such changes that are deemed necessary for the mission, but also that are affordable and have an acceptable risk of failure.  If those changes are successful, then they will be the starting point for the next design.  Hence moving from the Sopwith to the F-16.

Continue reading “Evolution and Engineering” →