Electronic Design

Bob's Mailbox

Dear Bob:

I was amused once by a professor of history when he made the comment that physicists are unique among the educated.  He stated in jest that no matter how little they know about a given subject, they always have an opinion on it.  Years after hearing this comment I still chuckle over it, but have found it to be true on several occasions.  However, after reading Peter R. Vokac's two letters in your column (June 11, 1992, and December 3, 1992), I am beginning to think that this phenomenon may not be unique to physicists alone.  At first I was hoping Mr. Vokac was just joking, but due to the nature of some of his comments as well as yours, I concluded that he was not.

To begin with, Mr. Vokac seems to be confused with terminology, the first of which are the terms "digital" and "discrete."  Although I have noticed that some electrical engineers tend to use the terms "digital" and "discrete" interchangeably and synonymously, this is not the case from a mathematical point of view.  "Digital" refers to a type of electronic hardware, whereas "discrete" refers to the mathematics that describe the signals processed by that hardware.  Similarly, "analog" refers to a type of electronic hardware, but "linear" and "continuous" refer to the mathematics involved in that signal description.

If these definitions are to be accepted, then Mr. Vokac is certainly confused insofar as his terminology is concerned.  For example, he implies that "time" and "clocks" are synonymous when he said, "Time is digital because all clocks tick."  Just because clocks tick does not mean time is digital or discrete.  Clocks are simply a measuring device, while time is the thing being measured.  Clocks tick because that is the nature of their mechanism; the nature of the mechanism does not necessarily infer anything as to the nature of time.  If Mr. Vokac's statement were true, then a potential difference is analog when measured with a meter using a D'Arsonval movement and "digital" when using a digital meter.  Even an undergraduate in electrical engineering can see the obvious fallacy in this reasoning.

Mr. Vokac did make a valid point when he stated that, "Acoustic waves are digital at the molecular level where they are a sequence of bumpings."  This is true (if we substitute the word "discrete" for the word "digital"), as kinetic theory bears testimony.  Fluids are no different.  However, this is only true on the molecular level.  On the macroscopic level (which is the world we live in), it is often impractical and totally unnecessary to discuss the individual motions of particles that have a population on the order of Avogadro's Number.  Thus, a continuous approach is necessary and extremely helpful.

Mr. Vokac is still further confused by the relationship between mathematics and physical reality.  This was evident when he was discussing photons in the December 3 column.  The notion of wave-particle dualism exists due to our inability to describe the universe properly and completely.  Sometimes it is proper to describe a photon as a discrete particle, as in the photoelectric effect, and sometimes it is proper to describe it as a continuous wave, as in diffraction and interference phenomena (Young's Double Slit Experiment is an excellent example of this).  The description truly depends upon the context of the physical situation.  The universe only provides answers that are as good as the question.  If the question is not complete, the answer will not be complete, either.  This is why the concept of wave-particle dualism exists.

However, quantum mechanics has been a highly successful area of physics, even if the questions that are asked are incomplete.  The laser, elementary particle research, and nuclear weapons are living proof.  It is unfortunate that Mr. Vokac does not find the statistical nature of quantum mechanics a "satisfying solution."  This is also an interesting point.  Mr. Vokac seems to be ready to accept the statistical nature of Kinetic Theory (i.e., acoustical molecular bumping), but unable to accept the statistical nature of quantum mechanics.  It must be noted that the two fields are intimately related and that they are also related to statistical mechanics.  All of these fields have been highly successful and have predicted numerous new phenomena.  Mr. Vokac has unwittingly contradicted himself.

For Mr. Vokac to say that a "new physical theory is just around the corner" is highly debatable.  A new physical theory will in all probability only come into being when our present view of the universe becomes inadequate to describe any new physical phenomena encountered.  Mr. Vokac's proverbial "corner" could be centuries away.

John Lewis, Socorro, N.M.

Thanks for your efforts to critique Mr. Vokac's odd arguments about the "digital world."  I tend to agree with your opinions.  But, hey, I'm a physicist, too!-RAP

Dear Bob:

Peter Vokac's letter was the most fun I've had in a long time except for one thing, it scared me.  He belongs in politics, not electronics.

If he's "looking forward to the first invasion of digital wave-shaping circuitry into those arcane and untrammeled bastions of analog design: Microwave and X-ray," he probably thinks Nyquist is a brand of snack cracker.  He's got the cart before the horse.  If he's working with a top of the line resolution color display, odds are there are already microwave-style transistors in the CRT gun drive circuits.  (Let's see now, I need a high resolution color display to run Spice models to design the drive circuits for my new high-resolution color display to run Spice...)

Later on, I might question him, "If an optical, shadow projection of a rolling wheel in stress-less contact with a rail falls off, does the optical, shadow projection of the derailing train make a sound???"

But the best one was the revelation that photons are digital, but have strange behavior.  (Under his theories, does that mean there are also five other types of photons?)  He must have taken those college physics classes of long ago from Bohr himself.

Please Bob, tell me that he's really you writing under a pseudonym to insert a little levity.  If not, to paraphrase an old English prayer, "Lord preserve me from the wrath of people who 'KNOW...'"

Frank R. Borger, Instrumentation Section Head, Dept. of Radiation Therapy, Michael Reese Medical Center, Chicago, Ill.

Honestly, I did not write Mr. Vokac's letter.  Not even on April 1.-RAP

Dear Bob:

I couldn't resist commenting on your claim that your VWs do not pollute any more than new cars.  Don't think that I am against old cars; the newest car I have ever owned is the '79 VW convertible, which I now drive.  I haven't yet had the bug emission-tested, but my '72 Mercury Cougar produces hydrocarbon and CO numbers very similar to those you reported in your November 12 column.

The problem is that hydrocarbons and carbon monoxide are only part of the story.  They are relatively easy to keep at low levels, as our old cars demonstrate.  The real problem is oxides of nitrogen (NOX).  NOis a real bad guy, producing acid rain, and, by interaction with hydrocarbons, smog and ozone.

When the air/fuel mixture on a car without emission control equipment is adjusted to produce minimum HC and CO emissions, NOX production is maximized.  All that fancy junk on new cars allows them to move off of the NOX peak by adjusting the air fuel mixture, then eliminating the extra HC and CO by "burning" it in the catalytic converter.  Another way to reduce NOproduction is to reduce timing advance, coincidentally reducing the need for anti-knock agents like lead.  The problem is that performance suffers.  So, a bunch more fancy equipment goes into trying to regain the lost performance.

NOX usually isn't tested because it is hard to test, and as long as the car has anti-emission gear in place and operating, and the car is tuned to factory specs (e.g., low timing advance), then low HC and CO measurements indicate low NOX       measurements as well.  NOX is produced mostly under heavy load, not just high rpm, meaning that the test stations would need expensive dynamometers to actually perform the test.  Although I don't know of any states that test for it, the EPA does test NOX on new car designs.

One of my excuses for keeping old cars running is that I do all my own maintenance and older cars are easier to work on.  I never believe anybody that says new cars (even Japanese ones) never need work.  It seems that it is always true "except for just that once or twice."  The parts for older cars are also much less expensive.  My old cars are increasing in value, or at least holding steady, while new ones depreciate.  And I pay less insurance, and no interest on car loans.  But from any environmental standpoint, my argument is:  Look how much energy we save by not building another car, and look how much less junk that is in a landfill.

I have found that not only are old cars easier to diagnose, they also fail more gracefully (being that they're simpler).  Several times I have made an old car limp home where a new one would have simply stopped.  Often, the failure in a new car is traceable to some complex electronic gizmo in the engine compartment.  One day my sister's new-ish Mustang simply stopped running as she was driving along.  After a lot of effort on the mechanic's part (not me), the fault was traced to a 1-in.-square thick film hybrid performing an arcane function in the ignition system.  Upon inspection under a microscope, I found that a hairline crack had developed in one of the conductors.  Naturally, the whole module had already been replaced for $55, and at $40/hour.

VWs are about the simplest auto I have seen.  I have noticed that there are more old VWs than other cars for sale in the local auto trader magazine, even taking into account their initially bigger numbers.  I conclude from this that they are (1) more reliable and/or (2) easier to fix than other cars.  Does your research show that there are fewer of them Found On The Road Dead?

Daniel R. Morris, Project Engineer, Interpoint, Redmond, Wash.

Alas, my Dead Car List does not lead to any useful conclusions about the number of dead cars vs. the quantity of live ones on the road.  And thanks for the explanation about NO.  Most of us weren't aware of that.-RAP

Dear Bob:

Your column of August 20, 1992, titled "What's All This Spreadsheet Stuff, Anyhow? is accurate.  My spreadsheet horror stories come from inspecting financial models of businesses.  I certainly agree that people do not consider the assumptions the model makes, nor worry about risks.  But even worse, the model is often based on getting the right output (profit) and adjusting the available parameters (costs) to achieve the "correct" answer.  What is most appalling is that the people working on the model often fool themselves-a spreadsheet makes changing parameters easy, and after "playing with the numbers" for a couple of weeks often leads to faith in the answers that were the implicit input when the model was created.

My view is that a spreadsheet, like Lotus, is actually a very-high-level programming language.  Unfortunately, many of the people using spreadsheets have never learned to program in any other language.  Classes on spreadsheets cover the mechanics of using the tool and its commands, but never seem to address how to think logically about a problem.  I do not blame the tool as much as the user.  The worst problems with spreadsheets that I have seen are blatant programming errors, some of which have existed in important spreadsheets for a long time before being caught.

David Wilson, Workstation Laboratories, Humboldt, Ariz.

Gee, your insights are good.  We know that people twiddle with a spreadsheet to get an answer they like!-RAP

 

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