Teaching old dogs old tricks

[Skogsgurra]

I am now and then involved in activities that are supposed to bring back some of the electrical knowledge and ability to apply that knowledge to everyday situations that the audience hopefully once had. These guys is a mix with some very young, fresh out of school, and then the usual bunch that think that they lost their ability long time ago and now go by feel and routine.
I try to avoid math as much as I can. But have been able to show these guys that they can use math, if needed. A very practical part of a quiz that I am using is attached. What do you old dogs (and not-so-old pups) say?
Answers, reflections, corrections are welcome.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MacGyverS2000]

I could answer the first question without issue, but the rest were so ambiguous I didn't know where to start. I imagine this is aimed at a very specific audience or there is some introductory material not shown. The wording is...a bit stunted, for lack of a better word.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Skogsgurra]

Hmm.. There is no other background than what you learn in basic engineering school. We have done some refreshment of that material, but nothing very deep. You are supposed to observe and ponder. Not get the slide rule out first thing.

What does 'stunted' mean?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MacGyverS2000]

I have assumed "network" in this case means a black box with an input and an output, though that may not be the case.

Even when I zoom in, 3 of the lines look yellow (or a shade of orange). I see black as Channel 0, but where is brown for Channel 1? I have no idea what Channel 1 is actually referring to. And what are the other channels measuring, other point within the network?

I don't like to see graph axes labeled at the bottom of a page... show me volts on the Y-axis and time on the X-axis (and on both graphs, if that is what is appropriate).

Okay, I see a decrease in amplitude as frequency goes up, but is that due to capacitance or inductance? I suppose the "what is the other component" statement is to be taken as there are only two components in the network, so that could be combined with the phase shift to determine the component, I suppose, but it's not specifically stated. Then the next question mentions "the first stage of the network", leading me to believe the network has multiple stages, so I go back to being confused.

I'll confess to not having to worry much about lead/lag, frequency calculations, etc. for nearly 15 years (guess I'm one of those old dogs for these purposes), but this one would have me scratching my head a bit. Maybe that's a good thing, force me to think about it.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Skogsgurra]

One input and nine outputs, to be exact. All black boxes are not created four-poles. Sorry if colours don't come through clearly enough. Placement of scales - sorry again. Can't please all.

What does 'stunt' mean? I am one of those damn furriners, you know.

Gunnar Englund

http://www.gke.org

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[benta]

Mcgyvers, ICL8038 or XR2206?

Benta.

 

[Skogsgurra]

That's a very good question! What is your clue?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Skogsgurra]

Wait - don't spill them, yet!

Gunnar Englund

http://www.gke.org

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[IRstuff]

Dan,

Sounds like your monitor needs to be tweaked, or replaced. The curves, in order, are black, brown, red, orange, yellow, green, blue, violet, gray, turquoise, as advertised.

Gunnar,
The usage of "way" is not a normal for this type of problem; "propagation" would be a more common usage, at least, in the US. Units, when used as part of an adjectival phrase, ought to be singular, i.e., 3300-ohm resistor, just as one would not say, "5-kilometers race," at least, not in the US. Maybe European is different?

The black, input curve doesn't appear to be a clean sinewave, since it looks to have a decidedly "peaked" peak. Is that a symptom of the function generators cited?

TTFN

FAQ731-376

 

[ScottyUK]

Yes, it's a symptom. If it were a Micro$oft product it would be a feature.


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If we learn from our mistakes I'm getting a great education!

 

[zeusfaber]

Question 1b: The only correct answer is "because it is". Perhaps 1a should have been "Do you think this is a ..." (that way, the "why" becomes "why do you think" rather than "why is it")

Question 2: Channel 1 shows a brown(ish) sin(ish) curve. Channel 1 shows the output of the first stage of the network. Channel 1 shows a signal which lags channel 0 a bit with about half the amplitude.

Did you have an assumption that Question 3 applies to the first stage of the network in mind? If so, is it reasonable to assume that the student will have the same assumption in mind?

I think it's this sort of thing that macgyvers2000 meant while talking about ambiguity.

"Stunted" (as in insufficiently grown) is an unusual term to apply to prose. I wonder if it was a typo for "stilted" (meaning that the language does not flow readily) - having said that, the only bit that strikes me as at all deficient in that regard is the second line of the intoduction (which could do with another "the".

A.

 

[Skogsgurra]

"Apart from that, Mrs Lincoln, did you enjoy the play?"

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Skogsgurra]

OK, I got a few comments - but no solutions.

The first answer is that this is not a simulation but a real world recording. The pointed crests of the ch0 trace is typical for analogue function generators. Benta was right when asking 8038 or 2206.

Second question. Ambiguity, yes - perhaps. But if you consider that we are in 'Electronic engineering other topics', you can concentrate on just that. Electronics. Then, the fact that ch1 decreases when frequency goes from around 93 mHz to around 440 mHz points to some sort of a low pass link. A good guess would be 'the output from a low pass filter'.

Third. The hint that a 3300 ohms resistor is involved leaves two choices: either an LR link or an RC link. Making a low pass link out of an L and an R at these frequencies would be next to impossible, so a natural guess is that the other component is a capacitor.

Four. The words 'first stage' reveal that it is something 'multistage' and the fact that 'a resistor' is involved not two or several point to a first order filter between ch0 and ch1*. Finding attenuation at the two frequencies and using the fact that gain is 1 at zero Hz makes a rough Bode plot possible, from which f0 can be read.

Most of the 'old dogs' didn't like this. They thought the task was too complex and too badly defined. One bright youngster said that Bessel functions were way beyond what they were supposed to know about.

My goal with this exercise was to make the group aware that many everyday situations are like this. Ambiguous, badly defined, not complete, sometimes just confusing. I also wanted to show that a 'divide and conquer' strategy, where you analyze in small steps and keep assumptions that are consistent with what you see and know and scrap those that are not, is better than just staring at the situation and saying that it is 'impossible to do anything because we don't understand'. That latter reaction is very common and I think that 'old dogs' can do much better than that.

The rest of the channels? I really didn't ask about them. They are part of the confusion and need not be explained. But it wouldn't be fair not to. The whole network is a chain of RC low pass links without any active bufering between them. The R is 3.3 kohm(s) and the C is 4700 uF.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...