Ohm's Law Problem

I wasn't in any way suggesting that it is a "real world problem." If you imagine I were, you missed my point. I merely used that example because it happened to be true and provides emphasis. The actual point was elsewhere.

It helped to make the point, but wasn't the point.

Now, I know you missed the point. The method illustrated _just happens_ to be what Spice does. In no way is that _why_ I suggested the viewpoint. Again, Spice is providing an example to emphasize the underlying point.

It helps to make the case, it in no way _is_ the case.

I'm gradually becoming more sorry I even brought it up. This is way off the point I was making.

Oh, well.

My reason for even bothering to add more to this is _only_ because of the way you are writing about it, that seems to belittle the idea (and now appears to completely miss the point.) I don't think what others wrote is wrong, or bad, or inappropriate. I only think that there is an underlying concept here that is important and shouldn't be down played.

Spice's approach to solving these problems wasn't an accident and it comes from this 'much wider' view that applies to a LOT more than electronics. It is appropriate to almost any system of diff eq with boundary conditions and that is a very wide field, indeed. But in no way am I arguing against practicality. Don't mistake me on that.

In some ways, this is a continuing conflict in all of the human condition. Many people just want to know what works, right now, here, in this place. And have no interest in going beyond what is right in front of them. That is a very practical stand to take. But It takes nothing away from that practical perspective to also admit that going beyond what is directly in front of you, taking a longer view, is also of some value, too.

I'll stop. I just wasn't prepared to go create a white paper or exhaustive survey on some broad topic. It's just something that has proven useful to me. If others don't see that point, I'm fine accepting it and simply moving on.

My apologies.

Jon

Hi Jon,

My apologies for missing much of your point...

Ah. Well, I was attempting to suggest that if one encountered such a problem in the course of daily events, the most pragmatic approach is probably not the one you used, in my opinion... but there's certainly nothing wrong with it and I recognize there's plenty of value in it in general.

Yeah, I agree and very much recognize that conflict in that it shows up prominently when schools are trying to figure out what to teach -- particularly as technology itself advances so out of necessity some techniques have to be dropped to make up for other, newer techniques that are more in demand in industry. Often the argument does boil down to the balance between educating people for what's in demand today vs. giving them enough background they're be able to understand and create new contributions building upon what's already known. Personally I believe that too many people do lean too heavily towards just "what's needed for today" without enough emphasis on "the longer view," as you say.

---Joel

Guys, it's not that hard:

8.4 = 100 * I + 570 * (I + 0.005) + 240 * (I + 0.010) and solve for I. One equation, one unknown. Bada-bing.

If I was grading this, I'd give credit for the approach but I'd probably subtract points for carrying out the result to an unreasonable number of significant figures.

I3 here is *not* 3.46153846mA, it's 3.5 mA. That's as far as the precision is known; farther than that is just making stuff up.

Not picking on you in particular, pims. It's an all too common practice nowadays, as evidenced by most of the other, similar, answers in the thread.

--
Rich Webb     Norfolk, VA

Ohm's law? I thought that had been repealed ... :-)

Sadly, that's the kind of notion that drives potential EE candidates away, at least from analog. And now we have a serious shortage of those. They think they have to be a rocket scientists to be able to thrive and make money in analog. Which is wrong. I learned the majority of my skills by "winging it". IOW I built RF stuff before I knew squat about any of that. And it actually worked, some still does.

Note to potential candidates: If an author or professor says something like what must have been stipulated in this book, that you must be a top notch network analyst, do not listen. It's much more important to experiment, experiment, experiment, get a "feel" for what works, _then_ dive into the theory. Not the other way around. Just my 2 cents.

Whew. Now I feel better ...

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I always vote for too few analog engineers ;-)

Virtually everything I attack, I have no initial clue about how to make it work. That's what makes it fun ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Indeed! Be "weary".

As a member of the MIT Honors (electrical engineering) VI-B curriculum I had the joy of choosing _extra_ electives, so be _wary_ of courses with elementary in the title, such as "Elementary Number Theory" , I had an "F" at mid-term :-(, "B" at the end... what a ride :-(

Yep. I always prefer to reach in there and find the obvious, and then work outward from there.

I am quite familiar with duality, but I don't find it all that useful in actual practice.

I probably do more "Wye" to "Delta" (and vice versa) transformations if I'm working a difficult network.

I'm a bit of an Algebra nut, so none of this fazes me very much ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Yep. That's the kind of general formula I said later on (in the part you snipped) that can be put together and expanded for general use. I just presented it as quoted to illustrate the logic of derivation.

That's OK. The 9-digit precision is just for illustration. A practice encouraged, in part, by easy access to electronic aids. Still, for a practical design, I'd probably use somewhat more precision than two significant figures. Just how many digits would depend on how the results are to be used.

To determine the operating point of a BJT linear amplifier for example, I'd probably use 3.46mA. If the result is to be used in a few more steps of calculation where errors can become cumulative, I may use 3.4615mA. Where relatively small differences can be important, I may use even more digits.

It is an 8 and a half digit meter.

No, not good. It hurts our economy and there comes a day when you and I and the other guys are pushing daisies. And then?

Same here. Like an injector thingie last year. Works :-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Sure, that's why it takes nine digits to express the reading.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

We will be a watermelon-dominated society, so who will care ?:-)

(:-0) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

The only two values the first digit can have with the others filled up is zero or one. That is only half a digit in meter speak. I'll leave it to you, this time around, to figure out the simple reason why.

Same. I always tell my prospects/customers that, not knowing it's impossible, I've way more chances than the previous half baked attempts...

-- Thanks, Fred.

So... if an Engineer makes $175,000 per year, does she have a 6-digit income or a 5-1/2 digit income?

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Reminiscing over Harry B. Lee I found this...

He was my instructor in passive analysis (1959-1960) when he received the Goodwin Medal. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

--> First Master of Engineering degree awarded (1994)

My undergraduate alma mater (University of Wisconsin - Madison) is always sending me mail, trying to get me to sign up for this

Sounds like a soft-core business degree designed for those who got tired of actual engineering work and wanted to get into management. :-) Of course, tuition is much higher than regular old undergraduates pay...

I'm not planning on taking it... ever.

She has a one and three quarter tenths of a million dollar a year salary.

Here's a question I'd like an honest answer to: I've studied analog design for a long time as a hobby, but I was never able to attend a university program of study for it during my 20s due to a series of illnesses, and having to work hard when I was well enough to stay afloat. I'm now 30, and I'm fortunate to currently be in a stable enough situation to attempt a degree. I love EE, and would like to study it formally, but if the future is truly as bleak for US engineers (particularly ones who who will be at least 35 before they land their first job) I should probably really let that sink in before starting.