Find the voltage at the 2 junctions of a 3 element voltage
divider across a supply voltage of 8.4 volts. The two
junctions of the divider both supply external current of 5mA.
+8.4
|
R1 = 240
|
.---------> 5 mA
|
R2 = 570
|
.---------> 5 mA
|
R3 = 100
|
|
GND
A more basic problem can be solved using Thevenin's
idea with only 2 resistors of say 570 and 240 ohms
and a 6.9 volt supply, and 5mA of current from
the single junction.
+6.9
|
R1 =240
|
.----------> 5 mA
|
R2 =570
|
GND
The output impedance at the junction is the
2 resistors in parallel, or about 169 ohms.
The open circuit voltage ignoring the 5mA is
about 2.044 volts, and so the voltage drop
on R1 (240) is 2.044 - (169 * .005) = 1.2 volts.
But I don't see an easy way to apply Thevenin to
the other case where there are 3 or more resistors
and junctions with known currents from the junctions.
Any ideas?
-Bill
Apply it independently for each 5mA sink, then use superposition.
--
Thanks,
Fred.
Thevenin is a two port, nondependent equivalent, so if you're trying to
express something more multidimensional, it may not be the right approach.
Could you explain a bit more about what you're trying to do?
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"Bill Bowden" <wronga...@att.net> wrote in message
news:5a6868d4-f680-4d3a...@f15g2000yqe.googlegroups.com...
>Ohm's Law Problem:
>
> Find the voltage at the 2 junctions of a 3 element voltage
> divider across a supply voltage of 8.4 volts. The two
> junctions of the divider both supply external current of 5mA.
>
> Vc=+8.4
> |
> R1 = 240
> |
> Va a---------> 5 mA
> |
> R2 = 570
> |
> Vb b---------> 5 mA
> |
> R3 = 100
> |
> |
> Vg GND
><snip>
> Any ideas?
Use nodal analysis.
I've labeled a few things above. Vc=8.4, Vg=0, and you are
interested in Va and Vb, which are the voltages at node a and
node b, respectively. I assume the two 5mA currents are
"outward" due to the arrows showing. It's easier to use
these conductances:
G1 = 1/R1
G2 = 1/R2
G3 = 1/R3
Now, examine node a. It's equation looks like:
(1) Va*(G1+G2) + 5mA = Vb*G2 + Vc*G1
Before you say you may not be able to remember how to do
this, or even understand how I got the above equation, just
stop thinking about voltage _differences_ and think in terms
of superposition (currents flow two ways, at once) instead.
Current flows both inward and outward. The currents outward
flow via the only three paths that exist: R1, R2, and the 5mA
outgoing flow. The currents flowing inward flow via just two
paths (we've already accounted for the outward current, by
definition): R1 and R2.
Equation 1 then must first start with this realization:
"Current outward equals current inward." Which you must
know, since it isn't possible for electrons to pile up in the
node. Current in and current out must indeed match up. So
what is left is to put the currents IN and the currents OUT
onto the two sides.
Equation 1's left side reads like this: "The current that
spills outward from node a is simply Va times the conductance
outward via G1 and G2 (since it flows outward via both, you
add them), plus of course the 5mA that is also flowing
outward." Think of Va, here, as any arbitrary voltage that
mysteriously (without needing to know the surrounding
voltages) _forces_ current outward via R1 and R2. Since the
5mA is _known_ by definition, Va doesn't interact with it. It
just _is_. So just add that current since it is an outward
going one and belongs on this half of the equation.
Equation 1's right side reads like this: "The current that
spills inward into node a is simply Vc times G1 plus Vb times
G2." We've already accounted for the 5ma and it doesn't
spill inward. So it doesn't appear on this side. However,
the surrounding voltages _do_ force a reverse current via
whatever conductances they have available to them. So, of
course, you must include them on the right side.
That explains the first equation you need. Now, examine node
b. It's equation looks like:
(2a) Vb*(G2+G3) + 5mA = Va*G2 + Vg*G3
However, since we know out of hand that Vg=0, we can drop
that term:
(2b) Vb*(G2+G3) + 5mA = Va*G2
Okay, now you have two equations and two unknowns. Solve
them. From equation 2b we have:
(3) Vb = (Va*G2 - 5mA) / (G2+G3)
We can now substitute equation 3 into equation 1:
(4a) Va*(G1+G2)+5mA=G2*(Va*G2-5mA)/(G2+G3)+Vc*G1
(4b) Va*(G1+G2)=Va*G2^2/(G2+G3)-G2*5mA/(G2+G3)+Vc*G1-5mA
(4c) Va*(G1+G2)-Va*G2^2/(G2+G3)=Vc*G1-5mA-G2*5mA/(G2+G3)
(4d) Va*(G1+G2-G2^2/(G2+G3))=Vc*G1-5mA*(1+G2/(G2+G3))
(4e) Va*(G1+G2-G2^2/(G2+G3))=Vc*G1-5mA*(1+G2/(G2+G3))
(4f) Va=(Vc*G1-5mA*(1+G2/(G2+G3)))/(G1+G2-G2^2/(G2+G3))
Having solved for Va, let's compute it. For the values you
gave, I get slightly over Va=5.169V. Plugging that into
equation 3, I get just over Vb=346mV.
Jon
>Ohm's Law Problem:
>
> Find the voltage at the 2 junctions of a 3 element voltage
> divider across a supply voltage of 8.4 volts. The two
> junctions of the divider both supply external current of 5mA.
>
> +8.4
> |
> R1 = 240
> |
> .---------> 5 mA
> |
> R2 = 570
> |
> .---------> 5 mA
> |
> R3 = 100
> |
> |
> GND
>
>
Take the 8.4 volts, 240 ohms, and 5 mA and convert that into a
voltage+impedance. That reduces to 7.2 volts behind 240 ohms.
Add 570 and it looks like 810 ohms, 7.2 volts. Suck 5 mA out of that,
and so on. Just work your way down.
Or do what I increasingly do, sic Spice on it.
John
g1=1/240 g2=1/570 g3=1/100 vc=8.4
gz=g2+g3
va=(vc*g1-5e-3*(1+g2/gz))/(g1+g2-g2^2/gz)
vb=(va*g2-5e-3)/gz
va 5.169230769
vb 0.3461538462
Jon
For the "working man," I'm thinking John's approach or just superposition is
rather easier. E.g., for superposition:
Vb due to 8.4V source: 8.4*100/(100+570+240) = 923mV
Vb due to 5mA flowing out of Vb node: -100*.005*(570+240)/(100+570+240)
= -445mV
Vb due to 5mA flowing out of Va node: -100*.005*240/(100+570+240) = -132mV
Add'em all up, and you get 346mV
For Va, working back up the ladder you get Vb+(.005+Vb/100)*570=5.17V. For
double-checking, you can work from the top down...
8.4-240*(.005+.005+Vb/100)=5.17V as well.
John's approach perhaps has the best combination of "fast" and "lowest chance
of error."
I suppose another approach is to just write a single node voltage equation and
solve for the current in R3: 8.4 = 100*I + 570*(I+.005) +
240)*(I+.005+.005) --> 8.4 = (100+570+240)*I + (570*.005+240*(.005+.005)) =
910*I+5.25 --> I=3.46mA. Hmm, this approach has a lot to recommend it -- it's
easier to see how it would be extended to 4 or 5 or more resistors and
(potentially unequal) currents, and then you just work your way back up after
getting the bottom-most current.
This could be a fun interview question, just to see what approach someone
uses.
---Joel
I think you could convert the current sources to Thevenin sources, and
then use the Millman theorem to get a system of 2 equations for the two
voltages.
>Holy cow, Jon, that's a lot of work you did there... :-)
Nah. It just flows. Done it too many times.
>For the "working man," I'm thinking John's approach or just superposition is
>rather easier. E.g., for superposition:
I used superposition. The concept depends upon it. Just not
the same setup.
The method I illustrated is also how spice sets up its own
solutions. An approach I've come to appreciate. It is
something very hard to confuse and allows a narrow focus upon
each node without consideration of the rest. I happen to
like narrowing down the field of view. Also, it sets up your
matrix beautifully, should you be dealing with something a
little more like a Y or delta or nasty combinations of that
plus not just resistors but currents and voltages all
ascatter. Not having to _think_ about too much at once is
really very nice.
>Vb due to 8.4V source: 8.4*100/(100+570+240) = 923mV
>Vb due to 5mA flowing out of Vb node: -100*.005*(570+240)/(100+570+240)
>= -445mV
>Vb due to 5mA flowing out of Va node: -100*.005*240/(100+570+240) = -132mV
>
>Add'em all up, and you get 346mV
Um. You are _working_, too!!
>For Va, working back up the ladder you get Vb+(.005+Vb/100)*570=5.17V. For
>double-checking, you can work from the top down...
>8.4-240*(.005+.005+Vb/100)=5.17V as well.
>
>John's approach perhaps has the best combination of "fast" and "lowest chance
>of error."
I prefer the view I laid out. I've found it bullet-proof to
missing some detail since all you need to look at are the
paths right in front of your face, one node at a time. I've
made many fewer mistakes that way.
>I suppose another approach is to just write a single node voltage equation and
>solve for the current in R3: 8.4 = 100*I + 570*(I+.005) +
>240)*(I+.005+.005) --> 8.4 = (100+570+240)*I + (570*.005+240*(.005+.005)) =
>910*I+5.25 --> I=3.46mA. Hmm, this approach has a lot to recommend it -- it's
>easier to see how it would be extended to 4 or 5 or more resistors and
>(potentially unequal) currents, and then you just work your way back up after
>getting the bottom-most current.
>
>This could be a fun interview question, just to see what approach someone
>uses.
>
>---Joel
I suppose so! ;)
Just by way of closing this, once I mastered the "spill"
viewpoint, I've found I can mechanically solve quite a wide
variety of problems. It turns out that the exact same
approach works in solving a variety of electric charge and
field questions of rather complex structures (not just
spheres, but those one might find in an electric gun with the
Wehnelt cap and hole, etc. It's a thinking tool that solves
many _fundamental_ problems one may encounter. Of course, it
also works with the infinite resistor problem, too, and
allows an brain-dead easy setup of a solution for it that you
simply cannot fail to get right.
Jon
>Ohm's Law Problem:
>
> Find the voltage at the 2 junctions of a 3 element voltage
> divider across a supply voltage of 8.4 volts. The two
> junctions of the divider both supply external current of 5mA.
>
> V1 +8.4
> |
> R1 = 240
> |
> V2 .---------> 5 mA
> |
> R2 = 570
> |
> V3 .---------> 5 mA
> |
> R3 = 100
> |
> |
> GND
(V1-V2)/R1 = 5mA + (V2-V3/R2
(V2-V3)/R2 = 5mA + V3/R3
V1 is known (8.40V), so this is 2 equations in two unknowns and easily
solved for V2 = 5.169230769 V, V3=0.346153846 V.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
>On Sun, 14 Feb 2010 16:12:04 -0800 (PST), the renowned Bill Bowden
><wronga...@att.net> wrote:
>
>>Ohm's Law Problem:
>>
>> Find the voltage at the 2 junctions of a 3 element voltage
>> divider across a supply voltage of 8.4 volts. The two
>> junctions of the divider both supply external current of 5mA.
>>
>> V1 +8.4
>> |
>> R1 = 240
>> |
>> V2 .---------> 5 mA
>> |
>> R2 = 570
>> |
>> V3 .---------> 5 mA
>> |
>> R3 = 100
>> |
>> |
>> GND
>
>
>
>(V1-V2)/R1 = 5mA + (V2-V3/R2
>(V2-V3)/R2 = 5mA + V3/R3
>
>V1 is known (8.40V), so this is 2 equations in two unknowns and easily
>solved for V2 = 5.169230769 V, V3=0.346153846 V.
The Curse of the Calculator strikes again!
I3 = 3.5 mA, V3 = 0.35 V, and V2 = 5.2 V. Hard to justify more than two
significant figures here.
--
Rich Webb Norfolk, VA
Hey there, we wouldn't want some question of the correct value of the
NINETH digit on the 'ol Agilent 3458A, now would we.. ;-)
Nineth?
Doth thee haveth a nineth digit?
Well, eight and a half, so not directly applicable in this particular
case, but it's not totally ridiculous calculating DC voltages to 10 or
11 places when such tools are at hand. Certainly to 7 places.
Everyone is making it too difficult. Just write it down in sequence,
the answer falls right out...
http://analog-innovations.com/SED/OhmsLaw_SED_JustWriteItDown.pdf
At MIT, I was spared (*) from Guillemin's obtuseness, I had Harry B.
Lee for passive circuit analysis ;-)
(*) I was awarded honors at the end of freshman year and went into
course VI-B (just six of us, made for nice class sizes :-)
...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.
That's the same as what I ended up doing (in the later part of my post),
except that you use "V3/100" rather than just "I" for the current in the
lowest resistor. :-)
> At MIT, I was spared (*) from Guillemin's obtuseness, I had Harry B.
> Lee for passive circuit analysis ;-)
I had a guy who was a pretty talented teacher (he'd won a couple awards for
it, and I found him quite understandable), although he had little if any
real-world design experience.
I'd read some of Guillemin's book, and while I think the guy was pretty darned
sharp, I disagree with his notion that you have to have an incredibly thorough
understanding of network analysis down pat before you can get useful circuit
design or analysis done. Something like his "Introductory Circuit Theory"
strikes me as a good graduate-level course! (Be weary of any book with the
term "introductory" in its title...)
My opinion here is that in the real world your approach or mine (or
superposition if you insist) tends to be rather more productive and insightful
than Jon's somewhat pedantic approach. As soon as you go down the path of,
"well, this is how SPICE sets up the equations," I think you're largely giving
up on gleaning insight directly from the equations themselves and have to run
sweeps or Monte Carlo simulations to get some back.
> (*) I was awarded honors at the end of freshman year and went into
> course VI-B (just six of us, made for nice class sizes :-)
I had a fields & waves professor who thought I was good enough he let me sign
up for a graduate level EM course as a sophomore. Let's just say I was a bit
lost through much of it... :-)
Did you get to do the problems where, with a linear network, you'd transform
it to a "dual" network and then be able to directly compute 1st-order
sensitivities (e.g., dV_output_of_a_small_signal_amp/dC_be or similar -- the
first homework problem is usually
dV_output_of_a_simple_voltage_divider/dR_esistor_in_one_leg since it's easy to
compute and compare directly) by solving for the various node voltages and
loop currents? I thought that was amazingly cool when they taught it to us; I
rather doubt it would have ever occurred to me that you could get such
powerful results with such simple circuit machinations.
---Joel
This calls for a slide rule.
--
Paul Hovnanian pa...@hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.
><snip>
I actually take a very different view. And I'll tell you
why. When the infinite resistor grid problem showed up here
for the first time _I_ saw it (and it has, more than once, as
I participated in at least two such instances), the method
for setting up the closed solution integral as well as
forumlating a trivial numerical solution was obvious to me
_because_ of that "pedantic approach." It provides a very
broadly applicable method that applies across many fields and
provides a useful thinking tool that will serve well no
matter where you find yourself.
None of this takes away from what you are saying, either. I
just don't think you should belittle such a powerful tool.
Jon
"Jon Kirwan" <jo...@infinitefactors.org> wrote in message
news:pe7jn5pnjc9sq679e...@4ax.com...
[infinite resistor problem]
> It provides a very
> broadly applicable method that applies across many fields and
> provides a useful thinking tool that will serve well no
> matter where you find yourself.
Yabbut... few practicing engineers encounter the inifnite resistor problem in
real-world problems, whereas the "three resistors with current draws" is
something much closer to a real-world problem and, in fact, it used to be a
100% real-world problem back when tube radios would have a long, multi-tapped
wirewound resistor that supplied different voltages to different parts of the
circuit (...long before just giving everything its own regulated rail was
viable).
> None of this takes away from what you are saying, either. I
> just don't think you should belittle such a powerful tool.
Oh, I think SPICE is great; I expect that in a given day for, e.g., Jim, well
over 90% of it is spent in SPICE with less than 10% spent doing algebra
long-hand to try to analyze or design circuits. So I certainly wouldn't
suggest colleges drop coverage of the standard node voltage/loop current
matrix approach that's been taught for many decades, rather I'd add emphasis
on not-so-commonly-taught-but-useful concepts such as inverted poles and
zeroes that are quite helpful when resorting to long-hand algebra. (And I'd
find the time to teach this in that these days in a circuirt analysis class
you're not going to have to sit there and eliminate variables in a set of
simultaneous equations one by one when any decent calculator today will solve
for all the unknowns in well under a second.)
---Joel
Not having the benefit of a formal training in electronics, I'd
solve the problem by this method or some other approach using the
same method of logical derivation.
I1 = I2 + 5mA = I3 + 10mA
I3 = (8.4-I1*R1-I2*R2)/R3
= (8.4 - (I3+10mA)*R1 - (I3+5mA)*R2)/R3
I3*R3 = 8.4 - (I3+10mA)*R1 - (I3+5mA)*R2
= 8.4 - I3*R1 - 10mA*R1 - I3*R2 - 5mA*R2
I3*(R3+R1+R2) = 8.4 - 10mA*R1 - 5mA*R2
I3*910 = 8.4 - 2.4 - 2.85 = 3.15
I3 = 3.15/910 = 3.46153846mA
I1 = 13.46153846mA
I2 = 8.46153846mA
The voltages at the two tap points come by subtracting the
voltage drops across R1 and R2.
Upper tap = 5.1692307696V
Lower tap = 0.3461538474V, also = I3*R3
Variations to this method, but using the same logic, would be to
derive one of the unknown voltages first instead of I3.
A general formula for any values of "external curents" and any
resistance could be composed by using variables instead of
numerical values.
This approach may be cumbersome, plodding and mechanical, but it
does the job without relying on any established theorem except
Ohm's law, simple arithmetic and logical thinking.
It can also be expanded for any number of resistors and tapped
currents.
The word is Ninth. And no, that meter doesn't have that many either.
>"Jon Kirwan" <jo...@infinitefactors.org> wrote in message
>news:pe7jn5pnjc9sq679e...@4ax.com...
>[infinite resistor problem]
>> It provides a very
>> broadly applicable method that applies across many fields and
>> provides a useful thinking tool that will serve well no
>> matter where you find yourself.
>
>Yabbut... few practicing engineers encounter the inifnite resistor problem in
>real-world problems, whereas the "three resistors with current draws" is
>something much closer to a real-world problem and, in fact, it used to be a
>100% real-world problem back when tube radios would have a long, multi-tapped
>wirewound resistor that supplied different voltages to different parts of the
>circuit (...long before just giving everything its own regulated rail was
>viable).
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.
>> None of this takes away from what you are saying, either. I
>> just don't think you should belittle such a powerful tool.
>
>Oh, I think SPICE is great;
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 expect that in a given day for, e.g., Jim, well
>over 90% of it is spent in SPICE with less than 10% spent doing algebra
>long-hand to try to analyze or design circuits.
I'm gradually becoming more sorry I even brought it up. This
is way off the point I was making.
>So I certainly wouldn't
>suggest colleges drop coverage of the standard node voltage/loop current
>matrix approach that's been taught for many decades, rather I'd add emphasis
>on not-so-commonly-taught-but-useful concepts such as inverted poles and
>zeroes that are quite helpful when resorting to long-hand algebra. (And I'd
>find the time to teach this in that these days in a circuirt analysis class
>you're not going to have to sit there and eliminate variables in a set of
>simultaneous equations one by one when any decent calculator today will solve
>for all the unknowns in well under a second.)
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
My apologies for missing much of your point...
"Jon Kirwan" <jo...@infinitefactors.org> wrote in message
news:bfajn5tapei1s9ija...@4ax.com...
> 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.)
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.
> 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.
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
Ohm's law? I thought that had been repealed ... :-)
> That's the same as what I ended up doing (in the later part of my post),
> except that you use "V3/100" rather than just "I" for the current in the
> lowest resistor. :-)
>
>> At MIT, I was spared (*) from Guillemin's obtuseness, I had Harry B.
>> Lee for passive circuit analysis ;-)
>
> I had a guy who was a pretty talented teacher (he'd won a couple awards
> for it, and I found him quite understandable), although he had little if
> any real-world design experience.
>
> I'd read some of Guillemin's book, and while I think the guy was pretty
> darned sharp, I disagree with his notion that you have to have an
> incredibly thorough understanding of network analysis down pat before
> you can get useful circuit design or analysis done. ...
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.
http://www.eefocus.com/data/myspace/3/17997//blog/2a65afe9.jpg
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.
>I1 = I2 + 5mA = I3 + 10mA
>
>I3 = (8.4-I1*R1-I2*R2)/R3
>
>= (8.4 - (I3+10mA)*R1 - (I3+5mA)*R2)/R3
>
>I3*R3 = 8.4 - (I3+10mA)*R1 - (I3+5mA)*R2
>
>= 8.4 - I3*R1 - 10mA*R1 - I3*R2 - 5mA*R2
>
>I3*(R3+R1+R2) = 8.4 - 10mA*R1 - 5mA*R2
>
>I3*910 = 8.4 - 2.4 - 2.85 = 3.15
>
>I3 = 3.15/910 = 3.46153846mA
>
>I1 = 13.46153846mA
>
>I2 = 8.46153846mA
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.
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" <To-Email-Use-Th...@My-Web-Site.com> wrote in
>message news:11sin51vdubl64ouh...@4ax.com...
>> Everyone is making it too difficult. Just write it down in sequence,
>> the answer falls right out...
>> http://analog-innovations.com/SED/OhmsLaw_SED_JustWriteItDown.pdf
>
>That's the same as what I ended up doing (in the later part of my post),
>except that you use "V3/100" rather than just "I" for the current in the
>lowest resistor. :-)
>
>> At MIT, I was spared (*) from Guillemin's obtuseness, I had Harry B.
>> Lee for passive circuit analysis ;-)
>
>I had a guy who was a pretty talented teacher (he'd won a couple awards for
>it, and I found him quite understandable), although he had little if any
>real-world design experience.
>
>I'd read some of Guillemin's book, and while I think the guy was pretty darned
>sharp, I disagree with his notion that you have to have an incredibly thorough
>understanding of network analysis down pat before you can get useful circuit
>design or analysis done. Something like his "Introductory Circuit Theory"
>strikes me as a good graduate-level course! (Be weary of any book with the
>term "introductory" in its title...)
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 :-(
>
>My opinion here is that in the real world your approach or mine (or
>superposition if you insist) tends to be rather more productive and insightful
>than Jon's somewhat pedantic approach. As soon as you go down the path of,
>"well, this is how SPICE sets up the equations," I think you're largely giving
>up on gleaning insight directly from the equations themselves and have to run
>sweeps or Monte Carlo simulations to get some back.
Yep. I always prefer to reach in there and find the obvious, and then
work outward from there.
>
>> (*) I was awarded honors at the end of freshman year and went into
>> course VI-B (just six of us, made for nice class sizes :-)
>
>I had a fields & waves professor who thought I was good enough he let me sign
>up for a graduate level EM course as a sophomore. Let's just say I was a bit
>lost through much of it... :-)
>
>Did you get to do the problems where, with a linear network, you'd transform
>it to a "dual" network and then be able to directly compute 1st-order
>sensitivities (e.g., dV_output_of_a_small_signal_amp/dC_be or similar -- the
>first homework problem is usually
>dV_output_of_a_simple_voltage_divider/dR_esistor_in_one_leg since it's easy to
>compute and compare directly) by solving for the various node voltages and
>loop currents? I thought that was amazingly cool when they taught it to us; I
>rather doubt it would have ever occurred to me that you could get such
>powerful results with such simple circuit machinations.
>
>---Joel
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 ;-)
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.
>
>> I1 = I2 + 5mA = I3 + 10mA
>>
>> I3 = (8.4-I1*R1-I2*R2)/R3
>>
>> = (8.4 - (I3+10mA)*R1 - (I3+5mA)*R2)/R3
>>
>> I3*R3 = 8.4 - (I3+10mA)*R1 - (I3+5mA)*R2
>>
>> = 8.4 - I3*R1 - 10mA*R1 - I3*R2 - 5mA*R2
>>
>> I3*(R3+R1+R2) = 8.4 - 10mA*R1 - 5mA*R2
>>
>> I3*910 = 8.4 - 2.4 - 2.85 = 3.15
>>
>> I3 = 3.15/910 = 3.46153846mA
>>
>> I1 = 13.46153846mA
>>
>> I2 = 8.46153846mA
>
> 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.
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.
Sure, that's why it takes nine digits to express the reading.
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?
> Virtually everything I attack, I have no initial clue about how to
> make it work. That's what makes it fun ;-)
>
Same here. Like an injector thingie last year. Works :-)
We will be a watermelon-dominated society, so who will care ?:-)
>
>
>> Virtually everything I attack, I have no initial clue about how to
>> make it work. That's what makes it fun ;-)
>>
>
>Same here. Like an injector thingie last year. Works :-)
(:-0)
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?
Reminiscing over Harry B. Lee I found this...
http://www.eecs.mit.edu/facts.html
He was my instructor in passive analysis (1959-1960) when he received
the Goodwin Medal.
--> 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
(http://mepp.engr.wisc.edu/). 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.
>On Mon, 15 Feb 2010 15:02:09 -0800, the renowned life imitates life
><past...@thebarattheendoftheuniverse.org> wrote:
>
>>
>> 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.
>
>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
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.
You'll never learn much about circuit design in a course.
You'll learn some useful fundamentals.
But to be a circuit designer take those fundamentals, and a compendium
of circuits, like AoE, and ANALYZE them. (Be dubious of the
explanations in books). UNDERSTAND WHY they work. THEN you can be a
designer.
I was tinkering with circuits (and FLAMING many) for years before I
went off to MIT. Now I was lucky, landing at Motorola just at the
bare beginnings of integrated circuits.
I still learn something new every day. When that stops hopefully my
heart will stop at the same time ;-)
For a good analog guy it does not look bleak at all. But as Jim pointed
out you don't really learn much about real design in courses, you've got
to do that on your own. The reason why I did my masters was so I'd have
the degree in my hands. The only times I ever needed it was for visas
from governments etc. Nobody else ever asked about it.
How did I learn design? Mostly through the ARRL Handbook, cuts, bruises
and umpteen spools of solder :-)
The future isn't bleak at all, IMO; electrical engineering jobs will continue
to pay well above average for the foreseeable future, even if the jobs do
become scarcer in the U.S.
What kind of electrical engineering would you like to do? There are some
areas where, OK, you really do need to be well-above-average in your intellect
to make a go of things (people like Ulrich Rohde or Charles Wenzel definitely
don't play with kids' gloves), but I'm convinced that for anybody who manages
to make it through college with decent grades and a good understanding of what
they were taught, your ultimate limitations usually tend to be largely
self-imposed based on how much time and effort you're willing and able to put
into self-study rather than your innate abilities.
I would suggest that you take a few digital logic classes and a few
programming courses -- there are TONS of jobs out there for anyone who can
manage to write a little C code for a microcontroller or a little Verilog for
an FPGA, and many of those jobs are fundamentally pretty easy; they can tide
you over while you're figuring out what you really want to do and find
yourself a job doing it.
Objectively you may well be at a disadvantage from the twenty-somethings
graduating with their BSEEs today, but keep in mind that of those kids, a very
large percentage view engineering as just a 9-5 job and will never expend much
if any effort outside of work to improve their skills. Your years of having
electronics as a hobby will give you a leg-up here.
---Joel
>For a good analog guy it does not look bleak at all. But as Jim pointed
>out you don't really learn much about real design in courses, you've got
>to do that on your own. The reason why I did my masters was so I'd have
>the degree in my hands. The only times I ever needed it was for visas
>from governments etc. Nobody else ever asked about it.
>
>How did I learn design? Mostly through the ARRL Handbook, cuts, bruises
>and umpteen spools of solder :-)
I just put the empty of my first spool of solder I used in RST
Engineering in a jewel window case on the wall. It was on my very
first RST project in 1973 and I opened my second one-pound spool on
the replacement for that first product about a year ago. Of course, I
may have used bits and pieces of other spools from time to time, but
the date I wrote on that first spool is still valid ... Thanksgiving
Day, 1973.
As my brother the football star (and PhD economist) once noted,
"Damned few like us, and none to replace us."
Jim
It's much more fun to just built it and measure it:
http://www.eevblog.com/2009/08/15/eevblog-25-the-infinite-resistor-puzzle/
Dave.
--
================================================
Check out my Electronics Engineering Video Blog & Podcast:
http://www.eevblog.com
So, five equations with five unknowns--can be done by hand, but it's
easiest to use a linear algebra program like Octave (or Matlab
if you have extra cash and don't have Octave). With little practice
it's trivial to just write out the matrices, but for completeness
here's how to do it systematically.
We gather coefficients for each unknown in the respective
column ordered as [i1 i2 i3 V1 V2], and move the free terms to the RHS:
240*i1 + 0 + 0 + V1 +0 = 8.4
1*i1 - 1*i2 + 0 + 0 +0 = .005
0 + 1*i2 -1*i3 + 0 +0 = .005
0 + 0 +100*i3 + 0 -V2 = 0
0 + 570*i2 + 0 - V1 +V2 = 0
From this, it's clear that it is the linear system of equations A*x=B,
where x is the vector of unknowns [i1 i2 i3 V1 V2], and
A=[240 0 0 1 0
1 -1 0 0 0
0 1 -1 0 0
0 0 100 0 -1
0 570 0 -1 1 ]
B=[ 8.40000 .005 .005 0 0]'
and solve simply as a set of linear equations, using the command A\B
resulting in:
0.0134615
0.0084615
0.0034615
5.1692308
0.3461538
again, these are the three current i1, i2 and i3, and two voltages, V1
and V2. The result is of course the same as everyone else, V1=5.169V
and V2=0.346V.
><snip>
>It's much more fun to just built it and measure it:
>http://www.eevblog.com/2009/08/15/eevblog-25-the-infinite-resistor-puzzle/
I saw it, Dave! :) And enjoyed very much the time you spend
there.
Of course, you are a very special person. Not many would
just jump in like that and I very much respect what you did
and what you offered to others in preparing the video, as
well. It was (and is) a generous gesture, well above par.
Jon
><snip>
>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.
It's hard for most of us to get a feel for what works without
first having some idea of what to expect. Theory is primary
to interpreting and understanding experimental result.
What isn't known through theory defines the word 'random.'
Jon
Yes, that makes sense, thanks. But the trick is finding the most
useful equations. I tend to start with less useful stuff like
VR1+VR2+VR3 = 8.4 and then substitute currents for voltages like (IR1
* 240) +(IR2 * 570) +(IR3 * 100) = 8.4
which ends up with 3 unknowns and needs a couple sheets of paper to
figure out.
But, I misstated the current flow direction which should have been the
other way. I get confused with source and sink currents and think of
current going from the negative point to the positive, while others
think the other way. The circuit has 15mA in the 100 ohm resistor for
a voltage of 1.5 at V3 and 10mA in the 570 resistor for a voltage of
5.7+1.5 = 7.2 volts at V2 and the last 5mA goes into the 240 resistor
for a voltage drop of 1.2. All equals 8.4
So, using your idea with the current going the other way,
(V1-V2)/R1 = (V2-V3/R2) - .005
(V2-V3)/R2 = V3/R3 - .005
V1-V2 = R1*((V2-V3/R2) -.005)
V2-V3 = R2*(V3/R3 - .005)
V2 = R2 * (V3/R3 - .005) + V3
( R2 * (V3/R3 - .005) + V3) = R2*(V3/R3 - .005) +V3
R2*V3 / R3 - 2.85 +V3 = R2*(V3/R3 - .005) +V3
(570V3/ 100) - 2.85 = 570* (V3/100 -.005)
5.7V3 - 2.85 = 5.7V3 - 2.85
0V3 -2.85 = -285
And so... 0 = 0 , which doesn't say much.
It should be V3 = 1.5
What did I do wrong? I think I forgot the 8.4 volt known supply
voltage which
should be in here somewhere? I'll look at it again tomorrow.
-Bill
You never substituted your equation for V2 into the preceeding equation
(V1-V2=R1*...) -- you just took your equation for V2 and shuffled both sides
around until you got 0=0! (Effectively you had one equation but two unknowns
still -- V2 and V3 -- so the "0=0" tells you that there are infinitely many
values of V2 and V3 that satisfy the equation. You need the additional
constraint of the other equation to obtain a unique solution.)
---Joel
>On Mon, 15 Feb 2010 13:29:30 -0800, Joerg
As yet unobserved.
That would be the professor's thought process. To us back then things we
didn't understand were not random at all. For example, you simply "knew"
that the Q of a power matching network had to be at least 10 or you'd
get into EMI troubles. Or that grid-bias tube stages were way more
stable by nature. Or that certain modes of operation in a transistor
could lead to a phssst ... *BANG* (later I learned about the concept of
a SOA), and so on.
If it was all random we'd have had much more failing parts and homebrew
devices, but we didn't.
>Jon Kirwan wrote:
>> On Mon, 15 Feb 2010 13:29:30 -0800, Joerg
>> <inv...@invalid.invalid> wrote:
>>
>>> <snip>
>>> 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.
>>
>> It's hard for most of us to get a feel for what works without
>> first having some idea of what to expect. Theory is primary
>> to interpreting and understanding experimental result.
>>
>> What isn't known through theory defines the word 'random.'
>>
>
>That would be the professor's thought process. To us back then things we
>didn't understand were not random at all. For example, you simply "knew"
>that the Q of a power matching network had to be at least 10 or you'd
>get into EMI troubles. Or that grid-bias tube stages were way more
>stable by nature. Or that certain modes of operation in a transistor
>could lead to a phssst ... *BANG* (later I learned about the concept of
>a SOA), and so on.
>
>If it was all random we'd have had much more failing parts and homebrew
>devices, but we didn't.
"phssst ... *BANG*" - Joerg "Failure Noise du Jour" Schulze-Clewing
Some engineering is empirical, based on experience, experiment, and
instinct. Just because there's no effective theory doesn't mean we
can't design things that work.
The best way to get a feel for what works is to build things. Most
good electronics designers did that when they were fairly young,
before they understood much theory.
John
Actually back then I did more with tubes, because they were essentially
free. Then the failures sounded more like this:
... tck ....... tck .... tck .. tck .. t .. t ..TICK ... pheeeooouu ...
*POF* ... followed by the sound of falling glass pieces.
I've made plates sag, but never blew any glass.
Bitrex,
Do you have a degree presently? Did you get another degree back in
the deeps of time? If so, then go for a masters in EE. Easier, and
more fun!
Charlie
>
>I've made plates sag, but never blew any glass.
>
> ...Jim Thompson
I ran an 807 (a 1625, actually, an 807 with a 12 volt filament) to the
point where the glass sucked in on itself to make a VERY skinny tube,
but it never cracked.
Jim
That is because you were not a ham radio operator on a tight budget. We
had glass turning mildly liquid, being sucked in and ending up snug on
the plates. That was the time to turn off the rig. A few seconds more in
transmit and there'd be a loud bang.
I knew to back off on the bias when the plates turned cherry red ;-)
Had nothing to do with bias. We had "dynamic bias", meaning bias was
only applied when a drive signal was detected by a Ge diode and
transistor. Else the tube consumption per year would reach fiscally
unfathomable levels, at least for a student.
Problem was that we squeezed them out real hard. For example an amp with
five H-deflection tubes for color TVs delivering a sustained 1200 watts
of raw RF output power. No joke, this was measured with a calibrated
Bird wattmeter and was legit back then in Germany. It blew up my
antennas numerous times. The loudest bang was a balun where the T200
Amidon core was literally gone afterwards. Shoulda stacked two cores but
only had the money for one ...
I1 V1 +8.4
|
R1 = 240
|
V2 .---------> 5 mA current source I2
|
R2 = 570
|
V3 .---------> 5 mA current source I3
|
R3 = 100
|
|
GND
By solving for the current into V1, you will have enough information to
solve for the voltage drops.
The current into V1 can be found by using the substitution method for
simultaneous equations.
#1 The voltage across R3 = Ir3*R3
#2 The voltage across R2 = (Ir3+I3)R2
#3 The voltage across R1 = (Ir3+I3+I2)R1
The sum of the resistor voltages = 8.4 volts therefore -
#4 Ir3*R3 + (Ir3+I3)R2 + (Ir3+I3+I2)R1 = 8.4
And the total current into V1 is
#5 I1 = Ir3+I2+I3
Solve Eq#5 for IR3
#6 Ir3 = I1-I2-I3
Substitute equation #6 for Ir3 into Eq#4
#4 Ir3*R3 + (Ir3+I3)R2 + (Ir3+I3+I2)R1 = 8.4v
#7 (I1-I2-I3)R3 + (I1-I2-I3+I3)R2 + (I1-I2-I3+I3+I2)R1 = 8.4v
Simplifiy #7
#8 (I1-I2-I3)R3 + (I1-I2)R2 + (I1)R1 = 8.4v
Carry out the multiplication indicated
#9 (R3I1-R3I2-R3I3) + (R2I1-R2I2) + (R1I1) = 8.4v
Move all I1's to the left and everything else to the right
#10 R3I1+R2I1+R1I1 = 8.4v +R3I2+R3I3 +R2I2
Factor out I1
#12 I1(R3+R2+R1) = 8.4+R3I2+R3I3+R2I2
Divide by (R3+R2+R1)
#13 I1 = 8.4+R3I2+R3I3+R2I2 / R3+R2+R1
Seeing as I1 = I2 I can simplify this to
#14 I1 = 8.4+.005(2R3+R2) / 910
I1 = 8.4 + 3.85 / 910
I1 = 0.0134615384615384615384615384615385
Now that the current into V1 is known, the voltages can be found
The current through R3 is I1-10ma or 0.00346 and the voltage across R3 = V3
= .346
The current through R2 is I1-5ma or 0.00846 and the voltage across R2 is
4.823 which makes the voltage at V2 = 5.169
The Haig Dimple whisky bottle looks like a 6146 or an EL 500
after a contest.
Been there, tried that.
--
Tauno Voipio, OH2UG (for nearly 50 years)
tauno voipio (at) iki fi
De Thevenin works also here:
1. Cut the circuit below the upper 5 mA drain. The
power supply and the top resistor with the drain
form a new supply with an EMF of 8.4 V - 5 mA * 240 Ohms.
2. Perform the same operation with the lower drain.
The EMF of step 1 will be dropped by 5 mA to 240 + 570 Ohms,
and the internal resistance of the new supply is 240 + 570 Ohms.
3. Connect the bottom resistor to the supply of step 2
and solve your result.
The current drains have been marked as constant-current
elements, so their infinite impedance does not enter the impedances.
--
Tauno Voipio
I think a lot of people missed bits of the thread, since I think we've seen
pretty much each solution repeated at least once now.
Wow, I've never made a 6146 suck in its glass. I had the well past
cherry-red though.
you is right again Jim !!
>Jon Kirwan wrote:
>> On Mon, 15 Feb 2010 13:29:30 -0800, Joerg
>> <inv...@invalid.invalid> wrote:
>>
>>> <snip>
>>> 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.
>>
>> It's hard for most of us to get a feel for what works without
>> first having some idea of what to expect. Theory is primary
>> to interpreting and understanding experimental result.
>>
>> What isn't known through theory defines the word 'random.'
>
>That would be the professor's thought process. To us back then things we
>didn't understand were not random at all. For example, you simply "knew"
>that the Q of a power matching network had to be at least 10 or you'd
>get into EMI troubles. Or that grid-bias tube stages were way more
>stable by nature. Or that certain modes of operation in a transistor
>could lead to a phssst ... *BANG* (later I learned about the concept of
>a SOA), and so on.
I think you missed my meaning. It's not that theory must
exist for the observation itself. It's that theory is
primary to interpreting and understanding experimental
results.
I've used the concept of a small-angle pendulum swing here,
before. I added then the point about "observing"; that the
period itself, when better timing becomes available to notice
(itself, depending upon prior theory), is not well-enough
predicted. That's an example of interpreting and
understanding experimental results.
What remains (let's say, the idea that the diameter of the
hole and the different diameter of the pin must be accounted
in some way) is consistent -- at that moment -- with the idea
of 'random.' The values may then be subjected to _other_
theory, the idea of Poisson events and its integral (Gaussian
distribution) to see if the distribution has a skew to it for
which some rule of thumb might then be applied, though
otherwise ignorantly until better theory is developed. No
one is prevented by what I wrote from accounting for an issue
by making up rules that "seem to work until something better
comes along." A bias, or skew, or some other element can
certainly be found.
But take note, using _other_ theory to do so and inform that
choice.
Your example takes place amidst a great deal of existing
theory of one kind or another, as well. All of which helps
to inform some rule of thumb, as well. Which makes the point
well.
To strip away all of the veneer of cultural training, imagine
a neanderthal posed along a mountain ridge, looking into the
distance at a slightly curving horizon. Without any concept
of "sphere" in mind. With that theory firmly held, _we_ are
_able_ to "observe" that curve and adduce it to a spherical
Earth 'theory.' We can "see" it. However, the neanderthal
probably wouldn't have any way of even noticing the effect.
I might argue that theory not only informs observation, in
many regards the lack of it prevents such observation from
even taking place.
Now, let's add a "theory of a flat world surface" to this
neanderthal's mind. Now, the neanderthal _can_ observe the
curve, because it _differs_ from existing theory. And might
even be able to formulate some rule of thumb about the
deviation observed vs relative height on a mountain, perhaps.
But again, observation through theory.
>If it was all random we'd have had much more failing parts and homebrew
>devices, but we didn't.
Well, I hope the point I was making is clearer. Or not. ;)
Jon
I am lazy... I will spend hours finding the easiest way :-)
I drive my wife bonkers... she'll ask me to fix something, I'll study
it for a week or two, then fix it... click... click... click... in 10
minutes... I keep her away from knives ;-)
But she's ultimately always happy... I can cut up a cabinet, change
door placements, etc., and you'd never know it from the original.
Ok, but: Lets say the guy with the pendulum never really had a chance to
visit a school, very common in medieval days. But he wants to make
clocks. Good clocks. So he might decide to conduct numerous long term
experiments to see which pendulum works best without actually fully
understanding why it does. IOW, not having a grasp on the theory does
not preclude him from making clocks of superb quality and consequently a
nice chunk of money.
> Your example takes place amidst a great deal of existing
> theory of one kind or another, as well. All of which helps
> to inform some rule of thumb, as well. Which makes the point
> well.
>
> To strip away all of the veneer of cultural training, imagine
> a neanderthal posed along a mountain ridge, looking into the
> distance at a slightly curving horizon. Without any concept
> of "sphere" in mind. With that theory firmly held, _we_ are
> _able_ to "observe" that curve and adduce it to a spherical
> Earth 'theory.' We can "see" it. However, the neanderthal
> probably wouldn't have any way of even noticing the effect.
>
Or he does notice, starts walking up to the curved horizon and the dang
thang keeps moving away from him. Hence, the horizon must be afraid of
him :-)
> I might argue that theory not only informs observation, in
> many regards the lack of it prevents such observation from
> even taking place.
>
True.
> Now, let's add a "theory of a flat world surface" to this
> neanderthal's mind. Now, the neanderthal _can_ observe the
> curve, because it _differs_ from existing theory. And might
> even be able to formulate some rule of thumb about the
> deviation observed vs relative height on a mountain, perhaps.
>
> But again, observation through theory.
>
Or he might decide "Ah, what the heck, let's get something to eat" :-)
>> If it was all random we'd have had much more failing parts and homebrew
>> devices, but we didn't.
>
> Well, I hope the point I was making is clearer. Or not. ;)
>
There are two ways to arrive at good product. Theoretical and empirical,
or a combination thereof. I've heard many old masters respond to
questions "Well, that's just how it is" and these guys were real masters
in their profession.
I grew up in medical ultrasound. Back in the 80's a lot of stuff around
PZT-based transducers was not understood. Yet the front end parts and
transducers of the old machines are not that much different in
performance from the ones today, where we have oodles of computer
horsepower to simulate and calculate just about anything. If we had said
"Oh shoot, we don't understand the theory so let's not build but keep
studying until we do" a lot of people in hospitals would have needlessly
died.
Understood and point taken, as well. Life goes on. People
could float on a board in the water before they had much more
than a vague idea about it -- drawn from some collected
observations.
...
This moves now into a protracted discussion, which I'd better
not enter deeply here. But ad hoc rules, regardless of
apparent value, are rarely any more than the vague appearance
of a common "rule" from specific, repeated observation. Not
a very good foundation, as ideas go, to build upon. As such
things doesn't extrapolate very well to areas we haven't yet
trod. (More on this in a moment.)
One can succeed with induction like this, almost as well with
Tarot cards, as necromancy, as pretty much any idea that
"seems to work" for some point in time and understanding.
Some are okay as far as they go, of course. But it is very
much like unearthing stones (fragments of utility) to make a
farm wall. Each bit of this kind of inductive knowledge
exists by itself and is barely connected to any other bit.
Works great so long as you don't go outside the experience
which created it.
Still, a farm wall is useful and may keep the cows in. No
arguing with that. If you blow a hole in one part of it, the
rest stays, too. That is it's power, in a way. A rock over
on this part of the wall does NOT much depend upon a rock
over 'there' for its strength. But at the same time, that's
also its weakness. Structures formed like this cannot be
efficiently used to carry extremely heavy loads, since almost
none of it builds upon the strengths of other parts. They
must be in close proximity to cooperate.
Science, of late, has focused upon deductive theory --
preferring to test and falsify based up deduction of general
theory predicted into specific cases, given the particulars.
It yields knowledge structures that are quite different.
Induction still plays a role, but not nearly as important as
before. In science knowledge, the parts are highly unified.
So in keeping with the above 'farm wall' concept, I'd now
introduce the archway concept. Stones in science are shaped
and fashioned so that they cooperate with each other, like
stones in a grand, curving archway; with each piece lending
strength to other pieces. The result is a structure that
_can_ carry a heavy load. Of course, if you blow a huge hole
in it, the whole thing falls down. ;)
Same nuggets of stone, two different structures resulting.
In fact, what separates science from other forms of knowledge
isn't that science is "true" and the others less so. It's
the unifying nature of the resulting body. It's no more
"true" than anything else. But it is MUCH more unified.
I like to think of science knowledge as being "Borg." You
can easily tell just how Borg some bit of knowledge is by how
well connected it happens to be with "the collective." If it
isn't connected into the collective, it's not Borg. And it's
not science. Doesn't mean it is wrong. Doesn't mean it is
useless. Just means it's not Borg/science.
Jon
P.S. There is a great book on knowledge; IMHO very easily
grasped and extremely very well argued in six separate
lectures. The author is Jacob Bronowski and the book is
called, "The Origins of Knowledge and Imagination," 1979.
Copies are available for very little money (only a few
dollars) via abebooks or alibris. I consider it to be an
excellent primer, enjoyably told, and I gladly recommend it
to anyone. No matter how you come down on anything I write,
I think you'll enjoy his lectures -- they were given to very
young students and are very easy to follow, while
simultaneously engaging, too.
Yes, I found it.
(V1-V2)/R1 = (V2-V3/R2) - .005
8.4 = R1*(V2-V3/R2) -1.2 +V2
8.4 +1.2 -V2 = (R1V2 -R1V3)/R2
R2(9.6 -V2) = R1V2 -R1V3
570(9.6 -V2) = 240V2 - 240V3
5472 - 570V2 = 240V2 - 240V3
5472 = 810V2 - 240V3
240V3 = 810V2 - 5472
810V2 = 240V3 + 5472
V2 = ( 240V3 + 5472) /810
V2 = .296V3 + 6.76
(V2-V3)/R2 = V3/R3 - .005
Substituting V2 from previous
((.296V3 + 6.76) -V3)/570 = V3/100 -.005
.296V3 +6.76 -V3 = 5.7V3 - 2.85
.296V3 +6.76 = 6.7V3 - 2.85
9.6 = 6.4V3
V3 = 9.6 / 6.4 = 1.5 V
-Bill
What a pathetic story. But as always just your limited experience. I also
worked for a company(Krautkraemer) in the 80s and those guys from the
transducer department were called "the Phds" in the company. They knew what
they were doing. The whole principle of operation was actually
found/invented by 2 brother professors in the 40s who later founded the
company, hardly any "Neandertals".
ciao Ban
Are you sure you're talking about yourself and not about me? :-)
No such luck I'm afraid, Charlie. I did several semesters of college as
a Comp Sci major, back in the late 90s, but I made a poor choice of
school and things didn't work out. I was searching for somewhere to
transfer to when I fell ill the first time. After recovering from that
I had to give up my educational aspirations in favor of making a living,
at least until I fell seriously ill the second time...Go on like that
for a while and suddenly a decade has passed.
I do have a lot of "gen ed" prerequisite courses for transfer credit
under my belt, I did them here and there at various community colleges
(and Harvard's adult education program) over the years with the hope
that someday I'd have the chance to enroll in a full degree program.
Circumstances have granted me that opportunity now, and I feel this is
probably my last chance.
then, your greatest problem might be just getting accepted into a
program. Many EE programs are 'impacted', i.e. they have many more
applicants than they have slots for students, so they become very
selective. I know that twenty years ago, when I decided to go back
and get an EE degree, I ended up moving out of state to get accepted
to a program. Later, I found that I could get a masters in EE, even
with my bachelors in psychology, and so was able to move back...
Charlie
Just put on your application that you were tutored by Bill Ayers...
you'll get admitted immediately... particularly if you apply to
Berkeley ;-)
I say go for it. I don't think it's your last chance, but 30-ish is
definitely a good time to return to school: You're still young enough you
don't stick out like a sore thumb from the standpoint of getting job
internships, going to recruiting events, etc.
One way around this is to sign up initially as a "non-degree seeking
student" -- you're just paying tuition but not impacting the school's
"quality," so usually anyone can get in as such. Then you go around and find
a few sympathetic professors who'll let you sign up for their EE classes
(usually non-degree seeking student require instruction permissoin to take any
so-called "professional" level courses), do well in them, and then the next
year petition for acceptance into the department... now with several
professors on your side.
[...]
However, you have picked a rather extreme example. And even with the
farm wall people have managed early on by experimenting how to arrange
them into arrays so they would cling to each other better.
I could take an example of the other extreme: Winemakers and grape
growers. They have induced pretty much everything, until recently there
hasn't been a real science around any of this. Yet mighty fine wines
have been produced even back in the days of the Romans. And whether the
science around it really benefited the trade is highly disputed.
> Science, of late, has focused upon deductive theory --
> preferring to test and falsify based up deduction of general
> theory predicted into specific cases, given the particulars.
> It yields knowledge structures that are quite different.
> Induction still plays a role, but not nearly as important as
> before. In science knowledge, the parts are highly unified.
>
> So in keeping with the above 'farm wall' concept, I'd now
> introduce the archway concept. Stones in science are shaped
> and fashioned so that they cooperate with each other, like
> stones in a grand, curving archway; with each piece lending
> strength to other pieces. The result is a structure that
> _can_ carry a heavy load. Of course, if you blow a huge hole
> in it, the whole thing falls down. ;)
>
> Same nuggets of stone, two different structures resulting.
>
But we don't know how ancient tribes found out. It might also have been
something like "Oh, look, it holds up better that way".
> In fact, what separates science from other forms of knowledge
> isn't that science is "true" and the others less so. It's
> the unifying nature of the resulting body. It's no more
> "true" than anything else. But it is MUCH more unified.
>
> I like to think of science knowledge as being "Borg." You
> can easily tell just how Borg some bit of knowledge is by how
> well connected it happens to be with "the collective." If it
> isn't connected into the collective, it's not Borg. And it's
> not science. Doesn't mean it is wrong. Doesn't mean it is
> useless. Just means it's not Borg/science.
>
I think both deduction and Borg have their place. But I bristle at the
notion that we should refrain from attempting anything unless we have
the science down pat. In my job it's 50:50. When I design a switcher
there's lots of sheets of math and stuff, then I draw it up. Clearly the
science path you prefer. When I do EMC it's more the opposite, seat of
the pants. Without practical experience one typically gets nowhere.
There were projects where engineers tried their darndest to calculate
EMI effects, using software that cost as much as a nice family sedan.
Didn't solve it. Now I don't want to sound arrogant here but 15-25h on
my part and the root causes were found. Some initial disbelief at times
but then they ran it through the EMC lab one more time and ended up with
a nice report of conformity report in hand with the remark "Passed".
Typically with very cushy margins.
> Jon
>
> P.S. There is a great book on knowledge; IMHO very easily
> grasped and extremely very well argued in six separate
> lectures. The author is Jacob Bronowski and the book is
> called, "The Origins of Knowledge and Imagination," 1979.
> Copies are available for very little money (only a few
> dollars) via abebooks or alibris. I consider it to be an
> excellent primer, enjoyably told, and I gladly recommend it
> to anyone. No matter how you come down on anything I write,
> I think you'll enjoy his lectures -- they were given to very
> young students and are very easy to follow, while
> simultaneously engaging, too.
I hope some day I'll have more time to devote to the more philosophical
books. Right now I work in so many new fields that I have to constantly
study (mostly ME stuff).
Perhaps I wasn't very clear. My example was _abstractly_
drawn. I was speaking with an allegory here.
>I could take an example of the other extreme: Winemakers and grape
>growers. They have induced pretty much everything, until recently there
>hasn't been a real science around any of this. Yet mighty fine wines
>have been produced even back in the days of the Romans. And whether the
>science around it really benefited the trade is highly disputed.
The point was allegorical. And missed, I see. My fault. And
as I said, this is getting far afield. So I'll leave it for
the book I recommended to paint better than I have.
>> Science, of late, has focused upon deductive theory --
>> preferring to test and falsify based up deduction of general
>> theory predicted into specific cases, given the particulars.
>> It yields knowledge structures that are quite different.
>> Induction still plays a role, but not nearly as important as
>> before. In science knowledge, the parts are highly unified.
>>
>> So in keeping with the above 'farm wall' concept, I'd now
>> introduce the archway concept. Stones in science are shaped
>> and fashioned so that they cooperate with each other, like
>> stones in a grand, curving archway; with each piece lending
>> strength to other pieces. The result is a structure that
>> _can_ carry a heavy load. Of course, if you blow a huge hole
>> in it, the whole thing falls down. ;)
>>
>> Same nuggets of stone, two different structures resulting.
>
>But we don't know how ancient tribes found out. It might also have been
>something like "Oh, look, it holds up better that way".
You didn't get the allegory, it seems, so let's 'hold off' on
a response from me on this.
>> In fact, what separates science from other forms of knowledge
>> isn't that science is "true" and the others less so. It's
>> the unifying nature of the resulting body. It's no more
>> "true" than anything else. But it is MUCH more unified.
>>
>> I like to think of science knowledge as being "Borg." You
>> can easily tell just how Borg some bit of knowledge is by how
>> well connected it happens to be with "the collective." If it
>> isn't connected into the collective, it's not Borg. And it's
>> not science. Doesn't mean it is wrong. Doesn't mean it is
>> useless. Just means it's not Borg/science.
>
>I think both deduction and Borg have their place. But I bristle at the
>notion that we should refrain from attempting anything unless we have
>the science down pat.
Of course!! Engineers must _design_ in the here-and-now with
whatever is available for the task at hand. I certainly
wasn't arguing there.
>In my job it's 50:50. When I design a switcher
>there's lots of sheets of math and stuff, then I draw it up. Clearly the
>science path you prefer. When I do EMC it's more the opposite, seat of
>the pants. Without practical experience one typically gets nowhere.
>There were projects where engineers tried their darndest to calculate
>EMI effects, using software that cost as much as a nice family sedan.
>Didn't solve it. Now I don't want to sound arrogant here but 15-25h on
>my part and the root causes were found. Some initial disbelief at times
>but then they ran it through the EMC lab one more time and ended up with
>a nice report of conformity report in hand with the remark "Passed".
>Typically with very cushy margins.
I think this is why there is art _and_ science in
engineering.
If I had to put a cap on what you are saying, I'd simply say
that you should choose the best at hand. If there is very
good, quantitatively predictive theory floating around for
something, use it. If not, use what you have. Trial and
error certainly has a place. So does an instinct that is
developed through what you suggested, "experiment, experiment
and experiment."
>> P.S. There is a great book on knowledge; IMHO very easily
>> grasped and extremely very well argued in six separate
>> lectures. The author is Jacob Bronowski and the book is
>> called, "The Origins of Knowledge and Imagination," 1979.
>> Copies are available for very little money (only a few
>> dollars) via abebooks or alibris. I consider it to be an
>> excellent primer, enjoyably told, and I gladly recommend it
>> to anyone. No matter how you come down on anything I write,
>> I think you'll enjoy his lectures -- they were given to very
>> young students and are very easy to follow, while
>> simultaneously engaging, too.
>
>I hope some day I'll have more time to devote to the more philosophical
>books. Right now I work in so many new fields that I have to constantly
>study (mostly ME stuff).
Hehe. Me, too. However, I think that book is extremely
readable and enjoyable in each and every paragraph. You'll
find it no trouble at all. And cheap, besides. Why not
expose yourself to something merely on a lark once in a
while. Might expand a horizon and find something fun you
didn't realize was in you. ;)
Jon
[...]
>>> P.S. There is a great book on knowledge; IMHO very easily
>>> grasped and extremely very well argued in six separate
>>> lectures. The author is Jacob Bronowski and the book is
>>> called, "The Origins of Knowledge and Imagination," 1979.
>>> Copies are available for very little money (only a few
>>> dollars) via abebooks or alibris. I consider it to be an
>>> excellent primer, enjoyably told, and I gladly recommend it
>>> to anyone. No matter how you come down on anything I write,
>>> I think you'll enjoy his lectures -- they were given to very
>>> young students and are very easy to follow, while
>>> simultaneously engaging, too.
>> I hope some day I'll have more time to devote to the more philosophical
>> books. Right now I work in so many new fields that I have to constantly
>> study (mostly ME stuff).
>
> Hehe. Me, too. However, I think that book is extremely
> readable and enjoyable in each and every paragraph. You'll
> find it no trouble at all. And cheap, besides. Why not
> expose yourself to something merely on a lark once in a
> while. Might expand a horizon and find something fun you
> didn't realize was in you. ;)
>
Ok, but we spend the evenings with bible reading, card games and (full
confession here) lately some TV. We discovered a secondary digital
channel which carries "THIS-TV". Tons of documentaries, old movies,
westerns and so on.
Krautkraemer was located pretty close to us, I used to work in Solingen.
But it seems you do not know much about medical ultrasound. It's a heck
of a lot more complicated than NDT and the competition is very fierce.
Did you ever design parts of something like this?
http://www.volcanocorp.com/files/pdf/datasheet-eagleeye.pdf
I did. Actually I ran the imaging division when it was EndoSonics and
they don't let you do that with a limited experience :-)
Hint: There are 64 transducer elements in the tip, plus five integrated
circuits. Oh, and the machine that goes with it has full color flow
capabilities despite the fact that the blood flow is perpendicular to
the beam direction. Many groups tried but we never had any competition
in electronic IVUS, they still don't. Oh, and HP threw in the towel and
shut down their IVUS business. That should give you a taste of how
difficult this stuff is.
Oh, my, J�rg! Cut a TV show or two!! The book requires
maybe three hours. It's not a bible, or something.
By the way, I've spent many thousands of hours reading the
bible -- and even doing my own translations of parts of it,
from source materials and references. I keep shelves full of
various books and parallels (you might know what these are,
don't know), as well. A couple of years of university level
theology training does that to one, I suppose. What I'm
asking is _nothing_ like that! It's easy reading.
And card games appeared to also be the usual fare for us
Swedish family types, though I've long since dropped most of
that habit. ;)
But every evening doing bible reading??!!?! if you are
spending that kind of time, I highly highly recommend taking
some serious, high quality, university level coursework. You
really need to be able to know where to go to get the raw
materials and do some of your own work in finding out exactly
what source materials exist (fragments only, in many cases,
if you use the earliest stuff), how they vary each from
another (and they do, in some cases a lot), and gain some
knowledge about _how_ people wrote and thought about things
back then so you can place what you see into some cultural
context, as well. Cripes, if you are working that hard, you
should get a leg up on the more academic side of this. You've
obviously got the energy and interest for it.
Jon
But it's hard to forego a great western :-)
> By the way, I've spent many thousands of hours reading the
> bible -- and even doing my own translations of parts of it,
> from source materials and references. I keep shelves full of
> various books and parallels (you might know what these are,
> don't know), as well. A couple of years of university level
> theology training does that to one, I suppose. What I'm
> asking is _nothing_ like that! It's easy reading.
>
Well, I got to be honest here. I don't have all that much fun reading
the more philosophical texts.
The theology training I do not have, sometimes I wish I did. But got to
retire first ;-)
> And card games appeared to also be the usual fare for us
> Swedish family types, though I've long since dropped most of
> that habit. ;)
>
One of our house rules: We never play for money, with anyone. Just for
fun. In the same way we never visit casinos.
> But every evening doing bible reading??!!?! if you are
> spending that kind of time, I highly highly recommend taking
> some serious, high quality, university level coursework. You
> really need to be able to know where to go to get the raw
> materials and do some of your own work in finding out exactly
> what source materials exist (fragments only, in many cases,
> if you use the earliest stuff), how they vary each from
> another (and they do, in some cases a lot), and gain some
> knowledge about _how_ people wrote and thought about things
> back then so you can place what you see into some cultural
> context, as well. Cripes, if you are working that hard, you
> should get a leg up on the more academic side of this. You've
> obviously got the energy and interest for it.
>
Interest, yes, but not sure about the energy. The author of "40 Days of
Purpose" wrote something that kept ringing in my mind: "You can do the
umpteenth bible study but at some point you've got to take what you know
and get out there with it, and do stuff", or something like that.
I won't dive into any project unless I can hash out the details on the
computer first. The wife wised up when I tried to apply that to the lawn
mowing. My newest excuse is that I don't have the right tool, and I don't
want to buy one becuase I'm waiting for the newest model that comes with a
remote. We'll see how long this lasts.
Remember the old OH2AM team in many contests decades ago?
I have seen the phenomenon with 807, 813, 6146, EL 500, EL 509
and some TV line output tubes with US markings (6LQ6 & co).
--
Tauno Voipio
Not sure, last time I participated in contests was in the late 70's.
> I have seen the phenomenon with 807, 813, 6146, EL 500, EL 509
> and some TV line output tubes with US markings (6LQ6 & co).
>
Even 807? Yikes. I've mostly seen it with PL509 tubes and maybe the
occasional 6KD6.
Ah. Well, it certainly won't help you build the next thing.
;) I try and keep fingers on both sides. For example, I
both _designed_ the entire home for my son, doing all of the
engineering calculations required, as well as personally dug
the foundation (alone), laid the foundation boards and placed
the rebar, added rebar clamps, built a cubic foot wooden box
to hold and measure gravel and cement, and mixed and poured
it. I think _all_ is important, theory _and_ practice.
>The theology training I do not have, sometimes I wish I did. But got to
>retire first ;-)
hehe. Well, I have a million recommendations there, too.
There's a great web site now that actually places up the
photographs of various fragments of source materials, for
example. Lots to study, there. I can assure you of one
thing... if and when you ever get around to doing that work
for a while, your entire perspective WILL change. No
question. I don't mean to suggest it will change your
beliefs -- my favorite teacher of theology was a Catholic nun
and she would certainly run rings around me on this subject.
So you will hold your beliefs, likely. But I can assure you
that some facets of how you think about it will markedly
change from the experience.
>> And card games appeared to also be the usual fare for us
>> Swedish family types, though I've long since dropped most of
>> that habit. ;)
>
>One of our house rules: We never play for money, with anyone. Just for
>fun. In the same way we never visit casinos.
Hehe. I don't remember betting on canasta around here. :)
>> But every evening doing bible reading??!!?! if you are
>> spending that kind of time, I highly highly recommend taking
>> some serious, high quality, university level coursework. You
>> really need to be able to know where to go to get the raw
>> materials and do some of your own work in finding out exactly
>> what source materials exist (fragments only, in many cases,
>> if you use the earliest stuff), how they vary each from
>> another (and they do, in some cases a lot), and gain some
>> knowledge about _how_ people wrote and thought about things
>> back then so you can place what you see into some cultural
>> context, as well. Cripes, if you are working that hard, you
>> should get a leg up on the more academic side of this. You've
>> obviously got the energy and interest for it.
>
>Interest, yes, but not sure about the energy. The author of "40 Days of
>Purpose" wrote something that kept ringing in my mind: "You can do the
>umpteenth bible study but at some point you've got to take what you know
>and get out there with it, and do stuff", or something like that.
Well, don't do the umpteenth. Just the first, second, and
third. If you are arguing that ONE BOOK is a dedication of
your life, well.... I just don't know what to say to that.
Jon
I guess just about every son would want a dad like that :-)
>> The theology training I do not have, sometimes I wish I did. But got to
>> retire first ;-)
>
> hehe. Well, I have a million recommendations there, too.
> There's a great web site now that actually places up the
> photographs of various fragments of source materials, for
> example. Lots to study, there. I can assure you of one
> thing... if and when you ever get around to doing that work
> for a while, your entire perspective WILL change. No
> question. I don't mean to suggest it will change your
> beliefs -- my favorite teacher of theology was a Catholic nun
> and she would certainly run rings around me on this subject.
> So you will hold your beliefs, likely. But I can assure you
> that some facets of how you think about it will markedly
> change from the experience.
>
It always amazes me when we ask our pastor a tough question and then he
says "I'll better go all the way back to the source material on that
one". Even between 2-3 modern language translations there can be serious
differences and consequently misunderstandings.
>>> And card games appeared to also be the usual fare for us
>>> Swedish family types, though I've long since dropped most of
>>> that habit. ;)
>> One of our house rules: We never play for money, with anyone. Just for
>> fun. In the same way we never visit casinos.
>
> Hehe. I don't remember betting on canasta around here. :)
>
A lot of people form little private clubs and count rommee points and
all that. After a couple years there's often enough in the kitty for a
little bowling trip with the whole group. Not much money involved, but
we like to keep it clean, no money. Just the fun part.
>>> But every evening doing bible reading??!!?! if you are
>>> spending that kind of time, I highly highly recommend taking
>>> some serious, high quality, university level coursework. You
>>> really need to be able to know where to go to get the raw
>>> materials and do some of your own work in finding out exactly
>>> what source materials exist (fragments only, in many cases,
>>> if you use the earliest stuff), how they vary each from
>>> another (and they do, in some cases a lot), and gain some
>>> knowledge about _how_ people wrote and thought about things
>>> back then so you can place what you see into some cultural
>>> context, as well. Cripes, if you are working that hard, you
>>> should get a leg up on the more academic side of this. You've
>>> obviously got the energy and interest for it.
>> Interest, yes, but not sure about the energy. The author of "40 Days of
>> Purpose" wrote something that kept ringing in my mind: "You can do the
>> umpteenth bible study but at some point you've got to take what you know
>> and get out there with it, and do stuff", or something like that.
>
> Well, don't do the umpteenth. Just the first, second, and
> third. ...
Done.
> ... If you are arguing that ONE BOOK is a dedication of
> your life, well.... I just don't know what to say to that.
>
I've read a few more than just one :-)
>Jon Kirwan wrote:
>> On Wed, 17 Feb 2010 12:37:08 -0800, Joerg
>> <inv...@invalid.invalid> wrote:
>><snip>
>>> Well, I got to be honest here. I don't have all that much fun reading
>>> the more philosophical texts.
>>
>> Ah. Well, it certainly won't help you build the next thing.
>> ;) I try and keep fingers on both sides. For example, I
>> both _designed_ the entire home for my son, doing all of the
>> engineering calculations required, as well as personally dug
>> the foundation (alone), laid the foundation boards and placed
>> the rebar, added rebar clamps, built a cubic foot wooden box
>> to hold and measure gravel and cement, and mixed and poured
>> it. I think _all_ is important, theory _and_ practice.
>
>I guess just about every son would want a dad like that :-)
hehe. I took it on for the _same_ reasons that I stated in
this group on the Vbe multiplier: "I'd rather _keep_ the
money and _keep_ the education for myself. That way it pays
off, again and again." It was for _my_ benefit, as well as
his. Saved a hell of a lot of money, too!
>>> The theology training I do not have, sometimes I wish I did. But got to
>>> retire first ;-)
>>
>> hehe. Well, I have a million recommendations there, too.
>> There's a great web site now that actually places up the
>> photographs of various fragments of source materials, for
>> example. Lots to study, there. I can assure you of one
>> thing... if and when you ever get around to doing that work
>> for a while, your entire perspective WILL change. No
>> question. I don't mean to suggest it will change your
>> beliefs -- my favorite teacher of theology was a Catholic nun
>> and she would certainly run rings around me on this subject.
>> So you will hold your beliefs, likely. But I can assure you
>> that some facets of how you think about it will markedly
>> change from the experience.
>
>It always amazes me when we ask our pastor a tough question and then he
>says "I'll better go all the way back to the source material on that
>one". Even between 2-3 modern language translations there can be serious
>differences and consequently misunderstandings.
><snip>
Yes! But I have learned that if I want to find out for
myself and not rely upon the interpretation of others, I have
to go back to copies of the source materials (and as much of
it as possible.) For example, did you know that the very
earliest pieces of the new testament date to about 125 AD?
Fragments from Matthew held, last I heard, at Oxford's
Magdalen College. Bits from chapter 26, for example. Just a
few words here and there.
Jon
The trick is knowing when it's cheaper overall to just purchase a product or
service. :-) In personal life, for most of us this choice is clear-cut (it's
only folks like Warren Buffet who would very likely be losing money if they
chose to build their own home), whereas with businesses it seems common when
small businesses struggle to grow beyond a certain threshold due to the
founders being unwilling to risk others starting to make some of the big
decisions... or somewhat alternatively, trying to develop all their skills
internally when it'd be much cheaper and faster to hire a good consultant.
[...]
> Yes! But I have learned that if I want to find out for
> myself and not rely upon the interpretation of others, I have
> to go back to copies of the source materials (and as much of
> it as possible.) For example, did you know that the very
> earliest pieces of the new testament date to about 125 AD?
> Fragments from Matthew held, last I heard, at Oxford's
> Magdalen College. Bits from chapter 26, for example. Just a
> few words here and there.
>
Some of its history has even made in into wikipedia:
http://en.wikipedia.org/wiki/Magdalen_papyrus
There are people finishing their BS in their 50s and later. I was over 40.
The bottom line is never quit, never say die. And then one day you graduate.
Trust me that can be a delicious moment. Especially if there are/were
family/friends that did not believe you could make it.
Only in parts of Europe. :)
--
Greed is the root of all eBay.
Oh my dear, I don't like to brag about my work. This US flaw detector for
example still in use after 20+ years.
http://www.fh-rosenheim.de/2184+M54a708de802.html Thousands of students must
have pressed the buttons...
In the first place it was a joint effort of all 14 design engineers and 6
softies and my colleagues were very capable and we helped each other. Then
in 1986 when we did this it was challenging to make a portable and reliable
instrument with digital control. I was just doing the analog front end and
helped with the deflection amp for the CRT (no LCDs yet). I designed and
prototyped a couple of hybrids for this, one is the 2"x1" input amp. Almost
everything else is surface mount.
And I can say *everybodies* life depended on it many times. Die Bahn and
British Rail testing steel axles or all airplane companies, nuclear
reactors, space shuttle, mines used and still use it. It is working at -20�C
in Siberia with the specified accuracy as well as at +80�. And the company
regained the 85% world market share it had lost before and it was sold 5
times more than projected more than 20000 units ...
And again I was just part of the team tho the only consultant and without
the help of Dr. Volkmann who came from R&S, I wouldn't have been able to
succeed at all :-(
ciao Ban
I don't either (well, ok, sometimes ...), just wanted to show that your
ad hominem statement about limited experience is plain wrong. I am doing
this since 1986, to be exact.
> ... This US flaw detector for
> example still in use after 20+ years.
> http://www.fh-rosenheim.de/2184+M54a708de802.html Thousands of students must
> have pressed the buttons...
> In the first place it was a joint effort of all 14 design engineers and 6
> softies and my colleagues were very capable and we helped each other. Then
> in 1986 when we did this it was challenging to make a portable and reliable
> instrument with digital control. I was just doing the analog front end and
> helped with the deflection amp for the CRT (no LCDs yet). I designed and
> prototyped a couple of hybrids for this, one is the 2"x1" input amp. Almost
> everything else is surface mount.
Ah, hybrids. We probably did ours at around the same time. Mine were
then produced at Philips Krefeld and also Turck in Halver. I had a lot
of fun designing hybrids but unfortunately that era has ended :-(
> And I can say *everybodies* life depended on it many times. Die Bahn and
> British Rail testing steel axles or all airplane companies, nuclear
> reactors, space shuttle, mines used and still use it. It is working at -20�C
> in Siberia with the specified accuracy as well as at +80�. And the company
> regained the 85% world market share it had lost before and it was sold 5
> times more than projected more than 20000 units ...
Ok, nice, and I don't want to belittle this technology in any way. It is
needed and will ensure safe operation of public transportation and other
gear, as you wrote. But technologically it is a very different ballgame
versus medical ultrasound. It looks like a classic A-mode system where
the transducer has only one element. Or maybe several in annular array
configuration for focus.
A-mode is gone from medical, since the 70's. State-of-the-art is now
beamforming with 64 or more channels running at the same time. <5nsec
delay granularity, apodization, the whole nine yards. The one I am
working on right now will support transducers with several hundred
elements and will provide 3D rendering. You cannot possibly do that all
in discrete, not even SMT. Which is why I had to start getting into chip
design, to some extent, in the late 90's.
> And again I was just part of the team tho the only consultant and without
> the help of Dr. Volkmann who came from R&S, I wouldn't have been able to
> succeed at all :-(
Same here, there have to be real scientists involved and those are often
Ph.D. with a serious physics background. Same on the project I am
working on today. All I wanted to say is that there always was and still
is stuff in ultrasound that's next to impossible to grasp from a science
or simulator point of view. Even where it is, when a sim on the hottest
screaming machine takes weeks you have to cut to the chase at some
point, so you get to market in time. This is also why a lot of recipes
(filler, backing material, acoustic lens, and so on) are closely guarded
trade secrets. You won't find any info about this stuff here at the
office, it's all destroyed the minute I don't need it anymore, only the
respective client keeps it.