Re: Creating a folder on the desktop
Re: Creating a folder on the desktop
- Subject: Re: Creating a folder on the desktop
- From: Bill Briggs <email@hidden>
- Date: Wed, 7 Sep 2005 02:48:10 -0300
At 11:32 PM -0500 9/6/05, John C. Welch wrote:
>On 9/6/05 22:36, "Bill Briggs" <email@hidden> wrote:
>
>>> The US Navy teaches negative to positive.
>>
>> I've got maybe a hundred EE texts on my office shelf, and not a single one
>> has this convention you mention. Not electronics, not circuit analysis, not
>> networks, not transmission lines, nothing. I only teach it, I don't pretend to
>> understand it. But I'm more inclined to believe that you are recalling
>> incorrectly than that the US Navy teaches something that is opposite of the
>> convention of the discipline (mission accomplished). If you can offer proof,
>> go for it. I'll bring the IEEE in to back up my case.
>
>I'm not saying you're wrong. I'm saying that the Navy taught "hole flow", at
>least in the late 80s, early 90s. Since that's straight from someone who
>taught basic electronics FOR the navy, I see no reason to think they were
>lying. He never went into why, just that the navy did things differently.
Careful, you're shooting yourself here. "Holes" are the name given to "the absence of an electron", or in other words, a positive charge, and the conventional current is precisely the same as that. It's the direction in which the positive charges would flow if they weren't bound in the metal's crystal lattice. So "hole flow" is in exactly the same direction as the current convention. But that's the opposite of the direction in which the mobile charge carriers (the electrons, charged negative) happen to flow. Electrons flow from negative to positive. Holes, if you wish, move from positive to negative. So the navy guy is not wrong, he's just using a jargon (holes) that's normally reserved for discussions of semiconductor electronics, not current flow. And "holes" aren't really in motion. It's the electrons that drift as a consequence of the applied potential.
> >> When I was in school in the US Air Force, I learned it all heads for the
>>> ground, however that happens to be defined in the circuit
>>
>> And that's a totally bone headed notion. Ground is a reference point for
>> electrical potential and has nothing to say about the direction that current
>> is headed in a given circuit. My first year students have problems with this
>> too, but they learn and grow out of it by second year. And they don't argue
>> about it after that, because there's no argument. If you knew what a Hall
>> effect sensor was you would know immediately that the above statement was a
>> crock as it can be so easily disproved using said sensor. The fact is that any
>> circuit will have current flow in the same direction no matter what single
>> point in the circuit you happen to ground. Again, I'm totally inclined to
>> question your memory rather than to abandon the conventions of Physics and
>> Electrical Engineering. "A little knowledge is a dangerous thing, drink deeply
>> or not at all." I comment, you decide. If I were you I'd do some careful
>> research before arguing this further. You're in my bread and butter now John,
>> and you need to know that I'm not just giving opinion or faint memories of
>> courses of the past. The established direction of current flow is from the
>> anode (positive terminal) to the cathode (negative terminal) and there's
>> nothing debatable about it. If you make an honest effort to look into it,
>> you'll satisfy yourself that this is the case.
>
>Again Bill, you're mistaking "This is what they did" with "This is the
>correct way for every situation". I'm not saying they taught it the best
>way. I'm saying, and with absolute certainty, that when we traced current
>through circuits, they taught us to find the damned ground or most grounded
>point, (airplanes here, so 'ground' and 'earth' are shall we say, sometimes
>a tad virtual compared to a building)
Ground has many meanings, depending on the context. It's not just "connected to the earth".
> and that was how the damned current went. Were they perhaps oversimplifying things in the interest of speed? Probably. They had between 9.5 months to 11.5 months to get us from absolute zero to being able to build shit by hand if we had to. Taking 4-8 years wasn't an option.
On this one there's no other interpretation. Ground is nothing more or less than a reference point for potential. It's not a place to which current runs. You can hook up a circuit with a 12 V battery and ground the positive terminal or the negative terminal (not both) and the circuit behaves the same way and the current flows in the same direction. Changing the grounding point doesn't change anything about the direction of current flow, all it does is shift the potential levels relative to ground (even if ground is not the earth). No wiggle room.
>I was in that program for 6 hours a day for a *year*. Really. Six hours. 5
>days a week. No summer break. No spring break. A handful of holidays. I can
>give you an exact count on the hours if you like, I still have the
>certificates. My memory's on REAL firm ground here. It's not just a faint
>memory. Spending 40 hours a week learning how every single circuit works in
>an AN/ALQ-119A ECM Pod works, tracing every.single.connection, RF and
>Electrical in it, for every possible power state, then taking the thing
>apart and putting it back together has a way of embedding itself in your
>memory. Same thing for a B-1B. All 170 or so LRUs on it. IEEE STP bus system
>for power control. I can probably still find every friggin' load that
>affected our systems, and show you the locations of the ACL/ICL/LCL breakers
>for the coolant systems on a B-1B and which had to be pulled for engine runs
>vs. ground power/APU runs. If you want to arrange it, I can probably walk
>under the wing glove area still and tell you what boxes are in what panel,
>and how many it takes to stop a full-grown Canadian Goose traveling at a
>relative speed of just over Mach 1. I can also tell you that if they're
>testing the HF system on that pig, you don't want to be within 5' of the
>skin of that aircraft unless you like waking up 30' from where you were
>standing, and sore as hell. I spent almost 6 years doing that 40 hours a
>week, sometimes more. No spring break. No summer break.
>
>You want to tell me that the way the were teaching it was utter crap, okay,
>I'm not arguing, you're FAR better qualified to tell me that than most folks
>I know. But if you want to tell me that they didn't teach it that way at
>all, and I'll tell you you're wrong, pure and simple.
I'd bet a king's ransom that they didn't teach that current ran to the ground, unless they limited the discussion to strictly negative earth systems, and failed to note that current has to move in a loop, since it doesn't actually "come from" something and "flow into" something. It circulates (Kirchoff's Law, if you want to look it up). Back many years ago the British made cars that had positive earth systems, and they work just exactly the same as our North American negative ground systems, except for the "relative potential" of the chassis to the other terminal of the battery. Current never just "goes to ground". Some source, let's say a battery, raises the potential of charges (in this case by chemical reaction) and those charges move through the connected load experiencing a decrease in potential. But the charge flow is in a loop, and it's caused by the source of potential, and how it flows in a given circuit has nothing to do with which part of the circuit is grounded. I don't care how much Canada Goose shit you can find on an airplane, that's the way it is. To abstract this a bit further and get out of circuits and into fields, electric field strength and absolute potential are uncoupled entities. No guff.
It's late on the east coast, I'm outa here.
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