I hate imperial units

Spehro Pefhany a écrit :

Tell this to JL :-)

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Thanks,
Fred.

L is, of course, our inductance. B is the flux density and H is the magnetising force. All of these sums use something called the SI system of units which was worked out by the French because the British Imperial system is shit. Unfortunately the British landed the Americans with Imperial units so all their data sheets are messed up. The British noticed that the French system was better but could not admit it so they had to join the European Community. Then the Belgians forced them to use it and, after a lot of complaining, the British gave up and said OK neatly avoiding having to give the French credit for anything, and we still get to buy our potatoes in pounds and ounces. Politics ay?

The other parts of the sums are the number of turns of wire on the inductor, N, and the current in that wire, I. Then there is the special one, Uo, which is the permeability of free space. That one works with inductors, there is another one used with capacitors called Eo which is the permittivity of free space. These 'normalise' everything so the units work. As it happens the speed of light is given by 1/SQRT(Uo.Eo) which is why Einsteins equations have lots of square roots in them. You can not travel faster than the speed of light in free space (outer space) because then all the electerons fall off the back of your rocket and it dissapears in a flash of light. If you watch Star Trek then you will know about this effect.

Uo is 4.pi.E-7 which looks a bit suspicious, I mean 'What are the chances of that!'? That was done to confuse the Russians. What you have to realise is that Eo is 8.85E-12 which is a pretty meaningless number and back in those days the Russians had comparatively slow calculators with which to try and factorise such a number to find out if there was some hidden meaning. Of course when the Russians join the EU we'll tell them about that one and everyone can drink lots of Good Vodka and roll about laughing.

DNA

Me? I do all my thermal stuff in SI units. What I hate is the way people randomly use calories and joules/watts when specifying thermal conductivity.

This is neat: you can use Spice to model thermal dynamics. Just equate...

1 K/w == 1 ohm

1 K == 1 volt

1 gram aluminum == 1 farad

1 second == 1 second.

Works to about 5%

John

Cool. Diffeq's is diffeq's.

Best regards, Spehro Pefhany

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

If you're really intent on it you can use SPICE to solve mechanical systems as well... I remember spending one class years back going through the equations, and somewhere around here I have the conversion charts.

I do remember being told that the main problem with simulating mechanical systems like this is that real viscious dampers are horribly non-linear, even springs aren't great, etc.

It's all a bunch of baloney! It doesn't make any difference what the units are, the math is the same. The metric system, more specifically SI, is fine for school kids and ingenues who need their ten fingers to count and figure things but it is a red herring elswhere. A decimal inch micrometer works just as well as a mm one. It makes no difference. Much of the imperial system was/is binary making calculation even easier than base ten. For example take 1/2 cup, 1/4 cup, 1/8 cup, etc. These are powers of two as are the fractional inch numbers. It's all a matter of what you are use to. Furthermore, the metric system has some curious anomalities in it as does the imperial system. Did you know that a cubic centimeter equals 0.00099997 liters? So, things arn't as simple as you have been taught. I personally don't care what the units are and don't undersand why a technical person would be befuddled by one particular set vs. another. So, as an exercise for the class: figure the speed of light in furlongs per fortnight. When you are done, you will find that it is just a number as meaningles to a human as

2.99776*10^8.

I got used to non-metric units, except maybe when I lay tile where I still use centimeters a lot for tiles with really complicated cuts.

When I see a tree I sometimes think out loud "Oh, that one would be about 20,000,000 BTUs". Drives people crazy.

--
Regards, Joerg

http://www.analogconsultants.com

It depends when you said it.

A BTU was a Board of Trade Unit = I kWh = 3.6 Megajoules A BThU was a British Thermal Unit = 1.05 Kilojoules

Then some nincompoop decided to abolish the BTU and rename the BThU to BTU. So a "BTU" could mean either of the above, depending on when it was said.

What a mess!

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

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I have often wondered about the intransigence of Americans and Britons when it comes to SI. If an alien race invaded Earth, they would see immediately that we are a lazy race. We have spent millions on publicity campaigns to convert, and nothing has changed really.

Declaring a law that all printed matter on government-approved consumables will use solely SI unit might force the transition, and perhaps the idea came up in the governments, but their are probably people in the House of Lords and the Senate who like football too much. "Let's see...would the 50-yard-line become the 50-meter-line? And what would happen to all those football statistics. And so what if we confuse ourselves every now and then and lose a $125 million spacecraft?"

-Le Chaud Lapin-

If you need inches. If you need mm, it avoids a conversion and a possible source of errors, especially when the numbers are oddball sequences of digits and humans are involved.

Yes, and if you use gills, be sure to specify US or British gills.

How do you know what we've been taught or have taught others? The liter is defined as 1 dm^3 = 0.001m^3 *exactly*. It has been since

1964 (!). This just in... be sure to check out the 'new' definition(s) of the inch from around that period (both US and British inches changed, in the opposite directions to converge at the 2.54mm definition).

Hmm.. well, let's us take those units out of the particular problem domain they were designed for and try to figure out how many watts it takes to maintain temperature difference of 10°C (18°F) across a 0.5" (12.7mm) piece of P20 steel 3/8" (9.52mm) thick. Convert between W and BTU, between in or mm and square feet etc. Lots of unnecessary work and possible places for errors.

Au contraire, at least if you consider EEs to be human. You ever think about how long it takes a signal to get across a PCB (or along the clock lines on a chip, for that matter). A 10E-9 second is a long time in some problem domains..

Best regards, Spehro Pefhany

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

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Did you mean to say a cc of water =3D 0.00099997 kg?

The volume a gram of water occupies is temperature dependent, but I think it's defined as 1 g water =3D 1 cc at 4 degrees C. Plus or minus at different temperatures...

Michael

You don't own one of those sliding pins thingies ?:-) Wonderful for transferring a door facing shape to a tile cut.

Really ?:-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Thought about it but then I always figured that after finishing this one more room I'd be done tiling for the next 20-30 years. Wrong! I am married, so...

What works really nicely is to cut several odd vellum templates. Those can be angled at will and then fastened to each other with some masking tape. The tape comes off with ease and you can re-use the templates for all the other odd tiles to come. Until a splotch of mortar accidentally lands on it, that is. However, every time it almost broke my heart not having used that sheet for a nice high-tech super-gizmo schematic.

[ ... ]

--
Regards, Joerg

http://www.analogconsultants.com

My Great Grandfather was a member of the Britsh Thermal Unit in World War One. They fought many heated battles!

I have been known to accurately measure the WHOLE house, then lay down a hexagonal placement grid on the plan and slide it around for best fit, with mostly near-1/2-tile cuts, and best look to the eye... with fudging to accommodate a long hallway with almost an inch of TAPER :-(

I generally transfer the pin gauge info to full page label paper, cut out and stick to the tile, where it stays while I wet saw ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Our neighbor is a civil engineer. Before he even thinks about firing up the saw he does the whole project on AutoCad. Even if it's just the guest bath. That drives his wife crazy because it can take a long time.

If it's any consolation I also had to fudge the hallway. Did the kitchen first and calculated it all so the 1/2-tile symmetries came out nicely. I had no choice but to either compromise the kitchen or fudge the (long) hallway because its end is almost 1/2" off track. Opted for making the kitchen perfect because that's where everybody always hangs out.

I did it the Sharpie way :-)

--
Regards, Joerg

http://www.analogconsultants.com

Snip....

Watts don't convert to BTU's one is power the other is energy, Right? Don't you need some time in the conversion somewhere? It seems to me that's a much bigger issue than how many sq feet there are in a sq meter, or whatever. The unit conversions are trivial but physical relationships, not so much.

A nano second is how long it takes light to go one foot a very convenient way to think about it. Right now my wife is 12 nanoseconds away and, of course, I see her in the past the way she was nanoseconds ago. To know how long it takes a signal to go across a PCB you'd have to know something of the dielectric constant, Right? Bob

Sharpie washes off in the wet saw :-(

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Usually but if you let it dry a minute or two it's just perfect. Then it holds almost until the end of the cut. Problem with my saw is that I wore it out pretty good so it doesn't cut very straight anymore. It also doesn't want to cut ferrite too well anymore and that's a real drag.

Drilling a 3/8" hole into porcelain tile to mount a toilet etc. is a whole 'nother matter.

--
Regards, Joerg

http://www.analogconsultants.com