General > General Technical Chat
why is the US not Metric
Zero999:
--- Quote from: KL27x on January 20, 2020, 06:36:19 pm ---Secondly, with AWG, you just go down 3 gauge sizes to double the cross section and halve the resistance. (And you move 6 steps to double/halve the diameter). Every gauge size larger, the diameter of the wire increases by 12.3%. Thus the cross section increases by 1.123^2, or by 26% per step. Going down in size, that is 10.5% decrease in diameter or 20.7% decrease in area. If you know piR^2, you only need to know any one of these numbers. 12.3% is from the 39th root of 92 = 1.122932197. This is because from AWG 36 to 0000, there are 39 steps, and a 0000 wire is 92 times the diameter of a 36 AWG wire.
So e.g.,
If you want double the cross sectional area of an AWG 16 wire, you go to AWG 13.
If you do this by cross section, you go from 1.32mm^2 wire to 2.64mm wire. Then you find out that this doesn't exists. And you select the 2.5mm^2 wire. In AWG, you can also be aware of and calculate each step up or down without looking at a chart, only knowing your starting point.
You can say it is easier to circumvent AWG and just call it by cross section. But most people probably don't calculate how much cross section they need for a wire, first, then look up the wire, after. Most people probably look a chart or spec sheet to begin with. And naming/buying/selling wires by their cross section isn't necessarily better for your manufacturers and marketplace and engineering codes.
You can all it archaic. I call it reality. These are the sizes we (american companies) make wires in and make engineering codes in. You choose from these sizes; you don't design your own spec as you go, unless you crap money like NASA. And in many cases it is easier to use AWG names/standards than to use cross sectional area as a name. If you're gonna use units, you gotta list the units, somewhere, firstly. And when you get smaller than 30 AWG, watch what happens to your names/numbers.
AWG is not absolutely empirical. But it is based on the 10.5% reduction in diameter which can be achieved by draw dies on copper alloy. That number is empirical, in a way; it's the average of what can be done, practically, using our current manufacturing techniques and dies and lubricants and alloys. After that, it's a matter of designating a reference/zero/calibration point. Then you know what sizes are actually available by this ratio of 1.122932197 : 1, within a very small margin of error. It would be nice it it were a rounder number, but this is the result of what is the biggest step size in practical application. That's where it ended up, and that's fine. This standard contains, in itself, knowledge of the physical universe and know-how of making wire. Why it goes backwards? Probably because this can be done smaller and smaller, if needed. But going larger is/was determined by other factors (which may have been improved/increased at least 3 times in history? >:D)
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That sounds very complicated and only reaffirms my point: it's much easier to use physical dimensions such as cross-sectional area or even diameter. Take a step back. Suppose you've never heard of AWG or SWG. If you saw a drawing with cable cross-sectional area specified, then it would be obvious what it means. No need to look anything up. We're not even talking about metric vs imperial here, but simply defining a physical property vs some complex system. Even wire diameter in inches or thou would be much easier to use.
Here in the UK we use a stupid system for shoe sizes. I wish we'd move over to something more straightforward, based on simple dimensions.
KL27x:
Tooki, Don't you measure the milk and spirits out separately, sos you dont accidentally pour too much into the cake? Whether by the cup or scale? (You could convert your recipe grams of milk to ml and vice versa, so why not use a metric measuring cup?)
Incidentally, I estimated about 15.5 us fl oz to be about 1 lb of water, calculating from memory, mostly cuz I have been involved with this thread, and doing all the math in my head. Could this be close?
Using a calculator, I come up with 1 US pint of distilled water is 1.04125 lbs. ANS^-1 * 16 = 15.366 us fl oz. Not shabby.
A cup / half pint/ 8 fl oz oz / 8/16ths (pint) ~ half a lb / 8 oz *
half cup / quarter pint / 4 fl oz ~ quarter pound / 4 oz *
*plus 4% extra, for "good measure" :)
KL27x:
--- Quote from: Zero999 on January 21, 2020, 10:34:44 am ---That sounds very complicated and only reaffirms my point: it's much easier to use physical dimensions such as cross-sectional area or even diameter. Take a step back. Suppose you've never heard of AWG or SWG. If you saw a drawing with cable cross-sectional area specified, then it would be obvious what it means. No need to look anything up. We're not even talking about metric vs imperial here, but simply defining a physical property vs some complex system. Even wire diameter in inches or thou would be much easier to use.
--- End quote ---
Easier to use...for who, though?
Have you ever had to spec an SIL/DIL PCB connector that comes in multiple numbers of connections? And then you have to use some formula of (n+1)*dimensions/pins/pads on the footprint mechanical drawing to even create the PCB footprint? Wouldn't it be "so much easier" if they just listed the footprint for every single size of connector? (Heck, wouldn't it be easier if they even showed the entire footprint for just one of these components, say the smallest one, just for reference?>:D) But they don't usually do this. And there are communication/clarity/future-proofing reasons for this decision, as well as efficiency/brevity.
If I had never heard of or seen AWG? I would look it up and RTFM. How would that be any worse than just guessing what diameter of wire I need? Or do you suppose you just learn the conductance of copper per square mm per meter in high school and remember it ever after? And then have to do algebra to figure out the minimum diameter you need, including heat dissipation and ambient temp and temp coefficient, and then still have to look up the closest size? (And still not know the actual legal/lawyer ampacity?)
You seem to be concerned with "ease of use" for Jack and Jane, specifically. In America, perhaps we are more concerned that our brighter bulbs have as much info as could possibly be useful to them in making an informed decision and not so very much concerned if Mary Sue Arduino-noob easily can begin to calculate for herself the cheapest possible wire to theoretically do some job and hopefully do it right. We will forgo this 0.0013% of the wire market to better serve the vast majority.
--- Quote ---Here in the UK we use a stupid system for shoe sizes. I wish we'd move over to something more straightforward, based on simple dimensions.
--- End quote ---
You mean more sizes/shapes/combos? Or just a more intuitive way to name them? The former, yeah. The latter? Well, most people only have to figure that out so many times until their feet stop growing. >:D
tooki:
--- Quote from: KL27x on January 21, 2020, 11:04:08 am ---Tooki, Don't you measure the milk and spirits out separately, sos you dont accidentally pour too much into the cake? Whether by the cup or scale? (You could convert your recipe grams of milk to ml and vice versa, so why not use a metric measuring cup?)
--- End quote ---
You weigh each ingredient separately.
The reason for weighing the liquids is simplicity: why dirty a measuring cup when you already have the scale out to weigh the flour? (Measuring flour by volume is a fool’s errand, and it’s quite telling that professional bakers in USA go by weight, not volume.) So you just add an ingredient, tare the scale, add the next ingredient, tare again, etc.
SilverSolder:
+1 for weighing ingredients in the kitchen.
When using the bread-bakery machine, I put the pan on the scale, tare it to zero, and start adding ingredients by weight. There are literally zero extra utensils needed for the job, and hence zero mess / washing up. The bread is consistent every time.
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