General > General Technical Chat
why is the US not Metric
bsfeechannel:
A few days ago I was considering the use of a piece of nichrome wire I have as a current shunt for a project. Nichrome is not the most solder-friendly material around, but it has a better temperature coefficient than copper, in fact 10 times better. So I decided to investigate its viability. I needed to basically decide its length and calculate the maximum current so that the temperature rise does not change its resistance above a certain tolerance. There are several on-line nichrome wire calculators and the most popular seems to be the Jacobs nichrome calculator. This is a screen shot of it.
The calculator is pretty good and intuitive and, since the Jacobs company is based in the US, it is using primarily imperial units. But then I decided to "metricate" their calculator and this is the result.
Look how uncluttered, clean, coherent and consistent it is now. All the units are metric, instead of a mishmash of different units from the same system (feet and inches, AWG and inches) and from different systems (feet, inches, °F, AWG and cm, °C, volts, ohms and watts).
CatalinaWOW:
You made an error in your metrification. The label on the area row says gauge, not area. So even metric doesn't pay much attention to these foibles. If it works you go with it.
I will note that the calculator is much cleaner and simpler if you eliminate the metric units. Not quite as good as metric, but yet another proof that the systems are nearly equal in ease of use. The standard one would be as clean if you used the single unit of inches for distance, but Jacobs decided to be friendly to all of their customers. Metric is better, but not so overwhelming as you seem to think it is.
Think of it this way, use of the existing US system of units requires memorization of perhaps a dozen or so constants, compared to the one touted for metric. (Will ignore all of the weird units not widely used. The drams, the furlongs, and all of that long list of traditional units. We are just talking about the common units used in science and industry.) The average speaker of a modern language has a vocabulary of at least 5000 words. Many have a vocabulary much larger - 15000 is common and many even know 35000 or more words. For an operating system that easily memorizes that quantity of information a difference of a dozen is so far down in the mud that it hardly bears discussion.
bsfeechannel:
--- Quote from: CatalinaWOW on January 12, 2020, 07:06:20 pm ---You made an error in your metrification. The label on the area row says gauge, not area. So even metric doesn't pay much attention to these foibles. If it works you go with it.
--- End quote ---
I did that on purpose.
One crucial data for a wire is its cross sectional area. For a given maximum current density, the cross sectional area is directly proportional to the maximum current. So calculations are straightforward. For a given length, its resistance will be inversely proportional to the area. This means that the maximum power dissipated by the wire will be too directly proportional to the area.
"Gauging" wires by their cross sectional area in mm² is therefore far more advantageous than using the traditional AWG. And that's why in some places people already offer wires and cables dimensioned exclusively in mm², not in any gauge system.
--- Quote ---I will note that the calculator is much cleaner and simpler if you eliminate the metric units.
--- End quote ---
If you eliminate the metric units, the calculator becomes useless, because, alas, the imperial system has no units for voltage, current or resistance, but you can still use HP for power.
CatalinaWOW:
So using an American term for size is acceptable in metric, as long as you use metric units? Labeling something incorrectly is a more rational system? :palm:
Your reply has another error, repeated throughout this thread. While it may be true that the Imperial system has no volts or watts or whatever, as has been repeated over and over, America is metric. From the 1800s. So we do use those units. And have for as long as any other metric country. America uses what we call the standard system, which has some units that are identical to Imperial units (feet and miles) and some that resemble Imperial units (gallons and others).
forrestc:
--- Quote from: Zero999 on January 12, 2020, 08:57:44 am ---360 is better because having more factors than 400, so 1/3 of a turn or 120 degrees can be expressed without using a fraction.
--- End quote ---
This allows me to bring up a point that I've been going to make for a while.
In some cases decimal based systems aren't very convenient when translating a measurement to the real world. It's pretty easy to divide a line segment in half through various methods, including the quite accurate method from classical geometry using a compass and a straight edge. Dividing it into 10 equal pieces is a fair bit more involved.
On a circle, dividing a circle into 6 or 12 (or 24) equal pieces is relatively straightforward as well, but 10 is quite a bit more difficult.
It would not surprise me to find that this is the root cause of why inches are generally expressed as whole numbers and fractions where the divisor is a power of two. And why there are 12 or 24 hours in a day.
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