SI-units

Hello !
Would it be a good idea if people would use the SI-system units when writing?
The rest of the world excluding USA and GB uses the metric system and SI-units in normal life ( i tought USA and GB signed the aggreament to use this system years ago?).
It would help if all people here would speak the same "language".

Remember what happened with the "mars explorer" when the units didn't match...crash

?????

Well

Most people in science and industry in the UK use the metric system anyway. Children (including myself when i was at school) were taught using the metric system in every field. I only know how to use the imperial system as my parents use it all the time. I think in the UK, before long, everyone will use the metric system for everything except speed with respect to cars and long distances. In the UK everything except speed and distance has to be written in the metric system first and possibly in the imerial system if needed.

The USA has a much greater problem. Most Americans don't want to conform with the rest of the world as the USA is "the best country in the world". They don't like changing to be like others. Their government doesn't want to force them to use the metric system like our government has done so it might be a while before the Americans use the SI standards...

I'm not having a go at Americans by the way

Actally, the SI system is the only one legally "endorsed" in the US, and has been for a couple of hundred years. Unfortunately, most people in the US still think and work in "English" units. Because our internal economy is so large (California alone would represent the fourth largest economy in the world) we can get away with it. It isn't a question of chauvinism, or American boosterism, or defiance. It is simply inertia and habit, and if people don't have to change they won't. In Europe you had small fragmented economies during the early industrial revolution, and since the local units had to change anyway it made sense to go with the rational system developed by France, then the largest continental economy.

When I was in college several decades ago, my professors told me that in ten years the English system would disapear. My intern, a college senior, says that they are telling him the same thing now. A number of technical societies have tried to make the SI system the only one used, but they have usually backed off because their audience complained about having to translate all units to the terms they understood.

My opinion is it really doesn't matter. We do some work in Europe, and simply use SI units in the logic and the display because the operators think that way. In the US we use conventional English units because the operators think that way. After all, in practice in both logic and mental judgements, we simply convert the measurement to a "value" anyway. We think in terms of "too high" or "too low" or "about right". I don't see any problem with an American poster using English units, a poster from the rest of the world using SI, and the responders can convert if necessary.

Fortunately, electrical units are already SI, so most of the time it doesn't matter anyway.

SI has conquered only one product here in the USA.


2 Liter Bottles of Soda Pop.

... oh yes, we give our age in metric also

Well, Tom, while I agree with you from the down-and-dirty technical side of things (and, of course, the fact that I too speak American) that inside the PLC it really doesn't matter, nif's point is valid.

I think it would be better if we Americans (for instance) would post our calculations and such using SI units. We have the conversion tools you speak of, too. After all, many of the regulars here have to convert their posts to their own language already. To me it seems like a small and reasonable courtesy.

Anyway that's my 2 cents (ummm....or whatever the currency) FWIW.

Steve

The automotive industry in the US is heading metric. The part drawings we get in are almost alwasys dimensioned in metric. I started programming CNC stations on our machines in mm years ago.

As more and more companies in the US work on a global scale, the change will come. I think that we won't get beyond what the UK is now, though.

How do you american guys size cable? For example a 2 core and earth 2mm^2 PVC circular. What would you call it?

Canada adopted the metric system (SI - system internationale) in 1976. I was in grade 1. I was never taught anything but metric in school. Still, in my culture, everything is feet, pounds, miles, inches. You can legislate all you want, you can't change people. I think I will use these measurements until I die. Sure I have to use metric sometimes, usually after I've calculated what it was in imperial measurements first. Need 100 feet of 3c/#8? order 33M. Also, most of the metric nuts and bolts we have come from Japan. We still use 7/16, 3/8 wrenches etc, 95% of the time. Ask me how tall I am and I'll tell you 6 feet. Not 185 cm. Anyway, what I'm saying is you can't change the way people think. Also, the culture of the US in the past has been to not be European. Just like lots of Canadians that have to prove they are not American. In other words, no, we will not all be speaking the same "language", but in Canada, that is encouraged. What you are proposing would be considered "Assimilation". That's a swear word here.

Think of all the manufacturing companies in the United States or any company using the English system. There's thousands, 10's of thousands. All of them using the English system. Now tell them that they all need to change there tooling and measuring devices. Your talking big bucks. If it does happen, and I don't think it will in any of our lifetimes it will happen very slowly.

"How do you american guys size cable?"

Well, now that is a "system" with only the most tenuous ties to logic. American wire, and sheet metal, and shot for shot guns, all are measured in guage(AWG = American Wire Guage). Except for a couple of coincidental guages, there is no correlation between the guage number and the diameter, but each guage has a diameter 1.123 times the diameter of the next smaller guage. A #12AWG wire is 0.081 inches, which is 6,530 circular mils which is 0.00513 sq. inches which is 0.033 square centimeters.

In large wires we use 0 (ought), 00(double ought), 000(triple ought), 0000 (four-ought) and then we go to things like 250 MCM and so on.

To make it interesting, the lager the guage the smaller the wire - 14 guage is smaller than 12 guage and so on. I think the whole thing traces back historically to making shot in shot towers. They poured molten lead through a sieve, and the guage represented the number of wires per inch in the sieve. That is why a higher guage number is a smaller diameter.

I think the system is insane, but I am not in any position to change it!

... along those same lines ...

normally I don’t post stuff like this ... but it’s a slow day and this seems to fit right in with the topic under discussion ... it came across in my e-mails a few weeks ago ... you might have already seen it but maybe someone will find it interesting ...




How Specifications Live Forever
================================

When you see a space shuttle sitting on the launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are the solid rocket boosters, or SRBs.

The SRBs are made by Morton Thiokol at a factory in Utah.

Originally, the engineers who designed the SRBs wanted to make them much fatter than they are. Unfortunately, the SRBs had to be shipped by train from the factory to the launch site in Florida and the railroad line runs through a tunnel in the mountains. The SRBs had to be made to fit through that tunnel.

Now, the width of that tunnel is just a little wider than the U.S. Standard Railroad Gauge (distance between the rails) of 4 feet, 8.5 inches.

That's an exceedingly odd number. Did you ever wonder why that gauge was used? Because US railroads were designed and built by English expatriates, and that's the way they built them in England.

Okay, then why did the English engineers build them like that?

Because the first rail lines of the 19th century were built by the same craftsmen who built the pre-railroad tramways, and that's the gauge they used.

I'll bite, why did those craftsmen choose that gauge? Because they used the same jigs and tools that were previously used for building wagons, and you guessed it, the wagons used that wheel spacing.

Now I feel like a fish on a hook! Why did the wagons use that odd wheel spacing?

Well, if the wagon makers and wheelwrights of the time tried to use any
other spacing, the wheel ruts on some of the old, long distance roads would break the wagon axles. As a result, the wheel spacing of the wagons had to match the spacing of the wheel ruts worn into those ancient European roads.

So who built those ancient roads?

The first long distance roads in Europe were built by Imperial Rome for the benefit of their legions. The roads have been used ever since.

And the ruts?

The initial ruts, which everyone else had to match for fear of destroying their wagons, were first made by Roman war chariots. And since the chariots were made by Imperial Roman chariot makers, they were all alike in the matter of wheel spacing.

Well, here we are. We now have the answer to the original question. The
United States standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman army war chariot.

Specs and bureaucracies live forever.

That's nice to know, but it still doesn't answer why the Imperial Roman war chariot designers chose to spec the chariot's wheel spacing at exactly 4 feet, 8.5 inches.

Are you ready?

Because that was the width needed to accommodate the rear ends of two Imperial Roman war horses!!!

Well, now you have it. The railroad tunnel through which the late 20th century space shuttle SRBs must pass was excavated slightly wider than
two 1st century horses' butts.

Consequently, a major design feature of what is arguably the world's most advanced transportation system was spec'd by the width of a horse's behind!

So, the next time you are handed a specification and wonder what horses' rear end came up with it, you may be exactly right. Now you know what is "behind" it all.

Author Unknown

I think the original author had a long boring day ahead of him when he came up with that story..........

If you have about 10 minutes to kill follow this link: http://www.snopes.com/history/american/gauge.htm

In large wires we use 0 (ought), 00(double ought), 000(triple ought), 0000 (four-ought) and then we go to things like 250 MCM and so on.

Click to expand...

The term MCM used "M" as the roman numeral 1000. That was changed at least three or four NEC publications ago. The correct term is kcmi, 1000 circular mils.

How do you american guys size cable? For example a 2 core and earth 2mm^2 PVC circular. What would you call it?

Click to expand...

The most common translations for control wiring 2 core = 2 conductor. Your 2.5mm = our #14 awg (almost all panel control wiring). Your 4mm = our #12 awg (most power wiring up to 20amps non continuous and 16 amps continuous loads). I believe 1.5mm = to our #16 awg (used to most instrumentation).

"That was changed at least three or four NEC publications ago. The correct term is kcmi, 1000 circular mils."

That is undoubtedly true, but there is still a lot of manufacturers info out there using MCM for wire sizes. This gets us back to the original question about why us yanks don't use SI unit - those old habits are very hard to break!

I always wondered why my grandmas 16 gauge shotgun was smaller than my mums 12 gauge shotgun.

Incidentally, a 16 gauge kicks like a mule.