Author Topic: why is the US not Metric  (Read 66665 times)

0 Members and 4 Guests are viewing this topic.

boffin

• Supporter
• Posts: 976
• Country:
Re: why is the US not Metric
« Reply #125 on: October 27, 2019, 04:09:35 pm »
litres per 100km alwoys confused me. I mean why?
I am more confused by MPG-e ratings of EVs that donâ€™t have petrol tank.

Exactly why /100km makes more sense.  Much easier to compare
7litres / 100km  against  17kWh / 100km (Golf v eGolf for example).

You can more directly understand the difference.

Simon

• Global Moderator
• Posts: 15341
• Country:
• Did that just blow up? No? might work after all !!
Re: why is the US not Metric
« Reply #126 on: October 27, 2019, 04:14:00 pm »
Yes but it's more difficult to calculate what is required of a certain journey which is why it is stupid. So i am going to drive 15m, how much fuel/electricity do I need? the first thing you will do either directly or indirectly is to reverse it to fuel/power per mile or km

james_s

• Super Contributor
• Posts: 12604
• Country:
Re: why is the US not Metric
« Reply #127 on: October 27, 2019, 05:14:45 pm »
Why do you need to calculate that? Don't they all show the amount of miles remaining? You don't keep a finite bucket of electricity around to fill up the car, you just plug it in and if you're in a hurry you wait until it indicates enough range for the trip you want. The actual kWh you put in is not really relevant in the moment.

Simon

• Global Moderator
• Posts: 15341
• Country:
• Did that just blow up? No? might work after all !!
Re: why is the US not Metric
« Reply #128 on: October 27, 2019, 05:24:09 pm »
no but for the sake of carrying out any calculation I would want i have to take the reciprocal of that measurement as none of the figures in the measurement are 1. if it was litres per 1 mile that would be usable directly.

IanB

• Super Contributor
• Posts: 9761
• Country:
Re: why is the US not Metric
« Reply #129 on: October 27, 2019, 05:32:32 pm »
Yes but it's more difficult to calculate what is required of a certain journey which is why it is stupid. So i am going to drive 15m, how much fuel/electricity do I need? the first thing you will do either directly or indirectly is to reverse it to fuel/power per mile or km

Precisely. If your car uses 0.1 litres per mile and you want to drive 15 miles your fuel required will be 15 x 0.1 = 1.5 litres. How could it be simpler?

(Or 10 L/100 mi leads to 15/100 * 10, which is basically the same thing.)
« Last Edit: October 27, 2019, 05:35:32 pm by IanB »
I'm not an EE--what am I doing here?

CatalinaWOW

• Super Contributor
• Posts: 3740
• Country:
Re: why is the US not Metric
« Reply #130 on: October 27, 2019, 05:40:05 pm »
These last few posts are typical of metric-imperial arguments.  I mean golly.  If you are able to do electronics you should be able to handle ratios and their inverses.  And use each to their best advantage.  It is kind of like arguing whether sines or arcsines are better.  Same applies to measurement systems.

The following users thanked this post: james_s

mariush

• Super Contributor
• Posts: 3983
• Country:
• .
Re: why is the US not Metric
« Reply #131 on: October 27, 2019, 05:42:36 pm »
Such estimations are a bit pointless. You get different mileage in towns where you stop and start often, compared to driving on highway or outside towns.

As for electric cars, knowing how many kWh were "pumped" is kinda pointless. Consumption will depend on how aggressive you are, if you climb a lot and also if you go down or break often (regenerative breaking) and you'll discharge battery faster in the winter when you heat up the air inside so you won't freeze.
Also in the winter, range goes up if you keep the car warm over night, instead of starting from cold.

Simon

• Global Moderator
• Posts: 15341
• Country:
• Did that just blow up? No? might work after all !!
Re: why is the US not Metric
« Reply #132 on: October 27, 2019, 05:47:22 pm »
These last few posts are typical of metric-imperial arguments.  I mean golly.  If you are able to do electronics you should be able to handle ratios and their inverses.  And use each to their best advantage.  It is kind of like arguing whether sines or arcsines are better.  Same applies to measurement systems.

No because L/100km has no practical use other than to say "oh look, this onu uses less than this one". It's not a unit of measure. Sure i can unse it but I want to know how far my car goes on a tank of fuel. Do I now need to measure my fuel tank in units of how many litres it takes to drive 100km? because i could do that but again it's a roundabout measurement. We say km/h not km/5h or h/100km. We cousd and we could work with them but they are not actual units of anything they have to be back converted to something useful.

If i wanted to work out haw many litres I usod per 100km on my last tank I would have to establish L/km or km/L first.

tooki

• Super Contributor
• Posts: 5528
• Country:
Re: why is the US not Metric
« Reply #133 on: October 27, 2019, 05:48:42 pm »
Besides the Altium grid lines "standard" being a dog's breakfast, many Chinese PCB manufacturers only specify their capability dimensions in imperial measurements (eg: minimum track width 7mils, rather than 0.18mm). This is only to appease US engineers who cannot fathom (sorry, 1.8288m) the metric system (Just kidding, sort of!).
I assure you, it's nothing but smug US haters telling you that Americans can't understand metric. It's been taught in schools for 50+ years now, and American engineers are absolutely, definitely, 100% going to be able to handle millimeters just fine.

Of course they don't, if they did people would put them in 120V outlets and things would explode. It should be readily apparent that you will require an appropriately non-interchangable fitting for such radically different supplies, whether you go the route of distributing them unreasonable distances or use local regulation..

Actually they do, well they're 12VDC.

Well, frankly, that's stupid.

Does not really happen here, with the exception of 110V lamps - but they're fairly restricted in availability.

E: Although it seems there's a handful of them making their way over from China thanks to your influence..
12V (and even 6V) E27 bulbs are sold in Europe, too, again for campers. I think they're simply one of those items most people are unaware of, because a local grocery, furniture, or lamp store will not sell them. (But you will find them at the camper supply shop.)

It's the restricted availability that keeps people from buying them by mistake. It's not as though 12V (incandescent) E26/E27 bulbs are in any way new. If this were a major problem, it would have reared its head many, many decades ago, when our parents were still in diapers.

It's a complete non-issue, I don't think I've ever personally known anyone who put an RV bulb into a household socket. I'm sure someone has done it somewhere but it's certainly not common. They say 12V right on the bulbs, they're significantly more expensive than standard bulbs and while they are fairly widely available you kind of have to go out of your way to get them. If you do give a 12V bulb 120V it just blows out, pop, no drama or excitement. I put a 6V cadelabra base lamp in a 120V socket once when I was a kid, blew it instantly but didn't cause any harm beyond that.

It's not just the US that uses 120V, there are a whole handful of countries:
https://www.school-for-champions.com/science/ac_world_volt_freq_list.htm
^^^ exactly.

CatalinaWOW

• Super Contributor
• Posts: 3740
• Country:
Re: why is the US not Metric
« Reply #134 on: October 27, 2019, 05:58:02 pm »
These last few posts are typical of metric-imperial arguments.  I mean golly.  If you are able to do electronics you should be able to handle ratios and their inverses.  And use each to their best advantage.  It is kind of like arguing whether sines or arcsines are better.  Same applies to measurement systems.

No because L/100km has no practical use other than to say "oh look, this onu uses less than this one". It's not a unit of measure. Sure i can unse it but I want to know how far my car goes on a tank of fuel. Do I now need to measure my fuel tank in units of how many litres it takes to drive 100km? because i could do that but again it's a roundabout measurement. We say km/h not km/5h or h/100km. We cousd and we could work with them but they are not actual units of anything they have to be back converted to something useful.

If i wanted to work out haw many litres I usod per 100km on my last tank I would have to establish L/km or km/L first.

So Siemens are not a unit of measure?  But Ohms are.  Or frequency is not a unit of measure but wavelength is?  I don't disagree about which is more convenient for your purpose, but surely the people on this forum are bright enough to deal with these things without skipping a beat.

Simon

• Global Moderator
• Posts: 15341
• Country:
• Did that just blow up? No? might work after all !!
Re: why is the US not Metric
« Reply #135 on: October 27, 2019, 06:12:08 pm »
they are units of something per 1 of something else. It's metres per second, not metres per 10s. simens is the inverse of ohm, not the inverse of the measurement in ohms times 100

IanB

• Super Contributor
• Posts: 9761
• Country:
Re: why is the US not Metric
« Reply #136 on: October 27, 2019, 06:13:22 pm »
12V (and even 6V) E27 bulbs are sold in Europe, too, again for campers. I think they're simply one of those items most people are unaware of, because a local grocery, furniture, or lamp store will not sell them. (But you will find them at the camper supply shop.)

It's the restricted availability that keeps people from buying them by mistake. It's not as though 12V (incandescent) E26/E27 bulbs are in any way new. If this were a major problem, it would have reared its head many, many decades ago, when our parents were still in diapers.

I remember being highly amused in 1970's Britain when I discovered a 12 V 60 W bulb with an ES base (for use in a car inspection lamp). At the time all domestic 240 V light fittings used a bayonet cap bulb and so it was impossible to mix things up. There were 240 V bulbs made with an ES or GES base, but these were mainly used in industrial or commercial settings, rarely in homes.
I'm not an EE--what am I doing here?

The following users thanked this post: tooki

IanB

• Super Contributor
• Posts: 9761
• Country:
Re: why is the US not Metric
« Reply #137 on: October 27, 2019, 06:18:05 pm »
they are units of something per 1 of something else. It's metres per second, not metres per 10s. simens is the inverse of ohm, not the inverse of the measurement in ohms times 100

Simon, there may be engineering conventions in the world at large that you have not come across yet. For instance, it is common to express pressure drop in pipes as "psi per 100 ft" or "Pa per 100 m", and mechanical engineers find these to be perfectly good units of measurement.
I'm not an EE--what am I doing here?

Simon

• Global Moderator
• Posts: 15341
• Country:
• Did that just blow up? No? might work after all !!
Re: why is the US not Metric
« Reply #138 on: October 27, 2019, 06:22:02 pm »
Pa per 100metres? wow, with what i deal in that would be a big number, no need to multiply it by 100. But these sound like things installers use as rules of thumb. Last pressure drop measurement i took was 80pa over 300mm that makes it in your units 26'600 Pa/100m. I'd preper to use 166Pa/m thankyou

james_s

• Super Contributor
• Posts: 12604
• Country:
Re: why is the US not Metric
« Reply #139 on: October 27, 2019, 06:28:58 pm »
I remember being highly amused in 1970's Britain when I discovered a 12 V 60 W bulb with an ES base (for use in a car inspection lamp). At the time all domestic 240 V light fittings used a bayonet cap bulb and so it was impossible to mix things up. There were 240 V bulbs made with an ES or GES base, but these were mainly used in industrial or commercial settings, rarely in homes.

At that time fluorescent tubes with ordinary BC caps on the ends were widely available there though, as were mercury vapor and SOX (low pressure sodium) lamps, any of which would be destroyed similarly by plugging one into an ordinary incandescent socket wired to 240V. They did use a 3 peg BC cap on HID lamps for a while but they were never common, I have a couple of the lamps but have never had a proper socket for one.

Today AC adapters with 2.1 and 2.5mm barrel plugs are widely used all over the world with all manner of different voltage ratings and no firm standard on polarity. I've seen a lot of stuff damaged by people assuming that if the plug fits it will work. You can't idiot-proof everything, sometimes one just has to use their brain a bit in order to navigate the world.

Zero999

• Super Contributor
• Posts: 14580
• Country:
• 0999
Re: why is the US not Metric
« Reply #140 on: October 27, 2019, 09:05:09 pm »
I, personally, have three problems with this particular device: (1) it is not UL-listed, (2) my nearest Home Depot does not stock 12VAC operated A19 LEDs, (3) I doubt it will work properly with Lurton Caseta dimmers.
No shit Sherlock. It's rated  for 230V AC therefore not for US market. And it's not a LED driver.
Thanks for letting me know before I ordered 50 of those. I was already pulling out credit card from the wallet.
That's what's commonly known as am electronic transformer. It's a Royer converter which outputs around 50kHz to 100kHz, modulated with double the mains frequency. There's no voltage regulation or rectification because it's designed for powering 12V halogen lamps and nothing else.

See the application note linked below.
https://www.st.com/content/ccc/resource/technical/document/application_note/e5/88/46/11/35/8c/4a/bf/CD00003902.pdf/files/CD00003902.pdf/jcr:content/translations/en.CD00003902.pdf

The only advantage I can think of for DC home wiring is, it would enable a large power factor corrected power supply to power many devices, rather than each using its own switched mode power supply, which will not have power factor correction. Of course this wouldn't mean distributing DC power over the grid, but converting it to something like 48V in every house. In reality it's not worth it because it would make wiring more difficult and most devices won't run directly off 48V, so more voltage conversion will still be required.
« Last Edit: October 27, 2019, 09:13:31 pm by Zero999 »

james_s

• Super Contributor
• Posts: 12604
• Country:
Re: why is the US not Metric
« Reply #141 on: October 27, 2019, 10:14:12 pm »
There's a good reason for having higher voltage distributed everywhere anyway. There are lots of large loads, toasters, vacuum cleaners, space heaters, air conditioners, hair dryers, dehumidifiers, microwave ovens, coffee makers, etc. Sure I don't need these things in every room of the house but at one point or another I have used at least one of these high powered appliances in every room of my house and even 120V is marginal for many of them.

Power factor is not even really an issue for residential customers. Ideally we want it to be close to unity but it doesn't affect your bill in most places. If it were really a problem then a sensible way of sorting it out would be a central active PF correction device wired into the panel.

The following users thanked this post: tooki

TimFox

• Super Contributor
• Posts: 1830
• Country:
• Retired, now restoring antique test equipment
Re: why is the US not Metric
« Reply #142 on: October 28, 2019, 01:08:29 pm »
Going back to the original question:  Please note that the US does not use the term "Imperial Units", except to refer to specific items such as the Imperial gallon and pint, which differ in magnitude from the US "Customary Units" the US gallon and pint.

The following users thanked this post: Macbeth, tooki

Simon

• Global Moderator
• Posts: 15341
• Country:
• Did that just blow up? No? might work after all !!
Re: why is the US not Metric
« Reply #143 on: October 28, 2019, 01:11:12 pm »
Quite, there are 3 systems on the go although the UK officially does not use imperial.

tooki

• Super Contributor
• Posts: 5528
• Country:
Re: why is the US not Metric
« Reply #144 on: October 28, 2019, 06:33:27 pm »
Oh yeah, I just remembered another US unit that's used worldwide: the foot, in aviation. Flight levels are practically always* in feet, because having a consistent system is far more important than which system it is. Switching would likely lead to some crashes during the transition period. With there being essentially no advantage to switching, the risks involved in switching just don't make sense, which is probably why aviation has stuck with feet, despite ICAO recommending a switch to metric since 1979.

(Given the altitudes in question, the unit used is essentially totally arbitrary, since one's "feel" for a unit in everyday life can't translate to the huge altitudes involved. And the actual amounts don't really matter, insofar as it's air traffic control telling a pilot what flight level to use.)

*Except China, Mongolia, North Korea, Kyrgyzstan, Kazakhstan, Tajikistan and Uzbekistan. Russia actually used to use metric flight levels, but in 2017, actually switched from meters to feet.

Simon

• Global Moderator
• Posts: 15341
• Country:
• Did that just blow up? No? might work after all !!
Re: why is the US not Metric
« Reply #145 on: October 28, 2019, 07:11:27 pm »
Something like flying altitudes are indeed best not messed with.

The following users thanked this post: tooki

boffin

• Supporter
• Posts: 976
• Country:
Re: why is the US not Metric
« Reply #146 on: October 28, 2019, 10:37:03 pm »
Oh yeah, I just remembered another US unit that's used worldwide: the foot, in aviation. Flight levels are practically always* in feet, because having a consistent system is far more important than which system it is. Switching would likely lead to some crashes during the transition period. With there being essentially no advantage to switching, the risks involved in switching just don't make sense, which is probably why aviation has stuck with feet, despite ICAO recommending a switch to metric since 1979.

(Given the altitudes in question, the unit used is essentially totally arbitrary, since one's "feel" for a unit in everyday life can't translate to the huge altitudes involved. And the actual amounts don't really matter, insofar as it's air traffic control telling a pilot what flight level to use.)

*Except China, Mongolia, North Korea, Kyrgyzstan, Kazakhstan, Tajikistan and Uzbekistan. Russia actually used to use metric flight levels, but in 2017, actually switched from meters to feet.

It's ugly in the aviation world (Canada, light aircraft example)

Fuel, sold in litres, but you care about weight (in lbs), and consumption (in US Gal/hr)
Altitude in hundreds of feet
Visibility is in statue miles (metres in Europe)
But speeds (wind, and your aircraft) in kts
Directions in degrees true (if you read it) or magnetic (if you hear it)
Runway directions in degrees magnetic (except far north where it's deg true)
Air pressure in inches of Mercury (altimeter settings) and/or Hectopascals (weather reports, and for altimeter outside of North America)
Temperature (Celsius for air, Fahrenheit for engine gauges)

How we don't end up with more Gimli Gliders, I'm not sure

The following users thanked this post: tooki

bsfeechannel

• Super Contributor
• Posts: 1129
• Country:
Re: why is the US not Metric
« Reply #147 on: October 28, 2019, 11:51:57 pm »
Oh yeah, I just remembered another US unit that's used worldwide: the foot, in aviation. Flight levels are practically always* in feet, because having a consistent system is far more important than which system it is. Switching would likely lead to some crashes during the transition period. With there being essentially no advantage to switching, the risks involved in switching just don't make sense, which is probably why aviation has stuck with feet, despite ICAO recommending a switch to metric since 1979.

(Given the altitudes in question, the unit used is essentially totally arbitrary, since one's "feel" for a unit in everyday life can't translate to the huge altitudes involved. And the actual amounts don't really matter, insofar as it's air traffic control telling a pilot what flight level to use.)

*Except China, Mongolia, North Korea, Kyrgyzstan, Kazakhstan, Tajikistan and Uzbekistan. Russia actually used to use metric flight levels, but in 2017, actually switched from meters to feet.

But in countries where metric is already the "customary" system, when addressing the passengers, the pilot converts the altitude to meters, because no one has absolutely any clue what 27.000 feet means.

That goes for seat screens: speeds in kilometers per hour and altitude in meters.

james_s

• Super Contributor
• Posts: 12604
• Country:
Re: why is the US not Metric
« Reply #148 on: October 29, 2019, 12:47:07 am »
I'm surprised people wouldn't have a rough idea of what feet is. For all the crap Americans get for supposedly not knowing other units, I think most of us have a pretty good idea of what a meter is. It's close enough to say it's about 3 feet.

The following users thanked this post: tooki

CatalinaWOW

• Super Contributor
• Posts: 3740
• Country:
Re: why is the US not Metric
« Reply #149 on: October 29, 2019, 01:21:45 am »
As if the passengers really care if they are at 10000 vs 11000 meters.  Ant most folk have a fair approximate idea of what a foot is.  Just look at where your body touches the ground.  For passengers evaluating flight altitude even 30 or 40 % errors are not a problem.

The following users thanked this post: tooki

Smf