The SI system is at least part of the modernization of the metric system. The two aren't different, but go hand in hand.
Under the heading "Punctuation and Spacing,"
2. Symbol Spacing. Use a space between the numerical value and the unit symbol.
Examples:
Correct - 2 A | 4 mm
Incorrect - 2A | 4mm
Under the heading "Punctuation and Spacing,"
2. Symbol Spacing. Use a space between the numerical value and the unit symbol.
Examples:
Correct - 2 A | 4 mm
Incorrect - 2A | 4mm
I like to take on board suggestions to correct any mistakes I make. I used to refer to db instead of dB until corrected. Silly me!
I won't be taking on Sofa's suggestions.
I won't be taking on Sofa's suggestions.
Well I think it is not always clear what you mean (not you personally, but whoever writes it) when you write Vac. For example, we all use 220Vac or 110Vac for line voltage, which is the RMS value, while Vac formally means, what, peak value?
jan
But it not the rms value.
It's the value of the single frequency sinewave.
The distortions are not accounted for, but are limited to <5% (I think I saw this on the Forum).
If they supply 238Vac and it contains 4% of distortion, we would "measure" ~247.5Vrms on a true rms meter, but the supply is still 238Vac. We don't use the 4% of higher frequencies.
I have never seen units put routinely in square brackets. Is this a German convention?KSTR said:
I have just checked a few textbooks. Both physics and engineering put a space between numbers and units, so my "100V" in an earlier post was wrong. No square brackets seen around units.
Yes but the 220 (or 238) Vac is the RMS value. On the scope you'll see a peak value of some 311 V. So the implication when you mention 220 Vac line is that you mean RMS without explicitly mentioning it. I could very well speak about 311 Vac line voltage meaning 311 Vac pk.
Looks like you're right. I checked this and found that it was used until like 1980 (at the time of my education) but it was a wrong convention in a strict sense.
We were taught to do that (in an American university) to indicate dimensional analysis, not when there were actual quantities involved, i.e., [m/s] meant "dimensions of meters per second," whereas if there were specifically 22 meters covered in one second, we would write 22 m/s (with the space).
And of course, to a chemist, the square brackets meant "concentration."
Ah yes, I had forgotten how we were taught to write dimensional analysis. I still use it as a tool, as my algebra is very prone to error nowadays, but I don't bother with exact ways of writing it down for my own use.
Is dimensional analysis still taught? A very useful tool; one can often guess the formula for something just from dimensions, apart from constants such as 2 or pi.
Is dimensional analysis still taught? A very useful tool; one can often guess the formula for something just from dimensions, apart from constants such as 2 or pi.
I was first taught dimensional analysis at school, in A-level physics (16/17 years old), but that was a long time ago.
I hope so. I used to drill this into my freshman students- "If the dimensions work out right, it's usually right. If the dimension work out wrong, it is always wrong."
We don't?
If you plug a lightbulb or heater into that socket, it will "see" and use 247.5 Vrms. All harmonic content will be used to generate heat (within certain realistic limits, imposed by things like the inductance of the filament, etc.).
We probably went to different schools together.
Although dimensional analysis was lightly covered in High School science classes, it was REALLY drilled into me in college freshman chemistry, circa 1969-70. I recognized its value, and have used it extensively ever since, though even then it seemed to be heavily used in only about half of all technical curricula. (I realized that when one of my officemates in grad school was amazed at how quickly I could check the results of some algebraic manipulations by going through the units.)
Dimensional analysis gets VERY powerful if you remember a few fundamental definitions - e.g., farads of capacitance are actually coulombs per volt, a watt-second is actually a joule, etc.
How do folks handle the nomenclature for "dimensionless" quantities? For example, voltage gain is a pure number (dimensionless), but I generally write it as "volts-per-volt" (V/V) - not just to avoid confusion because power gain and current gain are sometimes also called simply "gain", but as a reminder of where this value came from.
Dale
symbol conventions
I think that if the facility for using greek alphabetic symbols (at least) were included in the reply window a la this forum we might all be a little more pro-active in using correct or at least consistent symbols. I appreciate that you can learn ASCII codes for just about anything but it has never attracted much following, whilst I think this will.
If it is appropriate to request our forum management look into this, then let's get on with it.
Why make it hard for people to follow conventions when simple technology is already available?
I think that if the facility for using greek alphabetic symbols (at least) were included in the reply window a la this forum we might all be a little more pro-active in using correct or at least consistent symbols. I appreciate that you can learn ASCII codes for just about anything but it has never attracted much following, whilst I think this will.
If it is appropriate to request our forum management look into this, then let's get on with it.
Why make it hard for people to follow conventions when simple technology is already available?
I don't think swapping 'u' for 'mu' is the issue, as 'u' is a generally accepted and understood substitute. People still have trouble distinguishing between 'f' for femto and 'F' for farad. Others still use 'fd' for farad, and 'm' for micro instead of milli. Then when someone uses 'mf' we don't know if this is a typo for 'mF' or 'mfd', although context can often help.
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Well, you could be right about that but the widespread use of makeshift symbols is, I suggest, at the root of it. A little encouragement to conformance rather than open slather has got to be better communication, otherwise we wouldn't insist on their correct usage in academic circles.
I think that since most threads are started by non-techs with problems, we will always need to accept ignorance of terms and symbols but it helps when those replying use the right ones rather than perpetuate misuse. A symbol editor is just one more learning tool and a good one if those who know the difference bother to use it.
It also seems to me that newbs learn here from example, particularly E.s.l. members and I'm personally interested in seeing opportunity for everyone who posts here to contribute in some way to the excellence of this forum. The standard can be impressively high!
I reason that if we have ample space for a mass of "smilies" then we have room too, for something practical that facilitates our communication across many backgrounds. I don't wish to promote pedantry but neither do I wish to deter those who are generous in their posts by being precise and educative.
I give complete support to that thought!
The majority of symbol editors and special-character features I have used, while sometimes very powerful, are not very user-friendly. By the time you fumble around with the <ctrl><shift><Fcn Key> (or whatever) sequence it takes to add one of the special characters, you have lost the coherent thought you were trying to express. (If my memory is correct, the old WordPerfect program was especially bad about this. You could do ALL KINDS of fancy and impressive things with keyboard codes - but it took about 4 fingers and an elbow to enter the necessary key combination. Assuming, of course, that you correctly remembered which of several dozen combinations you wanted.)
You still have to recognize that giving users of THIS forum an easy way to add basic symbols (mu, omega, beta, integral signs, etc) does NOT carry over to dozens or hundreds of other communication channels (such as basic email). Setting and enforcing standards based on the "normal" keyboard characters is probably a more practical, though less correct and less flexible, approach.
As mentioned in this thread, the problem has been with us for decades - the SPICE syntax from the early '70's uses "m" for "milli-" and "meg" for "meg-".
Dale
I used to have a Word document open with many of the symbols I'd use, and then do a quick copy-paste into whatever app I need it - email, forum etc.
jan
jan
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