Post by thread:[OT] Units [Was: Beginners Problem ??]

On Fri, Mar 12, 1999 at 11:12:49PM -0500, Wagner Lipnharski wrote: > Hi Biswanath, > > I don't want to be a pest in your life, but by the fact > that you are learning, you would understand if I correct > you in few things, and I am sure some other people > around will learn it too. Sadly, there are competing "standards", which may not come from electronics per se but are a fact of life nonetheless. Many corrupting influences of course come from the vile world of computers, still somehow part of electronics, no? :-) > milli (m) 0.001 > micro (µ) 0.000,001 > nano (n) 0.000,000,001 > pico (p) 0.000,000,000,001 > deca (d) 10 > centi (c) 100 > kilo (k) 1,000 Yes, but kB always looks wrong, so in discussing memory capacity KB is not incorrect. In this context, of course, K is 2^10 instead of 10^3 anyway, so perhaps this is not a contradiction. Still, with this excuse, M meaning 2^20 and G meaning 2^30 result in a bit (NPI) of a conundrum. > Mega (M) 1,000,000 (upper case because the -m- milli) > Giga (G) 1,000,000,000 (upper case because -g- gram) > ...others > > For example, milli is just "m" it is not an abreviation > form, so it does not carry the dot "m." > Start using the right denomination as much as possible > and quickly you will do it without any effort. Of course, again in the context of computers, "b" is "bit" (0 or 1), while "B" is "byte" (eight bits). Thus we get "Kb" for 2^10 bits and "KB" for 2^13 bits, although one of course on occasion sees "kb" for 2^10 bits, as though the "K" needed to step down out of pity for the poor little bit. But surely "MB" is 2^23 bits, and "Mb" is 2^20 bits, and, my all-time favorite when it appears in print, "mb" is 0.001 bits. I'm still trying to figure that one out. > 10kOhms, or R10k, not 10K, someone can confuse it with > 10 Kelvin degrees. In this case, I will disagree. If 10kOhms can't be written "10K", then certainly 10 degrees Kelvin has no greater right to go around naked like that -- at least it needs to have the ¡, out of fairness if nothing else. But seriously, "K" by itself is not, AFAIK, assigned to *any* unit if measure; degrees Kelvin is ¡K, beginning and end of story; if you cannot write the ¡ symbol, use the word "degree". Horowitz and Hill argue vehemently that "10K" is unambiguously 10kOhms; the argument for this is that resistance is the only unit so fundamental to the study of electronics that it can be unambiguously stated without the use of the Omega or word Ohm. It is a judgement call whether or not to go along with this, but the potential for confusion with Kelvin isn't a valid argument against it, IMHO. The common usage of "5R1" for 5.1 Ohms and "5K1" for 5.1 kOhms is similarly contestable, but seems fairly well ingrained even in the labling of, say, 1% resistors. {Quote hidden}> 10uF, not 10mfd, someone can mixup it with milliFarads > or some bad name. > > Meter (m) doesn't make confusion with milli (m) since > milli alone doesn't exist. It is quantifying some other > unit, as Volts, grams, even meters (mV, mg, mm). > > "mts." for "meters", instead the simple "m", > "hrs." for "hours", "mints." for minutes, > "K" for "kilo", worse, KG for "kilogram", > looks like "a Kelvin degree in free falling > acceleration at G (gravity) 10m^2/s . As we drift out of symbols for units and into physical constants, "G" is the gravitational constant, approximately 6.6732x10^-11 N-m^2/kg^2, whereas "g", the acceleration due to gravity, is approximately 9.80621 m/s^2 at 45¡ latitude. (Note that, if a multiplicative prefix is used in a unit specification, (mA, or cm, for example), then a following exponant (e.g. cm^2) unambiguously applies to the entire combination, i.e. cm^2 is square centameters, not centasquaremeters.) Also, if units are combined, as in N-m for Newton-meters, a hyphen or a solidus should almost always be used, but no more than one solidus -- cm/s^2 is OK but cm/s/s is not. > Degrees use the "¡" symbol, as ¡F or ¡C, to type it > just press and hold ALT+SHIFT and type 0 1 7 6 at the > numeric keypad. > > The same for "µ" ALT+SHIFT+0181 (not 181) > "¸" ALT+SHIFT+0189 > "¹" ALT+SHIFT+0188 > "²" ALT+SHIFT+0190 This, I am afraid, depends greatly on one's choice of text editor and, perhaps, operating system. BTW, in preparing this response, I made extensive use of my trusty "Rubber Bible" -- the CRC Handbook of Chemistry and Physics, 55th edition, which is frighteningly dated 1974 (and purchased new by myself, I must add). I wish to report that Wagner's statement of the rules for SI multiplicative prefixes is exactly in agreement with that text, right down to "k" being lower case and "M" being upper. In good humor, --Bob -- ============================================================ Bob Drzyzgula It's not a problem spam_OUTbobTakeThisOuTdrzyzgula.org until something bad happens ============================================================

Hi Bob, At 12:55 AM 3/13/99 -0500, you wrote: [SNIP] >the ¡, out of fairness if nothing else. But seriously, "K" >by itself is not, AFAIK, assigned to *any* unit if measure; >degrees Kelvin is ¡K, beginning and end of story; if you >cannot write the ¡ symbol, use the word "degree". Horowitz Well,Bob,in some of my Physics classes, Kelvins have been considered to be a unit unto themselves (IOW, it is correct to say 10 Kelvin instead of 10 degrees Kelvin) It seems to me that there isn't real agreement on this point. It is probably not a really good way to differentiate,but how about the fact that usually, with resistance, the K is written right next to the value (i.e. 10K or 10k) and with temperatures, there is usually a space (i.e. 3 K cosmic background radiation). >BTW, in preparing this response, I made extensive >use of my trusty "Rubber Bible" -- the CRC Handbook >of Chemistry and Physics, 55th edition, which is >frighteningly dated 1974 (and purchased new by myself, >I must add). I wish to report that Wagner's statement >of the rules for SI multiplicative prefixes is exactly >in agreement with that text, right down to "k" being >lower case and "M" being upper. I've got the 1992-93 edition,but it seems to me that most of the material from it greatly pre-dates 1992 anyway,with the exception of the 1983 (IIRC) accepted constants. The CRC handbook really comes in handy because I can be pretty sure that if a prof. says "look it up",its in there! I didn't buy it,got it as a prize in a Chemistry competition. {Quote hidden}> >In good humor, > >--Bob > >-- >============================================================ >Bob Drzyzgula It's not a problem >.....bobKILLspam@spam@drzyzgula.org until something bad happens >============================================================ > | | Sean Breheny | Amateur Radio Callsign: KA3YXM | Electrical Engineering Student \--------------=---------------- Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 shb7KILLspamcornell.edu ICQ #: 3329174

At 00:55 03/13/99 -0500, Bob Drzyzgula wrote: >In this case, I will disagree. If 10kOhms can't be written >"10K", of course it can, and mA can be written Mamps... as long as you stay within a =small= context, everybody'll understand. >then certainly 10 degrees Kelvin has no greater right >to go around naked like that -- at least it needs to have >the ¡, out of fairness if nothing else. But seriously, "K" >by itself is not, AFAIK, assigned to *any* unit if measure; >degrees Kelvin is ¡K, beginning and end of story; nope. i don't know where the beginning of the story is, and i certainly don't know where the end will be, but "K" is the unit "Kelvin" for the absolute temperature in the SI ("Systme Internacional") -- no "¡", no "degree". Celsius, Fahrenheit and Reaumur use ¡, though. {Quote hidden}>Horowitz >and Hill argue vehemently that "10K" is unambiguously >10kOhms; the argument for this is that resistance is the only >unit so fundamental to the study of electronics that it >can be unambiguously stated without the use of the Omega >or word Ohm. It is a judgement call whether or not to go >along with this, but the potential for confusion with Kelvin >isn't a valid argument against it, IMHO. The common usage >of "5R1" for 5.1 Ohms and "5K1" for 5.1 kOhms is similarly >contestable, but seems fairly well ingrained even in the >labling of, say, 1% resistors. i still don't understand why you insist in using the upper case "k". it sounds everything fine, except for the upper case. =my= keyboard, at least, makes it even more comfortable to write 5k1 than 5K1. and i agree completely with you that for resistors, capacitors and inductors the form to write 5k1 or 4u7 is in most cases pretty unambiguous, especially when used in a schematic. and it's a whole lot safer against misreading than 5.1kOhm -- the dot sometimes gets pretty tiny. >square centameters, not centasquaremeters.) right, but it's "centimeters" (also in english, i think, but i'm no native speaker :) ge

On Sat, Mar 13, 1999 at 01:47:41AM -0800, Gerhard Fiedler wrote: > At 00:55 03/13/99 -0500, Bob Drzyzgula wrote: > >In this case, I will disagree. If 10kOhms can't be written > >"10K", > > of course it can, and mA can be written Mamps... as long as you stay within > a =small= context, everybody'll understand. I was mostly referring to the ommision of the unit, rather than the case of the "K", but you are right about the inconsistancy in my use of case. My only defense is that I wrote that *way* past my bedtime :-) This correction, of course, only lessens the risk of confusing 10k as a resistance and 10¡K as a temperature. {Quote hidden}> >then certainly 10 degrees Kelvin has no greater right > >to go around naked like that -- at least it needs to have > >the ¡, out of fairness if nothing else. But seriously, "K" > >by itself is not, AFAIK, assigned to *any* unit if measure; > >degrees Kelvin is ¡K, beginning and end of story; > > nope. i don't know where the beginning of the story is, and i certainly > don't know where the end will be, but "K" is the unit "Kelvin" for the > absolute temperature in the SI ("Systme Internacional") -- no "¡", no > "degree". Celsius, Fahrenheit and Reaumur use ¡, though. Then you know something that I didn't. As my reference here, I was using the CRC Handbook, which distinctly and consistantly uses the ¡K in its telling of the SI standard. The CRC Handbook also points out that, when speaking of a temperature *interval*, the indication of Kelvin or Celsius is irrelevent (being different only in offset) and thus it is considered proper to use only ¡, "deg" or "degree" in stating an interval when the scale is clear from context. Thus, from this I concluded that it is the ¡ that is considered the primary symbol for temperature, with "F", "K" and "C" being suffix indicators for scale and offset. I suppose that this could reflect the age of my copy? Perhaps someone has the source standard and can clear this up? Of course, the very same handbook then goes and violates its own advice in several other sections, using K by itself for example in the statement of the units in Boltzman's constant. I take this to mean that the use of the ¡ is offical and proper, but it is a pain in the behind to carry around all the time so everyone just winks at each other and omits it when they can get away with it. But it also could mean that the CRC's statement of the SI standard is incorrect. > >Horowitz > >and Hill argue vehemently that "10K" is unambiguously > >10kOhms; the argument for this is that resistance is the only > >unit so fundamental to the study of electronics that it > >can be unambiguously stated without the use of the Omega > > i still don't understand why you insist in using the upper case "k". it Because the last thing I was looking at did it that way and I didn't think sufficiently about it. Looking at several other references I see now that the lower case is much more frequently and correctly used; I stand corrected. > >square centameters, not centasquaremeters.) > > right, but it's "centimeters" (also in english, i think, but i'm no native > speaker :) Correct, thank you. I never could spell worth a damn. :-) Of course, it is "centimeters" in "American" but probably "centimetres" in "English"? :-) --Bob -- ============================================================ Bob Drzyzgula It's not a problem .....bobKILLspam.....drzyzgula.org until something bad happens ============================================================

At 07:57 03/13/99 -0500, Bob Drzyzgula wrote: >> nope. i don't know where the beginning of the story is, and i certainly >> don't know where the end will be, but "K" is the unit "Kelvin" for the >> absolute temperature in the SI ("Systme Internacional") -- no "¡", no >> "degree". Celsius, Fahrenheit and Reaumur use ¡, though. > >Then you know something that I didn't. As my reference >here, I was using the CRC Handbook, which distinctly >and consistantly uses the ¡K in its telling of the SI >standard. look at http://physics.nist.gov/cuu/Units/units.html where they tell a bit of the SI story (it's one of the top links of a web search on "units si", so it's not exactly hard to find anytime you might need it :). your handbook seems outdated. the difference is, as i see it, that Kelvin is an absolute unit, and therefore a "real" physical unit, and has no ¡. whereas the various "human" temperature scales are just that, and so they get the traditional ¡ in front of them. ge

Gerhard Fiedler wrote: > look at http://physics.nist.gov/cuu/Units/units.html where they tell a bit > of the SI story (it's one of the top links of a web search on "units si", > so it's not exactly hard to find anytime you might need it :). your > handbook seems outdated. > > the difference is, as i see it, that Kelvin is an absolute unit, and > therefore a "real" physical unit, and has no ¡. whereas the various "human" > temperature scales are just that, and so they get the traditional ¡ in > front of them. > > ge so I was right since the beginning. :)) Degree means basically rotation in a scale, and so it was in the old thermometers, a torsion device based on temperature. Each one build its own scale, so entitled it with his name. A whole degree in each one was meaning different temperatures, based on the way it was build. Different from Kelvin that is an absolute physical unit. I use a thermometer microchip that gives me Volts/Kelvin, easy, pure, no crazy conversions or factor tables. Wagner