FWIW let's limit this discussion to caps. You may put other descriptors on various engineering drawings but when it comes to descriptions on the parts list it's advantageous to use values that component manufacturers place on the actual part. Also discriptions should match for obvious aide to non-technical persons ie purchasing, shipping/receiving, kitting, and assemblers. Now let's go shopping for big caps between 1000uF and 1F use your favorite catalogs and take a look. For example Digikey Panasonic electrolytic look here
Nowhere do I see mF at least here in the USA. If someone in other markets can show otherwise it would be interesting.
Nowhere do I see mF at least here in the USA. If someone in other markets can show otherwise it would be interesting.
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mF is a legitimate unit, and if you look at something like the B&K 830B, it reads out in mF for the larger values. This makes sense, lest the display have to contend with too many zeros. OTOH, if you do a Google search on "mF capacitor", the number of good top hits is about two. Vishay uses mF, but not on their caps, just their web page, and the B&K meter. Almost all the other hits are people using mF in error, to mean uF, so I'll grant that the usage carries a fair risk of misinterpretation until I've re-educated everyone.
Yes it is, but the fact is.. it's just not used in the industry.
Mostly to create less confusion with the historical usage of mfd with the meaning of "micro farad" or uF. As you probably found out using the 'google' search engine for your due diligence.
Ok I guess so, maybe AndrewT will help you there as well. But if you use the term milliFarad it may cause problems until everyone is aware of the issue or it's forgotten completely.
IMO the future of larger capacitor values will be shrinking again for audio. ie Class D Amplifier and SMPS. yea I know I don't like it either.
capacitor culture
I find the markings on capacitors vary a lot depending on what decade they are manufactured, and where they are sold mf was used a lot in the 50's and early 60's in the US for microfarad, that is anathama now. In general for a disc capacitor from that era, a number without anything behind it meant what we mean as pf now. I've got of RS surplus ceramic disc junk from the early 70's rated 2 digit mf, I don't know what they meant because I tried them in an oscillator circuit recently and got weird results. Recent salvage from chinese products is labeled like 472 mf, which from the size (.25" dia diak) I take to mean 4700 pf but who knows? Unfortunately, I think it actually takes a data sheet from the manufacturer (they still don't put logos on) to figure out what they mean.
I find the markings on capacitors vary a lot depending on what decade they are manufactured, and where they are sold mf was used a lot in the 50's and early 60's in the US for microfarad, that is anathama now. In general for a disc capacitor from that era, a number without anything behind it meant what we mean as pf now. I've got of RS surplus ceramic disc junk from the early 70's rated 2 digit mf, I don't know what they meant because I tried them in an oscillator circuit recently and got weird results. Recent salvage from chinese products is labeled like 472 mf, which from the size (.25" dia diak) I take to mean 4700 pf but who knows? Unfortunately, I think it actually takes a data sheet from the manufacturer (they still don't put logos on) to figure out what they mean.
As the digikey link demonstrates (copying from the page HTML source, values up to 120000µF), the only "safe" abbreviation for milliFarad is "x1000uF" or (using a character outside the original 7-bit ASCII code that I learned so well back then) "x1000μF".
Not only do I remember microFarad as mfd, I recall picoFaad as mmfd. Yep, history can be "very, very wrong."
Capacitors historically only had multipliers of 10^-6 or 10^-12, and people added zeroes on whatever side of the decimal point needed to get to the appropriate value with the nearest multiplier. Nano is often used currently and doesn't cause the confusion that milli does, and it's quite understandable why milli is so often eschewed as a multiplier for capacitance.
I've yet to see anything like "472 mf" on a capacitor, but that's a hoot.
Not only do I remember microFarad as mfd, I recall picoFaad as mmfd. Yep, history can be "very, very wrong."
Capacitors historically only had multipliers of 10^-6 or 10^-12, and people added zeroes on whatever side of the decimal point needed to get to the appropriate value with the nearest multiplier. Nano is often used currently and doesn't cause the confusion that milli does, and it's quite understandable why milli is so often eschewed as a multiplier for capacitance.
I've yet to see anything like "472 mf" on a capacitor, but that's a hoot.
actually things have changed somewhat since this post. if you look at mouser and probably DK these days, small DC link and supercapacitors; mF is used a lot. It seems to be the standard actually
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mfd is a misnoner and is only used on old american schematics, etc, and by old people who remember it.
The rule says that you have to change the prefix if a number goes below 0,001, or reaches 1000, therefore 1000uF is supposed to be 1mF, 10,000 uF is 10mF, etc.
The rule says that you have to change the prefix if a number goes below 0,001, or reaches 1000, therefore 1000uF is supposed to be 1mF, 10,000 uF is 10mF, etc.
All those zeros and a capitalised U make it difficult to read.
Now where are my spex and maybe I will see if DigiKey meant 88mF or 880mF
Now where are my spex and maybe I will see if DigiKey meant 88mF or 880mF
That cap is measured in UF; what multiplier is 'U'? I know 'u' is used for micro because inserting Greek text is so messy, but 'U'?
Let's just remember that 'mfd' when it appears in historical documents means microfarads, but it should not be used nowadays. 'mF', when used today, means millifarads although not often used. 'mf' is either meaningless or means 10^-18 (milli times femto) - it is not a unit of capacitance.
Let's just remember that 'mfd' when it appears in historical documents means microfarads, but it should not be used nowadays. 'mF', when used today, means millifarads although not often used. 'mf' is either meaningless or means 10^-18 (milli times femto) - it is not a unit of capacitance.
Let's just remember that some have used the SI system since 1960, UK citizens didn't go metric till 1980, and the US still have to adopt it.
English speaking folks in particular might better refrain from making statements about SI units.
English speaking folks in particular might better refrain from making statements about SI units.
Just to add, in days gone bye, there was also "mmf" which stood for micro-micro farads and was equivalent to picofarads! Fortunately, this nomenclature is now obsolete.
Most old schematics from the 60's and back did use the terms mfd, MFD, mf or muf to abbreviate the word microfarad. there was no universal standardization and each manufacturer had their own rules. mmfd, puf, and pfd were common abbreviations for picofarads. You will also see CPS or cycles instead of Hz. mF and nF were not used in the old days, but have become common place now.
The abbreviations were probably different outside the USA. Schematics from abroad were not commonly available here in the 50's and 60's. No one outside the medical or scientific community here knew what a liter was in the 1950's. The internet and availability of European DIY electronics magazines have forced a globalization of standard terms.
Makes a difference if one grew up with metric/SI units at elementary school level, or not.
Back when i first had English classes, it was 20 shilling to the pound and 12 pence for a shilling.
Going to 100 new-p the pound a couple of years later in the early 70s was easy.
+10 years the €, and i still hate it each and every day.
Metrication in the United Kingdom - Wikipedia, the free encyclopedia
Fortunately indeed. The only reason that mmfd and mfd were used is that people/industry in the US did not know µF. It is plain wrong to write farad. It should be in capital as it is derived from a name like Volt, Ampere, Joule etc. so Farad. We have the SI system for a very long time (since 1960) and it makes life easier. Since they are also used for weight here the pieces of the puzzle fit even more. So mF (milliFarad) can be used and, although uncommon, kF can be used too just like femtoFarad or fF. In weight this would be mg (milligram), kg (kilogram) and fg (femtogram).
Since nothing is perfect we use inches, even mixed together with meters, for metal piping in the industry !?!? Like pipes and valves for water, gas etc. They are still measured in "duim" here ( 1 duim/thumb = 1 inch) and in quarter duim, half duim etc. but the length will always be in meters...... And in weight 1000 kg should be called megagram. We say ton instead which is not used in the SI system... And when we are talking money a ton suddenly is 100.000 Euro. There is a historical reason for that but that does not make it right.
To be honest the use of uF is making things not better but it is faster when typing. I vote for the use of µF as it should be.
http://en.wikipedia.org/wiki/Farad
http://www.engineeringtoolbox.com/si-unit-system-d_30.html
BTW here is a conversion list for the older US designations like mmf etc:
http://www.justradios.com/uFnFpF.html
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Reading your last link (Just Radios) for nostalgic purposes - what a confusion that is. On another page, they use mmfd, MMFD, mfd and MFD: Capacitor MF - MMFD Conversion Chart "Short forms for micromicrofarads include pF, mmfd, MMFD, MMF, uuF and PF...". In our quest for progress, such inefficiencies do take a little while to flush out.
I agree that the SI system is easier and more logical, yet we continue to measure our UK road distances in miles 😉 It wouldn't surprise me if someone preferred to express their speed in terms of 'furlongs per fortnight'...
hi hi => Tonne - Wikipedia, the free encyclopedia
(then there the gross ton, net ton, imperial ton, Panama ton, Suez ton)
Difficult indeed, there should be a space between the number and the units (no space is a pet peeve of mine, though I am probably guilty sometimes too). I presume that Digi-key avoids using "mF" for a good reason... the same reason that this discussion exists, and that so many different opinions are being expressed here.
I'll weigh in with my own opinion, and it is just opinion.
"mF" is a perfectly valid unit for "milli Farad", however, it should never be used due to inevitable risk of confusion with micro Farad. Now I understand that "uF" is not technically accurate, but it is much better to express micro Farad as "uF" than "mF" or "mfd".
As for "mfd"... really, America? I guess we can expect no better when you use "kph" instead of "km/h" for kilometers per hour, or "cc" instead of "cm3" for cubic centimeter - which should actually be mL (millilitre) in the first place. Forget international standards, we'll just do whatever we want, that's the American way! 🙄
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