Proper Value Notation -- how to write VDC and VAC?

[EE4me]

TL;DR Summary

When specifying DC vs AC voltage excitation, is it appropriate to type 50 VDC with DC as a subscript? OR should it be "V DC"?

When specifying DC vs AC voltage excitation, is it appropriate to type 50 VDC with DC as a subscript? OR should it be "V DC"? The same concept if it were AC.

 

[Baluncore]

Vdc is simple, but Vac often needs more than just AC.
Vac could be Vrms in the sinewave power distribution industry.
It could be Vp, in math or SPICE modelling software.
Or even Vpp, when measured on the screen of an oscilloscope.

 

[Rive]

I don't know about any specific standard, but we tend to use VDC and VAC as a marking for supposedly 'clean' DC and AC sources, while V_DC and V_AC as measurements of the specific components of a 'mixed' source.

But, again, I think it's just kind of intuitive usage and I don't know about any actual standards regarding this.

 

[Tom.G]

To add to the confusion, see: https://www.physicsforums.com/posts/3015351 from 12 years ago. (and for more confusion, there are a couple typing errors in it too!)

 

[EE4me]

To add to the confusion, see: https://www.physicsforums.com/posts/3015351 from 12 years ago. (and for more confusion, there are a couple typing errors in it too!)

I was looking at the IEEE guideline and noticed they specifically state that DC and AC are not capitalized. I've seen both and capital looks better to me so I'll probably stick with that. I haven't seen subscripts addressed so I was wondering if there was any specific notation. Since there's doesn't seem to be a "standard notation", I guess I'll just go with what looks best at the time. Or maybe adapt your suggestion earlier about clean signals vs measured components

 

[cemx86]

You say that 'VDC and VAC should be written with a capital letter for "V" followed by lowercase letters "DC" or "AC" respectively'. Then you don't follow your own rule. What?

 

[Baluncore]

Welcome to PF.

You say that ...

Who is "you" that says that?
To quote a post, highlight the text, then click on reply.

 

[DaveE]

The fact that you have to ask indicates that their both isn't a common standard, nor, IMO, does there need to be. Context is everything, explain what your discussing and people will understand your notation.

I'm sure you'll find something from IEEE, ANSI, IEC, etc. that says what the correct form is. But in my career, I never needed to know and never saw a trend. I always preferred Vdc or V_dc, similar to preferring Kilometer, or Km to KILOMETER, or KM.

 

[Baluncore]

I always preferred Vdc or Vdc, similar to preferring Kilometer, or Km to KILOMETER, or KM.

The V is capitalised as an initial, because Volta was a person.
The unit 'volt' is not capitalised, to differentiate it from the person.

The SI suffix 'k' for one thousand, is written in lower case.
The symbol 'K' is the kelvin, the SI unit of absolute temperature.
The SI unit of length is the metre, not the US customary unit; meter.
The m of metre is lower case because it is not named after a person.
One kilometre is therefore written as 1 km, all in lower case.

 

[Guineafowl]

^ In news articles, it’s more common to see the output of a wind turbine written as kelvin-watt-henry (KWH) than kWh. Power and energy are used interchangeably, too.

Another one they struggle with is car battery capacity (Ah), trying to turn it into a rate* (A/h or even A/H). Same with Wh.

* Millimetres written as m/m is common, also M/m or MM.

Subscripting (V_dc) seems consistent with other ways of labelling, such as V_load or V_rms. In reality, I can’t be bothered to hit the subscript button all the time, so Vdc is probably a good compromise.

 

[Dullard]

^ ...Power and energy are used interchangeably, too....

Mis-capitalization is (arguably) of class 'Typo.' Others are of class 'Brain-O.' It annoys the crap out of me. More generally, I'm amazed that so many people apparently don't dimension-check their work - there is no way that people who actually use (as opposed to appending) dimensions could be so sloppy with them. I suspect that the fact that my early training involved a pencil (and not a calculator) is an advantage in this regard. To this day, any units work that I do (in code) has a comment line describing the units of each operand - I'm sure that the youngsters think I'm nuts. I'm still waiting for the one who picks up this habit...

 

[DaveE]

^ In news articles, it’s more common to see the output of a wind turbine written as kelvin-watt-henry (KWH) than kWh. Power and energy are used interchangeably, too.

Another one they struggle with is car battery capacity (Ah), trying to turn it into a rate* (A/h or even A/H). Same with Wh.

* Millimetres written as m/m is common, also M/m or MM.

Subscripting (V_dc) seems consistent with other ways of labelling, such as V_load or V_rms. In reality, I can’t be bothered to hit the subscript button all the time, so Vdc is probably a good compromise.

Yes, you're right, of course. But you also knew what they meant, plus you were annoyed. Kind of like every time I hear "irregardless". These rate as tiny problems in my world.* If people don't know the context, the capitalization, or not, of the units won't save them. If they do, then it doesn't matter.

* except for the A/h example, that's just wrong and stupid.

 

[Guineafowl]

Yes, you're right, of course. But you also knew what they meant, plus you were annoyed. Kind of like every time I hear "irregardless". These rate as tiny problems in my world.* If people don't know the context, the capitalization, or not, of the units won't save them. If they do, then it doesn't matter.

* except for the A/h example, that's just wrong and stupid.

Not the end of the world, no. But if someone’s described as the ‘science correspondent’, and hasn’t grasped basic units, which is not difficult to do, it doesn’t speak much for their grasp of the subject.

 

[davenn]

* Millimetres written as m/m is common, also M/m or MM.

none of which are correct .... it is ... mm

capital M is for Mega = 1 million

so M/m would equal, Mega/metre, which doesnt mean anything

and MM = Mega Mega, again meaningless probably should be using Giga

 

[Guineafowl]

none of which are correct .... it is ... mm

capital M is for Mega = 1 million

so M/m would equal, Mega/metre, which doesnt mean anything

and MM = Mega Mega, again meaningless probably should be using Giga

Yes, I know. I meant these are common mistakes.

 

[Baluncore]

and MM = Mega Mega, again meaningless probably should be using Giga

It might be better if MM = mega mega, was replaced by 'T' for Tera.

The term "mil" could mean ...
One milliradian, military offset of 1 in 1000.
One millimetre.
One thousandth of an inch.
One million.