EEVblog #1300 - "Parts Per" Notation EXPLAINED - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: April 13, 2020, 11:40:32 pm
content: "Per Mille" is a trap for young players."Parts Per" notation explained, along with percentage and ppm.

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: April 13, 2020, 11:58:33 pm
content: If you real want to lose your mind !One part per billion (ppb) denotes one part per 1000000000 parts, one part in 109, 1/1000000000 × 100% = 0.0000001% (or 1% = 10000000 ppb) and a value of 1 × 10−9.One part per trillion (ppt) denotes one part per 1000000000000 parts, one part in 1012, and a value of 1 × 10−12.One part per quadrillion (ppq) denotes one part per 1000000000000000 parts, one part in 1015, and a value of 1 × 10−15. Tevel are sometimes performed

author: Neilm
author_rank: Super Contributor
timestamp: April 14, 2020, 06:51:30 am
content: I first came across this notation reading an old research paper. The paper had been scanned into pdf and had been through an OCR and none of the calculations made sense. Fortunately I found a pdf of the paper before it had been OCRed and saw this notation and had to look up what it ment. Turned out the OCR had replaced the permille with the percent symbol.

author: johnwa
author_rank: Frequent Contributor
timestamp: April 14, 2020, 09:23:52 am
content: Interesting, I didn't know there was an "official" unit for per-unit notation. I agree that the name and prefixes sound a bit silly, but the basic concept is used quite a bit, especially in fields such as power engineering, and really makes much more sense from an engineering perspective.The use of percentages probably stems from non-technical people being uncomfortable with decimal fractions. However, a consequence of this is formulas become littered with factors of 100 all over the place. (Also, the objection to decimals is rather spurious, given that the percentages themselves often have decimal fractions)E.g: Efficiency (%) = 100 * Pout/Pinor compound interestP' = P(1+r/100)^nIf the relevant quantities are simply treated as decimal fractions, the conversion factors disappear:Efficiency = Pout/PinP' = P(1+r)^nThis is generally what I do whenever I am building a calculation spreadsheet or program - any percentages as inputs are converted to per-unit as a first step, and then treated that way throughout. I am quite happy to view the results directly as decimals, but they can of course be converted back to percentages at the end if need be.I don't know how standard this is, but I have often seen per-unit values identified by "PU" E.g: "The efficiency of the transformer is 0.8PU". Alternatively, you could write "The per-unit efficiency of the transformer is 0.8".I hope this is a useful addendum to Dave's video. I really don't know why the power supply was specified like that though. If it was a marketer trying to make the numbers look bigger, they have really shot themselves in the foot this time!Edit: This is of course the same idea a specifying amplifier gains, etc in volts/volt or whatever...

author: hans
author_rank: Super Contributor
timestamp: April 14, 2020, 01:34:56 pm
content: Quote from: johnwa on April 14, 2020, 09:23:52 amWhich is why it is better to write equations as:Efficiency = 100% * Pout/PinThat way it is clear that the 100% is used to represent it as a percentage, however, since 100% = 1.0, the efficiency calculated is still the correct fraction.Things become a mess when you try to input these things in e.g. Excel or other computational programs. Excel/LibreOffice can use the percentage cell value formatter to do this conversion immediately, so no 100x factors in formulas needed. In addition, personally I found it's best practice to never convert anything 'presentation friendly' at an intermediate level, as un-doing these steps is prone to errors (e.g. you forget or apply the wrong conversion factor).Sometimes fraction representation is funny if you look at really low-power stuff. Typical CPU load measurements are done in percentage to indicate how busy a CPU is. If you go into really low duty cycles (e.g. a short computational burst on a 10 minute period), you may see that a particular task will only run for 50ms every 600 seconds. That's a CPU load of only 0.008333%, or as I'd like to represent it: 83.33ppm. I'd prefer the latter, as the decimal point is put at a place that makes the number easier to read.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: April 14, 2020, 03:38:30 pm
content: Over here it's standard for expressing blood alcohol content. It's also used for grade in railway industry and probably more fields that don't come to mind right now.PPM is used in medical field, but I have to admit I've never heard the "basis point" term.

author: Bud
author_rank: Super Contributor
timestamp: April 14, 2020, 04:02:56 pm
content: Next time your country's central bank changes interest rates, check their press release

author: tszaboo
author_rank: Super Contributor
timestamp: April 15, 2020, 06:53:50 am
content: When I was a young engineer, I got a task to design a current measuring device, with 0.05 PPM accuracy. I spent days, trying to do it, then I gave up. Told my boss it is impossible. But no, he insisted, it should be possible.Because 0.05 PPM = 0.05 parts per mille...

author: johnwa
author_rank: Frequent Contributor
timestamp: April 15, 2020, 07:47:39 am
content: Quote from: hans on April 14, 2020, 01:34:56 pmYeah, I have seen that, but I have never been too keen on the displayed value not equalling the actual numeric value in the cell. Though I guess it's no worse than displaying 1000V as 1kV.Quote from: hans on April 14, 2020, 01:34:56 pmFair enough, I guess you could always use scientific notation if you wanted to.Quote from: NANDBlog on April 15, 2020, 06:53:50 amYou should be thankful he didn't ask for it to have 100% reliability as well...

author: tszaboo
author_rank: Super Contributor
timestamp: April 16, 2020, 10:13:01 am
content: Quote from: johnwa on April 15, 2020, 07:47:39 amOh, that was my current boss. There was a destructive test, with pass fail output. I asked him for the confidence level requirement for the test, he said 99%. So I told him, I need to destroy most of the production units to have that confidence.

author: Howardlong
author_rank: Super Contributor
timestamp: April 23, 2020, 09:19:43 pm
content: What happens when you don't know what ppm means...https://www.bbc.co.uk/news/uk-england-sussex-52379192https://assets.publishing.service.gov.uk/media/5e9d5b4cd3bf7f0316b6a63a/AAIB_Special_Bulletin_S1-2020_G-POWN.pdf"The EASA Part-66 B1 licensed AMO engineer was not familiar with the term ‘ppm’."

author: Monkeh
author_rank: Super Contributor
timestamp: April 24, 2020, 12:18:18 am
content: Quote from: Howardlong on April 23, 2020, 09:19:43 pmThat's fairly disturbing on multiple points. I look forward to the full report.

author: thm_w
author_rank: Super Contributor
timestamp: April 24, 2020, 08:48:33 pm
content: QuoteSo somehow he calculated 30kg per 6200kg, when it should be ~0.8kg.I looked at a number of online calculators and couldn't find any that would give the wrong result. They will tell you 100mg/L, 100mg/kg, 0.1ml/L, etc which are all correct. None of these are close to 0.5% he used. I think there is a bigger screw up here than not knowing what ppm is, on top of not looking up a term you aren't familiar with..

author: THDplusN_bad
author_rank: Regular Contributor
timestamp: April 27, 2020, 03:09:47 pm
content: Thanks, Dave.yes, ‰ is a common symbol in the Medical field (i.e. for blood testing for alcohol) and in Economic studies and the like. It is not so common in Engineering Term, I agree.But then, I was not really surprised to see ppm used for accuracy and drift specs for real high-end T&M equipment such as the model 2002 DMM from Keithley - much easier to understand than counting zeros after the decimal point or comma...Cheers,THD+N bad

author: EEVblog
author_rank: Unknown
timestamp: May 02, 2020, 10:11:47 am
content: Quote from: THDplusN_bad on April 27, 2020, 03:09:47 pmYes, it's the same reason why the nanofarad was introduced. It was just getting silly saying 0.001uF or 10000pF etcI can remember "the great nanofarad" debate in the electronics magazine on whether or not they should start using the nF on schematics.

author: PathLoss
author_rank: Contributor
timestamp: May 04, 2020, 09:25:43 am
content: As an Aside... Dealing with orders of magnitude analysis (and more) in your brain - with or without the prefixes:* Fermi Estimate:https://brilliant.org/wiki/fermi-estimate/Excerpt: "A Fermi estimate is one done using back-of-the-envelope calculations and rough generalizations to estimate values which would require extensive analysis or experimentation to determine exactly."* Fermi problem - Wikipedia:https://en.wikipedia.org/wiki/Fermi_problemExcerpt: "In physics or engineering education, a Fermi problem, Fermi quiz, Fermi question, Fermi estimate, or order estimation is an estimation problem designed to teach dimensional analysis or approximation of extreme scientific calculations, and such a problem is usually a back-of-the-envelope calculation. The estimation technique is named after physicist Enrico Fermi as he was known for his ability to make good approximate calculations with little or no actual data. Fermi problems typically involve making justified guesses about quantities and their variance or lower and upper bounds."