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Old 22nd Sep 2018, 1:59 pm   #21
Chris55000
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Hi!

I can confirm this was very common practice in the 1920s and 1930s - if you look in Practical Wireless, Ameteur Wireless and early editions of the "Wireless Encyclopaedia" you'll find this notation frequently cropping up, so yes, 50,000ω is 50kohm and 2Ω is 2megohm!

By the time "preferred values" were introduced this notation had become totally obsolete!

Subsequently it became more common to write the unit in capital letters, e.g., "50,000 OHMS", particularly in the mid to late 1930s, then the transition-point to today's shorter methods of writing component-values, was in my opinion, about 1940-1943 - the exact date did tend to vary between the various magazine publishers and set-makers!

Chris Williams
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Old 22nd Sep 2018, 2:26 pm   #22
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Quote:
Originally Posted by ColinTheAmpMan1 View Post
When at university, I used to refer to the "ω" in ω=2πf with a shorter word - "bum", for what I thought was an obvious reason....
Colin.
Tone suitably lowered

Never mind- engineers and schoolboy humour are common bedfellows! Scatological terms for mnemonics, tools and test equipment are easier to remember than clean ones, too.

ES light bulb with side handles sketch ring any bells?
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Old 22nd Sep 2018, 3:18 pm   #23
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Thanks Terry, but I use an iPad, and I don’t seem to be able to add any other mathematical symbols etc.
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Old 22nd Sep 2018, 3:18 pm   #24
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

The use of Ω to represent Megohm was certainly common in the 1920's, attached is a typical circuit from Harmsworth's Encyclopedia showing a 2 Meg grid leak resistor.
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Old 22nd Sep 2018, 3:22 pm   #25
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Just wondered how would they represent 2ohms?
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Old 22nd Sep 2018, 4:23 pm   #26
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Quote:
Originally Posted by john10b View Post
just wondered how would they represent 2ohms?
2ω.

Quote:
Originally Posted by John10b View Post
I use an iPad, and I don’t seem to be able to add any other mathematical symbols etc.
If they've already been used in a thread, the easiest way is cut and paste - which I used above rather than opening up Character Map..
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Old 22nd Sep 2018, 4:47 pm   #27
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

You can add a Greek keyboard from the setting menu on the iPad, I have just added one.
Π ω Ω β etc
You can also install mathematical keyboards from the store.
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Old 22nd Sep 2018, 5:25 pm   #28
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Thank you Frank I didn’t know that.
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Old 22nd Sep 2018, 5:26 pm   #29
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Thank you also Dave.
Cheers
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Old 22nd Sep 2018, 6:12 pm   #30
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

On, April 15, 1867 W. H. Preece from the Electric and International Telegraph Company, Southampton Station, suggested use of the letter Omega from the Greek alphabet as a symbol for resistance because of its similarity in name with the British Association (B.A.) unit “Ohm”, using the small letter (ω) for B.A. units and the capital (Ω) for B.A. units x 1,000,000. He suggested that the symbols would be superscript and read “Ohm and Megohm”.

Now SI requires that unit names, such as “ohm”, are not normally capitalized and unit symbols, such as “Ω”, are capitalized when derived from the name of a person, in this case German physicist Georg Simon Ohm.

The letter written by W. H. Preece can be found here in reference 15:
https://en.wikipedia.org/wiki/Ohm

David

Last edited by Neutrino; 22nd Sep 2018 at 6:16 pm. Reason: Added commas
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Old 23rd Sep 2018, 7:55 am   #31
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

I have see "ω" marked on headphones, so wondered if it referred to impedance, as in 2000ω.

Mike
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Old 23rd Sep 2018, 1:14 pm   #32
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Well it does, in a way, but nothing to do with its radians/sec usage.
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Old 25th Sep 2018, 8:35 pm   #33
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

I've attached a Windows text file which contains a range of characters that I find useful in radio, electronics and maths.
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Old 25th Sep 2018, 11:43 pm   #34
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Very handy, that. I couldn't find the Ʊ symbol for Mho in the Libre Office WP.
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Old 26th Sep 2018, 12:07 am   #35
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

I remember at school an elderly physics teacher insisted on using "ω" for ohms and "Ω" for Megohms.

I think I have also seen old Murphy (?) service sheets where the capital letter "O" has been used to indicate Megohms.
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Old 26th Sep 2018, 8:28 am   #36
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Default Re: 'ω' and 'Ω' versus 'Ω' and 'MΩ'

Quote:
Originally Posted by julie_m View Post
The use of lower-case ω to represent 2 * π * frequency (and thereafter working in radians as opposed to cycles) is fairly common in circuit analysis...
That’s right Julie , that’s where I regularly see this specialist character, to represent radians ... (can’t reproduce on an iPhone keypad!)
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