
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Software Tools SPICE, PCB CAD, speaker design and measurement software, calculators 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
7th December 2012, 04:43 PM  #1 
diyAudio Member
Join Date: Jul 2004
Location: Edmonton, AB Canada

Calculating EIA standard values
I need the formula for calculating EIA standard decade values (RS276) and don't want to use a list. I've tried what I could find on the web and they all fizzle out the same way for E24 and less.
Example, calculating E12 (10%) values gives: 10, 12, 15, 18, 22, 26, 32, 38, 46, 56, 68, 82, 100 < using formula 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, 100 < EIA series It's not a rounding or truncation problem  the 27 value is actually 26.10, the 47 value is actually 46.42 Anyone know why the middle values are off? Formula: R = 10* 10 ^ (n / b) ; where ^ is exponentiation, and b is the series number (12 for 10%, 24 for 5%, 96 for 1%), and n is the step progression 0b. Some links I found useful: MightyOhm Blog Archive EIA Resistor Values Explained Excel Formula Calculates Standard 1%Resistor Values standard resistor value table  Ekswai 
7th December 2012, 05:07 PM  #2 
diyAudio Member
Join Date: Mar 2008

I don't think they actually follow a mathematical series. they are a convenient approximation to a mathematical series, which is why it slightly differs..

7th December 2012, 10:39 PM  #3 
diyAudio Member
Join Date: Jul 2004
Location: Edmonton, AB Canada

After a bit more research, it's a geometric series of "preferred numbers" derived from Renard numbers, dating back to the 1870's.
A guess is the E6 to E24 values are quirky and adjusted to keep some backward compatiblity with old E4 values. Source Otherwise I could find no reason for inconsistencies. The math works for E48 (2%), E96 (1%) and E192 (0.5%, 0.25%, 0.1%) tolerances. i.e. using MS Excel with resistor value in cell A1: E192 value=ROUND((10^(ROUND(192*LOG(A1),0)/192))/10^INT(LOG((10^(ROUND(192*LOG(A1),0)/192)))),2)*10^INT(LOG((10^(ROUND(192*LOG(A1),0)/192)))) E96 value =ROUND((10^(ROUND(96*LOG(A1),0)/96))/10^INT(LOG((10^(ROUND(96*LOG(A1),0)/96)))),2)*10^INT(LOG((10^(ROUND(96*LOG(A1),0)/96)))) E48 value =ROUND((10^(ROUND(48*LOG(A1),0)/48))/10^INT(LOG((10^(ROUND(48*LOG(A1),0)/48)))),2)*10^INT(LOG((10^(ROUND(48*LOG(A1),0)/48)))) It's in EIA standard RS385 and IEC 60063, but I don't have them. If you do these calcs in S/W watch there are many different ways to round off numbers i.e. "banker's rounding" 
7th December 2012, 11:41 PM  #4 
diyAudio Member
Join Date: Nov 2008

From another forum, a similar discussion: Some of the E24 values are wrong!

Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
calculating PS resistor values  valvehack  Power Supplies  10  22nd March 2012 11:44 PM 
Calculating resistor values  pk386  Solid State  4  10th April 2005 02:57 PM 
Pearl with standard cap values?  Petter  Pass Labs  5  25th January 2004 03:02 PM 
Help calculating RC values for rectifier snubber  Eric  Pass Labs  2  31st January 2003 06:57 PM 
New To Site?  Need Help? 