Determining Resistor Values - PowerPoint Presentation

1. Determining Resistor ValuesAIM:To be able to use the Resistor Colour Code and the BS1852 Resistor Printed Code to identify the value and tolerance of resistors PRIOR KNOWLEDGE: A basic understanding of resistance and resistorsThe standard prefixes such as Mega and kilowww.pfnicholls.com

2. IntroductionResistors are physically quite small most of the time and so it is inconvenient to simply write the value and tolerance on the resistor. A clear but compact code is needed!On circuit diagrams it is important not to miss the decimal place and use a 47kΩ resistor instead of a 4.7kΩ so clarity is required.The Resistor Colour Code uses coloured bands to make it easy to identify resistor values and tolerances and the Resistor Printed Code BS1852 gives a standard for printed markings on resistors and on circuit diagrams.You don’t actually need to learn these codes but it is a good idea to know them … it makes your life much easier when building circuits and it’s cool to know them anyway.

3. The Colour CodeFirst 3 bands:Fourth band:0123456789± 5%± 10%GOLDSILVER± 20%BLANKBLACKBROWNREDORANGEYELLOWGREENBLUEINDIGOGREYWHITE

4. Using the Colour CodeBecause the resistors (in this presentation) are all ± 5% or worse, there is no point in giving the value to a high level of precision using many significant figures. All resistor values are therefore given to 2 significant figures followed by the appropriate number of zeros. Band 1 = Value of Resistor (First significant figure)Band 2 = Value of Resistor (Second significant figure)Band 3 = Number of zerosBand 4 = Tolerance

5. Example 1Band 1 → Red → 2Band 2 → Red → 2Band 3 → Brown → 1Therefore the value is 22 followed by 1 zero = 220ΩBand 4 → Gold → ± 5%The resistor is 220Ω ± 5%

6. Example 2Band 1 → Brown → 1Band 2 → Black → 0Band 3 → Orange → 3Therefore the value is 10 followed by 3 zeros = 10,000ΩNote: 10,000Ω = 10kΩBand 4 → Gold → ± 5%The resistor is 10kΩ ± 5%

7. Example 3Band 1 → Yellow → 4Band 2 → Violet → 7Band 3 → Red → 2Therefore the value is 47 followed by 2 zeros = 4700ΩNote: 4700Ω = 4.7kΩ but the decimal place is easy to miss so the decimal place is represented by the position of the ‘k’ in the value. Therefore, 4.7kΩ is written as 4k7ΩBand 4 → Gold → ± 5%The resistor is 4k7Ω ± 5%

8. BS1852 Resistor Printed CodeThe BS1852 Printed Resistor Code uses letters and numbers to signify the value of the resistor. R means x1 K means x1000 M means x1000,000The position of the letter indicates the position of the decimal placeTolerance is indicated by adding a letter at the end: J = ± 5% K = ± 10% M ± 20%Given the number of letters available, it is a bit surprising that the standard code uses the same letters for value and tolerance but there you go!

9. Examples 1A 220Ω resistor with a tolerance of ± 5% is written as 220RJA 4700Ω resistor with a tolerance of ± 5% is written as 4K7JR = OhmsJ = ± 5%K = x1000Position shows decimal placeJ = ± 5%

10. More Examples3R9K has a value of 3.9Ω with a tolerance of ± 10%39RJ has a value of 39Ω with a tolerance of ± 5%390RM has a value of 390Ω with a tolerance of ± 20%3K9K has a value of 3900Ω ± 10%39KJ has a value of 39000Ω ± 5%390KM has a value of 390000Ω ± 20%3M9K has a value of 3900000Ω ± 10%39MM has a value of 39000000Ω ± 20%

11. Low Value ResistorsLow value resistors – those less than 10Ω – use the THIRD coloured to reduce the value of the resistor, not to increase it. The first two coloured bands still give the value but this is then DIVIDED by either 10 or 100 to give low values.÷10GOLDSILVER÷100For example:Yellow Violet Gold Gold would be 47÷10 = 4.7Ω ± 5%Green Blue Silver would be 56÷100 = 0.56Ω ± 20%A ZERO ohm resistor – useful as a wire link – is identified by a SINGLE black band

12. Low Value ResistorsGreen, Blue , Black = 56Ω(5, 6 and then no zeros)Brown, Black, Black = 10Ω(1, 0 and then no zeros)Brown, Black, Gold = 1Ω(Brown, Black = 10, Gold = ÷10)Both 10Ω but shown in different waysAll are ± 5%

13. High Precision ResistorsFor resistors with a tolerance of better than ± 5%, more than two significant figures are needed to represent the value.High precision resistors have 3 bands for the value and then 1 band for the number of zeros. The colour code otherwise works exactly the same.Note: 5th band gives tolerance where Brown = ± 1%Example: Brown (1) Orange (3) Black (0) Orange (3) Brown (1%)= 1 3 0 x 1000 ± 1%= 130kΩ ± 1%

14. A Different ApproachAn entirely different approach is adopted for Surface Mounted Device (SMD) resistors … and some other resistorsThe idea of 2 significant figures and then a 3rd digit representing the multiplying factor (number of zeros) is maintained but the numbers are simply printed on the device / resistor.Examples:102 = 1 0 x 100 = 1000Ω334 = 3 3 x 10,000 = 330kΩ221 = 2 2 x 10 = 220Ω560 = 5 6 x 1 = 56Ω

15. E12 Resistor SeriesResistors with a tolerance of ± 10% (Silver) form a series of 12 values, each approximately 20% bigger than the last. This series is the E12 series.The E12 series is:10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82… and all the subsequent decades / powers of 10Examples:100Ω, 15kΩ, 220Ω, 330kΩ, 4.7Ω, 6.8MΩ, 10kΩ, 1kΩ

16. E24 Resistor SeriesResistors with a tolerance of ± 5% (Gold) form a series of 24 values, each approximately 10% bigger than the last. This series is the E24 series.The E24 series is: (E12 shown in Blue)10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91… and all the subsequent decades / powers of 10Examples:110Ω, 13kΩ, 200Ω, 360kΩ, 4.3Ω, 6.2MΩ, 11kΩ, 1k3Ω

17. Summary Resistors use a code to represent their value and toleranceThe colour code uses 2 bands to represent the value and a 3rd band to represent the power of 10 (number of zeros). The 4th band is the toleranceThe BS1852 standard uses letters to represent powers of 10 (multipliers) and also the position of the decimal place and the toleranceResistors less than 100Ω use a slightly adapted colour codePrecision resistors use a four band + tolerance colour codeSMDs use a printed numerical code

18. Questions Brown Black Yellow Gold = ?Red Red Brown Silver = ?Orange Orange Black Gold = ?Yellow Violet Gold Gold = ?5K6J = ?68MK = ?Red Red Orange Brown Brown = ?Surface mounted, 472 = ?Surface mounted, 120 = ?

19. Answers 100,000Ω ± 5% or 100k Ω ± 5%220Ω ± 10%33Ω ± 5%4.7Ω ± 5% (3rd = Gold means x0.1 or /10)5600Ω ± 5%68,000,000Ω ± 10% or 68MΩ ± 10%2230Ω ± 1% (High precision)4700Ω12Ω (There are no zeros)