Electronic circuits and components
Examples: Resistor Specifications
A resistor has a marked value of 470Ω.
Determine the tolerance of the resistor if it has a measured value of 455Ω
The difference between the marked and measured values of resistance (the error) is (470Ω - 455Ω) = 15Ω. The tolerance is given by:
Tolerance = error / marked value x 100%
The tolerance is thus 15/470 x 100 = 3.2%
A 12V power supply is to be tested with a 12Ω load resistor.
If the resistor has a tolerance of 10% determine:
(a) the nominal current taken from the supply (b) the maximum and minimum values of supply current at either end of the tolerance range for the resistor.
(a)If a resistor of exactly 12Ω is used the current will be:
I = V/R = 12V/12Ω = 1A
(b) The lowest value of resistance would be (12Ω - 1.2Ω) = 10.8Ω. In which case the current would be:
I = V/R = 12V/10.8Ω = 1.11A
At the other extreme, the highest value of resistance would be: (12Ω + 1.2Ω) = 13.2Ω
In this case the current would be: I = V/R = 12V/13.2Ω = 0.91A