Engineering Principles V11

Clive W. Humphris

RESISTOR VALUE TEST: Select Random Value.

Resistor values can be determined using the Resistor Colour Code. For the 4-band type, the first two bands are numerical values the third is the multiplier or number of noughts.

For example 3.9kOhms = orange(3), white(9), red(2) = 3900ohms or 3.9kOhms. For values below 10ohms the third band is coloured gold which is a multiplier of 0.1. The fourth band indicates tolerance.

Resistor values are also available as 5-band types. You can select a routine to determine the value of both types Resistor Colour Codes in the Toolbox menu along with another selection for Preferred Resistor Values. Resistors are available in a number of ranges, the most common being the E12(10%) and E24(5%) series, the latter having a closer tolerance, therefore more values are required to ensure every likely value is covered.

The Toolbox also contains a routine for finding preferred types. Calculations will often produce odd resistor values and in some cases very close tolerance high stability types may be required. For this purpose the E48(2%), E96(1%) and E192(0.5%) ranges are available, obviously this closer precision is reflected in their cost.

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