Identifying Resistors

Overview

The resistor colour code is used to determine the value and tolerance of standard resistors. The BS1852 printed code is used to identify the value and tolerance of power resistors and provides a way to write resistor values on circuit diagrams. A different written code is used on surface mounted components where coloured bands are impractical. The E24 and E12 series of standard resistor values are the preferred values available to use in circuit construction. This lesson considers how to identify different resistors.

Learning Objectives

• Identify unknown resistors by using the colour codes for values and tolerances
• Identify unknown resistors by using the BS8152 codes for values and tolerances
• Recognise resistor values when written on circuit diagrams
• Identify unknown resistors using a printed numerical code
• Select resistors for use in a circuit from the E12 and E24 series values
• Use appropriate markings to determine the power rating of a resistor
• For a resistor of known value, state the corresponding colour code and printed code

Lesson Content

Reading: Using the webpage, learn the resistor colour code and understand how the colour code is used to identify the value and tolerance of a standard resistor. Read the first three sections and then work through the three examples. Find a way to remember the colour code without having to look it up each time - this saves a lot of time and avoids mistakes when circuit building.

Video (8 min): Watch the Interactive White Board tutorial which goes through several examples of different resistor values. Watch for the first 5:18 minutes up to the end of the 4th example.

Reading: Continue to read the webpage about the BS8152 printed code, small value and low value resistors and those with high precision values. Compare the BS1852 printed code to the colour code noting that the printed code uses a letter to represent multiplying factor and the position of the decimal place and that both methods allow the tolerance of the resistor value to be determined. Appreciate the reason why a letter is used instead of a decimal place when writing resistor values on circuit diagrams.

Video (8 min): Watch the remaining section of the Interactive White Board tutorial where more examples, using the two different numerical codes, are considered. Watch from 5:18 to the end.

Reading: Complete the webpage by reading about the printed numerical code used for surface mounted resistors and some other resistors where the value is printed. Compare the printed numerical code to the colour code noting that, in both cases, the first two significant figures of the value and then the number of following zeros are given. Appreciate that the printed numerical code does not provide information about the tolerance. Read about the E12 and E24 series of standard values. It is not necessary to remember these series of values but it is very useful to be familiar with them.

Exercise: Complete the exercises to consolidate your understanding of the colour code and the printed codes.

Lesson Review

Review your learning by working through the presentations or notes which summarise the website content.

Presentation: Powerpoint download. Examples of different resistor colour codes and printed codes.

Notes: PDF download. Notes about how to use the colour code and printed code to identify different resistors.

Self Assessment

Complete either the questions (pdf download) OR the on-line quiz. They are the same questions.

Quiz: On-line quiz to check your understanding.

Self Evaluation

I can:

• Use the colour code to determine the value of a resistor
• Use the colour code to determine the tolerance of a resistor value
• State the colour code for a resistor of a known value
• Recognise unusual cases such as low value resistors or high tolerance resistors
• Use the BS8152 printed code to determine the value of a resistor
• Use the BS8152 printed code to determine the tolerance of a resistor value
• State the BS8152 printed code for a resistor of a known value
• Appreciate why a letter from the BS8152 code is used in place of the decimal point in written resistor values on circuit diagrams
• Use the numerical printed code to determine the value of an unknown resistor
• State the three digit numerical value of a resistor of a known value
• Recognise standard resistor values from the E12 and E24 series