Lab 01: Digital Multimeter Resistance Measurement
- To understand the concept of electric resistance and learn how to read color-coded ceramic resistors.
- To become familiar with the use of digital multimeter (DMM) in reading resistance, current, and voltage.
- To learn how to measure voltage and current with a digital multimeter.
Standard Resistor Values and Color
Resistors are color coded for easy reading. To determine or calculator the resistance and tolerance value of a given resistor color, look for the gold or silver tolerance band and hold the resistor with this band to the right. Then read the resistor color code bands from left to right as shown in Figure 1.
Calculating Resistor Value
The Resistor Color Code system is all well and good but we need to understand how to apply it in order to get the correct value of the resistor. The left-hand or the most significant colored band is the band which is nearest to a connecting lead with the color coded bands being read from left-to-right as follows:
Digit, Digit, Multiplier = Color, Color x 10 color in Ohm's (Ω)
For example, a resistor has the following colored markings;
Yellow-Violet-Red = 4 7 2 = 4 7 x 102 = 4700 Ω or 4.7 KΩ
The fourth and fifth bands are used to determine the percentage tolerance of the resistor. Resistor tolerance is a measure of the resistors variation from the specified resistive value and is a consequence of the manufacturing process and is expressed as a percentage of its "nominal" or preferred value.
Typical resistor tolerances for film resistors range from 1% to 10% while carbon resistors have tolerances up to 20%. Resistors with tolerances lower than 2% are called precision resistors with the or lower tolerance resistors being more expensive.
Most five band resistors are precision resistors with tolerances of either 1% or 2% while most of the four band resistors have tolerances of 5%, 10% and 20%. The color code used to denote the tolerance rating of a resistor is given as:
Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 %
If resistor has no fourth tolerance band then the default tolerance would be at 20%.
- Give the 4-band color codes for the following resisters:
- 2Ω ±5%
- 0.5Ω ±10%
- 1KΩ ±20%
- The highest resistance range on a DMM is 20 MΩ. To measure a very large unknown resistor Rx, the unknown resistor is placed in parallel with a resistor that has previously been measured and has an actual value of 19.95 MΩ. The resulting DMM reading is 18.16 MΩ. Find the value of Rx.