Chapter 5: Resistors What is a resistor? Definition: A device used in electrical circuits to maintain a constant relation between current flow and voltage. Resistors are used to lower the voltage at different points in a circuit Resistors work as they turn voltage energy into heat 2 Functions: To limit current To produce desired voltage Analogy Resistors Resistors Schematic Symbol
Composed of a zig-zag line What is the value of the resistor on the right? Reference Designators 300 30k Surface Mount vs. Through Hole Surface Mount Resistors (SMT)
Surface Mount Technology Types of Fixed Resistors
Carbon Composition Metal Film Metal-Oxide Film Resistor Networks Wirewound Resistors Old-skool High accuracy Low noise and good thermal properties High accuracy at high resistance Many packaged resistors High power applications Resistor Properties Value in Ohms Accuracy
Power rating (Well look at this one first) What is Resistor Power Rating?
Examples: watt, Watt, 20 watts P = VI = V2/R = I2R Heat Sinks Determining Value and Accuracy
Tolerance Color Code: Brown = 1% Red = 2% Gold = 5% Silver = 10% Video See lecture notes first
More in class practice problems
Blue Blue Blue Gold Brown Black Red Silver Brown Black Orange Silver Orange Violet Black Gold 66 M +/- 3.3 M=62.7M to 69.3M 1000 +/- 100 = 900to1100 10000 +/ = to 37 +/ = to Find tolerance range as well or you can just measure it with an Ohmmeter! Reading Resistor Value on a Surface Mount Resistor
324 670 103 100 320,000 67 10k 10 Potentiometers are written on the same way What color is the following?
Green Black Violet Blue What color is the following?
Violet Brown Orange Red Homework Do problems 1 and 2 on page 85
Worksheet Resistance and Voltage Worksheet Include the range (if applicable)! Other Calculator Functions
Talk about change button Put Calculator in Write View (If doesnt say w-view at top, go to Setup menu, press 2, press 0) Talk about a/b button. Moving left and right to correct mistakes. Back space button Using previous answer Storing and recalling numbers Changing from Degree to Radian in SET UP x-1 button Pi button Sqrt button Negative button Using parenthesis a lot for parallel resistors PEN vs DEC mode Variable Resistors Variable resistors are designed so that their resistance values can be changed A potentiometer is a three terminal variable resistor used to divide voltage A rheostat is a variable resistor used to control current Pictures of Variable Resistors Linear vs. Logarithmic Pots Knob rotation (Usually 20 turns)
Linear vs. Logarithmic Pots Knob rotation (Usually 20 turns) See page 69 for schematic of application Resistance of a Wire The longer a wire is, the more resistive it is.
The thicker a wire is, the less resistive it is. (Think parallel) (Also think of a fire hose. There is always pressure drops across a pipe, but less pressure drop for bigger hoses.) Resistance is given by the following equation Therefore as a wire gets longer, the resistance change gets linearly larger. The larger the cross-sectional area of the conductor, the more electrons are available to carry the current, so the lower the resistance. The longer the conductor, the more scattering events occur in each electron's path through the material, so the higher the resistance. Different materials also affect the resistance. Resistors that change resistance with temperature
(Page 70 in book) RTDs (Need to be powered) Bolometers - Thermistors (NTC) /Barreters (PTC) Thermocouples (produces a voltage) Negative vs. Positive Temperature coefficient. Bad Resistors Resistors can go bad when too much current is passed through them. Signs of a resistor that has gone bad are: Burned or charred looking Smoky smell Melted Random Video of the Day