Other Calculator Functions Talk about change button Put Calculator in Write View (If doesn’t say w-view at top, go to Setup menu, press 2, press 0) Talk.

Other Calculator FunctionsTalk about change buttonPut Calculator in Write View (If doesn’t 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 buttonUsing previous answerStoring and recalling numbersChanging from Degree to Radian in SET UPx-1 buttonPi buttonSqrt buttonNegative buttonUsing parenthesis a lot for parallel resistorsPEN vs DEC mode

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

Resistor’s Schematic Symbol

Composed of a zig-zag line

What is the value of the resistor on the right?

Reference Designators

300 Ω 30kΩ

Surface Mount vs. Through Hole

Surface Mount Through Hole

Types of Fixed Resistors

Carbon Composition

Metal Film

Metal-Oxide Film

Resistor Networks

Wirewound Resistors

Old-skool

Low noise and good thermal properties

Many packaged resistors

High accuracy at high resistance

High power applications

High accuracy

Surface Mount Resistors (SMT)Surface Mount Technology

Resistor Properties

Value in Ohms Accuracy Power rating (We’ll look at this one first)

www.digikey.com

What is Resistor Power Rating?

Examples:¼ watt, ½ Watt, 20 watts

P = V·I = 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 http://www.youtube.com/watch?v=kvQBhX

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More in class practice problems

Blue Blue Blue Gold

Brown Black Red Silver

Brown Black Orange Silver

Orange Violet Black Gold

Find tolerance range as well

… or you can just measure it with an Ohmmeter!

66 MΩ +/- 3.3 MΩ

1000 Ω +/- 100 Ω

10000 Ω +/- 1000 Ω

37 Ω +/- 1.85 Ω

Reading Resistor Value on a Surface Mount Resistor

324

670

103

100

320,000 Ω

67 Ω

10k Ω

10 Ω

Potentiometers are written on the same way

What color is the following?Green

Black

Blue

Violet

What color is the following?

Brown

Red

Orange

Violet

Homework

Do problems 1 and 2 on page 85

Include the range (if applicable)!

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)

See page 69 for schematic of application

Linear vs. Logarithmic “Pots”

“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.”

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.

Resistors that change resistance with temperature

(Page 70 in book)

•RTD’s (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 lookingSmoky smellMelted

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