ATMN 110 Lecture 2: Components - Lecture Notes

Resistors

• Resistors limit current or divide voltage, and sometimes generate heat.
• Control Applications:
  • Speed Control
  • Power Control
  • Varying and Dividing Voltage
  • Vent or Eliminate Excess Power
  • Heat Components to maintain required operating temperatures
• Types of Resistors:
  • Wire-wound resistors: Used where high-power ratings are required.
  • Common resistors: carbon-composition, carbon film, metal film, and ‘wire-wound’.
  • Surface mount resistors: small resistor chips.
• Resistor Types Comparison:
  • Carbon Composite Resistors:
    • High Heat
    • Low Accuracy
  • Carbon and Metal Film Resistors:
    • Low Heat
    • High Accuracy

Potentiometers

• Variable resistors adjusted by an operator.
• Control Applications:
  • Volume & Sound Affect Control
  • Timer Adjustment
  • Speed Control
  • Dimmers in Lighting
  • Circuit Adjustment and Setting

Control Discussion (Resistors)

• Resistors control the speed of loads like motors and the brightness of lamps.
• Adding switches creates an extra level of control.
• Resistors resist the current to the motor; more resistance equals less speed.

Alphanumeric Labeling

• Resistance value identification uses two or three digits, and one of the letters R, K, or M.
• The letter represents a metric prefix and indicates the decimal point position.

Colour Codes (Resistor Colour Bands)

• A resistor’s value is identified by decoding its colour bands.
• Standard resistors have four coloured bands.
• High precession resistors use five coloured bands.

Resistor Band Decoding

• 1st band: first digit of the resistance value.
• 2nd band: second digit of the resistance value.
• 3rd band: multiplier (number of zeroes).
• 4th band: indicates the tolerance.
• Start with the band closest to one end of the resistor.
• Record the first digit of the resistance value.
• Record the second band as the second digit of the resistance value.
• The third band is the number of zeros following the second digit or multiplier.
• The fourth band indicates the tolerance and is usually gold or silver.
• Digit Colour Values:
  • Black: 0
  • Brown: 1
  • Red: 2
  • Orange: 3
  • Yellow: 4
  • Green: 5
  • Blue: 6
  • Violet: 7
  • Grey: 8
  • White: 9
• Multiplier Colour Values:
  • Black: 1
  • Brown: 10^1
  • Red: 10^2
  • Orange: 10^3
  • Yellow: 10^4
  • Green: 10^5
  • Blue: 10^6
  • Violet: 10^7
  • Grey: 10^8
  • White: 10^9
  • Gold: 10^{-1}
  • Silver: 10^{-2}
• Tolerance Values:
  • Brown: 1
  • Gold: 5
  • Silver: 10
  • No band: 20

Tolerance (Accuracy of Manufacturing)

• Tolerance is coded in the last coloured strip.
• The tolerance of a resistor is a range of values below and above the Nominal Value of that resistor.
• The measured value of the resistor should be within this range.
• Tolerance is expressed in %.
• Typical Resistor tolerances are 1%, 5%, 10% and 20%.

Resistor Band Decoding Example

• 1st Band → Brown → 1
• 2st Band → Black → 0
• 3rd Band → Red → 2 (Exponent)
• 4th Band → Silver → 10%
• R = 10 \times 10^2 \Omega \pm 10\%
• R = 1000 \Omega \pm 10\%
• R_U = 1100 \Omega
• R_L = 900 \Omega

Calculating Tolerance

• Nominal Value (R_N) = 1000
• Tolerance Value = 10%
• Upper Limit (RU) = RN \times (1+%)
• R_U = 1000 \times (1+0.1) = 1100 \Omega
• Lower Limit (RL) = RN x (1-%)
• R_L = 1000 x (1 - 0.1) = 900 \Omega

Examples

• Determine the colour codes for the following values: (assume 5% tolerance)
  • 2.2 k\Omega → 2,200 \Omega → Red, Red, Red, Gold
  • 56 k\Omega → 56,000 \Omega → Green, Blue, Orange, Gold
  • 100 k\Omega → 100,000 \Omega → Brown, Black, Yellow, Gold
  • 39 M\Omega → 39,000,000 \Omega → Orange, White, Blue, Gold
  • 2.2 \Omega → 22 x 10^{-1} \Omega → Red, Red, Gold, Gold

Capacitors

• Capacitors store electrical charge in an electric field and block DC and pass AC.
• Control Applications:
  • Signal Filters
  • Timer Circuits
  • Sensors
  • Energy Storage (temporary)
  • Audio and Radio Tuning
  • Dimmers in Lighting
  • Voltage Regulation
  • Manage Spikes and Fluctuations

Control Discussion (Capacitors)

• After closing the switch, the motor will delay coming on.
• The capacitor steals some of the power before it gets to the motor. Once the Cap is full, the motor then sees the voltage.

Inductors

• Inductors, or coils, store energy in an electromagnetic field.
• Control Applications:
  • Signal Filters
  • Sensors
  • Energy Storage (temporary)
  • Transformers
  • Relays
  • Motors
  • Solenoids

Transformers

• Transformers are inductive devices used for AC coupling, or to increase/decrease AC voltages.

Control Discussion (Transformers)

• A transformer can be used to run a 12-volt lamp with 120 volts.
• A transformer can change the voltage, but not the POWER.

Summary

• Resistors have Nominal and Measured values – Never the same – They vary within Tolerance.
• Resistors limit electric current.
• Capacitors store electrical charge.
• Inductors store energy in their electromagnetic field.
• Transformers magnetically couple ac voltages and may step these voltages up/down.