310102a Resistors 2025 (TF)

Instrument Technician

• Topic: Resistors

Objectives of Resistors

1. Categories of Resistors

   • Identify and describe two categories of resistors including fixed and variable.

2. Determining Ratings

   • Explain methods to assess the ratings of fixed resistors.

3. Color Code Chart

   • Use a color code chart to ascertain the resistance value of a resistor.

Resistance

• Definition: Resistance opposes the flow of current (electron flow).

• Collision Effects:

  • Collisions between free electrons and atoms produce heat.

  • More collisions result in greater heat production.

• Conductors:

  • Even wires conducting current face resistance due to electron collisions.

• Symbol and Units:

  • Symbol for resistance: R

  • Measurement unit: Ohms (symbol: Ω)

• Load in Circuits: The total resistance in a circuit is referred to as a load, which can contain multiple loads.

Fixed Resistors

• Construction:

  • Fixed resistors are designed to possess specific resistance values.

  • Typical construction ratio includes a carbon-based alloy, resin (binder), and insulating filler.

  • The resistive value is determined using color codes.

Types of Fixed Resistors

• Composition Resistors

  • Made primarily from a carbon base alloy.

• Film Resistors

  • Constructed with a thin film of resistive material around a glass or ceramic core.

  • Materials: Carbon, metal-alloy, or metal oxide.

  • Color codes help in determining the resistive value.

• Wire Wound Resistors

  • Comprised by winding a wire around a ceramic core.

  • Able to withstand high temperatures (up to 450˚C)

  • Materials: Nickel-chromium or copper-nickel alloy, with resistive value and wattage rating printed externally.

Variable Resistors

• These resistors can change resistance values.

• Construction:

  • Made from wire wound around a core or film construction.

  • Wire types: Nickel-chromium or copper-nickel alloy; film styles: carbon, metal-alloy or metal oxide.

  • Maximum resistive value and wattage rating are printed on the cover.

  • Resistance value is changed via an electrical contact sliding along the resistor.

Types of Variable Resistors

• Rheostats

  • Two-terminal resistor with a slider or wiper contact allowing variable resistance.

• Potentiometers

  • Three-terminal resistor that forms an adjustable voltage divider, also known as “trim pots.”

  • Features a sliding contact for adjusting resistance.

Resistance and Tolerance Colour Codes

• 4-band Colour Code Determination:

  • 1st significant digit, 2nd significant digit, multiplier, and tolerance values.

  • Example: Brown (1), Black (0), Red (100), Silver (±10%) resulting in 10 x 10² = 1,000 Ω ±10% or 1kΩ ± 10%.

• Colour Code Table:

  • 1st Band to 3rd Band values and multipliers for resistors.

  • Sample Values: Black (0), Brown (1), Red (2) for significant digits; various colors indicate multipliers and tolerances.

Mnemonics for Resistor Colour Code

• Ways to Remember:

  • Exploring phrases such as: "Bad Beer Rots Our Young Guts But Vodka Goes Well" to memorize the color codes.

Complete Self Test 310102a

• Review and complete Assignment 1.