AS

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.