2. Circuit Components + Measurements

• Circuit Components and Measurement

  • Power supplies
  • Battery
  • Chemical Energy
  • Electrical energy

  
• Power supplies


  • Solar cell
  • Electronic Power supplies
  • Generator

  
• Current Flow in Conductors

  • Random motion of free electrons in a material
  • Conduction of Current along Wires
• Charge per carrier (e) = 1.6 x 10-19 Coulomb
• Current in amps (I) = rate of flow of charge (Q) passing a Point in a conductor


  I = v A n e
• Switches


  • Toggle
  • Rocker
  • Rotary
  • Push button
  • Rocker
  • Dual in line (DIL) package

  
• Switch types


  • (a) DPST
  • (b) DPDT
  • (a) NOPB
  • (d) NCPB
  • (e) Single pole rotary 6 position

  
• Resistor Construction


  • Carbon composition
  • Carbon Film
  • Metal Oxide
  • Metal Film
  • Metal Glaze
  • Wirewound
  • Surface mount (SMT)

  
• Precision Resistors


  • R indicates decimal point
  • F +/- 1%
  • G =/-2%
  • J+/-5%
  • K +/- 10%
  • M +/- 20%
• Variable Resistor: Potentiometers


  (A) Typical potentiometers

  (B) Trimmer potentiometers with construction views
• Application of Potentiometer


  • Fuel Level Indicator
• Multimeters


  • Analogue
  • Digital
• The Multimeter


  General Purpose: current, voltage and resistance, dc and ac, several ranges – auto-ranging

  
• The Moving Coil Multimeter


  Measure currents up to specified maximum values

  Accuracy: +/- 0.5 divisions

  Sensitivity: minimum value indicated by fsd
• Current Measurement


  Excess current bypasses the coil via the parallel or shunt resistor
• Voltage Ranges


  Rs ensures that full scale deflection current flows when the Required full scale deflection voltage is applied across the Overall meter
• Resistance Ranges


  Battery supplies emf Vs – current flows through meter (RM) and Rs and the unknown resistor Rx

  Non linear scale, half way when Rx = 30 kΩ, zero deflection when Rx - > infinity
• The Digital Multimeter


  Electronic circuit: input voltage -> digital -> display (base 10)

  1. D converter: analogue to digital converter

  Electronic amplifier: high input resistance, gain can be varied

  
• Voltage measurement


  Voltage gain of amplifier is varied to provide different fsd voltages
• Current measurement


  Current flow through a low resistance resistor, meter measures the voltage across resistor, different resistor values for each current range
• Resistance measurement


  Electronic circuit generates a constant current which flows through resistor under test, voltage drop measured by the meter, different ranges via different constant currents
• Ammeters and voltmeters


  Ammeters: low resistance, Voltmeter: high resistance, Multimeter: measure V, I, R
• Sensitivity


  Smaller the value -> larger sensitivity