Electronics Electronic Components by tiz18123

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									                     Electronics                                          Electronic Components
• most instruments work on either analog or digital             • Resistors: resists the flow of electron through a
  signals                                                         circuit
• we will discuss circuit basics                                   – units of Ohms (Ω) with symbol =
  – parallel and series circuits                                • Capacitors: resists changes in the voltage of a
  – voltage dividers                                              circuit (capacitive reactance)
  – filters – high-pass, low-pass, band-pass filters               – units of Faradays (usually μF or nF)
                                                                   – with symbol =               OR
• the main purpose of this chapter is to get you to             • Inductors: resists changes in the current of a
  understand the electronic filters                               circuit (inductive reactance)
  – they help to reduce electronic noise                           – units of Henry’s (H) with symbol =
  – less noise = a clearer signal (more on this in Chapt 5)




   Resistors and Basic Circuit Laws                                                  Basic Circuits
 • a few Laws to provide equations                              • series batteries
    – (V = voltage, I = current, R = resistance)                   – voltage adds to produce a
    – Ohm’s Law: V=IR                                                higher voltage
    – Power Law: P = IV OR            P = V 2/R


 • Kirchoff’s Laws
    – current law: the algebraic sum of the current             • parallel batteries
      around any point in a circuit is zero                        – currents add to add a higher
    – voltage law: the algebraic sum of the voltages                 current capacity
      around a closed electrical loop is zero




                     Basic Circuit                                             Voltage Dividers
• series resistors                                            • since the same
                                                                current goes
  – resistance add directly                                     through each
           RT= R1 + R2 + ...                                    resistor, there is
  – same current through each                                   different
                                                                voltage drop
                                                                across each
• parallel resistors
  – resistance add as reciprocals                             • the total voltage
         1/RT= 1/R1 + 1/R2 + ...                                divides across
                                                                the series
  – same voltage drop across each




                                                                                                                      1
        Example : a Voltage Divider                          Example : a Voltage Divider
 • Calculate the magnitude of the voltages across     • Calculate the magnitude of the voltages across
   each resistor                                        each resistor
• Steps to solve                                     • Steps to solve          V = 100. V
   – calc. RT                                           – calc. RT             R1 = 50. Ω
                                                                               R2 = 150. Ω
   – calc. IT                                           – calc. IT             R3 = 250. Ω
   – calc. each V        V = 100. V                     – calc. each V
                         R1 = 50. Ω                                            RT = 450. Ω
                         R2 = 150. Ω                 V = IT R T
RT= R1 + R2 + R3         R3 = 250. Ω
                                                     or IT = V/RT
RT= 50+150+250
RT=450 Ω                                             IT = 100. V/450. Ω
                                                     IT = 0.222 A




        Example : a Voltage Divider                                  Current Dividers
 • Calculate the magnitude of the voltages across      • since the voltage is the same across each
   each resistor                                         resistor, the current across each is different
                          V = 100. V
                             R1 = 50. Ω                • the total current is divide across each parallel
V 1 = IT R 1                 R2 = 150. Ω                 path
V1 = (0.222 A)(50. Ω)        R3 = 250. Ω
V1 = 11.1 V = 11 V           RT = 450. Ω
                                                                                  •scan fig 2-3 on page 24
                             IT = 0.222 A
V 2 = IT R 2
V2 = (0.222 A)(150. Ω)
V2 = 33.3 V

V 3 = IT R 3
V3 = (0.222 A)(250. Ω)
V3 = 55.5 V




       Example : a Current Divider                          Example : a Current Divider
  • Calculate the magnitude of the current through     • Calculate the magnitude of the current through
    each loop and the total current                      each loop and the total current




V = 100. V
R1 = 50. Ω
                    • Steps to solve                 V = 100. V
                                                     R1 = 50. Ω
                                                                    I1=V/R1=100.V/50. Ω=2.0 A
R2 = 150. Ω           – calc. each I                 R2 = 150. Ω
                      – calc. IT                                    I2=V/R2=100.V/150. Ω=0.667 A
R3 = 250. Ω                                          R3 = 250. Ω
                                                                    I3=V/R3=100.V/250. Ω=0.400 A




                                                                                                             2
        Example : a Current Divider                                                 Loading Error
  • Calculate the magnitude of the current through                    • making a measurement causes an uncertainty
    each loop and the total current                                     in the measurement (analogous to the
                                                                        Heisenburg Uncertainty Principle)

                                                                          VM − Vx
                                                                  Er =            × 100%
                                                                            Vx

V = 100. V                                                                 − RS
R1 = 50. Ω
                        IT = I1+ I2 + I3= 2.0 + 0.667 + 0.400 A   Er =            × 100%
R2 = 150. Ω             IT = 3.066 A = 3.1 A                              RM + RS
R3 = 250. Ω




                           Loading Error                                                 AC Circuits
                  0

                 -10                                              •
       % Error




                 -20
                                                                  • Chopping (AAS)
                 -30

                 -40                                              • electrochemistry
                 -50
                   1,000            100,000        10,000,000     • electrochemistry
                                    R M (Ω )

  • The error drops as the internal resistance of the
    meter increases




                       Inductors/Capacitors                                        RC Calculations
  • Capacitors: resists changes in the voltage of a                   • reactance: the capacitor's equivalent to
    circuit (capacitive reactance)                                      resistance
     – units of Faradays (usually μF or nF)                             – there is a frequency dependence
     – with symbol =               OR                                                       1    1
                                                                                   XC =        =
  • Inductors: resists changes in the current of a                                         2πfC 2ωC
    circuit (inductive reactance)                                     • impedance: the total “resistance” in an RC
     – units of Henry’s (H) with symbol =                               circuit
                                                                        – there is a frequency dependence
  • AC signals are constantly changing, so                                                                    2
                                                                                            ⎛ 1 ⎞
    including these components in the circuit                                Z = R + X = R +⎜
                                                                                     2     2
                                                                                           C⎜ 2πfC ⎟
                                                                                                   2
                                                                                                   ⎟
    affects the signal                                                                      ⎝      ⎠




                                                                                                                     3
                      RC Filters                                                                                          RC Filters
                                                                                                             • At high freq. the capacitor becomes
• since this circuit is a voltage
                                                                                                               practically a wire
  divider                                                                                                    • its reactance goes down and no
  – the voltage across the resistor is                                                                         voltage is dropped across it
              R      R                R
   VR = V ×      =V × =V ×
              RT     Z                           2
                                     ⎛ 1 ⎞                                                                                            100%
                                     ⎜ 2πf C ⎟
                                R2 + ⎜




                                                                                                               Voltage (% of input)
                                             ⎟                                                                                                                       VR
                                     ⎝       ⎠                                                                                        75%
                                                                                                                                                                     VC
  – the voltage across the capacitor is                                                                                               50%
                        ⎛ 1 ⎞                    •   as f ↑, VR ?   ↑
                        ⎜        ⎟
                        ⎜ 2 πf C ⎟
                                                                                                                                      25%
           X            ⎝        ⎠               •   as f ↑, VC ?   ↓
   VC = V × C = V ×                                                                                                                    0%
            Z                         2          •   as f ↓, VR ?   ↓
                         ⎛ 1 ⎞                                                                                                               10       100      1,000    10,000
                       2
                         ⎜
                      R +⎜        ⎟
                                  ⎟              •   as f ↓, VC ?   ↑                                                                             Signal Frequency (Hz)
                         ⎝ 2 πf C ⎠




              RC Circuit Distortion                                                                                       RC Filters
 • Distortion is dependent on the size of RC                            • See homework problems




                    RC Circuits                                                                                RC Circuits
• the capacitor cause a time lag in the voltage                         • the phase shift is frequency dependent,
  (phase shift)       dV                 ⎛ 1               ⎞              decreasing as the frequency increases
                   i=C                           ⎜ 2 πf RC ⎟
                                     φ = arc tan ⎜         ⎟
                           dt                    ⎝         ⎠
                                                                          Phase Shift (degrees)




                                                                                                  12
                                                                                                                                                          R = 1 kΩ
                                                                                                                                                          C = 1 nF
                                                                                                  8
                                                                                                                   ⎛ 1 ⎞
                                                                                                  4                ⎜ 2 πf RC ⎟
                                                                                                       φ = arc tan ⎜         ⎟
                                                                                                                   ⎝         ⎠
                                                                                                  0
                                                                                                   100                     10,000                  1,000,000     100,000,000

                                                                                                               Signal Frequency (Hz)




                                                                                                                                                                                 4
         Electronics Definitions                                Other Components
• resistance ≡ how a resistor effects a circuit     • diode ≡ allows current to flow in only one
                                                      direction; used in regulators
• reactance ≡ how a capacitor or inductor effects   • transitors ≡ can act as an amplifier or switch
  a circuit                                           – replaced the vacuum tube
                                                    • transformer ≡ converts one AC voltage to others
• impedance ≡ the combination of resistance and
  reactance                                         • rectifier & filter ≡ converts AC to DC
                                                    • regulator ≡ prevents surges in current from
                                                      changing the voltage of a power supply
                                                    • oscilloscope ≡ a device to read and analyze signal
                                                      and circuits




                                                                                                           5

								
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