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2018-10-05

2018-10-05

作者: carpediemmlf | 来源:发表于2018-10-05 23:34 被阅读0次

  • Physics: take measurements and capture behaviour in mathematical form

  • Deviations from mathematical form implies the need to revise something

  • ideas of planning, executing and assessing measurements

  • Progress in physics
    \xrightarrow[]{Change\ quantity} System \\ \xrightarrow[]{Effect} Device/transducer \\ \xrightarrow[]{} Signal\ handling \\ \xrightarrow[]{} Data\ Recording

  • Insights

  1. Transducer should not affect system/device seen
  2. Track changes easily
  3. Deal with noise
  • Equivalent output circuit: ideal voltage source + output impedance
  • Equivalent input circuit: ideal voltage metre | input impedance

V_{in} = V_{1} \frac{Z_{in}}{Z_{in} +Z_{out}}

  • Desirable:
  1. Transducer with low output impedance
  2. 'scope with high input impedance

  • Compensate the transducer with a complex impedance probe to avoid degrading of V_{in} at high f

  • For other measurements:

  1. Current: small Z_{in} for 'scope
  2. Power: Z_{in} = Z_{out} to get the same maximum power measurable
  • Operational amplifier: high gain, high input impedance
    For an ideal OP:
  1. A = \infty
  2. Z_{in} = \frac{\partial V_{in}}{\partial i_{in}} = \infty
  3. Z_{out} = \frac{\partial V_{out}}{\partial i_{out}} = 0
  • Golden rules for an ideal OP:
  1. GR1: i_{+} = 0 \mathrm{A} = i_{-}
  2. GR2: V_{+}=V_{-} if not saturated (proof by considering the non-inverting amplifier to calculate using current conservation and Ohm's Law)
  • Inverting voltage amplifier
  1. Closed loop gain: -\frac{R_{2}}{R_{1}}
  • Non-inverting voltage amplifier
  1. Closed lop gain: 1 + \frac{R_2}{R_1}
  2. Other persepctive: potential divider
  • NB:
  1. Needs negative feedback
  2. V_{out} \leq +15 \mathrm{V} e.g. not saturated. After saturation
  • Make Z_{2} frequency-dependent to perform filtering and selected amplification

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