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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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