SaM ~ Vibration Measurement Based on Strain Gauge

• Where:
  • $R$ : sensor, in this particular example we assume to have a strain gauge.
  • $R_W$ : wires resisitance.
  • $I_{DC}$ : current sources.
  • $V_{CC}$ : voltage soruce.
  • CMRR : common mode rejection ratio, in this case: CMRR of an AC-coupled differential amplifier.
    ⇒ So a large CMRR value.
  • ($C_{R1}^{+}$ - $E_n$), ($C_{R2}^{+}$ - $E_n$) : capacitive couplings with $E_n$ (electrical noise).
    ==Only the short part of the circuit which is exposed to the electrical noise is affected, so $C_{R1}^{+}$ and $C_{R2}^{+}$ are small capacitances==.
• The noise is common mode.
• With this kind of readout electronics, we can see the very small variation of strain due to vibrations.
• ==In this circuit everything should be shielded, differential and AC coupled, in order to reject as much as possible all the sources of errors==.