The SubVI of Gain.vi, FG1Chan.vi, sends out a signal with sine-wave peak Vs (Chan1_out). The first measurement is with only capacitor Cg installed. Be sure to conform to the capacitor polarity requirement. Set the Signal Frequency to 1000 Hz. Set your value of RS and check VDD = 10 V. Run Gain.vi to measure the gain. The gain should be less than 1 without the source bypass capacitor. A signal of Vs ≈ 0.5 V should thus suffice for good linearity and measurement precision.
Now install the capacitor Cs. Note that the source is at a positive voltage. Run the VI while setting Vs at various values. Adjust Vs until the THD% (total harmonic distortion, %) is reduced to below about 5%.
Continue to lower Vs and run Gain.vi. Verify that the measured gain, av, is invariant for smaller values of Vs except as eventually limited by DAQ resolution and noise. Find the largest Vs (up to 5% THD), which is consistent with a constant gain measurement with increasing Vs.
Run the VI again with a lower frequency (e.g., 800 Hz) to verify that the gain is not frequency dependent in this frequency range. Now default and save the Front Panel.
