In the first session of this laboratory the tachometer signal is deformed when the rectifier is attached.  To rectify that situation, you can put an isolation amplifier between the tachometer and the rectifier.  However, to avoid drawing too much current you might also need to put an isolation amplifier at the output of the rectifier.  Here's the entire circuit including the second isolation amplifier.

You need to get the measurements needed to answer the questions on the Lab Summary.  Connect the circuit.

• Use a 1.0mf capacitor.
• The resistor (R) should be 10kW.

• Jump the input (motor voltage) from zero to 6 v and observe the filtered output on the scope.  You might want to try to get the starry night along with it.  If that doesn't work out, get the output of the filter and record it.  Do you get a good measurement of the transient?  Explain.
• Do the same going from 6 v to zero v.  (i.e. turn off the power supply to the motor). Do you get a good measurement of the transient?  Explain.

      Here is a link to a note on using the 741 Operational Amplifier as an Isolation Amplifier.  Note the drawing of the circuit board and the connections.  And, you may want the pinout for a 741.  That's shown below.