Chapter 3
Analysis Techniques

m3.3 Superposition

In the circuit of Fig. m3.3:

1. Apply the superposition method to determine the current I_a and the voltage V _b, i.e., find the current I_a1 due to the current source I₁ acting alone, the current I_a2 due to the voltage source V ₂ acting alone, and the current I_a3 due to the voltage source V ₃ acting alone, and then evaluate the sum I_a = I_a1 + I_a3 + I_a3. Make use of current dividers and voltage dividers as much as possible.
2. Use the superposition method to determine the voltage V _b.
3. Apply the node-voltage method to find I_a and V _b, and then compare these results to those of the superposition method.

Use these component values: I₁ = 1.84 mA, V ₂ = 3.0 V, V ₃ = 4.9 V R₁ = 1.0 kΩ, R₂ = 2.2 kΩ, and R₃ = 4.7 kΩ.

NI Multisim Measurements

Enter the circuit of Figure m3.3 into NI Multisim. Use interactive analysis and the voltmeter and ammeter indicators.

• Place the AMMETER_V and VOLTMETER_H components to display the current I_A and the voltage V _B.
• Set the active source to its intended value, and then set all of the other sources to zero. After stopping the simulator, press Ctrl+Z (“undo”) two times to return the sources to their original values.
• Repeat to determine the responses due to each source acting alone.

NI myDAQ Measurements

1. Build the circuit of Figure m3.3. Use the myDAQ DMM to measure I_A and V _B when all sources are active.
2. Measure I_A1 to I_A3 by activating only one source at a time. Disable the other sources by disconnecting the current source (replace it by an open circuit) and disconnecting the voltage source and replacing it with a jumper wire (short circuit).
3. Repeat for V _B1 to V _B3.
4. Add your results together for each source acting alone, and then compare this result to your original measurement when all sources were active.

Additional helpful tips:

• Implement the voltage source V ₂ according to the circuit diagram of Figure B.2 in Appendix B.
• Measure V ₂ with the myDAQ DMM voltmeter and adjust the potentiometer to set the voltage as close to 3.00 volts as possible. Record the actual voltage you measured.
• Implement the voltage source V ₃ with the NI myDAQ 5V power supply. Connect the myDAQ digital ground DGND terminal to the analog ground AGND at your breadboard.
• Measure V ₃ with the myDAQ DMM voltmeter when the circuit is connected. Expect to find this value slightly less than 5.0 volts. Record the actual voltage you measured.
• Implement the current source I₁ according to the circuit diagram of Figure B.4 in Appendix B. Use a 680 Ω resistor for the adjustment resistor R.
• Measure I₁ with the myDAQ DMM ammeter and confirm that the current is close to 1.84 mA. Record the actual current you measured.