Chapter 3
Analysis Techniques

m3.1 Node-Voltage Method

Apply the node-voltage method to determine the node voltages V ₁ to V ₄ for the circuit of Figure m3.1. From these results determine which resistor dissipates the most power and which resistor dissipates the least power, and report these two values of power. Use these component values: I_src1 = 3.79 mA, I_src2 = 1.84 mA, V _src = 4.00 V, R₁ = 3.3 kΩ, R₂ = 2.2 kΩ, R₃ = 1.0 kΩ, and R₄ = 4.7 kΩ.

NI Multisim Measurements

Enter the circuit of Figure m3.1 into NI Multisim. Use DC operating point analysis to determine the four node voltages and the power dissipated by each resistor.

• Display the net names and rename them to match the four node voltages V ₁ to V ₄; use only the numbers for the net names.
• Set up a Simulate → Analyses → DC Operating Point analysis to display the four node voltages and the power associated with each resistor.

NI myDAQ Measurements

Build the circuit of Figure m3.1. Use the myDAQ DMM (digital multimeter) as a voltmeter to measure each of the four node voltages.

• Implement the voltage source V _SRC according to the circuit diagram of Figure B.2 in Appendix B.
• Measure V _SRC with the myDAQ DMM voltmeter and adjust the potentiometer to set the voltage as close to 4.00 volts as possible. Record the actual voltage you measured.
• Implement the current source I_src1 according to the circuit diagram of Figure B.5 in Appendix B. Use a 330 Ω resistor for the adjustment resistor R.
• Measure I_src1 with the myDAQ DMM ammeter and confirm that the current is close to 3.79 mA. Record the actual current you measured.
• Implement the current source I_src2 according to the circuit diagram of Figure B.4 in Appendix B. Use a 680 Ω resistor for the adjustment resistor R.
• Measure I_src2 with the myDAQ DMM ammeter and confirm that the current is close to 1.84 mA. Record the actual current you measured.

Further Exploration with NI myDAQ

As you are by now aware, the analytical solution and the simulation results always agree very well, largely because you can enter exact component values into the simulator. However, the physical circuit component values do not match the nominal values exactly: the 5%-tolerance resistors can vary ±5% from the nominal value represented by the color-coded bands, and the “1250/R mA” formula for the LM317-based current source is an approximation.

Explore what happens when you recalculate the analytical solution using measured component values.

1. Recalculate the four node voltages using the nominal resistor values and the measured values for I_src1, I_src2, and V _SRC. Create a data table to compare these values with your analytical results in terms of difference and relative difference.
2. Measure and record the five resistances R₁ to R₄.
3. Recalculate the four node voltages using the measured resistor values and the measured values for I_src1, I_src2, and V _SRC. Create a data table to compare these values with your analytical results in terms of difference and relative difference.
4. Summarize your results: What level of agreement did you achieve between the analytical solution and the physical measurements?