Lab #3
Network Theorems

Purpose
To experimentally verify the Superposition, Thevenin and Norton, theorems.

Pre-Lab

  1. Review the material in your textbook to familiarize yourself with the theorems mentioned above.
  2. Using PSpice, simulate  and obtain the the voltages and currents for each resistor in Figure 1.
  3. Create a table (with the above values) with columns for Resistance, Calculated Voltage and Current and Measured Voltage and Resistance (total of 5 columns).
  4. Calculate Voc (Figure 2)  and Isc (Figure 3). When using PSpice, make R5 very large (10000000000k) for finding Voc and very small (0.00000000001) for finding Isc. From that calculate RThevenin (Rth=Voc/Isc) for the circuit of Figure 1.
  5. Draw the Thevenin (Figure 4) and Norton (Figure 5) equivalent circuits at terminals a-b in  Figure 1 and label the circuit elements. (i.e. Replace Rth, Vth and Ith with the calculated values.)
  6. Calculate Vab in Circuit 1 from the Thevenin (Figure 4) Norton (Figure 5) equivalent circuits you labeled in Section 5 above.
  7. For the circuit in Figure 6 use the Principal of Superposition to:
        a) calculate the portion of Vab due to the 5V source.
        b) calculate the portion of Vab due to the -12V source.
    When setting the voltage sources to 0 in PSpice use a very small number (0.000000001) as PSpice doesn't like 0's.
  8. Calculate Voc (Figure 7)  and Isc (Figure 8) and Ro=Voc/Isc for the circuit of Figure 6.
  9. Draw the Thevenin (Figure 9) and Norton (Figure 10) equivalent circuits at terminals a-b in Figure 6 and label the circuit elements. (i.e. Replace Rth, Vth and Ith with the calculated values.)
       

Equipment
Proto Board
Short pieces of wire
Resistors  2-6.81k, 8.25k, 15.0k, 5.62k  Click for Color Code
2 DC Power Supplies (HP for +5 V and Digital Lab for -12 V)
Multimeter

Procedure

Part 1:

Construct the circuit as shown in Figure 1.
    1. Measure and record the resistance of each resistor. Show me how Record your data in the table prepared in Section 3 of the Pre-lab.
    2.   Measure and record the voltages across each resistor including Vab. Show me how Record your data in the table prepared in Section 3 of the Pre-lab.
    3. Measure the open-circuit voltage Voc (Figure 2).
    4. Measure the short-circuit current Isc (Figure 3). Show me how
    5. From the measurements made in b) and c), calculate the Thevenin equivalent resistance Rth=Voc/Isc
    6. Label the circuit elements in the Thevenin and Norton equivalent circuits shown in Figure 4 and Figure 5.

Part 2:

Construct the circuit as shown in Figure 6. Use the variable -15 Volt supply in the Digital Lab for the -12 Volt source. (Connect the Digital Supply GND (ground) to the negative of the HP supply that goes to R4.
     1.   Measure the voltage Vab.
     2. Measure the open-circuit voltage Voc (Figure 7).
     3. Measure the short-circuit current Isc (Figure 8).
     4. From the measurements made in b) and c), calculate the Thevenin equivalent resistance Rth=Voc/Isc
     5. Label the circuit elements in the Thevenin and Norton equivalent circuits shown in Figure 9 and Figure 10.

Part 3:

For the first circuit given in Part 2 (Figure 6), determine Vab by the principle of Superposition by measuring:

  1. The portion of Vab due solely to the 5V source by replacing the -12V source with a piece of wire.

  2. The portion Vab due solely to the -12V source by replacing the 5V with a piece of wire.

  3. The sum of these two voltages.  

    NOTE: Do not place a short circuit across a voltage source. When setting a voltage to zero, first disconnect it and then replace it with a piece of wire (a short circuit).

Results

  1. Compare (in a table) and comment on how your Pre-lab Section 2 calculations for Circuit 1 compared with your measurements in Section 2 of Part 1 above.

  2. From Part 1of the Procedure:
    - Calculate Vab from the experimental Thevenin equivalent circuit in Figure 4.
    -     Calculate Vab from the experimental Norton equivalent circuit in Figure 5.
    Compare and comment on how these calculations compare with your Pre-lab Section 6 voltage calculations for Circuit 1.

  3. From Part 2 of the Procedure:
    - Calculate Vab from the experimental  Thevenin equivalent circuit in Figure 9.
    -     Calculate Vab from the experimental Norton equivalent circuit in Figure 10.
    Compare and comment on how these calculations compare with your Pre-lab Section 9 voltage calculations for Circuit 1.

  4. Compare and comment on how your Pre-lab Section 7 calculations compared to your measurements in Part 3 above.

Remember, a formal report is required as indicated in the "Introduction".