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Lab Experiment No. 5 Voltage and Current Maps I. Introduction The purpose of this lab is to gain additional familiarity with making measurements on electrical networks. The experiments involved in this lab address the following topics – (a) reading and understanding a schematic diagram, (b) proper layout of a network on a breadboard, (c) application of electronic test equipment to make voltage and current measurements, (d) generation of a voltage, current, and power map of a network under test (NUT), and (e) performing the least number of measurements necessary to generate the map. The theory and equations associated with these experiments are covered in your class notes. Your job in this session is to build and apply two measurement methods on each of the given networks in order to expand your hands-on experience in working with networks and test equipment. For each network included, make use of the parts supplied by the GTA, and the DMM and dc power supply located on the lab bench. II. Breadboard construction and network measurements The schematics for three resistive networks are shown in Figures 1 through 3. Node ‘0’ is the designated ground or reference node for each network. Each network has three corresponding data tables that are to be filled out. You are to perform the following tasks. (a) Direct measurement method i. Build the network on your breadboard with particular attention paid to strict layout procedures. ii. Measure with the DMM the resistance of each resistor and record it in Table xx1(a) in the column where indicated. iii. Power the network with the dc power supply set to the specified voltage indicated on the schematic. iv. Use the DMM to measure the voltage drop across each resistor and label on the schematic with a positive sign (+) the resistor’s positive terminal. Record the voltage reading in Table xx(a) where indicated. v. Complete Table xx(a) entries by computing with Ohm’s law the current through (use the measured resistor values in Table xx(a)) and the power dissipated by each resistor. Use KCL to compute the current through and the power dissipated by the power supply. (b) Indirect (node) measurement method i. Using the same network breadboard layout in (a), measure the voltage at each node (Vni) with respect to the ground node (node ‘0’) and record in Table xx(b) where indicated. Label on the schematic the polarity of the node voltage with a positive (+) or negative (–) sign. ii. Apply KVL to the node voltages to calculate the voltage across each network resistor. Record the KVL expression and resistor voltage in Table xx(c). iii. Complete the entries in Table xx(c) by computing with Ohm’s law the current through (use the measured resistor values in Table xx(a)) and the power dissipated by each resistor. Use KCL to compute the current through and the power dissipated by the power supply. III. An example An example network is worked with the results presented in Tables at the end of this lab statement. Node ‘B’ is the designated ground node for this network. IV. Comparisons, comments and conclusions Compare the voltages, currents and power dissipation in Tables xx(a) and xx(c) for each network. Make comments on which measurement method is more efficient, practical and easier to perform. 1 ‘xx’ refers to the Figure number; ‘1’ for Figure 1, ‘2’ for Figure 2, etc. Network N1 R1 1 R2 2 33K 47K R5 R7 3 56K 22K R3 12K 5 Eps R6 6 N1 10V R4 0 68K 4 18K Figure 1 Resistive network N1 Table 1(a) Variable map for network N1 from direct measurements Component Spec value R1 33KΩ R2 47KΩ R3 12KΩ R4 18KΩ R5 56KΩ R6 68KΩ R7 22KΩ Eps 10V Measured value VRi (V) Table 1(b) Node-to-ground voltages Node i 1 2 3 4 5 6 Vni (V) IRi (A) PRi (W) Table 1(c) Variable map for N1 from node measurements Component R1 R2 R3 R4 R5 R6 R7 Eps KVL VRi (V) IRi (A) PRi (W) Network N2 R7 10K R1 1 R2 2 47K 33K R8 Eps R9 15V 82K R6 5 N2 3 R5 20K R3 8.2K 68K R4 0 13K 4 39K Figure 2 Resistive network N2 Table 2(a) Variable map for network N2 from direct measurements Component Spec value R1 47KΩ R2 33KΩ R3 68KΩ R4 39KΩ R5 20KΩ R6 13KΩ R7 10KΩ R8 82KΩ R9 8.2KΩ Eps 15V Measured value VRi (V) Table 2(b) Node-to-ground voltages Node i 1 2 3 4 5 Vni (V) IRi (A) PRi (W) Table 2(c) Variable map for N2 from node measurements Component R1 R2 R3 R4 R5 R6 R7 R8 R9 Eps KVL VRi (V) IRi (A) PRi (W) Network N3 R1 1 4 100 Eps1 R4 12V 1.2K R2 0 3 R8 2.4K R7 6 R5 1.8K 2.7K 120 2.4K Eps2 1.2K 12V R9 R6 R3 2 5 100 Figure 3 Resistive network N3 Table 3(a) Variable map for network N3 from direct measurements Component Spec value R1 100Ω R2 120Ω R3 100Ω R4 1.2KΩ R5 1.8KΩ R6 1.2KΩ R7 2.7KΩ R8 2.4KΩ R9 2.4KΩ Eps1 12V Eps2 12V Measured value VRi (V) Table 3(b) Node-to-ground voltages Node i 1 2 3 4 5 6 Vni (V) IRi (A) PRi (W) Table 3(c) Variable map for N3 from node measurements Component R1 R2 R3 R4 R5 R6 R7 R8 R9 Eps KVL VRi (V) IRi (A) PRi (W) Example Network R1 R2 A 1 4 10K 3.3K Vps 56K R5 680 R3 10V R6 R4 B 2 56K 3 51K Figure 4 Example resistive network Table 4(a) Variable map for the example network from direct measurements Component Spec value Measured value VRi (V) IRi (A) PRi (W) R1 10KΩ 9.832KΩ 1.07043 108.87µ 116.53µ R2 47KΩ 3.2473KΩ 0.17961 55.31µ 9.934µ R3 12KΩ 674.49Ω 37.316m 55.32µ 2.064µ R4 18KΩ 49.938KΩ 2.7577 55.22µ 152.29µ R5 56KΩ 55.538KΩ 2.9745 53.56µ 159.3µ R6 68KΩ 55.405kΩ 6.0255 108.75µ 655.29µ Vps 10V 10.09V 10.09 -108.75µ -1.0972m Table 4(b) Node-to-ground voltages Node i Vni (V) 1 9.0 2 6.0255 3 8.7832 4 8.8205 A 10.09 Table 4(c) Variable map for example network from node measurements Component KVL VRi (V) IRi (A) PRi (W) R1 VA – V1 1.09 110.86µ 120.84µ R2 V1 – V4 0.17948 55.27µ 9.919µ R3 V4 – V3 37.316m 55.32µ 2.064µ R4 V3 – V2 2.7577 55.22µ 152.29µ R5 V1 – V2 2.9745 53.55µ 159.3µ R6 V2 6.0255 108.75µ 655.29µ Eps VA 10.09 (-IR1) -108.97µ -1.0985m
