Steady-State AC Behavior of Passive Circuit Elements ECE 2100 Circuit Analysis Laboratory updated 1 December 2008 Pre-Laboratory Assignment 1. Consider the circuit of Figure 1 with a 16 volt peak-to-peak 5000 Hz sinusoidal voltage source. Rcsr is a current sampling resistor and Rs is the internal resistance of the voltage source (a waveform generator). Resistor Rcsr will enable display of the current I through R1 using an oscilloscope (an instrument that can only measure voltage). Using phasor analysis, find the voltage V across R1 and I through R1 assuming that Rs and Rcsr are shorts. Then simulate the circuit with the given values of Rs and Rcsr using a transient analysis. Set “Stop Time” to 3 ms, “Time To Start Saving Data” to 1 ms, and “Maximum Time Step” to 0.1us in your SPICE engine, plot V(t) for 2 ms by plotting V(2)-V(1) in SPICE. On the same plot, plot 1000*(V(1)/10); that graph shows the current I through R1 in mA. Note that SPICE will show units of V instead of mA. Your plot should look like Figure 2. What is the phase relationship between the resistor voltage and current? Insure that your hand analysis and simulation results (for voltage amplitude, current amplitude, and phase angle) closely agree (they will not match exactly – Why not?). Figure 1. Circuit to Measure Steady-State Behavior of a Resistor 12. Replace R1 with a 39 mH inductor and repeat pre-laboratory step 1. 3. Replace R1 with a 0.026 uF capacitor and repeat pre-laboratory step 2. 4. Bring an electronic copy of your simulation files to lab. Figure 2. Steady State Voltage (smaller signal has units V) and Current (larger signal has units mA) for a Resistor. Procedures Part One 1. Build the circuit of Figure 1. Use the function generator as the voltage source. Since one lead of the oscilloscope is grounded, we cannot directly measure V(2)-V(1). Connect oscilloscope CH 1 to node 2 (with the ground of the oscilloscope lead connected to the ground of the waveform generator). We will consider V(2) to be the voltage across R1; this is not correct, but we can get away with this here. Connect oscilloscope CH 2 to measure V(1). Note that V(1) is directly proportional to the current through R1. Setup the scope to display at least two complete cycles of the waveforms. Verify the frequency of the source. Find the phase angle between the resistor voltage and current. Compare these experimental results (voltage amplitude, current amplitude, and phase angle) with simulation (SPICE) and hand analysis results (use a table). Find experimental errors using the hand analysis results as the reference. Part Two 2. Replace R1 with a 39 mH inductor. Compute the value of the inductor using your measurements of V and the source frequency. Update your hand analysis and simulation (SPICE) results with this measured value as needed. Repeat laboratory procedure step 1. Part Three 3. Replace R1 with a 0.026 uF capacitor and repeat laboratory procedure step 1. 2Analysis 1. Why can the voltage V(2) be considered as roughly the same as V(2)-V(1)? 2. Prepare phasor diagrams that show phasors V and I for laboratory procedures parts 1-3. 3. What is the primary source of the error between experimental and hand analysis results for this experiment? Credits and Copyright Adapted from material developed by current and former ECE faculty, including Professor Joseph Kelemen. © 2008 Damon A. Miller. All rights reserved.