ENG 100 Lab #2 Passive First-Order Filter Circuits


In Lab #2, you will construct simple 1st-order series RL and RC circuits and both calculate and measure their responses to a sinusoidal input signal. Amplitude will be in units of dB, and phase in degrees.


First, before you show up for the lab, you will need to calculate the amplitudes and phases of these circuits, plot/draw them on log-log or semi-log paper, and bring them to class.


Second, you will build and measure them in lab, plot/draw them on the same curves that you calculated and brought with you, answer a few questions for each circuit, and turn in a "report": those sheets with the plots and the answers to the questions. Each person must hand in a report, not just each work group.


Use miscellaneous parts to build the circuits; use the function generator to generate a sinusoid signal input; use either the DMM or the scope to measure the signal amplitudes; use the scope to measure phase. No breadboards are needed for this lab.


I. Pre-Lab Work


A. Calculations and Plots for Series RL Circuit


For the series LC circuit shown below:



L = 100 mH


+


-


+


-


V2


R = 1 kW


V1




Calculate the amplitude and phase for the following frequencies:


50 Hz, 100 Hz, 200 Hz ,400 Hz, 800 Hz, 1600 Hz, 3200 Hz, 6400 Hz, 12800 Hz.


Plot amplitude (dB) and phase (degrees) versus frequency (log scale for frequency) on semilog paper or similar scales; make sure you have paper with enough decades for the frequency axis.


Using the amplitude and phase results for 1600 Hz, and the fact that w = 2pf radians/second, solve for f2 and td express the output, v2, in the form: v2(t) = V2Ścos(2pft+f2) = V2Ścos[2pf(t-td)].


Bring these calculations and plots to lab with you; you will be recording measurements on the same plots and comparing them to your calculations.



B. Calculations and Plots for Series RC Circuit, I


For the series RC circuit shown below:



+


-


+


-


V2


R = 1 kW


V1


C = 1 mF




Calculate the amplitude and phase for the same frequencies as the LR circuit, and plot as before.


Bring these calculations and plots to lab with you; you will be recording measurements on the same plots and comparing them to your calculations.


C. Calculations and Plots for Series RC Circuit, II


Switch the R and C in part B, above, calculate and plot the amplitude and phase for the same frequencies as before; bring them to lab.


II. Laboratory Measurements


A. Series RL Circuit Sinusoidal Response


Set up the signal source and measuring instruments.


function generator: Set the output to a 1 Vrms sinusoid at 1 kHz and 0 VDC offset. Verify the generator output on the scope with a BNC-to-BNC cable. The generator output can then be connected to the circuit input with a BNC-to-alligator cable.


oscilloscope: You will need two scope probes for this lab; use two BNC-to-alligator cables for probes.


Set up the scope to view two signals at once (V1 at Channel 1, V2 at Channel 2) according to the handout instructions. Set both Volt/Div scales to the same value and set the Time/Div scale to show two full periods of the input. Adjust the vertical positions to have the input in the top half of the display, the output in the bottom half of the display.


DMM: Set the DMM to measure V AC. Since a 1 Vrms input will be used, which measurement range should be selected?


Power supplies: None are needed for this lab.


Build the circuit and instrument set-up.


1. Circuit: Get a 1 kW resistor and a 100 mH inductor from the issue room. Twist or clamp them together so they are connected at one node.


2. Input Signal: Connect the function generator to the circuit with a BNC-alligator cable: Clip the black (ground) alligator clip to the open end of the resistor, clip the red (signal) alligator clip to the open end of the inductor.


3. Scope Connection: Clip the Channel 1 oscilloscope probe\'s ground clip to the ground side of the resistor and the Ch 1 probe\'s signal clip to the input side of the inductor. Clip the Channel 2 probe\'s ground clip to the ground side of the resistor and the Ch 2 probe\'s signal clip to the output side of the inductor (where the L and the R are connected).


4. DMM Connection: Using banana-alligator cables,