ECE205 Lab 3_ RMS

pdf

School

University of Illinois, Urbana Champaign *

*We aren’t endorsed by this school

Course

205

Subject

Electrical Engineering

Date

Apr 3, 2024

Type

pdf

Pages

Uploaded by soroco33

ECE 205 Lab 2: Regulators Contributors: Pertinent Dates: Lab Work Performed: 10/05/23 Report Submitted: 10/05/23 Statement of Purpose: The purpose of this lab is to explore the “bandwidth” of our DMM, using the function generator as a source, and measure its output with both the DMM (AC V) and the RMS mode of the oscilloscope. Also, the maximum frequency (separately, for sine and square waves) where the DMM and the oscilloscope continue to reasonably agree, should be determined. Plan: In order to explore the bandwidth of the Digit Multimeter, we used the waveform generator as a source with different waveforms, offsets, and coupling. Next, we can measure the output using both the DMM and an oscilloscope to see the RMS voltage measured. We can also explore the maximum frequency at which the DMM and oscilloscope reasonably agree by changing the frequency from the waveform generator until we see a significant increase or decrease in the RMS.

Figure 1. A diagram of the setup used for this experiment. Execution The setup for the experiment was constructed using the following: ● a multimeter ● a function generator ● an oscilloscope ● red and black banana plug cables, one of each color ● two coaxial cables The circuit was set up as shown in Figure 2.

Figure 2. A picture of the actual setup for this experiment. For each of the combinations of waveform, offset, and coupling as shown in Table 1 below, we recorded the RMS voltage as shown by the DMM and Oscilloscope. After recording data from the oscilloscope, the RMS voltage was calculated using Excel by squaring, averaging, and then taking the square root of all the values measured. All these measurements are shown in Table 1 below. Table 1. Measured or calculated RMS values for the output voltage of the circuit and the voltage drop across the LM317 regulator. DMM RMS (mV) Oscilloscope RMS (mV) Excel RMS (mV) sine wave 1V peak-peak, 1.00 kHz 352.6 353 352.9

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

offset = 0 square wave 1V peak-peak, offset = 0 1.00 kHz 498.8 499 498.5 triangle wave 1V peak-peak, offset = 0 1.00 kHz 287.9 288 288.3 sine wave 1V peak-peak, offset = 0.25V, DC coupled 1.00 kHz 352.6 428 427.9 sine wave 1V peak-peak, offset = 0.25V, AC coupled 1.00 kHz XXXXX 355 354.6 Next we explored the maximum frequency for the sine wave and square wave combinations with 1 V peak to peak voltage and no offset. We determined a significant change in voltage to be 5%, so we began by calculating what a 5% increase would be in RMS and then we adjusted the frequency of the waveform generator until we saw that 5% increase or decrease. Last, we recorded the frequency at which this change occurred in Table 2 shown below. Table 2. Measured maximum frequency values for the sine wave and square waves with 1V peak to peak voltage and no offset. Waveform DMM RMS (mV) 5% difference Maximum Frequency (kHz) sine wave 352.6 +17.63 1,005 square wave 498.8 +24.915 548 Results and Conclusions We explored the bandwidth of our DMM by measuring RMS values from the DMM itself, the oscilloscope, and by manually calculating RMS. We tested this for multiple waveforms, offsets, and DC/AC coupling. As it can be observed in the last two rows of Table 1, there is a difference

of around 75 mV between the DC coupled and AC coupled setups. This is because AC coupling ignores the DC values, whereas DC coupling takes both the AC and DC values, so the DC coupled values will be higher than the AC values. The scope can be set to AC or DC coupled with the menu in the bottom left of the screen. We also explored the maximum frequency for sine waves and square waves by changing frequency in the oscilloscope until we saw a significant difference (5%) in RMS. We observed that the max frequency for sine waves (1005 kHz) was much larger than the maximum frequency for square waves. This can be explained by the nature of the waves themselves. A sine wave only has one frequency whereas square waves are a linear combination of multiple frequencies, so when the DMM is estimating the RMS, it is much harder to do for the square waves. Through this lab, we learned about the effectiveness of DMM’s for AC sinusoidal circuits. This is important because the DMM must estimate the RMS value using the peak AC voltage. Depending on the use of your DMM, it can be important to know how accurate your DMM is depending on how accurate your RMS value needs to be.