Lab 6 Re-Write

7/27/2019 Lab 6 Re-Write

1/6

Calculating RMS ECE206

Lab 6

Names:Sung Joo An, Benjamin Domash

Due Date:10/16/2013

Statement of Purpose:

Learn to use the DMM and oscilloscope in order to measure the RMS voltage.

Challenge:

a) Explore the bandwidth of our DMM, using the function generator as a source, and

measuring its output with both the DMM and the RMS mode of the oscilloscope. Confirm that

the DMM and the oscilloscope agree on RMS measurements of symmetric signals, at least at

1kHz. Determine the maximum frequency (separately, for sine and square waves) where the

DMM and the oscilloscope continue to reasonably agree.

b) Construct a 555-based oscillator that a generates a variable (controllable) period (t1+t2) of a

waveform, while keeping the discharge time constant (t2). Measure this asymmetric signal with

the DMM and the oscilloscope at 2 (two) frequencies within the audible range. Confirm that

the DMM and the oscilloscope agree on RMS measurements of this asymmetric signal.

Plan:

For part A, we set up the oscilloscope, DMM, and the function generator so that the function

generator is the source and we measure the output with the DMM and the oscilloscope. Then we

drive the function generator till the DMM's readings and the oscilloscope's readings start to differ.

Repeat for square and triangle wave forms.

For part B, we will construct the same circuit used in lab 4 using the NE555. Using two different

values of R so that we can vary the time constant. Using that we can measure the RMS values.

Execution:

Part A

Using the Function Generator as the source we set up the DMM and Oscilloscope to measure the

output. the set-up is pictured below in Figure 1.


2/6

Figure 1

Then using the DMM and oscilloscope we measured the RMS values listed and recorded them in

the table (shown in Results). Then using the intuilink program we extracted the data from the

oscilloscope graph and used excel to calculate the RMS using 1000 data points only one period

of values.We then drove the frequency up until the difference between the DMM's RMS value

and the Oscilloscope's RMS values was more than 5%. We then repeated the same thing while

the function generator was set to square waves and again when it was set to triangle waves.

Part B

We did the same measurement as before but this time using the NE555 circuit from the previous

lab. Initially weusedthe values of R1= 10k , R2 = 1k , and C = 0.5 F (two 1 F capacitors

in series). The circuit diagram is shown below in Figure 2 and the built circuit is shown in Figure

3. We measured the peak to peak voltage and the frequency and recorded the RMS values shown

on the DMM and Oscilloscope using nodes 6 and GND.NOTE: For part A, we could have usedeither AC or DC coupling on the scope as long as the signals had no DC offset. For part B,

however, we needed to set the scope to be AC coupled in order to obtain the proper results.

Using intuilink we extracted the data from our graphs and used excel to calculate the RMS. Then

we repeated the process after switching R1 to 1k while keeping all the other components the

same.


3/6

Figure 2 Figure 3

Results and Conclusions:

DMMRMS

OscilloscopeRMS Excel RM

sine wave 1V peak-peak, offset=0 1.00kHz 0.7162V 0.7301V 0.7309692

square wave 1V peak-peak, offset=0 1.00kHz 1.0141V 1.0356V 1.0359991

triangle wave 1V peak-peak, offset=0 1.00kHz 0.5848V 0.5956V 0.5959473

asymmetric wave

#1 2V peak-peak, offset=0 0.326kHz 2.711V 2.761V

2.8054906

asymmetric wave#2 2V peak-peak, offset=0 1.282kHz 2.597V 2.648V

2.67883

Max frequency for sine waves (1V peak-peak) = 1.100MHzo At 1.1 MHz, DMM reads 800.0mV and Oscilloscope reads 760.0mV

Max frequency for square waves (1V peak-peak) = 1.077MHzo At 1.077 MHz, DMM reads 1.113V and Oscilloscope reads 1.058V

Answer this question:Why is this frequency limit (square waves) smaller than the frequency

limit for sine waves?

A square wave is anon-sinusoidal periodic waveform (which can be represented as an infinite

summation of sinusoidal waves), in which the amplitude alternates at a steadyfrequencybetween

fixed minimum and maximum values, with the same duration at minimum and maximum. The

DMM has a fixed bandwidth, which means that more frequency components exist outside the

operating range when the fundamental frequency increases.
http://en.wikipedia.org/wiki/Non-sinusoidal_waveformhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Non-sinusoidal_waveform


4/6

Graphs for Part A

Sine wave

Square Wave


5/6


6/6

Asymmetric wave #2:R1=1k ; R2=1k ; C=0.5 F

Documents

Lab 6 Re-Write