will be measuring a DC voltage and different A.C. voltages using an oscilloscope and a
DMM (Digital Multi-Meter).

While a DC voltage is
only defined by its amplitude, the interesting parameters of an A.C.
voltage are:

voltage amplitude V<sub>MAX.

peak-to-peak value V<sub>pp

root-mean square value V<sub>rms

period T
frequency f = 1/T.
waveform (sinusoidal, triangular, square, etc).

v

time

V<sub>MAXAX

T

V_ppAn electric
signal (voltage), that follows a sinusoidal law, can be mathematically
described as:

 v = V<sub>m
sin 2f t     (1)

v       
=  instantaneous value of the signal.

V<sub>MAX = 
maximum amplitude of the signal.

2f    
= angular frequency of the signal ().

t        
=  time.

T       
=  period of the signal (1/f).

    
The root-mean square value V<sub>rms is obtained by calculating
the mean of the square of the instantaneous voltages during one period
then taking the square root of the result:

   
...(2)

Combining equation (1)
and (2) leads to the rms value of a sinusoidal signal:

          
(3)

Introduction

    
In this experiment, the electric voltage from a function generator is
simultaneously measured using an oscilloscope and a DMM. Also a DC voltage
from a battery will be measured with these two instruments. The oscilloscope
presents the advantage of the graphical representation of the signal
under investigation because the voltage (signal) is plotted on the screen
of the instrument as a function of time.

     A grid divides the
screen into divisions and it is possible to change the vertical scale
using the Volt/Division knob, while the horizontal scale can be changed
using the Time/Division knob.

     Since the oscilloscope
allows the visualization of the waveform, it can be used to measure
the amplitude voltage V<sub>MAX, the peak-to-peak value V<sub>pp,
and the period T of the signal. The root-mean square V<sub>rms,
and the frequency of the signal can be calculated.

     Note that the DMM,
when used to measure AC voltages, gives the rms value V<sub>rms.

Equipment provided

One 1.5 Volts battery.

One function generator.

One dual-trace oscilloscope.

One digital multi-meter (DMM).

Connecting BNC cables.

One BNC T (to split the signal).

Procedure

1.  Connect
the output of the function generator to the oscilloscope and simultaneously
to

the DMM in order to measure the same signal with the two instruments.

2.  Turn on
the oscilloscope. The input signal must be connected with the coupling
switch

     
in AC position. 

3.  Turn on the DMM and select the AC voltage measurement.
Take note of the voltage       

     
measurement simultaneously with the oscilloscope.

4.   The
signals to be set on the function generator are:

Sinewave 1000 Hz.

Squarewave 20000 Hz.

Sinewave 1 Hz.

Sinewave 2 MHz (2000000 Hz).

5.  Verify the period and
the amplitude of the signal coming from the function generator. The
function generator has a frequency counter on the front panel. Verify
this frequency matches the one obtained with the oscilloscope.

6.  Adjust
the Volt/Division and the Time/Division so that one waveform is well

    
displayed on the screen.

7.  Switch
the input coupling to GND. You will get a line.

8.  Using the
X, Y position knobs make sure the line is centered on the screen.

  9. 
Switch the coupling back to AC.

10. Measure the
Period of the signal.

11. Measure the
amplitude and the peak-to-peak value of the signal. See question 2

12. Calculate the
rms value of the signal.

13. Switch the input
coupling to DC and measure the peak-to peak value. See question 2

14. Repeat the procedure
for each of the signals of instruction 4.

15. Disconnect the
function generator and replace it with the battery.

16. Set the DMM
to measure DC voltage.

17. Observe the
screen of the oscilloscope when the input coupling switch is in AC

      
position and in DC position. See question 3

18. Fill in the
included Data sheet and answer all questions on a separate sheet.

      Provide
all the calculations.

19. Staple the provided
datasheet with your answer sheet and slip it in the mail-box

     
outside the Meas. Lab by 9.30a.m. of the next day after performing the
experiment.

N.B.

In the M columns
of the data-sheet write D if the measurement was direct, write C
if the value is calculated, and write NOT if the parameter cannot
be obtained with that measurement instrument.

Questions:

Explain the use of the Volt/Division and the Time/Division
knobs.
Write your observations related to steps 11 and 13. Explain.
Write your observations related to steps 17. Explain.
The nominal value of the voltage measured from a common household
outlet is 117 Vac. This is the rms value. Calculate the maximum amplitude
V<sub>MAX and the peak-to-peak value V<sub>pp.