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Physics 5620 Laboratory 1
Laboratory Equipment and DC Circuits
Objective: In this laboratory session, you are to become familiar with the electronic
equipment in the laboratory, to learn proper operational procedures, and to know
the capabilities and limitations of the equipment. Most importantly, you are to
learn how to take good care of the equipment. You will need to consult with the
instructor for an explanation of details about the equipment and its operation.
Introduction: The laboratory workstations are based on the National Instruments
program NI ELVIS (Educational Laboratory Virtual Instrumentation Suite)
which runs on top of NI LabView. The workstations include software based test
instruments and a breadboard on which you will construct your circuits. The
breadboard permits you to assemble circuits using 22 gauge jumper wires without
the need to solder components together. This allows rapid prototyping of many
circuits during the lab period. Some of the more useful software based
instruments you will encounter are:
Function Generator This instrument provides you with choices for the type of
output waveform (sine, square, or triangle), amplitude selection, and frequency
settings. In addition, the instrument offers DC offset setting, frequency sweep
capabilities, and amplitude and frequency modulation.
Oscilloscope This instrument provides the functionality of the standard desktop
oscilloscope found in typical undergraduate laboratories. The NI ELVIS - Scope
has two channels and provides scaling and position adjustment knobs along with a
modifiable timebase. You can also choose trigger source and mode settings. The
autoscale feature allows you to adjust the voltage display scale based on the peakto-peak voltage of the AC signal for the best display of the signal. Depending on
the DAQ device cabled to the NI ELVIS hardware, you can choose between
digital or analog hardware triggering. You can connect to the NI ELVIS - Scope
from the NI ELVIS Prototyping Board or from the BNC connectors on the front
panel of the benchtop workstation. The FGEN or DMM signals can be internally
routed to this instrument. In addition, this computer-based scope display has the
ability to use cursors for accurate screen measurements. The sampling rate of the
Oscilloscope is determined by the maximum sampling speed of the DAQ device
installed in the computer attached to the NI ELVIS hardware.
Digital Multi Meter (DMM) This commonly used instrument can perform the
following types of measurements:
•
•
•
•
DC voltage
AC voltage
Current (DC and AC)
Resistance
•
•
•
•
Capacitance
Inductance
Diode test
Audible continuity
You can connect to the DMM from the NI ELVIS Prototyping Board or from the
banana-style connectors on the front panel of the benchtop workstation.
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Breadboard The NI ELVIS Prototyping Board connects to the benchtop
workstation. The prototyping board provides an area for building electronic
circuitry and allows the connections necessary to access signals for common
applications. You can use multiple prototyping boards interchangeably with the
NI ELVIS Benchtop Workstation.
Fig. 1. The NI ELVIS desktop system.
Experiments:
1.1
DC Voltages Measured by the Oscilloscope and the DMM
With the breadboard powered off, connect the +15 V supply to the DMM. You will
need to make connections to both the +15 V and Ground connections.
Question 1: Why do you need two connections to measure a voltage?
Measurement 1: Turn on the power to the NI ELVIS breadboard and use the DMM
to measure the DC voltage. Record the measurements in a table as shown below.
Next start the oscilloscope soft panel and measure the +15 V supply with the
oscilloscope set to DC coupling.
Voltage with DMM
Voltage with scope, DC coupled
Voltage with scope, AC coupled
Question 2: Notice that, with AC coupling to the oscilloscope, any DC voltage in the
input signal is cutoff. Why?
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1.2
AC Voltages Measured by the Oscilloscope and the DMM:
Use the function generator to display a 1 kHz sine wave (with zero VDC offset) at 2.5
V peak-to-peak and display it on the oscilloscope.
Measurement 2: Use the calibrated setting of the vertical amplifier input (DC
coupled) of the scope to measure the peak-to-peak value of the signal. Then use the
DMM to measure the rms (root-mean-square) value. Convert the peak-to-peak value
to an rms value to see if the two measurements agree. Repeat the measurements for
the frequencies and waveforms listed in the table below.
Frequenc
y
1 kHz
10 kHz
50 kHz
100 kHz
100 Hz
10 Hz
5 Hz
1 Hz
1 kHz
1 kHz
Waveform
Amplitude (Vpp)
sine
sine
sine
sine
sine
sine
sine
sine
square
triangle
2.5 V
2.5 V
2.5 V
2.5 V
2.5 V
2.5 V
2.5 V
2.5 V
2.5 V
2.5 V
Calculated RMS
DMM Reading
Question 3: On the basis of your observations, is there a frequency range or cut-off
frequency after which the DMM measurements of sinusoidal voltages becomes
inaccurate?
Question 4: Does the DMM measure a true RMS voltage value for non-sinusoidal
waveforms?
Question 5: Do you observe any distortion of the signals on the oscilloscope?
1.3
Resistance Measurements with the DMM:
Even though the DMM is functioning as an ohmmeter, it is still using its digital
voltmeter capabilities. However, in the Ω-function mode, the DMM supplies a current
to the external load resistance when connected to its output terminals and measures the
corresponding voltages at these terminals.
Measurement 3: Set the DMM function to Ω, and measure ≥ 4 different carbon
resistors (3 or 4 band resistors only). Compare the measured values to the nominal
values as determined by the resistor color code.
Question 6: Is the agreement within the indicated resistor tolerance (4th band)?
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Color Code
Nominal Resistance
Measured
Resistance
% Error
1.4
Introduction to the Breadboard:
The breadboard is a convenient, time-saving way to construct and test electrical
circuits. The NI ELVIS breadboards have their own power supplies with a +5VDC
terminal for TTL circuitry, ±15VDC terminals for CMOS and op-amp circuitry, and
several GND (ground) connections.
Measurement 4: Measure these voltages with respect to GND using the DMM in the
DC (voltage) mode with an appropriate voltage scale setting (i.e. voltage to be
measured ≤ voltage scale).
Terminal (voltage source)
+5VDC
+15VDC
-15VDC
DMM Reading
The breadboard consists of a series of metal clips that are interconnected in columns
and row with a plastic housing on the top which permit connections by wire jumpers.
Measurement 5: Using the DMM as an ohmmeter, determine with sockets (holes) are
interconnected in columns and which ones in row. Sketch a diagram of the
interconnections in Figure 2.
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Fig. 2. Bread Board Grid
1.5
DC Circuits and Verification of Kirchoff’s Laws:
Question 7: How would you express Kirchoff’s Laws in words?
Using the values R1 = 1.0 kΩ, R2 = 2.2 kΩ, R3 = 4.7 kΩ, construct the circuit shown in
Figure 3.
Measurement 6: Measure the currents (I1,2,3 ) and voltages (VA,B,C ) using the DMM.
Report the measured currents and voltages in a table. Calculate the quantities I1,2,3 and
VA,B,C , list them in the same table, and compare them with your measured values.
I1
R1
I3
B
A
5V
R2
R3
I2
C
Fig. 3. Voltage Divider Circuit
Question 8: Is the level of agreement consistent with the resistor tolerances and the
accuracy of your measurements?
1.6
The Resistor Color Code:
A discrete resistor typically is marked with a set of 3 or 4 colored bands which
encodes its
value. Table 1 below denotes the numerical values for the colors appearing in the first
3 colors in a color code:
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Value
0
1
2
3
4
5
6
7
8
9
Table 1. Resistor Color Code Values
The bands in a color code define the value (in ohms) of the resistor and its tolerance.
Figure 4 is a sketch of the bands on a resistor. The first band on the right is a digit in
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the 10’s place, the second band is a digit in the 1’s place, and the third band is the
power of ten to multiply the first two by. The fourth band denotes the tolerance or the
expected uncertainty in the value given by the first 3 bands. Table 2 contains the
tolerance values of the fourth band.
Color of 4th Band
Gold
Silver
Missing
Tolerance
±5 %
±10 %
±20 %
Table 2. Resistor Color Code Tolerances
Fig. 4. The Resistor Color Code