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Transcript
ECE 2210
Measurement Equipment
Laboratory 1
Objective
In an electrical engineering laboratory there are is equipment you must be familiar with to make
measurements. This laboratory will reacquaint you with the digital multimeter (DMM), function
generator, and oscilloscope. These are the basic tools of the lab and will be used throughout your
engineering career. We will use the measurement equipment in this lab to gain a deeper understanding
of their advantages and disadvantages.
Digital Multimeter (DMM)
The DMM is the most versatile tool available in electrical engineering. At the very least it has the
capability to measure voltage, current, and resistance. In ECE2100 you went through a lab title Basic DC
Meter Design. The lab had you construct an analog meter from a galvanometer and resistors. While the
DMM is more complex, the fundamental principles of measurement are the same.
Voltage Measurement
Voltage is the easiest measurement to make in a circuit, typically with the least impact. The voltage
measurement is taken across an element or from ground. In AC the meter reads all voltages as a root
mean square (RMS) average. Recall for a sine wave the RMS average is:
š‘‰š‘šš‘Žš‘„
š‘‰š‘Ÿš‘šš‘  =
āˆš2
This equation works only for sine waves. If our ac input is a square wave, for example, the RMS average
will not be so easy to calculate. The general equation is:
1 š‘‡ 2
2
š‘‰ = āˆ« š‘£ (š‘”)š‘‘š‘”
š‘‡ 0
š‘‰š‘Ÿš‘šš‘  = āˆšš‘‰ 2
We needed to remember the DMM AC voltage measurement is always a RMS average.
Function Generator
The function generator allows us to apply a voltage with variable frequency, shape, amplitude, and DC
offset. We will use the function generator in most of our labs as the input to our circuits. There are
several realistic aspects of the function generator we must remember. The most important aspect of the
function generator we needed to remember is the 50ļ— of source resistance. When working with very
large resistances the source resistance is within the margin of error of the resistors and we can ignore it.
For this lab we will need to include the source resistance of the function generator.
1
ECE 2210
Measurement Equipment
Laboratory 1
Pre-Lab
None
Procedures
1. Voltage Measurement in AC (Sine Wave, Square Wave, Triangle-wave)
a.
b.
c.
d.
e.
f.
g.
h.
Setup the voltage divider circuit using R1 = 470ļ— and R2 = 1 kļ—.
Use the oscilloscope to set the function generator to 5v amplitude at 1 kHz.
Measure the voltage across R2 using the oscilloscope.
Measure the voltage across R2 using the DMM.
Switch to a Square-wave. Adjust the amplitude of the square wave to a 5v amplitude.
Measure R2 with the oscilloscope and the DMM.
Switch to a Tringle-wave. Adjust the amplitude of the triangle wave to a 5v amplitude.
Measure R2 with the oscilloscope and the DMM.
Oscilloscope
DMM
RMS Calculation
Sine
Square
Triangle
2. Differential vs. Single Sided Measurements
a. Use the voltage divider from procedure 1. Set the function generator to 5v amplitude at
1 kHz.
b. Measure the voltage of R1 using the DMM.
c. The oscilloscope cannot measure R1 directly. You will need Ch2 of the Oscilloscope. Place
the red alligator clip from Ch1 at one end of R1 and the red alligator clip of Ch2 to the other
end of R1. Tie both ground clips to the supply ground.
d. Press the MATH button on the oscilloscope and set the operation to subtract Ch1 from Ch2.
e. Measure the voltage of R1.
R1
DMM
Oscilloscope Ch1-Ch2
Calculation
VR1
2
ECE 2210
Measurement Equipment
Laboratory 1
3. Phase Angles
a.
b.
c.
d.
Turn off the function generator.
Replace the R2 with a 1ļ­F capacitor.
Apply a Sine-wave with a 5v amplitude at 500 Hz to the circuit.
Measure the voltage across R1 and R2 with the DMM and oscilloscope.
DMM
Oscilloscope Ch1-Ch2
Calculation
VR1
VR2
Notice |š‘‰š‘…1 | + |š‘‰š‘…2 | ā‰  š‘‰š‘–š‘› . Why?
4. Phase Angle Measurement
a. Set the function generator to 5V at 500Hz.
b. Place Ch1 on the voltage input and Ch2 across C1.
c. On the oscilloscope use the Cursors to measure the time shift between the source voltage
and VC1.
āˆ†š‘” = ______________________
āˆ†š‘”š‘š‘Žš‘™š‘ = ______________________
Analysis
A. Determine by hand the RMS values for R2 and complete the table in Procedure 1. Do your RMS
values calculated by hand and oscilloscope measurements match your DMM reading?
B. Calculate the phasor voltage for VR1. Include the resistance of the function generator in your
hand analysis.
C. Hand calculate the phasor voltage for VR1 and VR2. Compare the hand calculated values to your
DMM and oscilloscope readings.
D. Hand calculate the phase of the Capacitor voltage. Compare the calculated and measured
phases.
3