Basic Elec. Engr. Lab - t U Slides.pdfAsst. Prof. Dr. Prapun Suksompong [email protected] 1 Basic...
Transcript of Basic Elec. Engr. Lab - t U Slides.pdfAsst. Prof. Dr. Prapun Suksompong [email protected] 1 Basic...
Asst. Prof. Dr. Prapun [email protected]
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Basic Elec. Engr. Lab ECS 204
Lab 5• RC Circuit with Voltage Step Input• Frequency Response of Series RLC Circuit • AC vs DC modes of the Oscilloscope• AC vs DC modes of the DMM• Function generator: Offset
Triggering
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Triggering
3
Here, originally, the trigger level was set too high at around 5V so the trigger mechanism can’t “see” the signal. We then use the trigger level knob to adjust the trigger level to around 2.8V which stabilizes the display.
Triggering
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Triggering
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Trigger controls
50 inside the function generator
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Set the (open-circuit) voltage across the output of the signal generator at 6Vp-p.
Connect the generator output across a 100Ω resistor.
Measure the voltage across the generator again.
When nothing is connected across the function generator’s output, Vo = Voc.
Here, Vo is set to be 6 Vp-p. So, Voc is also 6 Vp-p.
When a 100 resistor is connected across the function generator’s output, Voc is split between the 50 inside and the 100.
If you did not adjust the function generator, then Voc is
still at 6 Vp-p and Vo 6 4Vp-p.
50 inside the function generator
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Ch 1: VG
Ch 2: V2
Ch 2 GND
Ch 1 GND
R1
R2
In lab 4, ….
50 inside the function generator
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Ch 1: VG
Ch 2: V2
Ch 2 GND
Ch 1 GND
R1
R2
In lab 4, ….
All ground clips should be together
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Ch 1: VG
Ch 2: V2
Ch 2 GND
Ch 1 GND
R1
R2
Ex: Wrong measurement of V1
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Ch 2 GND
Ch 1 GND
Ch 1: VG
Ch 2: V1?R1
R2
An attempt to use CH2 to measure V1.
Ex: Wrong measurement of V1
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Ch 2 GND
Ch 1 GND
Ch 1: VG
Ch 2: V1?R1
R2
Ex: Correct measurement of V1
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Ch 1
Ch 2
Ch 2 GND
Ch 1 GND
R1
R2
CH1 CH2V VUse to measure the voltage across any pair of nodes in the circuit
while still keeping the ground clips together. Differential Measurement
Part A: RC Circuit
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1k
0.1 F
Voltage across the generator output.
Voltage across the capacitor.
Square wave!Not sinusoid!
RC Circuit with Voltage Step Input
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0out inout
v t v tdC v tdt R
Assume the input voltage vin(t) is fixed at a particular value VS
from time t1 to t2.
1
1 1 2,t t
out S out Sv t V v t V e t t t
RC
in
out
(DE)
iCiC iR
iR
Charging vs. Discharging
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1
1 1 2,t t
out S out Sv t V v t V e t t t
RC
1
1 0
1
out
t t
out S
v t
v t V e
Chargingt1 t2
Charging vs. Discharging
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1
1 1 2,t t
out S out Sv t V v t V e t t t
RC
1
1
0St t
out out
V
v t v t e
Dischargingt1
Charging vs. Discharging
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1
1 1 2,t t
out S out Sv t V v t V e t t t
RC
1
1
0St t
out out
V
v t v t e
1
1 0
1
out
t t
out S
v t
v t V e
Charging Dischargingt1 t1
Demo: DC Offset
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no-offset OffsetVoutv t v t
Note: the ground level of the oscilloscope stays at the same place on the screen.
4 Vp-p Square Wave
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2V
-2V
Ground level
4V
Ground level
No DC OFFSET
With 2V DC OFFSET
t
t
DMM: DC vs. AC Modes
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VDC = Measured value of the voltage using DMM in DC mode Theoretically, VDC = Average value = DC offset voltage = DC component
VAC = Measured value of the voltage using DMM in AC mode Theoretically, for “True RMS” DMM,
For non-true-rms DMM, the measurement is calibrated so that the above property hold for sinusoids.
Theoretically,
0
0
DC1V
t T
t
v t v t dtT
0
0
2 2 2 2RMS AC DC
1V V Vt T
t
v t v t dtT
2AC DCV Vv t
DMM: DC vs. AC Modes
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VDC = Measured value of the voltage using DMM in DC mode Theoretically, VDC = Average value = DC offset voltage = DC component
VAC = Measured value of the voltage using DMM in AC mode Theoretically, for “True RMS” DMM,
For non-true-rms DMM, the measurement is calibrated so that the above property hold for sinusoids.
Theoretically,
0
0
DC1V
t T
t
v t v t dtT
0
0
2 2 2 2RMS AC DC
1V V Vt T
t
v t v t dtT
2AC DCV Vv t
Same when VDC = 0.This is why, in lab 4, VAC = Vrms.
Square Wave
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Ground level
Voffset = VDC
VP-PVAC
For square waveform (w/ or w/o DC offset), p-pAC
VV
2
“True rms”
p-pAC
VV
22 2
“Rectified average”
Oscilloscope: DC vs. AC Modes
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Input signal:
DC mode: Show
AC mode: Show vAC(t) always have 0 average (theoretically)
when VDC = 0.
v t
DCVACv t v t
DCv t v t
AC DCv t v t
Part A: Find
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Three different methods:
Measure t0.37.
Measure thalf. Then, calculate
Measure R and C. Then, calculate
= RC. 04 V
02 2V 01 .4 7 V e
h a lft 0 .3 7t
half ln 2t
00.37V
1k
0.1 F
0
t
outv t V e
Part B.1
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0V
0 2V
RV
01
2f
LC
R2Sine-wavegenerator
LC
8 Vp-p
22 mH
0.01 F0.47 F [474]0.1 F [104]
OscilloscopeCh-1 Ch-2
100
Part B.2
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f0 f
Peak-to-peak reading from the scope
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Peak-to-peak reading from the scope (1/3)
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Peak-to-peak reading from the scope (2/3)
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Peak-to-peak reading from the scope (3/3)
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Peak-to-peak reading from the scope
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