[PPT] - Basic Elec. Engr Basic Elec. Engr. Lab . Lab ECS 204 ECS 204 PowerPoint Presentation

SLIDE 1

Asst. Prof. Dr. Prapun Suksompong

prapun@siit.tu.ac.th

1

Basic Elec. Engr Basic Elec. Engr. Lab . Lab

ECS 204 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

SLIDE 2

Triggering

2

SLIDE 3

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.

SLIDE 4

Triggering

4

SLIDE 5

Triggering

5

Trigger controls

SLIDE 6

50 inside the function generator

6

 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, V

= V
c.

Here, V

is set to be 6 Vp-p. So, V
c is also 6 Vp-p.

When a 100 resistor is connected across the function generator’s output, V

c is split between the

50 inside and the 100. If you did not adjust the function generator, then V

c is

still at 6 Vp-p and Vo

6 4Vp-p.

SLIDE 7

50 inside the function generator

7

Ch 1: VG Ch 2: V2

Ch 2 GND Ch 1 GND

R1 R2

In lab 4, ….

SLIDE 8

50 inside the function generator

8

Ch 1: VG Ch 2: V2

Ch 2 GND Ch 1 GND

R1 R2

In lab 4, ….

SLIDE 9

All ground clips should be together

9

Ch 1: VG Ch 2: V2

Ch 2 GND Ch 1 GND

R1 R2

SLIDE 10

Ex: Wrong measurement of V1

10

Ch 2 GND Ch 1 GND

Ch 1: VG Ch 2: V1? R1 R2

An attempt to use CH2 to measure V1.

SLIDE 11

Ex: Wrong measurement of V1

11

Ch 2 GND Ch 1 GND

Ch 1: VG Ch 2: V1? R1 R2

SLIDE 12

Ex: Correct measurement of V1

12

Ch 1 Ch 2 Ch 2 GND Ch 1 GND

R1 R2

CH1 CH2

V V 

Use to measure the voltage across any pair of nodes in the circuit while still keeping the ground clips together. Differential Measurement

SLIDE 13

Part A: RC Circuit

13

1k 0.1 F  

Voltage across the generator

utput.

Voltage across the capacitor. Square wave! Not sinusoid!

SLIDE 14

RC Circuit with Voltage Step Input

14

     

ut

in

ut

v t v t d C v t dt 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

ut

S

ut

S

v t V v t V e t t t RC



 

     

in

ut

(DE) iC iC iR iR

SLIDE 15

Charging vs. Discharging

15

   

 

1

1 1 2

,

t t

ut

S

ut

S

v t V v t V e t t t RC



 

     

   

1

ut

t t

ut

S

v t v t V e

  

        

Charging t1 t2

SLIDE 16

Charging vs. Discharging

16

   

 

1

1 1 2

,

t t

ut

S

ut

S

v t V v t V e t t t RC



 

     

   

1

1 S t t

ut
ut

V v t v t e

  

 

Discharging t1

SLIDE 17

Charging vs. Discharging

17

   

 

1

1 1 2

,

t t

ut

S

ut

S

v t V v t V e t t t RC



 

     

   

1

1 S t t

ut
ut

V v t v t e

  

 

   

1

ut

t t

ut

S

v t v t V e

  

        

Charging Discharging t1 t1

SLIDE 18

Demo: DC Offset

18

   

no-offset Offset

V

ut

v t v t  

Note: the ground level of the oscilloscope stays at the same place on the screen.

SLIDE 19

4 Vp-p Square Wave

19

2V

2V

Ground level

4V

Ground level

No DC OFFSET With 2V DC OFFSET

t t

SLIDE 20

DMM: DC vs. AC Modes

20

 VDC = Measured value of the voltage using DMM in DC mode

 Theoretically,

 VDC = Average value = DC offset voltage = DC component

 V

AC = 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,

   

DC

1 V

t T t

v t v t dt T



 



   

2 2 2 2 RMS AC DC

1 V V V

t T t

v t v t dt T



   



 

2 AC DC

V V v t  

SLIDE 21

DMM: DC vs. AC Modes

21

 VDC = Measured value of the voltage using DMM in DC mode

 Theoretically,

 VDC = Average value = DC offset voltage = DC component

 V

AC = 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,

   

DC

1 V

t T t

v t v t dt T



 



   

2 2 2 2 RMS AC DC

1 V V V

t T t

v t v t dt T



   



 

2 AC DC

V V v t  

Same when VDC = 0.

This is why, in lab 4, VAC = Vrms.

SLIDE 22

Square Wave

22

Ground level

V

ffset = VDC

VP-P VAC

For square waveform (w/ or w/o DC offset),

p-p AC

V V 2 

“True rms”

p-p AC

V V 2 2 2   

“Rectified average”

SLIDE 23

Oscilloscope: DC vs. AC Modes

23

 Input signal:  DC mode: Show  AC mode: Show

 vAC(t) always have 0 average (theoretically)



when VDC = 0.

 

v t

   

DC

V

AC

v t v t  

   

DC

v t v t 

   

AC DC

v t v t 

SLIDE 24

Part A: Find 

24

Three different methods:

 Measure t0.37.  Measure thalf. Then, calculate  Measure R and C. Then, calculate

 = RC.

4 V  2 2 V  1 .4 7 V e 

h alf

t

0 .3 7

t

half ln2

t  

 

0.37V 

1k 0.1 F  

 

t

ut

v t V e 





SLIDE 25

Part B.1

25

V 2 V

R

V

1 2 f LC  

R2 Sine-wave generator L C 8 Vp-p 22 mH 0.01 F 0.47 F [474] 0.1 F [104] Oscilloscope Ch-1 Ch-2 100 

SLIDE 26

Part B.2

26

f0 f

SLIDE 27

Peak-to-peak reading from the scope

27

SLIDE 28

Peak-to-peak reading from the scope (1/3)

28

SLIDE 29

Peak-to-peak reading from the scope (2/3)

29

SLIDE 30

Peak-to-peak reading from the scope (3/3)

30

SLIDE 31

Peak-to-peak reading from the scope

31