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

• Asst. Prof. Dr. Prapun Suksompong

prapun@siit.tu.ac.th

1

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

ECS 204 ECS 204

Lab 4

• AC Circuit
• Time-varying Signal
• Oscilloscope
• Function generator
• Capacitor and Inductor

Time-varying periodic signal (voltage)

2

 Suppose the period is T.  Instantaneous value at time t:  Average value  RMS value  Peak value  Peak-to-peak value

 

v t

   

1

t T t

v t v t dt T







   

2 2

1

t T t

v t v t dt T







 

max

t t t T v t   

 

 

 

 

max min

t t t T t t t T v t

v t

     



 

DC

V

 

V

p

V    

p p

V     

 

rms

V

In this lab, VDC = 0 makes Vrms = VAC. Vp-p T Vp

Sinusoidal signal (voltage)

3

 The period is  Instantaneous value at time t:  Average value  RMS value  Peak value  Peak-to-peak value

   

2 2

1

t T t

v t v t dt T







 

max

t t t T v t   

 

 

 

 

max min

t t t T t t t T v t

v t

     



 

V

p

V    

p p

V     

 

rms

V 1 2 T f    

   

cos v t A t      2 A  A  2A 

t v(t) T/2 T

A

• A

   

1

t T t

v t v t dt T







 

DC

V

1 2

Steady-State AC Analysis

4

 Phasor Domain:  Time Domain: Z  V I Resistor Inductor Capacitor Z R  Z j L   1 Z j C  

“CIVIL” ∘

Adding 90∘ to the phase 1 ∘ Removing 90∘ from the phase

Oscilloscope (scope)

5

 Draw a graph of a voltage over time as a trace on its screen.  Cathode-ray oscilloscopes (CROs)

 Electron gun emits a beam of electrons (historically called

“cathode rays”, hence the name)

 which is deflected according to the signal being measured.

 The trace is produced by the electrons striking a phosphor

screen, which glows green where they hit.

Demo 1: Cathode-ray oscilloscope (CRO)

6

Cathode-ray tubes: ELECTRON GUN and DEFLECTION SYSTEM.

Caution: An overly bright trace can damage the phosphor of the screen if the dot is moving too slowly.

You may have seen an

• scilloscope in use, in the

form of a heart-rate monitor (electrocardiogram, or EKG)

• f the type seen in doctor's
• ffices and hospitals.

Oscilloscope: Display

7

 Notice the grid markings on the

screen.

 These markings create the

graticule.

 Each vertical and horizontal line

constitutes a major division.

 The graticule is usually laid out in an

8-by-10 division pattern.

 The readout for volts/div and

time/div always refer to major divisions.

 The tick marks on the center

horizontal and vertical graticule lines are called minor divisions.

 Dual-channel Oscilloscope: Can

handle two signals at once. time/div volts/div

Oscilloscope: Sketching Waveform(s)

8

The screen on the scope actually shows MORE than the 8-by-10 grid area.

In your sketch, don’t make the mistake of thinking the boundary of the whole screen is the same as the boundary of the provided grid area.

Voltage/Division _________ Time/Division _________

1 V/DIV (CH1 & CH2) 0.1 ms/DIV

Oscilloscope Preparation

9

 Follow III.3 and III.4.  POWER (1)  INTEN control (2)  FOCUS control (4)  CH1 (15) and CH2 (16)  CH 1’s GND (19) and CH

2’s GND (20)

Front panel Vertical controls Display controls

Oscilloscope Preparation

10

 Make sure that the TRIGGER MODE (26) is set to ATO

mode, otherwise the trace will not be shown.

 Use the CH1 and CH2 POSITION controls ((9) and (10)) to

align both traces on the center graticule.

Trigger controls

Oscilloscope Preparation

11

 Connect the probe tips to the CAL test point (6) of the

• scilloscope.

 The square wave of the calibrator signal will be displayed on

the screen.

VERTICAL: VOLTS/DIV ((13) and (14)) 1V COUPLING ((17) and (18)) DC ALT/CHOP/ADD (12) CHOP or ALT HORIZONTAL: MODE (22) MAIN TIME/DIV (21) 0.5ms TRIGGER: MODE (26) ATO SOURCE (29) CH1 COUPLING (28) AC

Make sure that ×1 is selected (not ×10)

Section III.4 in the manual.

Function Generator

12

Part A

13

Part C

14

R2 100 ohms Sine-wave generator Oscilloscope Ch-1 Ch-2

probe tip probe tip ground clip Ground clip

Z1

Part C.1: Z1 is a resistor

15

R2 100 ohms Sine-wave generator Oscilloscope Ch-1 Ch-2

probe tip probe tip ground clip Ground clip

Z1

Ch 1

Ch 2

GND

Cables

16

Select ×1 here

The ×10 mode simply acts as a 10:1 voltage divider for any measured

• signals. With this, you

will see tiny signal on the scope. Obviously, one use for a ×10 probe is measuring voltages beyond the normal range of an

• scilloscope.

For function generator, For oscilloscope,

Demo 2

17

Function Generator

 Connect the circuit.  The generator should

• utput a 4 Vp-p

sinusoid.

 Getting exactly 4 Vp-p

may be difficult to do visually on the

• scilloscope. We may

use the DMM to help.

R1 100 ohms R2 100 ohms Sine-wave generator Oscilloscope Ch-1 Ch-2

probe tip probe tip ground clip ground clip

DMM in AC mode

18

Demo 2: DMM in AC Mode

19

Similar to the DC Voltage measurement except that the rotary switch is set at the AC mode.

p-p rms

V 2 4 2 2 V 2 1.414 2 2 A A A       

Demo 2

20

Ch 1: VG Ch 2: V2

Ch 2 GND Ch 1 GND

R1 R2

R2 100 ohms Sine-wave generator Oscilloscope Ch-1 Ch-2

probe tip probe tip ground clip Ground clip

Z1

Demo 3

21

 (Probe) ground clips

The scope’s two “reference” or “ground” clips are electrically common with the oscilloscope’s metal chassis, they are electrically common with each other as well. It is very likely that the function generator is earth-grounded through its power cord as well.

Wrong measurement of V1

22

Ch 2 GND Ch 1 GND

Ch 1: VG Ch 2: V1? R1 R2

An attempt to use CH2 to measure V1. Function Generator

Wrong measurement of V1

23

Ch 2 GND Ch 1 GND

Ch 1: VG Ch 2: V1? R1 R2

Correct measurement of V1

24

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

Part C.2

25

R2 100 ohms Sine-wave generator Oscilloscope Ch-1 Ch-2

probe tip probe tip ground clip Ground clip

Z1

Part C.3

26

R2 100 ohms Sine-wave generator Oscilloscope Ch-1 Ch-2

probe tip probe tip ground clip Ground clip

Z1

Reading Capacitor Code

27

Code Value 102 0.001 F 103 0.01 F 104 0.1 F 473 0.047 F 474 0.47 F

4 4 4 4 6 2 2 6 1 6 6

p 10 10 10 47 10 F 47 10 F 47 10 F 10 47 10 10 F 47 10 F =0.47 F  

     

             

Measuring C and L

28

 We can use DMM to measure capacitance.  Special device (LCR meter) to measure inductance.

Capacitor and Inductor

29

 5 mH Inductor  0.47 F capacitor (474)

LCR meter