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

Basic Elec. Engr Basic Elec. Engr. Lab . Lab ECS 204 ECS 204 Asst. Prof. Dr. Prapun Suksompong prapun@siit.tu.ac.th RC Circuit with Voltage Step Input • Frequency Response of Series RLC Circuit • Lab 5 AC vs DC modes of the Oscilloscope • AC vs DC modes of the DMM • Function generator: Offset • 1

Triggering 2

Here, originally, the trigger level was set too high at around 5V so the trigger mechanism can’t “see” the signal. Triggering We then use the trigger level knob to adjust the trigger level to around 2.8V which stabilizes the display. 3

Triggering 4

Triggering Trigger controls 5

50  inside the function generator  Set the (open-circuit) voltage across the output of the signal generator at 6V p-p . When nothing is connected across the function generator’s output, V o = V oc . Here, V o is set to be 6 V p-p . So, V oc is also 6 V p-p .  Connect the generator output across a 100 Ω resistor.  Measure the voltage across the generator again. When a 100  resistor is connected across the function generator’s output, V oc is split between the 50  inside and the 100  . If you did not adjust the function generator, then V oc is ��� still at 6 V p-p and V o � ������ � 6 � 4 V p-p . 6

In lab 4, …. 50  inside the function generator Ch 1: V G Ch 2: V 2 R 1 R 2 Ch 2 GND Ch 1 GND 7

In lab 4, …. 50  inside the function generator Ch 1: V G Ch 2: V 2 R 1 R 2 Ch 2 GND Ch 1 GND 8

All ground clips should be together Ch 1: V G Ch 2: V 2 R 1 R 2 Ch 2 GND Ch 1 GND 9

Ex: Wrong measurement of V 1 An attempt to use CH2 to measure V 1 . Ch 1: V G Ch 2: V 1 ? R 1 R 2 Ch 2 GND Ch 1 GND 10

Ex: Wrong measurement of V 1 Ch 1: V G Ch 2: V 1 ? R 1 R 2 Ch 2 GND Ch 1 GND 11

Ex: Correct measurement of V 1 Ch 1 R 1 Ch 2 R 2 Ch 2 GND Ch 1 GND  Use V V to measure the voltage across any pair of nodes in the circuit CH1 CH2 while still keeping the ground clips together. Differential Measurement 12

Part A: RC Circuit 1 k  Voltage across the generator Voltage across output. the capacitor.  0.1 F  Square wave! Not sinusoid! 13

RC Circuit with Voltage Step Input i R i C i C i R out      v t v t in d     0 out in (DE) C v t out dt R Assume the input voltage v in ( t ) is fixed at a particular value V S from time t 1 to t 2 .  t t    1           , v t V v t V e t t t 1 1 2 out S out S   RC 14

Charging vs. Discharging  t t   1            , v t V v t V e t t t 1 1 2 out S out S   RC t 1 t 2 Charging    0 v t 1 out    t t  1     1    v t V e out S   15

Charging vs. Discharging  t t   1            , v t V v t V e t t t 1 1 2 out S out S   RC t 1 Discharging  0 V S  t t  1       v t v t e 1 out out 16

Charging vs. Discharging  t t   1            , v t V v t V e t t t 1 1 2 out S out S   RC t 1 t 1 Discharging Charging  0   V  0 v t S 1 out  t t  1          t t v t v t e  1     1 1  out out   v t V e out S   17

Demo: DC Offset       V v t v t no-offset Offset out 18 Note: the ground level of the oscilloscope stays at the same place on the screen.

4 V p-p Square Wave No DC OFFSET 2V Ground level t -2V With 2V DC OFFSET 4V Ground level t 19

DMM: DC vs. AC Modes  V DC = Measured value of the voltage using DMM in DC mode  Theoretically,  V DC = Average value = DC offset voltage = DC component  t T 1 0        V v t v t dt DC T t 0  V AC = Measured value of the voltage using DMM in AC mode  Theoretically, for “True RMS” DMM,     2   V V v t AC DC  For non-true-rms DMM, the measurement is calibrated so that the above property hold for sinusoids.  Theoretically,  t T 1 0          2 2 2 2 V V V v t v t dt RMS AC DC T t 0 20

DMM: DC vs. AC Modes  V DC = Measured value of the voltage using DMM in DC mode  Theoretically,  V DC = Average value = DC offset voltage = DC component  t T 1 0        V v t v t dt DC T t 0  V AC = Measured value of the voltage using DMM in AC mode  Theoretically, for “True RMS” DMM, Same when V DC = 0.     2   V V v t AC DC This is why, in lab 4, V AC = V rms .  For non-true-rms DMM, the measurement is calibrated so that the above property hold for sinusoids.  Theoretically,  t T 1 0          2 2 2 2 V V V v t v t dt RMS AC DC T t 0 21

Square Wave V AC V P-P V offset = V DC Ground level “True rms” V For square waveform (w/ or w/o DC offset),  p-p V AC 2  V “Rectified   p-p V AC average” 2 2 2 22

Oscilloscope: DC vs. AC Modes    Input signal: v t      DC mode: Show  v t v t DC      AC mode: Show   V v t v t DC AC  v AC ( t ) always have 0 average (theoretically)      when V DC = 0.  v t v t AC DC 23

Part A: Find  1 k  Three different methods:  0.1 F  Measure t 0.37 .   Measure t half . Then, calculate   half ln2 t  Measure R and C . Then, calculate  = RC .  4 V 0  2 2 V 0  1 .4 7 V e 0    0.37 V t    0  V e  v t t 0 0 .3 7 out t h alf 24

Part B.1 V 0 2 V 0 V R 1 Oscilloscope  f 0.01  F  Ch-1 Ch-2 0  0.47  F [474] 2 LC 0.1  F [104] 22 mH L C Sine-wave 100  R2 8 V p-p generator 25

Part B.2 � � � f f 0 26

Peak-to-peak reading from the scope 27

Peak-to-peak reading from the scope (1/3) 28

Peak-to-peak reading from the scope (2/3) 29

Peak-to-peak reading from the scope (3/3) 30

Peak-to-peak reading from the scope 31