Basic Elec. Engr Basic Elec. Engr. Lab . Lab ECS 204 ECS 204 Asst. Prof. Dr. Prapun Suksompong prapun@siit.tu.ac.th AC Circuit • Time-varying Signal • Lab 4 Oscilloscope • Function generator • Capacitor and Inductor • 1
Time-varying periodic signal (voltage) Suppose the period is T . Instantaneous value at time t: v t V Average value t T 1 0 v t v t dt V DC T t 0 RMS value t T 1 0 In this lab, 2 2 V v t v t dt rms V DC = 0 makes T t 0 V rms = V AC . Peak value max T v t V p t t t 0 0 Peak-to-peak value V p max min V T v t v t V p-p p p t t t t t t T 0 0 0 0 2 T
A v(t) Sinusoidal signal (voltage) t 0 T/2 T 1 2 -A The period is T f Instantaneous value at time t: cos v t A t V Average value t T 1 0 0 v t v t dt V DC T t 0 RMS value t T 1 A 0 2 2 V v t v t dt rms 2 T � 1 t 0 Peak value 2 max T v t V A p t t t 0 0 Peak-to-peak value 2 A max min V T v t v t p p t t t t t t T 0 0 0 0 3
Steady-State AC Analysis Phasor Domain: V I Z Resistor Inductor Capacitor 1 Z Z j L Z R j C 1 � � � ��� ∘ � � �� � � � ��� ∘ Time Domain: Removing 90 ∘ from the phase Adding 90 ∘ to the phase 4 “CIVIL”
Oscilloscope (scope) 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 deflect ed according to the signal being measured. The trace is produced by the electrons striking a phosphor screen, which glows green where they hit. 5
Demo 1: Cathode-ray oscilloscope (CRO) 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 oscilloscope in use, in the form of a heart-rate monitor (electrocardiogram, or EKG) of the type seen in doctor's offices and hospitals. 6
Oscilloscope: Display time/div 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 volts/div handle two signals at once . 7
Oscilloscope: Sketching Waveform(s) 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 Voltage/Division _________ 1 V/DIV (CH1 & CH2) the same as the boundary of the provided grid Time/Division _________ 0.1 ms/DIV area. 8
Oscilloscope Preparation Display controls Follow III.3 and III.4. POWER (1) INTEN control (2) FOCUS control (4) CH1 (15) and CH2 (16) Vertical controls CH 1’s GND (19) and CH 2’s GND (20) 9 Front panel
Oscilloscope Preparation 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 10
Oscilloscope Preparation Connect the probe tips to the CAL test point (6) of the oscilloscope. Make sure that ×1 is selected (not ×10) VOLTS/DIV ((13) and (14)) 1V Section III.4 in the manual. VERTICAL: COUPLING ((17) and (18)) DC ALT/CHOP/ADD (12) CHOP or ALT MODE (22) MAIN HORIZONTAL: TIME/DIV (21) 0.5ms MODE (26) ATO TRIGGER: SOURCE (29) CH1 COUPLING (28) AC The square wave of the calibrator signal will be displayed on the screen. 11
Function Generator 12
Part A 13
Part C Oscilloscope Ch-1 Ch-2 probe tip ground clip Z1 probe tip Sine-wave generator R2 100 ohms Ground clip 14
Part C.1: Z1 is a resistor Oscilloscope Ch-1 Ch-2 Ch 1 probe tip ground clip Z1 probe tip Sine-wave generator R2 100 ohms Ground clip Ch 2 GND 15
Cables For function generator, For oscilloscope, 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 oscilloscope. 16
Demo 2 Connect the circuit. Function The generator should Generator output a 4 V p-p sinusoid. Getting exactly 4 Vp-p may be difficult to do Oscilloscope Ch-1 Ch-2 visually on the oscilloscope. We may use the DMM to help. probe tip R1 ground clip 100 ohms Sine-wave probe tip generator R2 100 ohms 17 ground clip
DMM in AC mode 18
Demo 2: DMM in AC Mode Similar to the DC Voltage measurement except that the rotary switch is set at the AC mode. V 2 4 A p-p 2 A 2 A V 2 1.414 rms 2 2 19
Oscilloscope Ch-1 Ch-2 Demo 2 probe tip ground clip Z1 probe tip Sine-wave generator R2 100 ohms Ground clip Ch 1: V G Ch 2: V 2 R 1 R 2 Ch 2 GND Ch 1 GND 20
Demo 3 (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. 21
Wrong measurement of V 1 Ch 1: V G Function Ch 2: V 1 ? Generator R 1 R 2 Ch 2 GND Ch 1 GND An attempt to use CH2 to measure V 1 . 22
Wrong measurement of V 1 Ch 1: V G Ch 2: V 1 ? R 1 R 2 Ch 2 GND Ch 1 GND 23
Correct measurement of V 1 Ch 1 R 1 Ch 2 R 2 Ch 2 GND Ch 1 GND Use to measure the voltage across any pair of nodes in the circuit V V CH1 CH2 while still keeping the ground clips together. Differential Measurement 24
Part C.2 Oscilloscope Ch-1 Ch-2 probe tip ground clip Z1 probe tip Sine-wave generator R2 100 ohms Ground clip 25
Part C.3 Oscilloscope Ch-1 Ch-2 probe tip ground clip Z1 probe tip Sine-wave generator R2 100 ohms Ground clip 26
Reading Capacitor Code Code Value 0.001 F 102 0.01 F 103 0.1 F 104 0.047 F 473 0.47 F 474 4 4 1 2 4 6 6 47 10 p F 47 10 10 F 47 10 10 10 F 4 6 6 2 47 10 10 10 F 47 10 F =0.47 F 27
Measuring C and L We can use DMM to measure capacitance. Special device (LCR meter) to measure inductance. 28
Capacitor and Inductor 5 mH Inductor 0.47 F capacitor (474) LCR meter 29
Recommend
More recommend
