幻灯片 1 - HUST

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Transcript 幻灯片 1 - HUST

Department of Physics
Ke sheng-zhi
Contents
1. Objectives
2. Pre-lab Questions
3. Introduction & Apparatus
4. Procedure & Experiment
5. Problems
1. Objectives
 Learn how to handle the features of an
oscilloscope
 Teach yourself the functions of a signal
generator
 Measure the electric quantities of sine
voltage signals
 Observe Lissajous figures (optional)
2. Pre-lab Questions
 What does a voltmeter do?
 What is a cathode ray?
 What will happen when an electron beam
is moving in electric fields?
 Can you classify several typical waveforms?
2. Pre-lab Questions
 What does a voltmeter do?
Analog voltmeters
A digital voltmeter
 Voltmeters: measure the electrical potential
difference between two points in an electric circuit.
 Do you know the other instruments which also can be
used to determine the voltage ?
2. Pre-lab Questions
 What is a cathode ray?
The deflections of the beam are visible if viewed closely with very low ambient light level.
Cathode rays: streams of electrons observed in evacuated
glass tubes that are equipped with a cathode (negative
electrode) and an anode (positive electrode).
Anode rays
 Anode Rays?
Holes
Cathode rays
2. Pre-lab Questions
 Electron beams moving in electric fields?
y
vy
v
y
vz
d
vz
 Can you find out the vertical displacement y ?
z
2. Pre-lab Questions
 Can you classify several typical waveforms?
3. Introduction & Apparatus

OSCILLOSCOPE – The most commonly used instrument
Cathode ray tube
Vert. system
Z-axis
Y-axis
Horiz. system
X-axis
3. Introduction & Apparatus
 The Screen of the CRT
Vy
Signal
VOLTS
(Y-axis)
Vertical axis
Graticule
Horizontal axis
(X-axis)
TIME
t
Cathode ray tube

CRT – The heart of the oscilloscope
Intensity
grid
Focusing
Coil
Electron
beam
Vy
Cathode
Electron gun
Vert. plates
Y-deflection
Vx
Horiz. plates
X-deflection
Zero
signal
Fluorescent
screen
The Time Base Generator and The Trigger
Vy
SLOPE+
TRIG.
LEVEL
Y-axis
Periodic
signal
Vx
X-axis
Ramp
signal
t
Tx
Tx
Oscilloscope
 Operating principle
Oscilloscope
 Operating principle
x
y
Vy
Vx
t
 x  E x  Vx  t

 y  E y  Vy
T  Dx x

V p  D y y
Oscilloscope
 Get acquainted with the CRT
Screen
Graticule
Trace
INTENSITY control
Brightness
FOCUS control
Definition
TRACE ROTATION control
Slope
POWER switch
On/Off
Oscilloscope
 Get acquainted with the Vertical system
POSITION control
Useless for X-Y
POSITION control
For CH2(Y)
VERT MODE select switch
VOLTS / DIV switches
With calibrated steps
AC-GND-DC Input
coupling switches
VARIABLE controls
For continuous tuning
CH2(Y) jack
CH1(X) jack
X-Axis input for X-Y
Oscilloscope
 Get acquainted with the Horizontal system
POSITION control
Left or right
SLOPE switch
SEC / DIV switch
With calibrated steps
TRIG SOURCE switch
Only use one CH
LEVEL control
Triggering point
HORIZ MODE select switch
AUTO always sweeping
NORM stop triggering for
zero signal
X-Y mode operation
CH1(X) → X-Axis signal
VARIABLE control
For continuous tuning
Function Generator & Unknown Source

Function Generator

Unknown Source
4. Procedure & Experiment
 CAUTION





HANDLE THE SCOPE WITH CARE. DO NOT CARRY IT
AROUND. TURN THE KNOBS GENTLY.

DO NOT LEAVE THE INTENSITY HIGHER THAN
NECESSARY IN CASE OF DAMAGING THE SCREEN.
Basic operations of the oscilloscope
Peak-to-Peak Voltage Measurement
Period Measurement
Lissajous Figures (Optional)
4. Procedure & Experiment

Basic operations of the oscilloscope
Make sure the output of the YB1601 function generator
is attached to the CH1(X) input of the YB43020B
oscilloscope.
1. Turn on the POWER to the oscilloscope.
2. Set the FOCUS and INTENSITY control halfway.
3. Set the VERT. MODE setting to CH1(X).
4.
Set HORIZ. trigger MODE to AUTO, the trigger LEVEL to the
center of range, the TRIG. SOURCE to CH1(X) identical with
the VET. MODE setting so that a stationary voltage curve can
be easily displayed.
5. Set the SEC/DIV switch to 0.1 ms/DIV.
6. Set the VOLTS/DIV switch for CH1(X) to 0.5 V/DIV.
4. Procedure & Experiment
7. Se the VARIABLE controls rotated fully counterclockwise
to the CAL positions, respectively.
8. Turn on the POWER to the function generator.
9. Select a sine waveform FUNCTION, set the frequency
f = 1000 Hz. Adjust the AMPL control to zero.
9. Adjust the FOCUS and INTENSITY control to produce a
not too bright but clear line.
10.Adjust the vertical POSITION control for CH1(X) of the
oscilloscope until the trace is exactly on the center line of
the vertical display.
11.Adjust the AMPL control of the signal generator, and
watch.
4. Procedure & Experiment

Peak-to-Peak Voltage Measurement
Y
Vertical scale
V p  p  Dy Y
Dy  1 V / DIV  1 V / cm
Y  6.4 divisions  6.4 cm
Snap to grid
4. Procedure & Experiment

Period Measurement
Snap to grid
Horizontal scale
X
T  Dx X
Dx  0.2 ms / DIV  0.2 ms / cm
X  4.4 divisions  4.4 cm
4. Procedure & Experiment

Lissajous Figures (Optional)
A Lissajous curve depicts the composition of simple harmonic motions in
mutually perpendicular (X-Y) directions, produced by transverse electric
forces exerting on an election moving along the Z-axis direction, which
can be described by parametric equations:
Vx  Ax sin( 2 f x t )

Vy  Ay sin( 2 f y t   )
Vy
CH2(Y)
fx N y

fy Nx
CH1(X)
Vx
It can be done on an oscilloscope in X-Y mode.
Whenever a stationary pattern is achieved, the frequency ratio fx / fy of the
horizontal input to the vertical input is equal to the ratio Ny / Nx of the
number of vertical to horizontal points of tangency to a rectangle that
encloses the pattern, i.e., fx / fy is rational .
4. Procedure & Experiment

Unknown frequency Measurement
1. Connect the unknown sine voltage source to the CH2(Y) input
of the scope.
2. Turn on the POWER to the unknown source.
3. Set the horizontal sweep SEC/DIV switch at the position X-Y .
4. Use the COARSE and FINE control to adjust the frequency of
the function generator patiently in order that the stationary
patterns with ratio Ny / Nx = 1, 2, 2/3 are displayed on the screen,
respectively.
5. Record the frequency reading fx from the function generator,
draw the sketch map, and calculate the unknown frequency,
respectively.
5. Problems
 Tilted & Blurred Traces
Have a check
5. Problems
 Synchronous & Asynchronous Traces
Have a check
5. Problems
 An interesting problem:
The oscilloscope is in good condition, but
no trace appears on the screen, why?
(There are more than 2 answers !)