1. CATHODE RAY OSCILLOSCOPE
Popular instrument to show time,
voltage both DC and AC. Shows Volts /
Time.
Display waveforms. Spectrum scope shows volts to
Frequency
Cathode (-ve ) is heated, emits
electrons, accelerated toward a (+ve)
fluorescent screen. Intensity grid, Focus grid,
Accelerating anode. (Electron gun)
Horizontal deflection plates.
Vertical deflection plates
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13. OSCILLOSCOPE: CONTROL PANEL
Panel Function
VOLTS/DIV Select the vertical deflection factor of the CRT display
TIME/DIV Select the horizontal deflection factor of the CRT display
INTEN (Intensity) The INTEN (intensity) control (sometimes called BRIGHTNESS) adjusts the
Control brightness of the beam on the CRT. The control is rotated in a clockwise
direction to increase the intensity of the beam and should be adjusted to a
minimum brightness level that is comfortable for viewing.
FOCUS and ASTIG The FOCUS control adjusts the beam size. The ASTIG (astigmatism) control
(Astigmatism) Controls adjusts the beam shape. The FOCUS and ASTIG controls are adjusted together
to produce a small, clearly defined circular dot
TRACE ROTATION The TRACE ROTATION control allows for minor adjustments of the horizontal
Control portion of the trace so that you can align it with the horizontal lines on the
graticule.
BEAM FINDER Control When pushed, the BEAM FINDER pulls the beam onto the screen so that you
can use the horizontal and vertical POSITION controls to center the spot.
Horizontal and Vertical The horizontal and vertical POSITION controls are used to position the trace.
POSITION Controls Because the graticule is often drawn to represent a graph, some oscilloscopes
have the positioning controls labeled to correspond to the X and Y axes of the
graph. The X axis represents horizontal movement; the Y axis represents the
vertical movement.
AC-GDN-DC AC- Ac Signal
GDN - grounding the signal
DC- Dc Signal
14. FREQUENCY AND PERIOD.
Frequency: measured in Hertz
Definition: number of times the signal
repeats itself in one second
15. FREQUENCY AND PERIOD.
Period
Definition: the amount of time it takes
the signal to complete one cycle.
16. PHASE
1 cycle of a sine wave: 360⁰
Phase shift 90⁰
18. WAVEFORM MEASUREMENT (EXAMPLE)
Peak to peak voltage :
Vpp = (volt/div) (no div peak to peak)
Vpp(X) = (50mV/div) ( 8 div ) = 0.4 V
Vpp(Y) = (200mV/div) ( 4 div ) = 0.8V
23. CATHODE RAY OSCILLOSCOPE
When electrons hit the screen the phosphor is
excited and emits light.
Persistence. How long the display glows.
May need to reduce ambient light for older
instruments.
Connect a signal to Vertical deflection
plate.
At same time a voltage that increases
linearly with time (Ramp) is applied to
the Horizontal deflection plates.
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24. This horizontal linear deflection is
produced by the Sweep generator.
Sawtooth wave.
When the sweep signal returns to zero
ie the end of the sweep, the beam flies
back to the start position. The beam is
cut off during the flyback time.
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25. CROS
The display is made to appear
stationary.
This controlled by your adjustment
settings.
The eye sees a waveform.
X is <----> Horizontal
Y is ^ Vertical Height of trace
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26. The signal is amplified by the vertical
amplifier, applied to the vertical plates.
A portion of the vertical amp signal is
applied to the Sweep Trigger.
The sweep trigger generates a pulse
coincident with a selected point in the
cycle of the trigger signal.
This pulse turns on the sweep generator
initiating the sawtooth wave form.
The sawtooth wave is amplified by the
horizontal amp and applied to the
horizontal deflection plates
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27. The trigger can be based on 50 (60) Hz
Provision is made for an external
trigger.
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28. CRO TUBE CONTROLS
POWER on / off
Scale
Illumination
Focus. Create spot on screen
Intensity. Brightness (Don’t burn a
spot on your screen)
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29. VERTICAL AMP
Position on display
Sensitivity of vertical amp Calibrated.
Cal fully clockwise.
Variable sensitivity. Continuous range between
calibrated steps.
AC - DC - Gnd.
Selects desired coupling for incoming signal, or
grounds amp input. DC couples signal directly to
amp. AC connects via a capacitor. (Blocks DC)
Gnd = no signal. Gnd connects Y input to 0 volts.
Checks position of 0v on screen.
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30. VERTICAL AMP
Position on display
Sensitivity of vertical amp Calibrated.
Cal fully clockwise.
Variable sensitivity. Continuous range between
calibrated steps.
AC - DC - Gnd.
Selects desired coupling for incoming signal, or
grounds amp input. DC couples signal directly to
amp. AC connects via a capacitor. (Blocks DC)
Gnd = no signal. Gnd connects Y input to 0 volts.
Checks position of 0v on screen.
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31. HORIZONTAL SWEEP
Sweep time / Div (or CM) Select
desired sweep rate, or admits external sig to
horiz amp.
Sweep time / Cm Variable Continuously
variable sweep rates. Cal is fully clockwise.
Position Controls horizontal position of
trace.
Horizontal variable controls attenuation of
signal applied to Horz amp through Ext Horiz
connector.
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32. TRIGGER SET TO AUTO OR NORMAL
Trigger selects timing of the beginning
of the Horizontal sweep.
Slope selects trigger at +ve increasing or -ve
decreasing portion of signal.
Coupling Selects whether trigger is at a specific
DC or AC level.
Source: Int from Vertical Amp
Ext from Ext Trig Input.
Line AC line 50 (60) HZ
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33. VOLTS /DIV SWITCH
Volts / Div
Variable Fine adjustment
these controls can have a Pull out switch
position. May be 5 times mag.
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34. VERTICAL MODE
The operation of vertical deflection plates
Chan 1 and Chan 2 can each operate
separately.
Dual. Ch1 and Ch2 are swept alternatively.
Why Dual? Used to measure input and
Output signals of a device under test.
Ch1 and Ch2 can be added
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35. TIME BASE
Main, Max, Min, delay.
Selects the sweep for the main mix or delay mode and
also X-Y switch
Time/Div provides selection of sweep
rates. Range of 0.1 Second, 50 to .1 mS,
50 to 0.1uS per div. Note 5,2,1, sequence.
To determine a frequency use reciprocal.
Frequency = 1/time period (50Hz = 1/20mS)
Time period = 1/Frequency (number of div * ?ms/div.
Eg 4div*5ms/div = 20 ms)
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36. OTHER
Comp Test. Allows individual components to
be tested. Connect via banana jacks to test
resistors, capacitors, diodes, transistors, etc
Cal delivers calibrated voltage e.g. 2v p-p
1KHz square wave for setting scale.
GND. Earth terminal of scope
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38. BANDWIDTH
A 10MHz CRO does not mean it will correctly
measure signals at 10MHz.
Vertical Amps are not so wide-band as to amplify all
signals. 10MHz is the 3dB point. A 10MHz signal of
1v will measure 0.707v on the screen.
Clipping introduces odd order harmonics. A CRO
operating near the max freq. will not show the
harmonics and you think you are reading a clean
signal.
Square waves begin to look like sine waves.
A rule of thumb is 5 times. To measure 2MHZ use a
10MHz CRO. 3 times is suitable for most Amateur
work.
For 7MHz. Times 3 = 21. Use a 20 MHz CRO.
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39. EVERY CRO WILL BE DIFFERENT
Many instruments made for specific work.
Beam Finder push button
Trace rotation
Chan 1 Vertical input. During X-Y operation
this is X axis (abscissa)
Chan 2 Vertical input Chan 2. During X-Y this
becomes ordinate input.
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40. MINI EXERCISES
Obtain a trace
Brightness
Focus
Move trace up, down.
Move trace side ways
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