CRO

Cathode Ray Oscilloscope

Cathode Ray OscilloscopePopular instrument to show time, voltage both DC and AC. Shows Volts / Time.Display waveforms. Spectrum scope shows volts to FrequencyCathode (-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

1OSCILLOSCOPE: Cathode-Ray Tubes (CRT)

OSCILLOSCOPE: Cathode-Ray Tubes (CRT)

Electron gun


Deflection system


Fluorescent screen


Electron gun


Electron gun

To generate electronOSCILLOSCOPE: Cathode-Ray Tubes (CRT)

Electron gun

- Negative potential. - To control the brightness by controlling the electron flow and 2 anodes. OSCILLOSCOPE: Cathode-Ray Tubes (CRT)

Electron gun

Positive potential.

To focus the electron into narrow beams on the screen.OSCILLOSCOPE: Cathode-Ray Tubes (CRT)

Electron gun

Positive potential.

Accelerates the electronOSCILLOSCOPE: Cathode-Ray Tubes (CRT)

Deflection system

OSCILLOSCOPE:Vertical and HorizontalDeflection Plates

To control the electron beam at any direction.

OSCILLOSCOPE: Control Panel

Panel

FunctionVOLTS/DIVSelect the vertical deflection factor of the CRT displayTIME/DIVSelect the horizontal deflection factor of the CRT displayINTEN (Intensity) ControlThe INTEN (intensity) control (sometimes called BRIGHTNESS) adjusts the 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 (Astigmatism) ControlsThe FOCUS control adjusts the beam size. The ASTIG (astigmatism) control adjusts the beam shape. The FOCUS and ASTIG controls are adjusted together to produce a small, clearly defined circular dotTRACE ROTATION ControlThe TRACE ROTATION control allows for minor adjustments of the horizontal portion of the trace so that you can align it with the horizontal lines on the graticule. BEAM FINDER ControlWhen 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 POSITION ControlsThe horizontal and vertical POSITION controls are used to position the trace. 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 SignalGDN - grounding the signalDC- Dc SignalFrequency and Period.

Frequency: measured in HertzDefinition: number of times the signal repeats itself in one second

Frequency and Period.

PeriodDefinition: the amount of time it takes the signal to complete one cycle.

Phase

1 cycle of a sine wave: 360

Phase shift 90

Waveform measurement (example)

Given:volt/div X: 50mV/div, Y: 200mV/div time/div 1ms/div


Peak to peak voltage : Vpp = (volt/div) (no div peak to peak)Vpp(X) = (50mV/div) ( 8 div ) = 0.4 VVpp(Y) = (200mV/div) ( 4 div ) = 0.8V


Voltage peak:


TimeT = (Time/div) ( no div in 1 cycle) T(X) = (1 ms/div) ( 5 div) = 5msT(Y) = (1 ms/div) ( 5 div ) = 5ms



Cathode Ray OscilloscopeWhen 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.23This 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.24CROs

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 trace25The 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 plates26The trigger can be based on 50 (60) Hz Provision is made for an external trigger.

27CRO Tube ControlsPOWER on / offScaleIlluminationFocus. Create spot on screenIntensity. Brightness (Dont burn a spot on your screen)

28Vertical AmpPosition on displaySensitivity 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.29Vertical AmpPosition on displaySensitivity 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.30Horizontal SweepSweep 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.

31Trigger Set to Auto or normalTrigger 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 32Volts /Div switchVolts / DivVariable Fine adjustment these controls can have a Pull out switch position. May be 5 times mag.33Vertical modeThe operation of vertical deflection platesChan 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 34Time baseMain, Max, Min, delay.Selects the sweep for the main mix or delay mode and also X-Y switchTime/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)35Other Comp Test. Allows individual components to be tested. Connect via banana jacks to test resistors, capacitors, diodes, transistors, etcCal delivers calibrated voltage e.g. 2v p-p 1KHz square wave for setting scale.GND. Earth terminal of scope36ConnectionsVertical InputHorizontal InputExternal TriggerCal. Out

37BandwidthA 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.38Every CRO will be differentMany instruments made for specific work.Beam Finder push buttonTrace rotationChan 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.39Mini exercisesObtain a trace BrightnessFocusMove trace up, down.Move trace side ways

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