CATHODE RAY OSCILLOSCOPE Popular instrument to show time

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 1

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT)

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Electron gun

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Deflection system

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Fluorescent screen

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Electron gun

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Electron gun

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Electron gun

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Electron gun

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Electron gun

OSCILLOSCOPE: CATHODE-RAY TUBES (CRT) � Deflection system

VERTICAL AND HORIZONTAL DEFLECTION PLATES

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) Control The 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) Controls The 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 dot TRACE ROTATION Control The 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 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 POSITION Controls The 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 Signal GDN - grounding the signal DC- Dc Signal

FREQUENCY AND PERIOD. � Frequency: measured in Hertz � Definition: number of times the signal repeats itself in one second

FREQUENCY AND PERIOD. � Period � Definition: the amount of time it takes the signal to complete one cycle.

PHASE � 1 cycle of a sine wave: 360⁰ � Phase shift 90⁰

WAVEFORM MEASUREMENT (EXAMPLE) � Given: volt/div time/div X: 50 m. V/div, Y: 200 m. V/div 1 ms/div

WAVEFORM MEASUREMENT (EXAMPLE) � Peak to peak voltage : Vpp = (volt/div) (no div peak to peak) Vpp(X) = (50 m. V/div) ( 8 div ) = 0. 4 V Vpp(Y) = (200 m. V/div) ( 4 div ) = 0. 8 V

WAVEFORM MEASUREMENT (EXAMPLE) � Voltage peak:

WAVEFORM MEASUREMENT (EXAMPLE) � Time T = (Time/div) ( no div in 1 cycle) T(X) = (1 ms/div) ( 5 div) = 5 ms T(Y) = (1 ms/div) ( 5 div ) = 5 ms

WAVEFORM MEASUREMENT (EXAMPLE)

WAVEFORM MEASUREMENT (EXAMPLE)

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. 23

� 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. 24

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 25

� 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 26

� The trigger can be based on 50 (60) Hz � Provision is made for an external trigger. 27

CRO TUBE CONTROLS � POWER on / off � Scale � Illumination � Focus. Create spot on screen � Intensity. Brightness (Don’t burn a spot on your screen) 28

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 0 v on screen. 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 0 v on screen. 30

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. 31

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 32

VOLTS /DIV SWITCH � Volts / Div � Variable Fine adjustment � these controls can have a Pull out switch position. May be 5 times mag. 33

VERTICAL MODE � The operation of vertical deflection plates � Chan 1 and Chan 2 can each operate separately. � Dual. Ch 1 and Ch 2 are swept alternatively. � Why Dual? Used to measure input and Output signals of a device under test. � Ch 1 and Ch 2 can be added 34

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 m. S, 50 to 0. 1 u. S per div. Note 5, 2, 1, sequence. � To determine a frequency use reciprocal. � Frequency = 1/time period (50 Hz = 1/20 m. S) � Time period = 1/Frequency (number of div * ? ms/div. Eg 4 div*5 ms/div = 20 ms) 35

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. 2 v p-p 1 KHz square wave for setting scale. � GND. Earth terminal of scope 36

CONNECTIONS � Vertical Input � Horizontal Input � External Trigger � Cal. Out 37

BANDWIDTH � � � A 10 MHz CRO does not mean it will correctly measure signals at 10 MHz. Vertical Amps are not so wide-band as to amplify all signals. 10 MHz is the 3 d. B point. A 10 MHz signal of 1 v will measure 0. 707 v 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 2 MHZ use a 10 MHz CRO. 3 times is suitable for most Amateur work. For 7 MHz. Times 3 = 21. Use a 20 MHz CRO. 38

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. 39

MINI EXERCISES � Obtain a trace � Brightness � Focus � Move trace up, down. � Move trace side ways 40