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HACETTEPE UNIVERSITY ELE 271 MEASUREMENT LABORATORY EXPERIMENT #5 CATHODE RAY OSCILLOSCOPE Object : To learn the use of cathode ray oscilloscope. Preliminary Work : 1.1 CRT ( Cathode Ray Tube ) : Brilliance : varies the intensity of the display. Focus : controls the definition of the display. Astig : is used in conjunction with FOCUS for best overall definition. Trace Rotation : rotates the traces about the horizontal axis of the CRT and is used to align the traces with the horizontal divisions. Scale Illum : varies the intensity of the illumination, as well as serving as the supply ON-OFF switch. 1.2 Horizontal Display : Position : varies the location of the trace(s) in the horizontal axis, when not in the X-Y mode. Fine : acts as a more sensitive position control as well as the x5 horizontal gain switch. When pulled out in the x5 position, all sweep speed calibrations must be divided by 5. In the X-Y mode, FINE inoperative, x5 gain operative. 1.3 Sweep : Time/Div. : controls the speed of the main sweep. The sweep rates indicated are only valid if VARIABLE is fully clockwise and FINE position is pushed in for x1 gain. If FINE position is pulled out and VARIABLE is at CAL, the calibrations should be divided by a factor of 5 to ascertain the sweep speed. The position of this button shows the value of the each horizontal division in cm. on the screen. For example, if it points 0.1 msec/div., it means that the portion of the 10x0.1=1 msec.of any signal can be examined on the screen. . Example : If a sinusoidal wave with 1kHz frequency is applied to one of the inputs of the CRO, its period can be calculated as 1 msec by the following formula: T=1/f=1/1000=1 msec For the different scales of the button, the portion of the signal which is seen on the screen can be calculated as follows: 21
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Time/Div. (msec/Div.) Length of the screen (cm) Portion of the signal (msec) 0.05 10 0.5 0.1 10 1 0.2 10 2 At EXT.-X position, an external sweep voltage can be applied to EXT.-X input. By applying a signal to this input and another one to the channels, (CH1 or CH2) one can obtain Lissajous-patterns. Same pattern can also be obtained by applying two signals to CH1 and CH2 respectively and then pressing the TIME/DIV. button. Variable : enables speeds between that indicated by TIME/DIV. and the next lower speed to be selected. The control also selects X-Y operation when the knob is pushed in. Level :
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