18-08-2012, 11:51 PM
project report on cathode ray oscilloscope
18-08-2012, 11:51 PM
project report on cathode ray oscilloscope
11-10-2012, 05:04 PM
Cathode Ray Oscilloscope
CROs.ppt (Size: 157 KB / Downloads: 77) Look and play Read instructions Break into smaller parts Decide on a simple measurement Increase your level of difficulty Record pathway. How you got there. Store directions and short-cuts 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 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. CROs 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 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. 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. 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. 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. |
|