1.5CATHODE RAY OCLLOSCOPE (CRO)
ACRO iS an instrument for plotting one varying physical quantity -p.d, sound, and
beat-against current, displacement or time.
pressure,
The following are the main parts of the CRO
heart
(a) Electron gun
The gun comprises an indirectly heated cathode C, a grid G, and the two anodes Al and A2. C has
a negative voltage with respect to C, and controls the mumber of electrons reaching A from C. The
brightness of the screen S, is controlled by cotrolling the vollage on G; ie. if the voltage is made
less negative, then the brightness increases. The anodes have positive potential relative to C. They
accelerate the electrons to a high speed down the tube (A2-1000V, Al=-200 to 300V and G is
between -50V to zero)
(b) Deflecting system
The beam from A2 passes first between a pair of Y-plates and X-plates, which deflect the beam
vertically and horizontally respectively.
() Fuorescent Screen
The screenS is coated with a phosphor such as zinc sulphide, which produces light or fluorescence
when struck with fast moving electrons.
Electron beam
Sceen
Cathode =
Graphite ooating
Evacuáted gass
(d) Time base
When the voltage is applied to the Y-plates, the electron beam is deflected to the vertical. To trace
the wave-form of the voltage applied to the Y-plates, the X-plates are used to provide the time-axis.
Chatterbox tin
marviktintor
Uses of the CRO
1. Measures a.c and d.c voltages
2. Measures frequencies
3.4. Measures phase ditferences
Measures sinall time diferences.
ACRO iS an instrument for plotting one varying physical quantity -p.d, sound, and
beat-against current, displacement or time.
pressure,
The following are the main parts of the CRO
heart
(a) Electron gun
The gun comprises an indirectly heated cathode C, a grid G, and the two anodes Al and A2. C has
a negative voltage with respect to C, and controls the mumber of electrons reaching A from C. The
brightness of the screen S, is controlled by cotrolling the vollage on G; ie. if the voltage is made
less negative, then the brightness increases. The anodes have positive potential relative to C. They
accelerate the electrons to a high speed down the tube (A2-1000V, Al=-200 to 300V and G is
between -50V to zero)
(b) Deflecting system
The beam from A2 passes first between a pair of Y-plates and X-plates, which deflect the beam
vertically and horizontally respectively.
() Fuorescent Screen
The screenS is coated with a phosphor such as zinc sulphide, which produces light or fluorescence
when struck with fast moving electrons.
Electron beam
Sceen
Cathode =
Graphite ooating
Evacuáted gass
(d) Time base
When the voltage is applied to the Y-plates, the electron beam is deflected to the vertical. To trace
the wave-form of the voltage applied to the Y-plates, the X-plates are used to provide the time-axis.
Chatterbox tin
marviktintor
Uses of the CRO
1. Measures a.c and d.c voltages
2. Measures frequencies
3.4. Measures phase ditferences
Measures sinall time diferences.
