Sunday, April 10, 2016

Explain briefly blanking & spot size

Blanking : Each time the electron beams scans from left to right it is in WRITE mode. However at the end of each line the beam must be turned off(blanked) & redirected back to the left hand side of the CRT. The return sweep is called horizontal retrace blanking. Fig(b) shows this depict.;

vertical retrace blanking refers to the shutting off the electron beam as its returns from the bottom of the display at the end of a cycle to the upper left-hand corner to start a new cycle.

Spot : Every time the electron beam is turned on curing its journey across the display area, a "spot" of light is created. The spot size is preliminary a function of the diameter of the electron beam and the size of the phosphorous crystals coating the screen. To obtain the most pleasing image from a CRT, the spot should be just large enough to slightly overlap or be close to the eight spots surrounding it. If the spot size is to small the images on the display will appear "grainy" too large-and the images will appear "fuzzy". Fig(b) shows this depict-
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