Introduction
AD1200 Reference
the light intensity level there is a doubling in the number of
different states of illumination. We are able to resolve the light
intensity to smaller intervals to provide greater detail or
information about the light intensity.
Figure 1-6. Three Bit A/D Conversion.
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ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³
BIT PATTERN
³
ILLUMINATION LEVEL
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ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´
³
111
³
ON
³
³
110
³
LIGHTEST GREY
³
³
101
³
LIGHT GREY
³
³
100
³
MEDIUM LIGHT GREY
³
³
011
³
MEDIUM DARK GREY
³
³
010
³
DARK GREY
³
³
001
³
DARKEST GREY
³
³
000
³
OFF
³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
As the number of bits used increases the number of states
doubles, the resolution of the converter increases, the smallest
resolvable interval decreases in size and the digital representation
of the light intensity begins to approach the smooth continuously
variable real world situation. 8 bit A/D converters use 256 states
to represent analogue values. 12 bit A/D converters use 4096
states to represent analogue values. 16 bit A/D converters use
65536 states to represent analogue values. This is summarised in
Figure 1-7.
The AD1200 series of cards use 12 bit A/D and D/A
converters, that is an analogue input is differentiated into 1 of
4096 possible levels, an analogue output can be set to 1 of 4096
values. The percentage change between adjacent digital values is
0.0244% or 244 parts per million.
Chapter 1
Page 7
