GDP-32
II
INSTRUCTION MANUAL
May 2002 Section 16, Page 14
ANALOG-TO-DIGITAL CONVERTER
The analog-to-digital converter (ADC) converts the received analog signal to a digital
format that is stored in computer memory along with other card parameters.
Before the analog voltage signals can be digitally processed, they must first be properly
sampled and converted to digital format using an ADC. A 16 bit ADC is used for this
purpose on the standard BD183 analog boards. This means that there are 65,536 possible
output states on the 16 digital output lines. In the GDP, the states or counts are set up so
that 32,767 counts indicates positive full scale voltage, 0 counts indicates zero volts and -
32,768 indicates full-scale negative voltage. Full-scale values are determined by the
reference voltage (4.5 volts). For example, if an unknown voltage results in 7282 counts,
multiply 7282 times 4.5 (reference voltage) and divide by 32767. In equation form the
formula for converting digital counts to volts is:
volts =
4.5
32767
counts
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