Data Translation DT9871, Руководство пользователя

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Principles of Operation
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The FIFO on the instrument is used as a circular buffer. Acquisition continues indefinitely
until you stop the operation. When the FIFO is full, the operation wraps to the beginning of
the FIFO; values are overwritten starting at the first location in the FIFO. It is up to your
application to retrieve the data from the FIFO; refer to your software documentation for more
information.
The conversion rate is determined by the frequency of the input sample clock; refer to page 95
for more information about the input sample clock. The sample rate, which is the rate at which
a single entry in the channel list is sampled, is the same as the conversion rate due to the
simultaneous nature of the MEASURpoint instrument.
Figure 33 illustrates scanning a list of three enabled channels: channel 0, channel 1, and
channel 2. In this example, analog input data is acquired simultaneously on each clock pulse
of the input sample clock. Data is acquired continuously.
Figure 33: Continuous Scan Mode
Filtering
TEMPpoint, VOLTpoint, and MEASURpoint instruments use a Delta-Sigma analog-to-digital
converter (ADC) for each analog input channel to provide simultaneous sampling of all
inputs. The Delta-Sigma converter operates at 10 Hz effectively providing a filter that rejects
50 Hz and 60 Hz power line frequency components and that removes
aliasing , a condition
where high frequency input components erroneously appear as lower frequencies after
sampling.
In addition to the filter provided in hardware, you can further reduce noise by selecting one of
the following filter options in software: Moving Average or Raw. Refer to your software
documentation for more information on selecting a filter type.
Data Format
TEMPpoint, VOLTpoint, and MEASURpoint instruments return data as 32-bit floating-point
values. How the data is returned depends on the channel type, as described in the following
subsections.
Operation starts
Chan 0
Chan 1
Chan 2
Input
Sample
Clock
Data is acquired continuously
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2