Data Translation DT9834 Series, Руководство пользователя

Страница: 79 / 186

Principles of Operation
79
The DT9834 Series modules can acquire data from a single analog input channel or from a
group of analog input channels. The following subsections describe how to specify the
channels.
Specifying a Single Analog Input Channel
The simplest way to acquire data from a single analog input channel is to specify the channel
for a single-value analog input operation using software; refer to
page 84 for more information
about single-value operations.
You can also specify a single channel using the analog input channel list, described in the next
section.
Specifying One or More Analog Input Channels
You can read data from one or more analog input channels using an analog input channel list.
You can group the channels in the list sequentially (starting either with 0 or with any other
analog input channel) or randomly. You can also specify a single channel or the same channel
more than once in the list.
Using software, specify the channels in the order you want to sample them. You can enter up
to 1,024 entries in the channel list. The channels are read in order (using continuously paced
scan mode or triggered scan mode) from the first entry in the list to the last entry in the list.
Refer to
page 84 for more information about the supported conversion modes.
You can also use software to inhibit data collection from a specified entry in t he channel list.
This feature is useful if you want to discard acquired values from specific entries in the
channel list. Using software, you can enable or disable inhibition for each entry in the channel
list. If enabled, the value is discarded after the channel is read; if disabled, the value is not
discarded after the channel is read.
Analog Threshold Trigger in Channel List
If you select an analog input channel as the analog threshold trigger source, the channel used
for this trigger source must be the first channel specified in the channel list; refer to
page 87 for
more information about this trigger source.
Maximum Rate
The maximum rate at which the module can read the analog input channels depends on the
total number of analog input channels and/or counter/timer channels (see
page 80 ) in the list,
and whether or not you are reading the digital input port (see the next section).
For example, since the maximum throughput of the analog input subsystem is 500
kSamples/s, the module can read two analog input channels at a rate of 250 kSamples/s each
or four analog input channels at a rate of 125 kSamples/s each.