Data Translation DT9824, Руководство пользователя, Страница: 50 / 102

Chapter 5
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Specifying the Digital Input Port in the Analog Input Channel List
Using the DT9824 module, you can also read the digital input port (all 8 digital input lines) in
the analog input stream by specifying a channel index of 4 the channel-gain list. This feature is
particularly useful when you want to correlate the timing of analog and digital events. You
can enter channel 4 anywhere in the channel-gain list.
The digital input port is treated like any other channel in the analog input channel list;
therefore, all the clocking, triggering, and conversion modes supported for analog input
channels are supported for the digital input port, if you specify them this way.
Input Resolution
The analog input resolution of the DT9824 module is fixed at 24 bits.
Input Ranges and Gains
The DT9824 module supports an input range of ±10 V. In addition, you can choose from up to
4 gains (1, 8, 16, or 32).
Table 2 lists the supported gains and effective input range of each input
range on the DT9824 module.
Choose the gain that has the smallest effective range that includes the signal you want to
measure. For example, if the range of your analog input signal is ±1.05 V, specify a range of
±10 V for the A/D subsystem and use a gain of 8 for the channel; the effective input range for
this channel is then ±1.25 V, which provides the best sampling accuracy for that channel.
You can either specify the gain as part of the single-value operation. If you want to clock A/D
conversions, specify the gain for the channel entry in the channel-gain list.
A/D Sample Clock
The DT9824 module provides an internal A/D sample clock with a minimum sampling
frequency of 4.7 Hz and a maximum sampling frequency of 4800 Hz. All channels that are
specified in the channel-gain list are sampled simultaneously at the specified sampling
frequency.
Table 2: Effective Input Ranges
Gain Input Range
1 ±10 V
8 ±1.25 V
16 ±0.625 V
32 ±0.3125 V