Data Translation DT300 Series, User Manual

Page: 75 / 164

Principles of Operation
75
The digital channel 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 these digital I/O lines, if you specify them in this manner.
Input Ranges and Gains
Each channel on the DT301, DT302, DT303, and DT304 board can measure unipolar and
bipolar analog input signals, while each channel on the DT321 and DT322 board can measure
bipolar analog input signals only. A unipolar signal is always positive (0 to 10 V on a DT300
Series board), while a bipolar signal extends between the negative and positive peak values
(±10 V on a DT300 Series board).
Through software, specify the range for the subsystem as 0 to 10 V for unipolar signals or
−
10
V to +10 V for bipolar signals.
DT300 Series boards provide gains of 1, 2, 4, and 8, which are programmable per channel.
Table 6 lists the effective ranges supported by the DT300 Series board using these gains.
For each channel, 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 ±1.5 V, specify a
range of
−
10 V to +10 V for the board and use a gain of 4 for the channel; the effective input
range for this channel is then ±2.5 V, which provides the best sampling accuracy for that
channel.
The way you specify gain depends on how you specified the channels, as described in the
following subsections.
Specifying the Gain for a Single Channel
The simplest way to specify the gain for a single channel is to specify the gain for a
single-value analog input operation using software; refer to
page 77 for more information on
single-value operations.
Table 6: Gains and Effective Ranges
Gain
Unipolar Analog
Input Range
Bipolar Analog
Input Range
a
a. DT321 and DT322 boards support bipolar
analog input ranges only.
1 0 to 10 V ±10 V
2 0 to 5 V ±5 V
4 0 to 2.5 V ±2.5 V
8 0 to 1.25 V ±1.25 V