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Analog Input Features
2-3
Analog Input Features
The analog input section of a DAS-1800HC Series board multiplexes all
the active input channels (up to 64 single-ended or 32 differential) down
to a single, 12-bit sampling ADC (analog-to-digital converter). Other
features of this section include software-configurable input modes, a
channel-gain queue, data conversion modes, data transfer modes, and
trigger and gate control. These features are described in the following
subsections.
Differential/Single-Ended Selection
Using DriverLINX software, you can set DAS-1800HC Series boards to
operate at either differential or single-ended inputs (see “DriverLINX
Configuration Notes” on page C-1). Differential inputs measure the
difference between two signals. Single-ended inputs are referred to a
common ground, also called
common-mode ground reference.
Generally,
you want to use differential inputs for low-level signals whose noise
component is a significant part of the signal or if the signal has a
non-ground common mode. You want to use single-ended inputs for
high-level signals whose noise component is not significant.
There is no specific level at which one of these input configurations
becomes more effective than the other. However, you should generally
use differential inputs for voltage ranges of 100mV and below.
Unipolar/Bipolar Selection
Using DriverLINX, you can set the DAS-1800HC Series boards to
operate in either unipolar or bipolar input mode (see “DriverLINX
Configuration Notes” on page C-1). A unipolar signal is always positive
(0 to 5V, for example), while a bipolar signal can swing up and down
between positive and negative peak values (±5V, for example).
The DAS-1800HC Series boards use positive magnitude to represent
unipolar signals and 2’s complement for bipolar signals. In a given input
range with the same peak-voltage capacity for both modes, the unipolar
mode doubles the converter’s resolution.
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