National Instruments PCI-6281, User Manual

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Chapter 5 Analog Output
AO Offset and AO Reference Selection
AO offset and AO reference selection allow you to set the AO range. The AO range describes
the set of voltages the device can generate. The digital codes of the DAC are spread evenly
across the AO range. So, if the range is smaller, the AO has better resolution; that is, the voltage
output difference between two consecutive codes is smaller. Therefore, the AO is more accurate.
The AO range of a device is all of the voltages between:
(AO Offset - AO Reference) and (AO AO Reference)
The possible settings for AO reference depend on the device model. For models not described
below, refer to the specifications for your device.
• (NI 622
x
Devices) On NI 622
x
devices, the AO offset is always 0 V (AO GND). The
AO reference is always 10 V. So, for NI 622
x
devices, the AO range = ±10 V.
• (NI 625
x
Devices) On NI 625
x
devices, the AO offset is always 0 V (AO GND). The
AO reference of each analog output (AO <0..3>) can be individually set to one of the
following:
– ±10 V
– ±5 V
– ±APFI <0,1>
You can connect an external signal to APFI <0,1> to provide the AO reference. The
AO reference can be a positive or negative voltage. If AO reference is a negative voltage,
the polarity of the AO output is inverted. The valid ranges of APFI <0,1> are listed in the
device specifications.
You can use one of the AO <0..3> signals to be the AO reference for a different AO signal.
However, you must externally connect this channel to APFI 0 or APFI 1.
• (NI 628
x
Devices) On NI 628
x
devices, the AO offset of each analog output can be
individually set to one of the following:
– 0 V (AO GND)
– 5 V
– APFI <0,1>
– AO <0..3>
You can connect an external signal to APFI <0,1> to provide the AO offset.
You can route the output of one of the AO <0..3> signals to be the AO offset for a different
AO <0..3> signal. For example, AO 0 can be routed to be the AO offset of AO 1. This route
is done on the device; no external connections are required.
You cannot route an AO channel to be its own offset.