Chapter 4
Analog Input
4-4
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Working Voltage Range
On most S Series devices, the PGIA operates normally by amplifying
signals of interest while rejecting common-mode signals under the
following three conditions:
•
The common-mode voltage (V
cm
), which is equivalent to subtracting
AI <0..
x
> GND from AI <0..
x
> –, must be less than ±10 V. This V
cm
is a constant for all range selections.
•
The signal voltage (V
s
), which is equivalent to subtracting AI <0..
x
> +
from AI <0..
x
> –, must be less than or equal to the range selection of
the given channel. If V
s
is greater than the range selected, the signal
clips and information are lost.
•
The total working voltage of the positive input, which is equivalent to
(V
cm
+ V
s
), or subtracting AI <0..
x
> GND from AI <0..
x
> +, must be
less than ±11 V.
If any of these conditions are exceeded, the input voltage is clamped until
the fault condition is removed.
Note
All inputs are protected at up to ±35 V.
(NI 6154 Only)
The isolation features of the NI 6154 improve the working
voltage range in your applications. Refer to the
NI 6154 Specifications
for
more information.
AI Data Acquisition Methods
When performing analog input measurements, there are several different
data acquisition methods available. You can either perform software-timed
or hardware-timed acquisitions:
•
Software-Timed Acquisitions
—With a software-timed acquisition,
software controls the rate of the acquisition. Software sends a separate
command to the hardware to initiate each ADC conversion. In
NI-DAQmx, software-timed acquisitions are referred to as having On
Demand timing. Software-timed acquisitions are also referred to as
immediate or static acquisitions and are typically used for reading a
single point of data.
•
Hardware-Timed Acquisitions
—With hardware-timed acquisitions,
a digital hardware signal controls the rate of the acquisition. This
signal can be generated internally on your device or provided
externally.
