Chapter 2
Hardware Overview
©
National Instruments Corporation
2-3
Input Ranges
To optimize the ADC resolution, you can select different gains for the
PGIA so that you can scale your input signal to match the full input range
of the converter. The NI 5911 PGIA offers seven input ranges, from ±0.1 V
to ±10 V, as shown in Table 2-1.
Note
If you try to acquire a signal below the set input range, the sensitive front-end
components of the NI 5911 may become unstable and begin returning invalid data. To
return the digitizer to a stable configuration, switch to the maximum input range setting and
acquire an AC coupled or 0 V signal.
The input stage of the NI 5911 requires a settling time that depends on
which vertical range you are switching from and which vertical range you
are switching to. However, allowing for a delay of 250 ms between
configuring the input stage and starting the acquisition guarantees proper
settling.
Input Impedance
The input impedance of the NI 5911 PGIA is 1 M
Ω
between the positive
and negative input, ±2% depending on input capacitance. The output
impedance of the device connected to the NI 5911 and the input impedance
of the NI 5911 form an impedance divider, which attenuates the input
signal according to the following formula:
Table 2-1.
Input Ranges for the NI 5911
Range
Input Protection Threshold
±10 V
±10 V
±5 V
±5 V
±2 V
±5 V
±1 V
±5 V
±0.5 V
±5 V
±0.2 V
±5 V
±0.1 V
±5 V
V
m
V
s
R
in
R
s
R
in
+
--------------------
=
