© National Instruments Corporation
3-12
AT-MIO-16 User Manual
The common-mode input range of the AT-MIO-16 instrumentation amplifier is defined as the
magnitude of the greatest common-mode signal that can be rejected.
The common-mode input range for the AT-MIO-16 depends on the size of the differential input
signal (V
diff
= V+
in
- V-
in
) and the gain setting of the instrumentation amplifier. The exact
formula for the allowed common-mode input range is as follows:
V
cm-max
=
±
(12 V -
V
diff
* Gain
2
)
where the maximum value for V
diff
is as follows:
±
10 V range
V
diff-max
=
±
10 V
0 to +10 V range
V
diff-max
= 10 V
±
5 V range
V
diff-max
=
±
5 V
For example, for a differential voltage as large as 20 mV and a gain of 500, the largest common-
mode voltage that can be rejected is
±
7 V. However, if the differential signal is 10 mV with a
gain of 500, a
±
9.5 V common-mode voltage can be rejected.
The common-mode voltage is measured with respect to the AT-MIO-16 ground and can be
calculated by the following formula:
V
cm-actual
=
V+
in
+ V-
in
2
where V+
in
is the signal at the positive input of the instrumentation amplifier and V-
in
is the
signal at the negative input of the instrumentation amplifier.
If the input signal common-mode range exceeds
±
7 V with respect to the AT-MIO-16 ground,
you must limit the amount of floating that occurs between the signal ground and the AT-MIO-16
ground.
Analog Output Signal Connections
Pins 20 through 23 of the I/O connector are analog output signal pins.
Pins 20 and 21 are the DAC0OUT and DAC1OUT signal pins. DAC0OUT is the voltage output
signal for analog output channel 0. DAC1OUT is the voltage output signal for analog output
channel 1.
Pin 22, EXTREF, is the external reference input for both analog output channels. You must
individually configure each analog output channel for external reference selection in order for the
signal applied at the external reference input to be used by that channel. Analog output
configuration instructions are included in the Analog Output Configuration section of Chapter 2,
Configuration and Installation.
The following ranges and ratings apply to the EXTREF input:
•
Useful input voltage range
±
10 V peak with respect to AOGND
•
Absolute maximum ratings
±
25 V peak with respect to AOGND